Fluid sensor, flow passage, method for manufacturing the flow passage, and method for manufacturing the fluid sensor

Abstract

To provide a device with a simple structure which does not have a movable part for detecting the pressure of a fluid.SOLUTION: A part of a wall of a flow passage is formed of a flexible material and a surface of the wall formed of the flexible material is more rigid than the inside of the wall. Thereby, the wall of the flexible material is deformed by application of a pressure in the flow passage, and periodic wrinkles are generated in a surface part with a high rigidity by the deformation. Development of a structural color from the wrinkles makes it possible to detect the pressure in the flow passage.SELECTED DRAWING: Figure 2B

Description

[Technical field]

[0001] The present invention relates to a fluid sensor that measures the pressure of a fluid flowing through a flow channel from a structural color that appears on a flow channel wall in response to deformation of the flow channel wall due to the internal pressure of the flow channel through which the fluid to be measured flows.The present invention also relates to a flow channel configured to cause a structural color to appear on the flow channel wall in response to deformation of the flow channel wall due to the internal pressure of the fluid flowing through the flow channel, and a manufacturing method thereof.The present invention further relates to a manufacturing method of the above-mentioned fluid sensor that utilizes such a flow channel. [Background technology]

[0002] Measuring gas flow is a central problem in the field of fluidics. Many methods exist for measuring gas flow, but they typically use dedicated, highly constructed equipment. In contrast, far fewer methods exist that allow simple measurement of fluids using small, low-cost equipment or elements (hereafter referred to as devices). The provision of such devices would greatly expand the applications and uses of fluid flow measurement.

[0003] Among the various solutions, measuring fluid flow often reduces to determining the pressure required to produce a given flow rate. This is achieved by using pressure gauges, which are often cumbersome in both setup and reading. A typical pressure gauge works by measuring the strain caused by the pressure. The problem of measuring pressure is therefore reduced to measuring strain. In addition to a wide range of commercially available strain gauges, several tactile sensors can be used to make the strain measurement.

[0004] Furthermore, many advanced applications require two-dimensional measurements of pressure and therefore strain. Digital image correlation and related techniques can be used for this purpose. These techniques allow visualization of how strain is distributed throughout the entire channel. Although these techniques are powerful and well developed, their measurements rely on large and expensive equipment configurations. For example, microchannels made of polydimethylsiloxane (PDMS) combined with stimuli-responsive coloration have been developed for pressure sensing. Various means have been proposed for detecting color changes, such as photonic crystal lattices, lenses, interference, dyed solutions, and pressure-sensitive pigments. However, the fabrication of microchannels with such functions requires many steps using special equipment in a clean environment, and strain measurements typically require much more sophisticated equipment. Patent Document 1 also discloses strain measurements using a transparent material film with fine particles dispersed at regular intervals. Here, the distribution of strain over a large area is detected from the distribution of structural colors by utilizing the fact that the above-mentioned interval changes as the fine particle dispersion film expands and contracts due to strain, and the structural color changes accordingly. In the strain measurement of Patent Document 1, it is necessary to prepare a fine particle dispersion film suitable for such measurement, but it is not easy to realize such a device for strain measurement. In addition, in such a structure, the structural color essentially appears regardless of the presence or absence of strain, so the change in structural color is in the form of a change in the hue of the structural color that is always present. Depending on the detector or other detection conditions for detecting the structural color change, it may be preferable that the structural color does not appear when there is no strain, and that not only the wavelength but also the shade of the structural color changes as the strain increases, or that the presence or absence of the structural color changes. Therefore, it would be convenient if an element structure for strain measurement that can meet such detection conditions could be provided. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a flow channel having a greatly simplified structure and being easily manufactured, in which the structural color of the flow channel wall changes depending on the pressure of the fluid flowing through the flow channel, and a method for manufacturing such a flow channel, and also to provide a fluid sensor having a simple structure by using such a flow channel, and a method for manufacturing the same. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a fluid sensor having a flow path surrounded by a wall made of a material that deforms at least a portion of the surface of at least one of the walls on the side facing the flow path and the side opposite the flow path, and the deformation forms periodic wrinkles on at least a portion of the surface, and the wrinkles cause a structural color to appear on at least a portion of the at least one surface. wherein the at least one surface of the wall has a surface region that is more rigid than an interior of the wall; The wrinkles may be formed by at least a portion of the stiff region of the at least one surface being compressed by the deformation. In addition, a portion of the wall of the flow path may be constructed of a material that is less rigid than the remainder of the wall of the flow path, and the rigid surface area may be present on at least one surface of the flow path in a portion of the wall of the flow path that is constructed of a material that is less rigid than the remainder of the wall of the flow path. The low stiffness material may be polydimethylsiloxane. In addition, the material constituting the remaining portion of the wall of the flow path is a material containing silicon, and a first adhesive region on the surface of a first member made of polydimethylsiloxane and a second adhesive region on the surface of a second member made of the material containing silicon, which corresponds to the first portion of the surface of the first member, are bonded together, and an area surrounded by the bonded first and second adhesive regions and which is not itself bonded together may be used as the flow path. The silicon-containing material may be glass or silicon. The highly rigid surface region may be formed by subjecting the polydimethylsiloxane surface to an argon (Ar) plasma treatment. In addition, both the first adhesive region of the first member made of polydimethylsiloxane and the second adhesive region of the second member made of the silicon-containing material, or only the first adhesive region, may be treated with oxygen (O2) plasma. Furthermore, the surface of the first member that includes the first adhesive region and the surface of the second member that includes the second adhesive region may be flat surfaces. Furthermore, openings may be provided near one end and near the other end of the flow path, and the fluid may flow between the two openings. In addition, the flow path may be closed when internal pressure due to the fluid is not applied to the surface of the wall of the flow path, and when internal pressure due to the fluid is applied, the portion of the wall of the flow path made of the deformable material deforms, thereby opening the flow path. According to another aspect of the present invention, there is provided a method for manufacturing a fluid sensor, which comprises treating a portion of a surface area of ​​a member made of polydimethylsiloxane with Ar plasma, treating at least a portion of the remaining surface area of ​​the member with O2 plasma, and bonding the O2 plasma-treated area of ​​the member to a silicon-containing substrate, thereby using the Ar plasma-treated area as a flow path, and in which structural color is expressed on at least a portion of the surface in response to internal pressure applied by a given fluid. Here, the step of bonding the O2 plasma treated region of the member to the silicon-containing substrate may be performed by contacting the region of the member to a surface of the substrate. Moreover, the Ar plasma treatment and the O2 plasma treatment may be performed using masks in which the transmission-blocking relationship is reversed. In addition, the treatment with Ar plasma may use a mask that is transparent to Ar plasma in the area that is to be the flow path, and have a thin linear member in part of the area on the mask that should be transparent to the Ar plasma, thereby protecting the area of ​​the component located below the thin linear member from exposure to the Ar plasma. According to yet another aspect of the present invention, there is provided a flow path surrounded by walls made of a material that deforms at least a portion thereof due to internal pressure applied by a given fluid, wherein the deformation forms periodic wrinkles on at least a portion of at least one of the surfaces of the wall on the side facing the flow path and the side opposite the flow path, and the wrinkles cause a structural color to appear on at least a portion of the at least one surface. Here, the at least one surface of the wall may have a surface region that is more rigid than the interior of the wall, and the wrinkles may be formed by at least a portion of the more rigid region of the at least one surface being compressed by the deformation. In addition, a portion of the wall of the flow path may be constructed of a material that is less rigid than the remainder of the wall of the flow path, and the rigid surface area may be present on at least one surface of the flow path in a portion of the wall of the flow path that is constructed of a material that is less rigid than the remainder of the wall of the flow path. According to yet another aspect of the present invention, there is provided a method for manufacturing a flow path in which a structural color appears on at least a portion of a surface of a member made of polydimethylsiloxane, the member being treated with Ar plasma, and at least a portion of the remaining surface area of ​​the member being treated with O plasma, and the O plasma-treated area of ​​the member being bonded to a silicon-containing substrate, the Ar plasma-treated area serving as a flow path. Effect of the Invention

[0007] According to the present invention, a flow channel is provided in which the wall surface exhibits structural color in response to the fluid pressure within the flow channel in spite of its simplified structure, and therefore the flow channel can be suitably applied to a fluid sensor, etc. Furthermore, the fine-sized structure on the order of wavelength that exhibits structural color is a periodic wrinkle on the flow channel wall surface caused by deformation of the flow channel wall due to application of pressure to the flow channel, in other words, a fine structure formed spontaneously by deformation, and therefore such a fine structure itself can be easily manufactured in the sense that it does not need to be actively created during the manufacturing process. [Brief description of the drawings]

[0008] [Figure 1] Photographs of the entire device of one embodiment of the present invention are shown (a) when no gas flow is being applied and (b) while a nitrogen gas flow is being applied at a flow rate of 10 mL / min, as well as enlarged photographs of the Ar plasma treated and non-Ar plasma treated regions in the region near the Ar plasma treated / untreated boundary near the small circle drawn approximately in the center of the photograph of the entire device, and highly magnified photographs of the square areas of the Ar plasma treated and non-Ar plasma treated regions in the enlarged photographs. [Figure 2A] 1A-1D are schematic diagrams showing the manufacturing process of a PDMS device according to one embodiment of the present invention, with both top and side views shown for each step. [Figure 2B]Photographs of a device according to an embodiment of the present invention taken at nitrogen (N2) flow rates of 0 mL / min, 5 mL / min, 10 mL / min, 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, and 400 mL / min, respectively. Intensity profiles of red (R), green (G), and blue (B) (R, G, and B shown in dark gray, gray, and light gray, respectively) are also shown on the right side of the corresponding photographs. The intensity profile graphs also show a graph of the average intensity of R, G, and B (i.e., the intensity of light before three-color separation) with a black border line. These profiles show the intensity of each of these colors on a cut line obtained by cutting the photograph of the device taken along the horizontal dashed white line shown in the photograph with a flow rate of 0 mL / min. [Figure 2C] 1 shows the results of a finite element simulation of a device of an embodiment of the present invention, showing the stress induced in the y direction (perpendicular to the flow) on the inner wall of the PDMS slab by nitrogen gas at flow rates of 50 mL / min, 100 mL / min, and 400 mL / min from top to bottom, respectively. Here, the geometry of the simulation is the same as that of the device in FIG. 2B, but here an empty space (50 μm high) between the top PDMS and the bottom glass is assumed to aid in the simulation. [Figure 2D] Laser microscope image of wrinkles formed under 10 mL / min N2 flow in a device according to one embodiment of the present invention. The image was recorded in the center of the flow path. [Figure 2E] A graph plotting the average intensity along the flow path (meaning the intensity obtained by averaging the intensity along the flow path in the device for each position on the flow path) for R, G, B, and non-tricolor separated light (labeled as Gray in the figure; the same applies in other figures) as a function of flow rate. These values ​​were obtained by averaging the intensities shown in Figure 2B. [Figure 3A] FIG. 13 is a schematic diagram of the mask used to fabricate a second device, which is a modified version of the PDMS device according to one embodiment of the present invention. [Figure 3B]The photographs were taken when N2 was flowed through the second device at flow rates of 0 mL / min, 5 mL / min, 10 mL / min, 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, and 400 mL / min, respectively. In addition, the intensity profiles for R, G, and B are shown to the right of each corresponding photograph. These profiles show the intensity of each of these colors appearing on a cut line taken by cutting the photograph of the second device taken along the horizontal dashed white line shown in the photograph when the flow rate was 0 mL / min. [Figure 3C] Plots of the average intensity along the flow path for R, G, B, and the average of these three colors (labeled Gray in the figure) as a function of flow rate. These values ​​were obtained by averaging the intensities shown in Figure 3B over the positions. [Figure 3D] Laser microscope image of wrinkles formed in the second device under 10 mL / min N2 flow. The image was taken in the center of the flow path, indicated by the gray square near the center of the image, at a flow rate of 0 mL / min. [Figure 3E] Graph showing the displacement of PDMS in the second device as a function of flow rate, recorded in the center of the flow path, indicated by the gray square near the center of the photograph, where the flow rate was 0 mL / min. [Figure 3F] 1 is a graph of the results of repeated measurements showing the stability of the sensitivity of the second device, showing the normalized intensity of the trichromatically unresolved light (gray) measured at 500 mL / min as a function of the number of measurements. [Figure 4] Photographs of a device according to an embodiment of the present invention taken under various lighting conditions, where N2 gas was flowing at 400 mL / min. [Figure 5A] A perspective view of a 3D printed mold used for evaluation of wrinkles on curved surfaces formed under compression. [Figure 5B] Conceptual cross-section showing how a PDMS slab is bonded to a mold for evaluation of wrinkles on a curved surface formed under compression. [Figure 5C]Images of PDMS taken under strains of 0.8%, 1.3%, and 2.5% using molds with various radii of curvature for evaluation of wrinkles on curved surfaces formed under compression. Also shown to the right of each image is the strain magnitude profile recorded along the vertical dashed line drawn in the image. The three images shown on the left and the three images shown on the right were taken from two PDMS slabs that were plasma treated using different masks, one without lines on the left and one with lines on the right. [Figure 5D] Plots of the wavelength (top) and amplitude profiles (bottom) of wrinkles on a curved surface under compression as a function of strain. These values ​​are obtained from the strain magnitude profile shown in Figure 5C. The dotted curves are plotted according to the analytical model given in Eqs. (1) and (2). [Figure 5E] Stress-strain graph of PDMS. All error bars represent standard deviation. [Figure 6A] Figure 1 shows a cross-sectional model of a PDMS slab used in a finite element analysis of the strain vs. displacement relationship. The top shows the three-dimensional Cartesian coordinate system of the model, and the bottom shows the model's configuration and the constraints on its movement due to its fixation to the substrate. As shown in the bottom cross-sectional view, a uniformly distributed force is applied on the free surface of the PDMS (the surface between the parts fixed to the substrate at both ends). [Figure 6B] The strain vs. displacement graph is based on the finite element method used for the finite element analysis, with the displacements obtained from the simulation plotted as open circles as a function of applied force, and eight solid circles based on the experimental displacements shown in Figure 3E. [Figure 6C]The strain vs. displacement relationship is plotted as open circles for the simulated strain as a function of the simulated displacement based on the finite element method used for the finite element analysis. The experimentally obtained displacement points shown in Figure 3E are also plotted as eight solid circles. [Figure 6D] The relationship between strain and displacement was calculated by finite element analysis based on the finite element method, and the displacement on PDMS was mapped onto the cross-sectional shape of PDMS using shading. The results shown show the displacements obtained by the simulation expected under N2 flow rates of 5 mL / min, 10 mL / min, 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, and 400 mL / min, respectively, from top to bottom. [Figure 6E] The stress tensor on PDMS obtained by simulation based on the finite element method used for finite element analysis of the relationship between strain and displacement is mapped onto the cross-sectional shape of PDMS using shading. The results shown show the stress tensor obtained by simulation expected under N2 flow rates of 5 mL / min, 10 mL / min, 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, and 400 mL / min, from top to bottom. [Figure 6F] Graph showing the profile of the bottom surface of PDMS obtained by simulating the relationship between strain and displacement based on the finite element method used for finite element analysis. The horizontal axis of the graph is the distance from the fixed end of PDMS, and the vertical axis is the displacement. The eight curves shown in the graph correspond to the eight N2 flow rates in Figures 6D and 6E, respectively. [Figure 6G] FIG. 14 shows strain (solid line) and stress tensor (dashed line) profiles along the bottom surface of PDMS obtained by simulation based on the finite element method used for the strain vs. displacement finite element analysis. [Figure 6H]The strain as a function of the stress tensor is plotted as open circles, based on the finite element simulation described above. We also plot eight solid circles based on the simulated stress values ​​in Figure 6C, which correspond to the experimentally obtained displacements shown in Figure 3E. [Figure 7] Micrographs comparing wrinkles formed using two different methods: on the left, wrinkles formed using a N2 flow at 10 mL / min, and on the right, wrinkles formed using compression with a curved mold. [Figure 8] Images of PDMS slabs taken under strain rates of 0.8%, 1.3%, and 2.5% using molds with various curvatures. For each image, three amplitude profiles recorded along the three dashed lines running vertically in the image are shown to the right of the corresponding image. Of the six images and corresponding amplitude profiles, the left three are images and amplitude profiles obtained from PDMS slabs treated with Ar plasma using a mask without lines (shown at the top left of the figure), and the right three are images and amplitude profiles obtained from PDMS slabs treated with Ar plasma using a mask with lines (shown at the top right of the figure). [Figure 9] Graphs comparing wavelength (top) and amplitude (bottom) as a function of strain. The two leftmost graphs show data from a PDMS slab that was plasma treated using a mask without lines (top left), and the two rightmost graphs show data from a PDMS slab that was Ar plasma treated using a mask with lines (top right). The three amplitude profiles associated with each image in Figure 8 were used to generate the bar graphs in this figure. The three bars on the left, center, and right of each graph are plotted for the same strain and were generated using the data from the three corresponding amplitude profiles located on the left, center, and right of Figure 8, respectively. [Figure 10A]Photographs of a device according to another embodiment of the present invention, fabricated using a modified mask, taken under a flow of different gases, He, Ne, N2, Ar, CO2 and Xe, at a flow rate of 400 mL / min. The top photograph is taken without any gas flow (i.e., flow rate 0 mL / min). In addition, the intensity profiles for R, G, B and non-trichromatic light (shown in dark grey, grey, light grey and light grey with black border, respectively) are shown on the right side of each photograph. These intensity profiles are the result of measuring the intensity on the corresponding photograph along the horizontal dashed white line shown only in the 0 mL / min photograph. [Figure 10B] (b) Graph showing the average intensity along the flow path for R, G, B and non-trichromatic light (represented by squares, circles, up-pointing triangles and down-pointing triangles with black borders, respectively) as a function of density (left) and viscosity (right) for various gases as shown in Table 1, using a device of another embodiment of the invention fabricated with a modified mask. [Figure 10C] Graph showing displacement as a function of density (left) and viscosity (right) for measurements of various gases using a device according to another embodiment of the invention made with a modified mask. [Figure 10D] Graph showing pressure drop as a function of density (left) and viscosity (right) for various gases measured using a device according to another embodiment of the invention made with a modified mask, with squares and circles representing experimental data and calculated values, respectively. [Figure 10E] 13 is a plot of displacement as a function of pressure drop for measurements of various gases using a device according to another embodiment of the invention made with a modified mask, the dashed line showing the result of a linear fit. [Figure 11] Measurements of various gases using a device of another embodiment of the invention made with a modified mask show the average intensity along the flow path for grey (left graph), pressure drop (middle graph), and displacement (right graph) as functions of density. [Figure 12] Photograph of a PDMS device according to an embodiment of the present invention taken from the side when N2 gas was flowing at 400 mL / min. [Figure 13] Plot of pressure drop as a function of density, measured and calculated under the same conditions as in Figure 10D, where the squares and circles (open and closed) represent experimental data and calculated values, respectively, except that the calculated values ​​shown in the open and closed circles were calculated using the Bernoulli equation with and without the viscous loss term, respectively. [Figure 14A] FIG. 13 is a diagram showing the logo mark of the applicant of the present invention used as an example of a graphic displayed in an embodiment of a device that displays graphics by flow in the present invention. [Figure 14B] 14B is a diagram conceptually illustrating the structure of a device according to an embodiment for displaying the logo (a graphic portion excluding the letters "NIMS") shown in FIG. 14A. The dark colored portion, which has the same shape as the logo, is the area that has been treated with Ar plasma. [Figure 14C] Photograph of the device of the embodiment conceptually shown in FIG. 14B when N2 gas was flowing at 10 mL / min. [Figure 15] FIG. 1 is a diagram conceptually showing an example of the structure of a device that can use a liquid as the fluid to be measured. [Figure 16] Figure 15 shows a conceptual structure of the device. The stress tensor on the top surface of the device was calculated by a simulation based on the finite element method. The results are mapped onto (a) an oblique view and (b) a top view of the device using shading. [Figure 17] A device with the structure conceptually shown in Figure 15 was fabricated and photographs of the structural colors that appeared when N2 gas was flowed through it at a flow rate of 100 mL / min ((a)), and when liquid water was flowed through it at a flow rate of 1 mL / min ((b)) were taken from above the device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] According to an embodiment of the present invention, the flow of a fluid such as a gas in a flow channel is visualized by using a structural color that appears on the channel wall due to distortion caused by the flow of the fluid in the flow channel, and the flow is measured. A device for performing such measurements is realized by treating a plate-like member made of PDMS (hereinafter referred to as a PDMS slab) with two types of plasma, namely, argon (Ar) plasma and oxygen (O2) plasma. Here, O2 plasma is typically used to induce covalent bonds between PDMS and a substrate such as glass when bonding a cover (hereinafter also referred to as a substrate) to a device. That is, radicals and reactive side chains are generated on the surface of PDMS by O2 plasma treatment, and these form stable bonds such as covalent bonds with the surface of the substrate such as glass, thereby achieving adhesion. The formation of such bonds proceeds simply by pressing the PDMS and the substrate against each other, without the use of any chemicals or the like for promoting the reaction. If the surface of the substrate is also treated with O2 plasma, a large number of radicals and reactive side chains are generated on the surface, which makes the adhesion between the PDMS and the substrate surface stronger and more reliable, and is less likely to peel off during storage or use, which is preferable.

[0010] Here, the operation for bonding PDMS and the substrate can be explained as a simple operation such as stacking the PDMS slab and the substrate and applying pressure after O2 plasma treatment. In the device fabricated in the following examples, the stacked state was pressed by hand for about 10 seconds. By maintaining the temperature at an elevated level during or after the pressing operation, the adhesion can be made stronger and more reliable. In the examples, after the pressing operation, the PDMS slab was heated for several minutes in an oven set at a temperature of 65°C.

[0011] In the above, glass (specifically, a substrate made of soda lime glass is used in the following examples) is used as an example of the material of the substrate to be bonded to PDMS. However, the usable material is not limited to this, and any material may be used as long as it can be bonded to the O2 plasma-treated PDMS by forming the above-mentioned bond. Various processing conditions such as the necessity of O2 plasma processing on the substrate surface side and the processing time can be appropriately determined so that sufficient adhesive strength, adhesive reliability, etc. can be obtained for the use conditions of the device to be produced. This is also influenced by the material used for the substrate surface. For example, silicon may be used instead of glass as the substrate material, but in that case, in order to achieve the same adhesion as glass, a strong O2 plasma processing is required on the PDMS surface or on the PDMS surface and substrate surface compared to when glass is used as the substrate.

[0012] In contrast, Ar plasma hardly induces covalent bonds, but instead modifies the PDMS surface to form a more rigid glass-like coating on the surface. Due to the elastic step between this rigid layer and the flexible substrate (which is the layer underneath (inside) the rigid layer on the surface of the PDMS slab and can be called the PDMS substrate) a well-ordered wrinkle structure appears on the surface of the PDMS slab when the PDMS slab is deformed. Since the repetition wavelength of the wrinkles thus induced is in the range of a few micrometers, angle-dependent structural colors are observed on the deformed PDMS slab.

[0013] To fabricate a flow measurement device, a PDMS slab is locally treated with Ar plasma using a mask, and then the remaining part of the PDMS slab is treated with O2 plasma using an inverted mask. This allows the surface of the PDMS slab to be covalently bonded to a substrate such as glass, except for the Ar plasma-treated area. The Ar plasma-treated area remains chemically unbonded. This structure allows gases and other fluids to flow only between the untreated area and the substrate such as glass. When the surface of the PDMS slab is bonded to the substrate as described above, depending on the force applied during bonding and the warpage and surface irregularities of the substrate and PDMS slab, there may be little or no gaps between the unbonded areas due to the lack of chemical bonding, resulting in a closed flow path. In this way, even when no fluid is flowing, the lack of a flow channel structure (i.e., a structure in which a groove or the like that serves as a flow channel is formed on the substrate surface) maximizes the deformation of the PDMS caused by the flow of fluid, which can be measured by visualizing the structural color of the wrinkle pattern induced by the deformation.

[0014] Figure 1 shows photographs of the entire device with and without fluid flowing through it, as well as enlarged partial photographs of the top surface (PDMS slab surface) of the device's inner wall when fluid is not flowing and when it is flowing through the device, and a further enlarged photograph of a portion of the enlarged partial photograph. Looking at the enlarged photograph of the plasma-treated area of ​​the inner wall, it is clear that wrinkles that are not present when fluid is not flowing appear while fluid is flowing (i.e., while the flow path is formed by deformation due to the application of pressure). In contrast, in the non-plasma-treated area of ​​the inner wall, only a few relatively irregular wrinkles appear even while fluid is flowing. Also, in a photograph of the device taken from above, the areas that have been Ar plasma-treated and have clear wrinkles show a clear color, whereas the areas that have not been Ar plasma-treated and have only slight wrinkles show almost no color. This provides a simple and compact means of measuring the pressure of a flowing fluid such as a gas. It is shown that such a PDMS device can measure the flow of a fluid such as a gas by quantifying the color change. In addition, it is shown that the color depends on the density and viscosity of the fluid such as a gas. They also reveal that the technology can be used to display specific patterns such as logos.

[0015] Alternatively, the fluid to be measured does not necessarily need to be flowing, and it is also possible to measure pressure changes in a stationary fluid. In principle, the structure of such a fluid pressure sensor may have a surface with dynamic wrinkles in the sense that the wrinkles described in detail above are generated or eliminated, or the height of the wrinkles changes, as a result of deformation caused by the pressure of the fluid to be measured or by any other force. More specifically, the structure may be the same as that of the sensor for a flowing fluid described above, or a part of the wall surface of a container that contains the fluid to be measured may have such dynamic wrinkles. Alternatively, dynamic wrinkles may be formed on the wall of the sensor chamber, which has the same pressure as that of such a container or a space that is open in the sense that it is significantly larger than a normal container, by communicating with the sensor chamber.

[0016] The basic principle for the manufacture of the above-mentioned devices is to treat the PDMS with a gas plasma to form a channel between the PDMS and the substrate on which the PDMS is placed. The entire surface of the PDMS microchannel device is exposed to O2 plasma as is commonly done in the art. This increases the reactivity of the interface between the PDMS and the substrate, such as glass, and improves adhesion to the glass substrate. This method has been widely adopted to improve the sealing of microfluidic devices (Non-Patent Document 1). Another result of O2 plasma treatment is the formation of a thin and highly rigid layer on the surface of the PDMS (Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4, Non-Patent Document 5). The rigidity of this layer is significantly higher than that of PDMS (Non-Patent Document 6). Treating the PDMS surface with Ar plasma results in the formation of a very rigid and thin layer on the surface (Non-Patent Document 7, Non-Patent Document 8), but does not result in the formation of an adhesive surface. Thus, the Ar plasma-treated surface can be easily peeled off from the substrate, such as glass, and does not stick (adhere) to the substrate in the same manner as the O2 plasma-treated surface. In the present invention, this property is utilized to pattern the surface of PDMS with adhesive regions that will bond to a substrate such as glass, and regions that will not bond to glass or the like, but are significantly stiffer than the bulk of PDMS.

[0017] The thin, stiff layer of PDMS overlying a region of significantly lower stiffness also provides another useful feature, which can be observed when the PDMS is compressed. Because the thin, stiff layer resists compression much more strongly than bulk PDMS, it undergoes a buckling transition, which results in the formation of nearly periodic wrinkles on its surface (Non-Patent Document 9). These wrinkles have a spacing of approximately 1 μm, which corresponds to the wavelength of light. This wrinkle structure thus forms a diffraction grating structure, resulting in the diffraction of light of a specific wavelength that can be easily detected. Furthermore, both the spacing and the amplitude of these wrinkles (i.e., the depth and / or height of the wrinkles) are very sensitive to the degree of compression of the PDMS, i.e., the strain being applied to the PDMS. This provides a simple yet sensitive means of measuring strain on the PDMS. If the strain is caused by a flow of a fluid, such as a gas, this provides a sensitive means of detecting that flow.

[0018] In addition, to add a little more about the compression, when the channel wall is deformed by the internal pressure of the fluid in the channel, the curvature of at least a part of the channel wall changes. More specifically, the harder glass part of the channel wall is hardly deformed, but the PDMS side, which has a lower rigidity than the glass, is deformed. In general, when a thin plate-like member is curved, the outer part of the curve tries to stretch, so tension is applied to the surface of this part of the member, but the inner surface tends to be compressed. Therefore, compressive stress is applied to the inner surface of the above channel, so the above-mentioned roughly periodic wrinkles are formed. The diffraction of light of a specific wavelength caused by such periodic wrinkles produces structural colors.

[0019] To realize the wrinkle formation and the resulting color change caused by compression under flow, multiple regions with different adhesive properties can be created in PDMS by localized treatment with O2 plasma and Ar plasma using positive and negative masks, as shown in Figure 2A. The Ar plasma-treated portion can be peeled off even after the entire PDMS is bonded to a substrate such as glass, so that the Ar plasma-treated PDMS is deformed by injecting a fluid such as gas to form a temporary gap between the Ar plasma-treated region and the substrate such as glass. Importantly, such a structure maximizes the deformation of PDMS due to the flow of a fluid such as gas when no flow path is formed in advance. To realize this idea, as shown in the leftmost part of Figure 2A, the center of a PDMS slab (e.g., 2.5 mm thick) is exposed to Ar plasma through a positive mask shown in dark gray (the dark gray part covering the entire top view except the center of the top view at the leftmost part of Figure 2A). After Ar plasma treatment, the PDMS slab is stretched (e.g., to a strain of about 20% for a few seconds) to intentionally create cracks in a controlled manner in the thin, stiff layer formed by the Ar plasma treatment of the PDMS surface, as shown in the second from the left in Figure 2A. This process is useful for creating reproducible structures because the stretching process prevents uncontrolled crack formation due to unexpected folding or stretching somewhere in the fabrication process. As with the O2 plasma-treated PDMS, the Ar plasma-treated PDMS exhibits vivid angle-dependent color when it is stretched. The remaining surface of the PDMS slab is then exposed to O2 plasma while a negative mask is used to cover the Ar plasma-treated areas, as shown in the third from the left in Figure 2A. The PDMS slab is then bonded to a substrate such as glass to complete the device fabrication.

[0020] To test the functionality of the device, nitrogen (N2) gas was injected into the device at a flow rate of 400 mL / min, and structural colors were observed in the Ar plasma-treated areas as expected, as shown in Figure 2B. Simulations using finite element analysis (FEA) showed that the areas where the structural colors appeared overlapped with areas where the inner wall of the PDMS slab was compressed by the gas flow pressure, as shown in Figure 2C. This suggests that it is compression that causes the formation of wrinkles and thus the appearance of structural colors. This is supported by the fact that the structural color profile changes symmetrically in the direction perpendicular to the flow, which matches very well with the compression profile determined by FEA. The presence of wrinkles was confirmed by observing the device under a microscope in the presence of flow. As shown in Figure 2D, the wrinkles are oriented along the flow direction, and the wavelength of the wrinkles (the repeat period between wrinkles) is estimated to be approximately 2-3 μm. Several oblique cracks were also observed, which are likely the result of deformation along two directions, the flow direction and the direction perpendicular to the flow. Although the formation of such cracks is inevitable, once cracks are formed, their number does not change significantly. Therefore, measurements and analysis can be performed reproducibly even when such diagonal cracks are present. To investigate how the gas flow is related to the structural color, the color change was observed by changing the flow rate from 5 mL / min to 400 mL / min. The color was observable even at a low flow rate of 5 mL / min, but became brighter as the flow rate was increased. For further quantitative analysis, the intensity values ​​of red (R), green (G), and blue (B) for each flow rate were extracted from the observed images and plotted on the right side of the corresponding device photographs showing the structural color for each flow rate in Figure 2B. In addition, the average intensity of R, G, and B (the intensity of the entire visible region before being decomposed into these three colors) was also plotted in the graph. As shown in Figure 2E, the average intensity along the flow path for each of R, G, and B (the average intensity across the entire flow path shown in the device photograph shown in Figure 2B) clearly increased as the flow rate increased.The results indicate that a higher flow rate leads to a larger deformation of the PDMS slab, which in turn leads to a larger wrinkle amplitude and thus a larger color change. This observation is confirmed by the FEA simulations shown in Figure 2C.

[0021] Introducing defects can improve the regularity of the wrinkles and the sensitivity of the device. Here, the term "defect" means that the rigidity of the region on the inner wall surface of the flow channel where the periodic wrinkles are formed is not uniformly increased, but generally speaking, the rigidity of a part of the region is different from that of the surrounding area, and in the embodiment referred to below, this part of the region has a thin line shape. The rigidity of such a part of the region may be, for example, substantially the same as the rigidity of the bulk part of the inner wall of the flow channel below (i.e., the rigidity before the treatment to increase the rigidity is performed), or, depending on the method of Ar plasma irradiation and the size and structure of the mask used at that time, it may be a rigidity between the rigidity of the bulk part and the rigidity of the surrounding area. Therefore, this "defect" can also be called a "discontinuity in rigidity."

[0022] The effect of this defect is considered as follows. If the stiffness of the region where wrinkles are formed is uniform, there is a possibility that irregularities (non-periodicity) will propagate far away if they appear somewhere in the wrinkles. To prevent or reduce such propagation, a defect in the uniformity of stiffness is provided within the region. More specifically, to prevent irregularities from propagating far away even if they appear in the wrinkles formed nearby due to unintended structural / rigidity irregularities in the region where wrinkles are formed, low-stiffness "fire walls," i.e., thin, linear low-stiffness regions, are formed here and there on the region. Even if irregular wrinkles (i.e., their minute deformations) propagate up to such low-stiffness "fire walls," they can be absorbed and the propagation of irregularities beyond that point can be prevented. Conversely, by providing a "fire wall" with higher stiffness than the surrounding area, the "fire wall" will not respond to minute deformations caused by wrinkles formed on one side of the thin linear "fire walls," and the propagation of irregularities between adjacent regions can be blocked. In addition, because wrinkles do not form within the thin-line defect region as described above, the area in which wrinkles form decreases when looking at the entire region under the assumption that the strain is constant. This may also contribute to the effect of the defect.

[0023] For the purpose of introducing such defects, the positive mask used in the device fabrication can be replaced with a modified mask. The modified mask has, for example, three equally spaced thin lines with a width of approximately 0.6 mm aligned along the flow direction, as shown in FIG. 3A. The areas under these thin lines are believed to be protected against Ar plasma exposure, as can be seen by observing the boundary between the plasma-treated and non-plasma-treated areas in FIG. 1. This acts as a defect that allows the protected areas to have more regularly spaced wrinkles, resulting in a more pronounced structural color. It was confirmed that the device using this modified mask (hereinafter also referred to as the second device, and the device manufactured using the non-modified mask also referred to as the first device) exhibits a more intense structural color, as shown in FIGS. 3B and 3C, compared to the first device without the modified mask, characterized in FIGS. 2B and 2E. Moreover, as can be seen by comparing FIG. 3D with FIG. 2D, the second device has more dense and regular wrinkles. Despite the improved ordering and structural color, the second device shows the same trend as the first device, that is, the structural color becomes brighter as the flow rate increases. Here, this trend is confirmed by measuring a wide range of flow rates, from a few mL / min to hundreds of mL / min, as shown in Figure 3B. The flow rate dependence of the color change correlates with the displacement of the PDMS, as shown in Figure 3E.

[0024] Here, the displacement can be estimated by first taking an image without flow and then measuring how much the height needs to be adjusted to obtain a focused image under different flow rates. Although the displacement is a monotonically but nonlinearly increasing function of the flow rate, the sensitivity of the measurement is calculated to be roughly 1 μm per unit flow rate by assuming its linearity and using the displacement measured at 400 mL / min. This is a general form of sensitivity that describes the device of the present invention. It is possible to improve the performance by employing other analysis methods in addition to the optical detection using a CCD based on structural color. At low magnification, bright colors and their gradations are observed by changing the illumination conditions, as shown in Figure 4. In contrast, a device made without such lines shows a slightly paler color profile, as shown in Figure 2B. These results confirm that the introduction of the above-mentioned lines makes the wrinkles more dense in a limited area, which helps to enhance the structural color and enable high-sensitivity measurements.

[0025] In addition to the sensitivity, the device according to the present invention also has good other important characteristics such as stability and measurement error. In measuring these characteristics, the same device was used to turn on and off the N2 flow at least 50 times every 10 seconds. That is, a cycle of flowing N2 gas for 10 seconds and then stopping the supply of N2 gas for 10 seconds was repeated 50 times, and measurement data was collected every 10 cycles during the measurement. As a result, as shown in FIG. 3F, no significant change in normalized intensity was observed even after repeating such cycles many times. In these measurements, the flow rate was set to 500 mL / min, which is larger than the flow rate used in the other experiments mentioned above. The measurement error here was estimated to be as low as 1%, which indicates that the device has sufficient stability and reliability for repeated use.

[0026] To further explain the formation of wrinkles in the device of the present invention, a PDMS mold was fabricated with a curved surface as shown in Figures 5A and 5B. The curved shape of this PDMS mold was designed to mimic the top wall of a microchannel, which is deformed by the pressure caused by the flow through the channel. The deformation of the tube wall when a fluid is flowed through the microchannel is analyzed in Non-Patent Document 10, so please refer to this document for details such as the curved shape. The curved cross-section of this mold should be useful for reproducing the wrinkles formed in the device of the present invention by gas flow, and therefore for estimating how much bending strain is generated. For this purpose, FEA simulations were performed assuming that the flow-induced displacement is approximately reproduced by applying a uniform load to one side of a PDMS slab with both ends fixed as shown in Figure 6A. The results of this simulation are shown in Figures 6B to 6H. Based on the simulation results, the bending strain of PDMS was estimated to be in the range of approximately 1% to 4%. This resulted in three molds with different curvatures that induced equivalent bending strains of 0.5%, 1.3%, and 2.5%, respectively. By mounting the Ar plasma-treated PDMS on these curved molds, wrinkles were observed to form at bending strains as low as 0.8%. The wavelengths of these wrinkles were the same as those observed when N2 was flowed at 10 mL / min (strain of about 0.8%), as shown in Figures 5C and 7. The wavelengths were almost constant at about 2.8 μm and decreased slightly as the strain increased, but the amplitudes increased monotonically as a function of bending strain, as shown in Figure 5D. The wrinkles appeared at multiple locations (three locations) and were consistent with each other, as shown in Figures 8 and 9. The wavelength λ and amplitude A of the strain formed on the curved surface are calculated as follows:

[0027]

number

[0028] Here, λ0 is defined as follows:

[0029]

number

[0030] Also, ε is the strain, E f and E s are the Young's moduli of the top thin film formed by Ar plasma treatment on the surface of the PDMS slab and the PDMS bulk part underneath the thin film, respectively; ν is the Poisson's ratio of PDMS; and t f is the thickness of the upper thin film, where E f = 0.4 GPa and t f = 23 nm. These values ​​were determined for O2 plasma treated PDMS with similar plasma power, pressure and time. The reason for adopting the above method of determination is that detailed investigation of these values ​​for Ar plasma treated PDMS was not available, but it is expected that these values ​​will not be significantly different under similar processing conditions even if O2 plasma treatment is performed. A typical value of 0.499 was used for ν. Also, the value of Es was experimentally determined to be 0.13 MPa, as shown in Figure 5E. The analytical solution agreed well with the experimental results obtained for plasma treated PDMS using a thin line-free mask. In general, the amplitude increases with increasing strain, but the wavelength of the wrinkles is almost constant at about 1.9 μm regardless of strain, as shown in Figure 5D. The difference between the wavelengths of 2.8 μm and 1.9 μm shown in Figure 9 is exactly the value observed in the presence of flow using the two devices.

[0031] The color change is also influenced by other factors such as the density and viscosity of the gas at 20°C. To evaluate the effect of such factors on the measurement results, the color change was measured when six inert gases, helium (He), neon (Ne), nitrogen (N2), argon (Ar), carbon dioxide (CO2) and xenon (Xe), were flowed at a fixed flow rate of 400 mL / min in a device fabricated with three parallel lines. The densities and viscosities of the six gases are shown in Table 1. The differences in color intensity and pattern between the six gases are not very noticeable, but there are discernible differences, especially between He and Xe shown in Figure 10A. To quantify these results, the average of each RGB intensity for each result was calculated along the flow path. These average data are small, but nevertheless show a discernible dependence on both viscosity and density, as shown in Figure 10B. To better quantify the response of the device, the displacement of the PDMS in the middle of the flow path was measured for each of the six gases. The displacement dependence was similar to the intensity dependence, but showed more pronounced changes than those for density and viscosity as shown in Figure 10C. Interestingly, the pressure drop Δp, which is the difference in pressure measured between the gas inlet and outlet, also shows a similar trend, including discontinuous changes, as shown in Figure 10D. Importantly, the color intensity averaged over RGB (Figure 10B) shows roughly the same trends as both concentration and viscosity, including small differences between gases, but with a much smaller total variation. A detailed comparison is shown in Figure 11. The smaller changes are likely due to the strong nonlinear response of the device, and the intensity and displacement plateau at higher flow rates, as can be clearly seen in Figures 3C and 3E. All of these measurements were performed at higher flow rates, where the measurements are well saturated, and the changes were reduced.

[0032] [Table 1]

[0033] To account for the dependence of pressure drop on the gas properties, we use the modified Bernoulli equation for steady, non-uniform, incompressible viscous flow shown below as equation (4).

[0034]

number

[0035] Here, p is pressure, ρ is density, v is velocity, g is gravitational acceleration, z is elevation from the horizontal plane, and w μ denotes the energy dissipated by viscosity μ, and is given as a function of hydrodynamic resistance and flow rate. The subscripts 1 and 2 denote the inlet and outlet, respectively. The above modified Bernoulli equation is valid when the Reynolds number and Mach number are sufficiently smaller than the values ​​for the turbulent and compressible flows, respectively. Also, as shown in Figure 12, the flow in the device is not constant because the deformation of the flow channel becomes smaller as the flow moves from the inlet to the outlet. Since Δp=p1-p2 and the effect of gravity can be neglected, equation (4) can be transformed into equation (5) shown below.

[0036]

number

[0037] Here, the viscosity loss term w μ is expressed as follows:

[0038]

number

[0039] Here, Q is the flow rate, l is the length of the flow path, w is the width of the flow path, and h is the height of the flow path (i.e., the width of the flow path in the vertical direction). μThe values ​​of some of the specific constants in the formula for Δp ​​come from the parabolic cross section used to estimate Δp in the channel (see Non-Patent Document 11 for details). We also denote the z-displacements of the PDMS at the inlet and outlet by h1 and h2, respectively. We use these values ​​of 500 μm and 100 μm for the time being, based on the results shown in FIG. 10C and FIG. 12, which shows that h2 is a fraction of h1. To calculate the velocities v1 and v2, we make the simplifying assumption that the cross-sectional shape of the channel is triangular, and assume that h=(h1+h2) / 2. Remarkably, this calculation reproduces the experimental data almost exactly, including the seemingly random variations, as shown in FIG. 10D. In contrast, w μ If these values ​​were calculated using the Bernoulli equation without the Δp, the calculated results would show a linear relationship between Δp and density, which is quite different from the experimental results shown in Figure 13. From these results, it can be seen that such random behavior of the data reflects the sum of the kinetic energy and viscous losses of each gas, which depends on density and viscous losses, two gas-specific parameters that vary independently of each other, as listed in Table 1. It can also be seen that Δp depends linearly on the displacement, as shown in Figure 10E. Therefore, from the relationship between the gas properties, the PDMS displacement, and the color change, the physical properties of the gas can be determined based on the color pattern of the device of the present invention.

[0040] Flowing any gas through the Ar plasma treated area results in a color change, so this technique can also be used to display any pattern in the presence of a flow. To demonstrate this concept, a mask with the same shape as the applicant's logo shown in Figure 14A was used to fabricate a device whose structure is conceptually shown in Figure 14B. When a N2 gas flow was applied to the device at 10 mL / min, the gas flow deformed a portion of the PDMS that was almost identical in shape to the logo, causing it to display vibrant colors as shown in Figure 14C.

[0041] The dependence of the color intensity on the various parameters of the gas is determined by the pressure change and the amount of deformation required to achieve the desired flow rate, and thus the resulting color change corresponding to the pressure required to achieve the set flow rate. This dependence is non-linear and very complex, but the pattern is in fact detailed enough that advanced analytical techniques such as machine learning can be used to distinguish between different gases and their properties. The analysis of gases and the discrimination between them can be realized even in small devices by combining the device according to the invention with devices capable of determining density or viscosity.

[0042] [Conclusion] In the present invention, the flow of gas can be measured using a device consisting of, for example, a glass slide and a PDMS slab whose surface has been locally treated with Ar plasma and O2 plasma, but this is of course not limited thereto. Here, the use of Ar plasma results in a PDMS surface whose optical transmittance in the visible range changes in response to strain. This optical change in the form of structural color is due to the formation of distinct wrinkles on the surface of the PDMS under strain. Unlike O2 plasma treated PDMS, Ar plasma treated PDMS does not adhere to the glass surface. Thus, by using a mask, a PDMS slab is obtained in which only a portion of the surface is Ar plasma treated, while the remaining portion is O2 plasma treated. In this way, a PDMS device is created that does not have preformed flow paths but allows gas to flow only between the Ar plasma treated area and the glass surface. The gas flow deforms the PDMS, which leads to color changes that correlate to the flow rate, viscosity and density of the gases used, such as He, Ne, N2, Ar, CO2 and Xe. Here, the present application intends to demonstrate the feasibility of gas measurement using this very simple device. By clarifying the dependence of the PDMS on many factors, including its thickness and its Young's modulus, it becomes possible to more accurately measure a wide range of flow parameters by adjusting these factors. The present invention can also be applied to displaying arbitrary patterns such as logos by flow. The patterns show complex color gradations that reflect the causal relationships of several gas parameters, so that machine learning-based analysis can be used to distinguish various gas mixtures such as odors. The gas measurement and analysis method of the present invention will contribute not only to a wide range of scientific applications such as flow detection and display, but also to the fields of art and entertainment.

[0043] In addition, the device according to the present invention may be expressed as a "device without a flow path", but strictly speaking, when gas is not flowing, the flow path does not have any flow path (disappears), but the cross-sectional area of ​​the flow path becomes zero (that is, the flow path always exists, but when the gas pressure is zero, the flow path is closed). Injecting gas into the device in this state causes the PDMS to deform due to the gas pressure, causing the PDMS to rise from the substrate, and a flow path with a cross-sectional area larger than zero is formed there, that is, the flow path opens. Alternatively, the device can be configured so that the cross-sectional area of ​​the flow path becomes larger than zero even when the gas pressure is zero. If the device is configured so that the flow path cross-sectional area is zero when the gas pressure is zero, the PDMS may not deform sufficiently unless the pressure of the gas injected into such a device becomes large to a certain extent, and the flow path cross-sectional area may remain zero, so that depending on various structural parameters of the device, the device may not operate when the gas pressure is very low.

[0044] In addition, although glass (specifically, soda lime glass) is described as the material of the substrate, other materials can also be used. In the device actually fabricated by the inventor of the present application, the O2 plasma-treated area of ​​the surface of the PDMS slab and the area of ​​the glass surface to be bonded are also treated with O2 plasma, thereby generating radicals and reactive side chains on both O2 plasma-treated surfaces. After that, by contacting both surfaces, adhesion is achieved by the reaction between these radicals and reactive side chains. Therefore, as a substrate material, any material that causes the above reaction can be used instead of glass. Although not limited to this, it has been confirmed that a substrate made of silicon can also be used. Alternatively, a substrate having at least a surface containing a silicon-containing material may also be used. However, glass is suitable as a substrate material for the device according to the present invention in that it is inexpensive and products with various specifications are easily available.

[0045] When the PDMS slab and the substrate are brought into contact with each other, as described above, no chemicals are required to promote the reaction, and it is sufficient to simply press the PDMS slab and the substrate lightly so that they come into contact. Although not essential, the PDMS slab and the substrate can be held at a high temperature for a certain period of time (for example, at 65°C for several minutes) after the contact to achieve stronger adhesion. If the adhesion is to be ensured, the PDMS slab surface alone may be treated with O2 plasma, and then brought into contact with a substrate that has not been treated in this way (and subsequent heat treatment may be performed as necessary) to achieve adhesion.

[0046] It should be noted that the Ar plasma treatment is not essential for bonding the PDMS slab to the substrate, and any bonding method or means that is compatible with the structure and materials of the device of the present invention can be used. When using a bonding method or means other than Ar plasma treatment, a substrate made of any material that is compatible with such a method or means may be used instead of glass (or silicon, etc.).

[0047] In this application, PDMS is used as the material for the channel walls that show structural color when deformed by the internal pressure of the channel, but generally, materials other than PDMS may be used. The conditions required for such channel walls are as follows: The rigidity of at least a part of the inner surface of the flow path wall, which is the region of the flow path wall that exhibits the structural color, is greater than the rigidity of a portion of the flow path wall located inside the inner surface and adjacent to the inner surface. When a fluid to be measured is passed through the flow channel, at least the area of ​​the flow channel wall that is to exhibit the above-mentioned structural color is deformed by the internal pressure of the flow channel. The above-mentioned deformation causes periodic wrinkles to form on the highly rigid inner surface portion of the flow channel, and detectable structural colors are produced by the diffraction of light due to the periodically arranged wrinkles.

[0048] Therefore, although this application describes the use of PDMS as the material of the flow channel wall on which wrinkles are formed by the internal pressure of the flow channel, the material is not limited to PDMS as long as it satisfies the above conditions. In addition, the inner wall portion of the flow channel was hardened by Ar plasma treatment to form a highly rigid surface region, but the inner wall portion of the flow channel wall material may be hardened by other radiation, chemical treatment, or other methods and means, or the inner wall portion may be covered with a material for the inner wall surface other than the flow channel wall. In addition, a flow channel structure consisting of two types of members, in which a member having the above-mentioned properties is attached to a substrate made of another material, is not necessarily necessary, and for example, the flow channel may be formed with a single member. However, the device structure actually produced as an example in this application, that is, the structure and manufacturing method of bonding a PDMS slab, part of whose surface is hardened by Ar plasma treatment, to a glass substrate using surface activation by O2 plasma, has already been proven and established as being suitable for other types of fluid devices, so that by adopting this device structure and manufacturing method, the device of the present invention can be easily produced and a reliable device can be realized.

[0049] In this application, the device according to the present invention has been described as being used exclusively for gas measurement, but considering its principle, it is clear that it can be applied to any fluid, as mentioned above. However, even if an attempt is made to measure a fluid that has a much higher density than gas, such as a liquid, there is a problem that structural color is less likely to appear compared to gas measurement. To explain this specifically, in order to express structural color, interference must occur due to the reflection of light on the surface of the periodic wrinkles. In order for structural color to be clearly expressed, the above reflection must occur to a sufficient degree. However, since the inner wall of the flow channel on which the wrinkles are formed is the interface between the flow channel inner wall material and the fluid to be measured, in order for such sufficient reflection to occur, it is required that the refractive index of the flow channel inner wall material (about 1.412 in the case of using PDMS, and about 1.4 to 2.0 in the case of glass) and the refractive index of the fluid are significantly different. Since the refractive index of gas is almost the same as the refractive index of a vacuum (a value very close to 1.0), the above requirement regarding the refractive index is met for any gas. On the other hand, when a liquid is applied, the difference in refractive index is generally much smaller than that of a gas (the refractive index of water is about 1.3334, and that of ethanol is about 1.3618), so in many cases it is difficult to obtain a structural color that is easily recognizable by the naked eye. Of course, even if the fluid to be measured is a liquid, if its refractive index is significantly different from that of the surface portion of the inner wall of the flow channel, a structural color that can be easily recognized by the naked eye will appear, so in such cases the present invention can be easily applied. Furthermore, unless the refractive indexes of the two are completely the same, a weak structural color will appear, so measurements using the present invention can be made by using image processing or other measurement means that can detect such weak structural colors.

[0050] Furthermore, by making some modifications to the structure of the device, it is possible to fundamentally solve the above-mentioned problem caused by the refractive index being close between the liquid to be measured and the flow channel wall on which wrinkles are formed. The direct cause of the problem that structural color is difficult to appear when the fluid to be measured is a liquid is that the refractive index of the flow channel wall on which wrinkles are formed is close to that of the flow channel wall when the fluid to be measured (in this case, the liquid) comes into contact with the fluid. Therefore, it is sufficient to form wrinkles in the parts of the flow channel wall that are not in contact with the fluid to be measured. Of course, wrinkles may also be formed in the parts that come into contact with the fluid.

[0051] Specifically, in the device according to the present invention described above, the rigidity of the surface (inner wall surface) facing the inside of the flow channel of the member (e.g., PDMS slab) constituting a part of the flow channel wall is made higher than the inside of this member. When a part of the inner wall surface is compressed by the flow of fluid through the flow channel and the flow channel is deformed, wrinkles are formed only in the surface with high rigidity, and structural color appears there. However, the inner wall surface is not the only surface area that is compressed when the flow channel wall is deformed by flowing fluid through the flow channel. For example, refer to the stress distribution (FEA results) of each part of the PDMS slab when a fluid is flowed through a flow channel formed by a substrate and a PDMS slab with its periphery bonded to the substrate (since FIG. 6E is a cross-sectional view of a plane perpendicular to the flow channel, only the left and right ends are bonded in the figure) shown in FIG. 6E. Here, the darker the color, the greater the compressive stress applied. In FIG. 6E, the darker the color of the inner wall surface of the flow channel (the inner surface of the curved part in the center, i.e., the downward surface) is, the greater the compressive stress applied to this surface. Therefore, in the above explanation, wrinkles are formed on the inner wall surface of the flow channel when compressive stress is applied by Ar plasma treatment, and structural color is expressed. However, in Fig. 6E, dark colored areas also appear on the back surface of the PDMS slab (the outer wall surface of the flow channel, the upper surface in the figure). More specifically, both ends of the curved part of the PDMS slab, that is, the area near the boundary between the part where the PDMS slab is bonded to the substrate and the part where it is not bonded, are darker than the surrounding area. In other words, it can be seen that a large compressive stress is applied to the area near both sides of the flow channel in the direction along the cross section in Fig. 6E. Note that the part of the surface where a particularly large compression occurs compared to the surrounding area may be referred to as a compressed area below.

[0052] Figure 15 conceptually shows that a large compressive stress is also applied to the outer wall surfaces of such a channel corresponding to the regions near both sides of the channel. Figure 15 shows an example of the device structure specifically shown above, in which a PDMS slab is bonded to a highly rigid substrate. Of the two surfaces of the PDMS slab, the lower surface in the figure (lower surface) is treated with O2 plasma in the area to be bonded to the substrate, and the area that will become the inner wall surface of the channel is treated with Ar plasma. Furthermore, the opposite surface of the PDMS slab (upper surface) is treated with Ar plasma in the same way as the inner wall surface of the channel, so that the area of ​​the upper surface where compression has occurred will have wrinkles formed in the same way as the inner wall surface of the channel.

[0053] Figure 16 shows the results of a simulation based on the finite element method for the stress tensor on the upper surface of such a device, i.e., on the outer wall surface of the channel in the PDMS slab. In this figure, the device is mapped by shading on a perspective view ((a)) and a top view ((b)). In Figure 16, a fluid is fed from an inlet on the left side of the device and flows toward an outlet on the right side. As can be seen from the perspective view in (a), the inlet and outlet are connected to the vicinity of the start and end of the channel, respectively, via a tubular part extending downward from a circular opening provided on the upper surface of the PDMS slab. In the top view shown in (b) of Figure 16, the inlet and outlet are represented by small white circles near the left and right ends, respectively. The channel is connected to the outside only via the inlet and outlet. For the structure and position of the inlet and outlet, please also refer to Figure 2A. In the figure, the width (cross-sectional area) of the flow channel becomes smaller from the part connected to the inlet to the part connected to the outlet. This is to narrow the outlet side of the flow channel so that the pressure when the fluid is sent from the inlet does not drop significantly inside the flow channel. Such a tapered flow channel can relatively increase the pressure inside the flow channel even with a small flow rate. This causes the flow channel wall to deform more even with a low flow rate, resulting in a clear structural color.

[0054] When a fluid is poured into the device thus constructed, as shown in the lower part of FIG. 15, the fluid enters the unbonded portion between the PDMS slab and the substrate, deforming the PDMS into a dome shape, forming a flow channel. This deformation compresses a part of the inner wall of the flow channel (near the center in the figure), forming periodic wrinkles there, as already explained. However, as already explained with reference to FIG. 6E and as shown in FIG. 15, such periodic wrinkles due to compression also occur on the opposite surface (top surface) of the PDMS slab. Such compressed regions are formed near both sides of the flow channel, as shown in FIG. 15. Therefore, when the fluid flowing through the flow channel is a gas, structural colors are manifested on both surfaces due to wrinkles formed on both the inner and outer wall surfaces of the flow channel. On the other hand, when a liquid such as water is flowed through the flow channel, structural colors are hardly manifested on the inner wall surface in contact with the liquid, as already explained. However, on the outer wall side of the flow channel, the surface rigidity is higher than the inside due to Ar plasma treatment, just like the inner wall surface, and therefore similar periodic wrinkles are formed, especially in the compressed regions near both sides of the flow channel. Therefore, as long as the outer surface of the flow channel is exposed and not in contact with other members or coated with a liquid or solid, the structural color will appear there, regardless of whether the fluid in the flow channel is a gas or a liquid.

[0055] As is clear from the above explanation, if periodic wrinkles due to compression are formed on the entire outer wall surface of the flow channel or at least on the compressed region of the outer wall surface where significant compression occurs, it is possible to produce structural color due to deformation of the flow channel regardless of the presence or absence of a structure in which periodic wrinkles are formed in the compressed region on the inner wall surface of the flow channel. However, if there are circumstances in which the structural color produced on the inner wall side of the flow channel has a greater color intensity, for example, periodic wrinkles may be formed on both the outer wall surface and the inner wall surface of the flow channel. EXAMPLES

[0056] In the following, the embodiments of the present invention will be described in detail. However, it should be noted that the present invention is not limited to these embodiments, and the technical scope of the present invention is defined by the claims.

[0057] Two types of fluid sensors were fabricated using a glass substrate and PDMS using the method specifically described below and shown in Figure 2A. These two types of fluid sensors are hereinafter referred to as the first and second devices, respectively.

[0058] The inner wall of the first device thus fabricated was observed under a microscope with and without N2 gas flow. The results are shown in Figure 1. In addition, the structural colors that appeared when no gas was flowing through the first device and when N2 gas was flowing at various flow rates from 5 mL / min to 400 mL / min were observed. These photographs and the intensity profiles of R, G, B, and light before tricolor separation for positions along the gas flow are shown in Figure 2B. As can be seen from these, when no gas was flowing through this first device, the PDMS slab constituting the first device was not deformed by the internal pressure of the flow channel, so the structural color hardly appeared, but when gas was flowed, the internal pressure was applied to the flow channel, so the PDMS slab was deformed, and as a result, the structural color appeared. As is clear from Figure 2B and Figure 2E, which shows the average intensity profiles of R, G, B, and light not decomposed into tricolor for each flow rate along the flow channel, it was confirmed that this structural color changed in response to the change in flow rate, that is, the change in internal pressure.

[0059] In order to confirm that the deformation of the PDMS slab, which is the low-rigidity component of the flow channel in the first device, increases with an increase in the flow rate, we performed an FEA simulation, the details of which are shown in Figures 6A to 6H. The results are shown in Figure 2C. In this simulation, we directly obtained the stress in the direction perpendicular to the flow that the inner wall surface on the PDMS slab side of the flow channel receives for various flow rates, and this stress naturally causes deformation of the inner wall surface.

[0060] To confirm that the above-mentioned deformation of the inner wall surface caused periodic wrinkles, the first device was observed with a laser microscope while N2 gas was flowed at a flow rate of 10 mL / min. The microscopic image is shown in Figure 2D.

[0061] As an example of the external appearance of the device according to the present invention, a photograph of the first device of the embodiment in which N2 gas is flowing at 400 mL / min is shown in FIG.

[0062] In order to confirm the effect of introducing the above-mentioned defects into the PDMS surface of the inner wall of the flow channel, the rigidity of which has been increased by Ar plasma treatment, a second device, which is another embodiment of the present invention, was fabricated by carrying out the same treatment as the first device, which is the first embodiment, except that the mask used for the Ar plasma treatment was changed to the thin-line mask shown in FIG. 3A. As in the first embodiment, photographs of the second device fabricated in this manner when various flow rates of N2 gas were flowed are shown in FIG. 3B (corresponding to FIG. 2B of the first embodiment), and the average intensity profile of R, G, B, and non-tricolor-separated light for each flow rate along the flow channel is shown in FIG. 3C (corresponding to FIG. 2E of the first embodiment). As can be seen from these figures, the structural color of this embodiment, which uses the thin-line mask, changes more sensitively to changes in flow rate. In addition, by comparing FIG. 2D, which shows the results of observing the wrinkles formed in the first device, which is the first embodiment, with FIG. 3D, which shows the results of observing the second device, which is this embodiment, under the same conditions as the first device, it can be confirmed that more regular wrinkles are formed in the second device, which uses the thin-line mask.

[0063] In addition, the relationship between the displacement of the PDMS part of the flow channel inner wall and the flow rate in this embodiment is shown in Figure 3E. By comparing this result with the relationship between the flow rate and the intensity of the structural color shown in Figure 3C, it was confirmed that there is a strong correlation between the displacement of the flow channel inner wall and the intensity of the structural color. Furthermore, as shown in Figure 3F, it was confirmed that the intensity of the structural color did not change even when the experiment at a large flow rate (500 mL / min) was repeated 50 times, which demonstrated that the operation of the device according to the present invention was sufficiently stable.

[0064] Furthermore, the structural colors were compared when six types of gases, namely He, Ne, N2, Ar, CO2 and Xe, were flowed through the second device of this embodiment. The structural colors appearing in the second device when each gas was flowing and the intensity profile of the structural colors at each position on the flow path are shown in FIG. 10A. FIG. 10B and FIG. 10C show the gas concentration and viscosity and the average intensity of the structural colors in these experiments, FIG. 10D shows the relationship between the calculated and experimental values ​​of the gas density and viscosity and the pressure drop between the inlet and outlet of the flow path, and FIG. 10E shows the relationship between the pressure drop and the displacement. In FIG. 11, the graph on the left shows the average intensity, pressure drop and displacement along the flow path of the structural colors that are not separated into three colors as a function of density, respectively, in the results of measuring various gases using the second device. These results were used in the theoretical analysis described above and their interpretations are given, so please refer to the description for details.

[0065] Furthermore, as a third device, we fabricated a device with the same structure as the first device, but with an additional Ar plasma treatment performed on the outer wall side of the flow channel of the PDMS slab, so that clear structural colors would appear even if the fluid to be measured was a liquid. However, unlike the first device, the third device employs a flow channel that narrows from the inlet to the outlet, as explained above. We observed the structural colors that appeared when gas and liquid were respectively flowed through this device.

[0066] Figure 17(a) shows a photograph of the structural color that appears when nitrogen gas is passed through the third device, and Figure 17(b) shows a photograph of the structural color that appears when liquid water is passed through the same device. In Figure 17(a), the flow path is visible in almost the lower half of the photograph, but in Figure 17(b), the flow path is visible in almost the upper half of the photograph. In addition, the fluids flow from right to left in both cases. In Figure 17(a), where gas is flowing, the structural color that appears in the compressed region near the center of the inner wall of the channel can be seen in both the center of the channel (the part toward the bottom of the photograph (a slightly wide band that appears brighter than the surrounding area and extends horizontally from the right side of the part marked "N2" in the photograph) and the structural color that appears in one of the compressed regions near both sides of the channel on the outer wall of the channel that is within view (the structural color is the slightly wide band that extends horizontally, although it slopes slightly upward to the right, in the center of the photograph). In contrast, in Figure 17(b), where liquid is flowing, no structural color is seen in the center of the inner wall of the channel (a dark band extends horizontally at the top of the screen corresponding to the center of the channel), and only the structural color is seen in the compressed regions near both sides of the channel on the outer wall of the channel (a bright band that extends horizontally appears slightly toward the bottom of the center of the screen).

[0067] [Preparation of PDMS] PDMS slabs were fabricated using a chemical kit (Sylgard 184 from Dow Corning) containing PDMS base material and curing agent. The liquid PDMS mixture, consisting of a 30:1 weight ratio of base material and curing agent, was degassed and poured into a Petri dish. It was cured overnight at 65°C, after which the PDMS was cut into small pieces for further experiments.

[0068] [Plasma treatment] A low pressure plasma system (Femto, version B) purchased from Dieter electronic GmbH + Co. was used. Ar was used as the plasma source to obtain wrinkled PDMS due to strain, and O2 was used as another plasma source to generate an active surface for adhesion to the glass surface. The area to be exposed to the plasma was controlled by using a three-dimensional printed mask. The masked PDMS piece was placed in the plasma chamber and plasma-treated at a plasma power, pressure, and treatment time of 100 W, 0.6 mbar, and 1 min, respectively.

[0069] [Device fabrication] A PDMS slab (20 mm × 50 mm × 2.5 mm) was used to fabricate a device without a channel. The procedure is shown in Figure 2A. To create an inlet and an outlet, two holes (1.5 mm in diameter) were drilled at both ends of the area to be exposed to Ar plasma. A mask with a rectangular opening (25 mm × 10 mm) was used to cover the area to be exposed to O2 plasma later. Immediately after the Ar plasma treatment, the PDMS slab was stretched at a strain rate of 20% for a few seconds. When the PDMS slab was exposed to O2 plasma, a negative mask was used to cover the Ar plasma-treated area. A glass substrate was also placed in the plasma chamber and its surface was activated by O2 plasma. The plasma treatment conditions were 35 W, 0.6 mbar, and 20 seconds. The PDMS that had been subjected to the two types of plasma treatments in this way was bonded to the glass substrate. The device thus fabricated was placed in an oven and heated at 65 °C for a few minutes to ensure adhesion at the boundaries.

[0070] [Photographing the surface under compression using a mold] Ar plasma treated PDMS (20 mm × 50 mm × 2.5 mm) was bonded to the surface of the 3D printed mold as shown in Figure 5B. -1 , 10m -1 and 20m -1Three molds with different curvatures were fabricated, corresponding to strains of 0.8%, 1.3%, and 2.5%, respectively. The strained PDMS samples were observed in laser confocal mode using a 3D surface profiler (Keyence VK-X3000).

[0071] [Gas measurement] He, Ne, N2, Ar, CO2 and Xe were used and the flows were controlled by a mass flow controller (MFC) (SEC-N112MGM, Horiba, Ltd.). The program controlling the MFC was designed using LabVIEW (NI Corporation). The gas streams were injected from the inlet at various flow rates including 5 mL / min, 10 mL / min, 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min and 400 mL / min. To ensure the absence of leaks, the flow rates were measured at the outlet using a volumetric flowmeter (ProFLOW 6000 electronic flowmeter, Restek Corporation). For color analysis, the device was observed in the presence of flow using a stereo microscope (Leica S9i, Leica Microsystems). The color change of the device caused by flow was analyzed using the software ImageJ (version 1.53k).

[0072] [FEA Simulation] The deformation of PDMS under various gas flow conditions was modeled as a time-dependent problem using the FEA software COMSOL Multiphysics 5.6a. Since it is difficult to model the gapless contact interface peeling open due to the internal gas flow, the phenomenon of PDMS swelling due to the injection of gas flow to form a channel was modeled as the deformation of a narrow channel with a height of 50 μm under a 400 mL / min N2 flow, and the absence of contact force at the interface. This PDMS channel had a width of 10 mm, a length of 2.5 mm, and a top wall (PDMS slab) thickness of 25 mm. Note that the above dimensions were different from those used in the FEA simulation of the third device, which was configured to exhibit clear structural colors even when the fluid to be measured was liquid, as shown in Figure 16, etc. Furthermore, since it is similarly difficult to model the gapless contact interface opening due to the inflow of liquid, the initial channel height was modeled as 500 μm. Further details on the numerical model can be found in

[10] , where smaller channel deformations are calculated and verified experimentally. [Industrial Applicability]

[0073] INDUSTRIAL APPLICABILITY As described above in detail, the present invention can provide a device that is small, has a simple structure, and is easy to manufacture, and can be used for a variety of purposes, such as a fluid sensor, and thus can be widely used in industry. [Prior art documents] [Patent documents]

[0074] [Patent Document 1] Patent Publication No. 2006-242819 [Non-patent literature]

[0075] [Non-Patent Document 1] JMK Ng, I. Gitlin, AD Stroock, GM Whitesides, Electrophoresis 2002, 23, 3461.

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Non-licensed literature 9

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Claims

1. It has a flow path surrounded by a wall made of a material that is deformed at least in part by an internal pressure applied by a given fluid, Periodic wrinkles are formed by the deformation on at least a part of at least one surface of the flow path side and the side opposite to the flow path of the wall, A structural color is exhibited on at least a part of at least one surface by the wrinkles, Fluid sensor.

2. The at least one surface of the wall has a surface region that is more rigid than the inside of the wall, The fluid sensor according to claim 1, wherein the wrinkles are formed by compressing at least a part of the highly rigid region of the at least one surface by the deformation.

3. A part of the wall of the flow path is made of a material that is less rigid than the remaining part of the wall of the flow path, The highly rigid surface region exists on at least one surface of the flow path of the part made of a material that is less rigid than the remaining part of the wall of the flow path, The fluid sensor according to claim 2.

4. The fluid sensor according to claim 3, wherein the less rigid material is polydimethylsiloxane.

5. The material constituting the remaining part of the wall of the flow path is a material containing silicon, A first adhesion region on the surface of a first member made of polydimethylsiloxane and a second adhesion region on the surface of a second member made of a material containing silicon and corresponding to the first part of the surface of the first member are adhered, The region surrounded by the adhered first and second adhesion regions and not adhered itself is used as the flow path, The fluid sensor according to claim 4.

6. The fluid sensor according to claim 5, wherein the material containing silicon is glass or silicon.

7. The fluid sensor according to claim 5, wherein the highly rigid surface region is formed by subjecting the polydimethylsiloxane surface to Ar plasma treatment.

8. Both the first adhesion region of the first member composed of the polydimethylsiloxane and the second adhesion region of the second member composed of the silicon-containing material or only the first adhesion region are O ２ The fluid sensor according to claim 5, wherein the sensor is plasma-treated.

9. The surface of the first member including the first adhesion region and the surface of the second member including the second adhesion region are flat surfaces,

10. Openings are provided near one end and the other end of the flow path, and the fluid flows between the two openings.

11. In a state where the internal pressure by the fluid is not applied to the surface of the wall of the flow path, the flow path is closed, and when the internal pressure by the fluid is applied, a portion of the wall of the flow path made of the deformable material deforms, thereby opening the flow path. The fluid sensor according to any one of claims 1 to 10.

12. Treat a partial region of the surface of a member made of polydimethylsiloxane with Ar plasma, At least a part of the remaining area of the surface of the member is treated with O ２ plasma, The O of the member ２ By adhering the region treated with plasma to a substrate containing silicon, a flow path is formed in the region treated with the Ar plasma A method for manufacturing a fluid sensor in which a structural color appears on at least a part of the surface due to the internal pressure applied by a given fluid.

13. The O of the member ２ The method of manufacturing a fluid sensor according to claim 12, wherein the process of bonding the plasma-treated region of the member to the substrate containing silicon is performed by bringing the region of the member into contact with the surface of the substrate.

14. The treatment with the Ar plasma and the treatment with the O ２ The method for manufacturing a fluid sensor according to claim 13, wherein the treatment with the plasma is performed using a mask in which the relationship between transmission and shielding is reversed.

15. The treatment with the Ar plasma uses a mask that allows the Ar plasma to pass through the region to be the flow path, and By having a thin wire-like member in a part of the region on the mask through which the Ar plasma should pass, the region of the member located under the thin wire-like member is protected from the irradiation of the Ar plasma A method for manufacturing a flow path according to claim 12 or 13.

16. A flow path surrounded by a wall made of a material that is deformed at least in part by the internal pressure applied by a given fluid, Periodic wrinkles are formed on at least a part of at least one surface of the flow path side and the side opposite to the flow path of the wall due to the deformation, A structural color appears on at least a part of at least one surface due to the wrinkles, Flow path.

17. The at least one surface of the wall has a surface region that is more rigid than the inside of the wall, The wrinkle is formed by compressing at least a part of the highly rigid region of the at least one surface by the deformation. The flow path according to claim 16.

18. A part of the wall of the flow path is made of a material that is less rigid than the remaining part of the wall of the flow path, The highly rigid surface region exists on at least one surface of the flow path of the part of the wall of the flow path that is made of a material that is less rigid than the remaining part of the wall of the flow path, The flow path according to claim 17.

19. Treat a partial region of the surface of a member made of polydimethylsiloxane with Ar plasma, Treat at least a part of the remaining area of the surface of the member with O ２ plasma, The O of the member ２ By adhering the region treated with plasma to a substrate containing silicon, a flow path is formed in the region treated with the Ar plasma A method for manufacturing a flow path in which a structural color appears on at least a part of the surface due to the application of internal pressure.

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