Method and device for measuring dynamic contact angle value of liquid on solid surface

Abstract

The invention discloses a method and a device for measuring a dynamic contact angle of liquid on a solid surface. The method comprises the following steps: constructing a to-be-measured system containing a first liquid phase, a fluid phase and a solid phase; immersing the to-be-detected surface of the solid phase in the environment phase upwards or downwards; an end surface object is arranged opposite to the to-be-detected surface, and the two are immersed in the same environment phase; the relative distance and position of the two are adjusted, and a longitudinal fluid bridge is formed through the liquid adding device; the camera device obtains a fluid bridge interface contour image from the side surface; horizontally moving the surface of the end surface object or the solid phase, and applying transverse lateral dragging acting force to the fluid bridge to promote the fluid bridge to deform and contact the peripheral line to move or be about to move; and recording the time sequence change of the image, analyzing and calculating to obtain the time change relationship between the contact angle value and the three-phase contact point position value, and further determining the static, forward and backward contact angles and the contact angle hysteresis value. The method is simple and accurate, has wide applicability, and can cover reliable dynamic contact angle data measurement from hydrophilic to super-hydrophobic surfaces.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of surface science and applied measurement and characterization technology, in particular to a method and device for measuring dynamic contact angle of liquid on solid surface. BACKGROUND

[0002] Contact angle measurement is a key technical means for characterizing the wettability of solid surface. However, due to the existence of contact angle hysteresis, for the same liquid / solid system, the contact angle value is not a single value, but varies within a range, and the difference between the maximum value and the minimum value is called contact angle hysteresis. Therefore, only measuring the static contact angle is not enough to fully characterize the wettability of the surface, and dynamic contact angle measurement (measuring contact angle hysteresis) is more comprehensive and important. The current mainstream dynamic contact angle measurement methods have many limitations: 1. Droplet volume increase and decrease method: it needs to configure an automatic two-way liquid distribution device, and the liquid needle tube needs to be inserted into the droplet, which will interfere with the droplet shape and affect the measurement (calculation) accuracy. Moreover, for many systems, it is difficult to obtain a clear receding contact angle value, and it is also difficult to apply to the captive bubble method. 2. Inclined table method: it needs to configure a special inclined table, and the driving force for moving the droplet is only the gravity of the droplet itself. For systems with large adhesion or significant contact angle hysteresis, it is often difficult to drive the droplet to move, and the normal pressure of the droplet changes with the inclination angle. For some systems, it is difficult to obtain a clear receding contact angle value. 3. Centrifugal rotation table method: it needs to configure a special rotation table, the instrument is complex, the popularization rate is low, and the droplet is easy to evaporate during the measurement process. These methods generally have problems such as complex instrument configuration, tedious operation, narrow application range for sample surface properties, etc. Therefore, there is an urgent need in the field for a new dynamic contact angle measurement method that is simple to operate, widely applicable, and reliable in results. SUMMARY

[0003] The purpose of the present application is to provide a method and device for measuring dynamic contact angle of liquid on solid surface. The present application can provide reliable dynamic contact angle data for a wide range of surfaces from superhydrophilic to superhydrophobic, without the need for complex special extension modules, and has the advantages of simplicity, accuracy and wide applicability.

[0004] The technical scheme of the present application: a method for measuring dynamic contact angle of liquid on solid surface, comprising the following steps: Step 1: constructing a system to be tested, the system to be tested comprising a first liquid phase, a fluid phase and a solid phase, the fluid phase being a gas phase or a second liquid phase incompatible with the first liquid phase; Step 2: immersing the surface to be tested of the solid phase upward or downward in an environment phase, the environment phase being one of the first liquid phase, the gas phase or the second liquid phase; Step 3: arranging an end surface object opposite to the surface to be tested, the end surface of the end surface object and the surface to be tested being immersed in the same environment phase. Step 4, adjust the relative distance and position between the end surface of the end surface object and the solid phase surface, and distribute the fluid for building fluid bridge through the liquid adding device, to form a longitudinal fluid bridge between the end surface of the end surface object and the solid phase surface; the fluid for building fluid bridge is the first liquid phase or the fluid phase; Step 5, observe the fluid bridge from the side through the camera device to obtain the fluid bridge interface profile image; Step 6, controllably move the horizontal position of the end surface object or / and the solid phase surface to exert a horizontal lateral dragging force on the fluid bridge, so that the fluid bridge is deformed and the contact periphery line of the fluid bridge and the solid phase surface is moved or about to be moved; Step 7, record the change of the fluid bridge interface profile image over time, and analyze and calculate the image to obtain the change relationship of the contact angle value and the corresponding three-phase contact point position value over time; Step 8, determine the static contact angle, the initial contact angle, the advancing contact angle, the receding contact angle and the contact angle hysteresis value according to the change of the contact angle value over time or the three-phase contact point position.

[0005] The above-mentioned method for measuring the dynamic contact angle value of liquid on solid surface, the step of analyzing and calculating the image is realized by any one of the following ways: calculating after recording, real-time calculation, or real-time calculation while recording.

[0006] The above-mentioned method for measuring the dynamic contact angle value of liquid on solid surface, the horizontal lateral dragging force is exerted by separately moving the horizontal position of the end surface object or by separately moving the horizontal position of the sample surface.

[0007] The above-mentioned method for measuring the dynamic contact angle value of liquid on solid surface, the liquid adding device is provided with the fluid for building fluid bridge, and the formation of the fluid bridge is realized by one of the following ways: (1) first forming a fluid drop on the end surface of the end surface object or the solid phase surface, and then contacting the fluid drop with the other surface to form the fluid bridge by adjusting the relative distance; (2) first adjusting the distance between the end surface object and the solid phase surface, and then filling the fluid for building fluid bridge into the distance through the liquid adding device to directly form the fluid bridge.

[0008] The above-mentioned method for measuring the dynamic contact angle value of liquid on solid surface, in the process of forming the fluid bridge, the horizontal position of the sample surface or / and the end surface object is simultaneously changed, and the change direction is perpendicular to the observation direction of the camera device.

[0009] The method for measuring the dynamic contact angle of a liquid on a solid surface, wherein the end surface object is a liquid feeding needle tube, and the liquid feeding needle tube is connected to the liquid feeding device; and the liquid feeding device is controlled to form a liquid drop with a proper volume at the outlet end of the liquid feeding needle tube to form the liquid bridge.

[0010] The method for measuring the dynamic contact angle of a liquid on a solid surface, wherein the angle between the direction of the lateral pulling force and the direction of gravity is not less than 45 degrees.

[0011] The method for measuring the dynamic contact angle of a liquid on a solid surface, wherein the angle between the placement direction of the surface of the solid to be measured and the horizontal plane is not more than 45 degrees.

[0012] The method for measuring the dynamic contact angle of a liquid on a solid surface, wherein only one or several images of the liquid bridge interface profile are saved and / or calculated to obtain an approximate dynamic contact angle measurement result during the measurement.

[0013] A device for implementing the above-mentioned measurement method, comprising: a base; a background light source, a camera device, a sample platform adjusting device and a support arranged on the base; a sample platform arranged at the upper end of the sample platform adjusting device, the sample platform being used for placing a solid phase or a transparent test chamber; a suspended support platform arranged by the support, the suspended support platform being fixed with a liquid feeding device, and the liquid feeding device being arranged below an end surface object; at least one of the sample platform adjusting device and the suspended support platform is provided with a horizontal moving shaft, and the moving direction of the horizontal moving shaft is perpendicular to the observation direction of the camera device; a computer, and the camera device and the liquid feeding device are connected to the computer by cables.

[0014] Compared with the prior art, the present application can more quickly and reliably obtain more complete measurement data for a wider range of systems by using a simpler method to characterize and measure the wettability of a liquid on a solid surface, the uniformity of the solid surface, and the mutual adhesion between the liquid / solid interface.

[0015] In addition, the present application uses a liquid bridge as a probe for measuring the contact angle value, controls the size of the liquid bridge, and makes the interface shape (trend) of the liquid bridge in contact with the sample surface decoupled from the contact behavior of the other end of the liquid bridge, while maintaining the transmission of the force, the force being controllable and strong.

[0016] Compared with the existing measurement method using an inclined table, the pushing (dragging) contact line position movement force that can be applied is only limited by the force transmission limit, which is much higher than the maximum force of the inclined table method depending on the droplet weight itself, is suitable for measuring a wider range of liquid / fluid / solid systems, such as from a hydrophilic surface to a super-hydrophobic surface, and does not require an inclined table or the like, and the liquid pressure on the surface can be kept substantially constant during the measurement.

[0017] Compared with the conventional droplet volume increase / decrease method, the method of the present application can be performed manually, without the need for an automatic liquid feeding device, and there is no problem of random droplet sliding during the droplet volume increase process. Since the fluid bridge interface is dragged over the sample surface during the measurement, there is no long time difference between the advancing contact angle and the receding contact angle before the measurement, which avoids the possible influence of the long time contact of the liquid with the sample surface on the receding contact angle value, and the advancing and receding contact angle values can be obtained almost at the same time, so that the receding contact angle value in the obtained curve is more obvious (sensitive) and clear.

[0018] Compared with the method based on the rotating centrifugal force, the present application first does not need to configure a special rotating centrifugal measurement module for the instrument, and secondly does not have the problem of droplet evaporation due to rotation, and has low cost and stability.

[0019] For applications requiring the use of the captive bubble method for measurement, the present application provides a simpler measurement method. In the method of the present application, the sample surface is immersed in a (first) liquid phase, the surface to be measured is placed upward, and a fluid bridge is constructed using a gas phase for measurement. In the ordinary captive bubble method, the surface to be measured must be placed downward, and a hook-shaped needle tube with an upwardly turned outlet must be used for measurement, which is cumbersome to operate and difficult to measure the dynamic contact angle.

[0020] In summary, the present application is based on the ordinary optical video contact angle measuring instrument, and can be implemented without special hardware expansion, expands the function and application range of the ordinary optical video contact angle measuring instrument, has the characteristics of strong device universality, wide applicability, simple measurement, high reliability of the result, and powerful function. In addition, the device of the present application has the characteristics of simple structure, small space occupation, easy maintenance, high automation of calculation, and low requirement for the measurement environment. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic diagram of the overall structure of the measurement device in Example 1 of the present application; Figure 2 FIG. 2 is a schematic diagram of the detailed structure of the measurement device in the specific embodiment of the present application Figure 3 The interface profile images of the fluid bridge at different stages of measurement, from left to right, are the initial state before horizontal movement, the state in which the fluid bridge shape is severely deformed but the left contact line does not move, and the state at the moment before the end of movement; Figure 4 The curves of the contact angle value and the horizontal position value of the three-phase contact point versus the frame number of the video in Example 3; Figure 5 The initial state image of the fluid bridge before horizontal movement in Example 4; Figure 6 The state image of the fluid bridge at the end of horizontal movement in Example 4; Figure 7 The relationship between the contact angle value and the coordinate position of the three-phase contact point and the measurement time in Example 4; Figure 8 The schematic diagram of the cross-sectional image of the fluid bridge in the xz plane; Figure 9 The state of the fluid bridge before movement is shown; Figure 10 The state of the fluid bridge after the three-phase contact point slides.

[0022] The marks in the drawings are: 1 - base, 2 - sample platform adjusting device, 3 - sample platform, 4 - support, 5 - camera device, 6 - computer, 7 - up-down adjusting device, 8 - liquid adding driving device, 9 - syringe, 10 - liquid adding needle tube, 11 - background light source, 12 (sample platform adjusting device) up-down moving adjusting shaft, 13 - cable, 14 - sample, 15 - (suspended support platform) horizontal movement adjusting shaft, 16 - optical platform support, 17 - liquid adding device, 18 - (sample platform adjusting device) horizontal movement adjusting shaft, 20 - suspended support platform. DETAILED DESCRIPTION

[0023] The application will be further described below in conjunction with the drawings and examples, but it is not limited to the basis of the application.

[0024] Example 1: A method for measuring the dynamic contact angle value of a liquid on a solid surface, comprising the following steps: Step 1, constructing a system to be measured, the system to be measured comprising a first liquid phase (liquid phase 1), a fluid phase and a solid phase, the fluid phase being a gas phase (gas G) or a second liquid phase (liquid phase 2) incompatible with the first liquid phase; Step 2, immersing the surface to be measured of the solid phase upward or downward in the environment phase, the environment phase being one of the first liquid phase, the gas phase or the second liquid phase; Step 3, a hollow or solid end-faced object (hereinafter referred to as end-faced object) made of solid material is placed (submerged) in the same environmental phase, and the end face can be a plane or a curved surface. The specific object can be a rod / tube / block / ring; Step 4, adjust the relative distance and position between the end-faced object and the solid phase surface, that is, at least one of the solid phase (surface) and the end-faced object can be adjusted in horizontal position, and at least one of them can be adjusted in vertical height position; by controlling the liquid adding operation and amount of a fluid dispensing device (liquid adding device) containing liquid phase 1 (when the environmental phase is gas G or liquid phase 2), or gas G (when the environmental phase is liquid phase 1), or liquid phase 2 (when the environmental phase is liquid phase 1), and adjusting and controlling the (relative) vertical / horizontal distance or / and position between the end-faced object and the solid phase surface, a suitable volume and height of a longitudinal fluid bridge (bridge constructed by liquid phase 1 or gas G or liquid phase 2, hereinafter referred to as fluid bridge Liquid Bridge) is formed between the end face of the end-faced object and the solid phase surface, one end of which is in contact with the sample surface, and the other end is in contact with the end face of the end-faced object.

[0025] Step 5, observe the formed fluid bridge from the side by a camera device to obtain a fluid bridge interface side projection profile image (hereinafter referred to as fluid bridge interface profile image).

[0026] Step 6, by controllably moving (changing) the horizontal position of the end-faced object or / and the sample surface, a horizontal lateral pulling force is applied to one end or both ends of the fluid bridge bridgehead, causing the fluid bridge to deform in a horizontal lateral direction, and eventually causing the contact line (hereinafter referred to as CL) of the end in contact with the sample surface to move (or about to move), so as to cause the CL to advance (or about to advance) to the sample surface area which has not been contacted (wetted) by the fluid phase of the fluid bridge before, or / and (simultaneously or before and after) retract (or about to retract) to the sample surface area which has been contacted (wetted) by the fluid phase of the fluid bridge.

[0027] Step 7, record the change of fluid bridge interface profile image with time (t) from the side perpendicular to the moving direction, and analyze and calculate the recorded images afterwards to obtain the contact angle value (CA) and its corresponding three-phase contact point position value (3PCP) with time.

[0028] Step 8, by plotting CA versus 3PCP or versus t, the static contact angle, the initial contact angle or the spreading contact angle values can be obtained from the images before the force is applied; the dynamic changes of the contact angle values, including the left and right contact angle values (CA_L, CA_R) and the corresponding left and right three-phase contact point positions (3PCP-L, 3PCP-R), the contact diameter (CD) as a function of time (t), from which the maximum / minimum contact angle, the advancing contact angle, the receding contact angle, and the contact angle hysteresis (CAH), which is the difference between the advancing and receding contact angles, can be determined, can be obtained from the images after the force is applied, especially from the images in the time interval when the CL starts to move or is about to move. From the observation of the advancing / receding contact angle as a function of the sample surface position, further evaluation of the uniformity of the sample surface can be made.

[0029] In this embodiment, the end surface object is a liquid delivery needle tube, which is connected to a liquid delivery device containing a fluid phase (liquid phase 1 or gas G or liquid phase 2) for building a liquid bridge; by adjusting the distance between the outlet of the liquid delivery needle tube and the sample surface, and by controlling the liquid delivery amount of the liquid delivery device, a liquid bridge between the end surface of the needle tube outlet and the sample surface is formed by one of the following three methods for the measurement: (1) Method 1: first form a droplet or a bubble of a certain volume on the sample surface by the liquid delivery device, then let the end surface of the end surface object (here the outlet end surface of the liquid delivery needle tube) contact the droplet or bubble to form a liquid bridge; (2) Method 2: form a droplet or a bubble of a suitable volume on the outlet end surface of the liquid delivery needle tube, then adjust the relative vertical position to let the droplet or bubble contact the sample surface to form a liquid bridge; (3) Method 3: first adjust the distance between the outlet end surface of the liquid delivery needle tube and the sample surface, then control the liquid delivery amount of the liquid delivery device to let the fluid phase (liquid phase 1 or gas G or liquid phase 2) fill the gap between the two surfaces to form a liquid bridge of a suitable volume that simultaneously contacts the two surfaces.

[0030] In another embodiment, a liquid delivery device containing a fluid phase (liquid phase 1 or gas G or liquid phase 2) for building a liquid bridge, which is connected to a liquid delivery needle tube (or capillary tube) with a suitable outer diameter, length and shape, is used to form the liquid bridge between the end surface of the end surface object and the solid sample surface for the measurement by one of the following three methods: (1) Method 1: First, a certain volume of liquid or gas droplet is formed on the sample surface by the liquid adding device, and then the liquid adding device or the liquid adding needle tube (or capillary tube) connected with the liquid adding device is removed; then the end surface of the end surface object is contacted with the liquid or gas droplet to form a fluid bridge. (2) Method 2: First, a certain volume of liquid or gas droplet is hung or placed on the end surface of the end surface object by the liquid adding device, and then the liquid adding device or the liquid adding needle tube (or capillary tube) connected with the liquid adding device is removed; then the liquid or gas droplet is contacted with the sample surface by adjusting the relative vertical position to form a liquid bridge. (3) Method 3: First, the distance between the end surface of the end surface object and the sample surface is adjusted, and then the outlet of the liquid adding needle tube (or capillary tube) is inserted into the interval between the two surfaces, and by controlling the liquid adding amount of the liquid adding device, the fluid phase (liquid phase 1 or gas G or liquid phase 2) fills the interval between the two surfaces to form a fluid bridge with a suitable volume contacting the two surfaces at the same time.

[0031] During the formation of the fluid bridge, the horizontal positions of the sample surface and / or the end surface object are simultaneously changed, and the change direction is perpendicular to the observation direction of the camera.

[0032] In this embodiment, the specific process of calculating the contact angle value from the obtained fluid bridge interface profile image is as follows: Figure 8 A cross-sectional image of a fluid bridge in the xz-plane is shown, the sample surface is located in the xy-plane at z=0, and the coordinate position of the fluid bridge interface profile in the xz-plane can be represented by (x, z); p(x, z) is a coordinate point on the fluid bridge interface profile, and the tangent line and x-axis form an angle. q is a point on the three-phase contact edge line of the fluid bridge profile bottom and the sample surface, with coordinates (r, 0), and r is the bottom contact radius; is the contact angle formed by the fluid bridge and the sample surface.

[0033] The coordinate point set of the fluid bridge interface profile is obtained by image analysis on the obtained fluid bridge interface profile image , which is fitted to a suitable mathematical model, which can be the following generalized Laplace-Young equation: ; In the formula, is a system parameter, is a reference size, and is the principal curvature radius of the profile at the z height position, is the Bond Number for measuring the ratio of the gravitational force to the surface (or interfacial) tension force, which is defined as follows: ; wherein , and are the density difference, the interfacial tension, the gravitational acceleration, respectively, wherein is a constant, and are the system parameter values (which can be treated as known values).

[0034] Or other suitable curve equations such as quadratic curve equation, elliptic equation, polynomial equation, spline function (such as B-spline / B-Spline curve function) and the like, as well as combinations of multiple equations / functions. Different calculation methods result in different calculation accuracy. Figure 9 and Figure 10 show two fluid bridge interface profile images obtained in a measurement process, Figure 9 shows the fluid bridge state before movement, Figure 10 is the fluid bridge state when the movement has caused the 3PCP position to slide, and the left and right side contact angle values calculated therefrom (using the generalized Laplace-Young equation fitting method).

[0035] In this embodiment, the step of recording the fluid bridge interface profile images over time and then analyzing and calculating the recorded images is replaced by a method of recording and calculating simultaneously or only calculating.

[0036] In this embodiment, when the movement process reaches one end, the direction of movement is immediately reversed, and the fluid bridge interface is moved in the opposite direction, causing the fluid bridge interface to deviate from one side to approach the axisymmetric shape again and then deviate from the other side, finally driving the fluid bridge to slide relative to the sample surface along the contact edge line (CL) on the opposite side to continue the measurement. By comparing the contact angle values obtained from two different movement directions over time, comparing the advancing / receding contact angle values obtained from two different movement directions, and investigating the repeatability or degree of change of the corresponding values in a specific surface area.

[0037] In this embodiment, the adjustment of the horizontal position or the vertical height position can be manual or automatic control; the liquid adding device can be manually controlled or automatically controlled.

[0038] In the embodiment, the solid phase surface to be measured and the moving direction of the applied force are not parallel, and one or both of them can deviate from the horizontal direction, but the absolute value of the included angle between them is not more than 45 degrees. The included angle between the placement direction of the solid phase surface to be measured and the horizontal plane is not more than 45 degrees.

[0039] In the embodiment, the end surface of the support object for supporting one end of the fluid bridge can be circular, oval, egg-shaped (conical), or a polygon close to a circle, with a diameter or effective diameter of 0.1-10 mm, and the volume of the fluid bridge is 0.1-50 ul. The specific suitable value is related to the interfacial tension of the fluid bridge interface and the density difference between the two phases of the system (between the fluid bridge phase and the environment phase), and the wettability (dynamic contact angle value) of the sample surface: the smaller the (effective) diameter of the end surface of the support object, the lower the interfacial tension of the fluid bridge, the better the wettability of the fluid bridge on the sample surface, the greater the density difference of the system, and the smaller the suitable droplet or bubble volume; the (effective) diameter of the end surface of the support object is generally larger for measuring the sample surface with better wettability. The volume of the fluid bridge does not have to be known in advance, and does not have to be kept constant during the entire measurement process.

[0040] As a preferred solution, only one or several images in the process can be saved and / or calculated for the measurement to obtain a (fast) approximate measurement result. The step of analyzing and calculating the images is realized in any of the following ways: video recording and then calculation, real-time calculation, or real-time calculation while video recording.

[0041] Embodiment 2: A device for implementing the measurement method of embodiment 1, as shown in Figure 1 and Figure 2 , comprising: a base 1; a background light source 11, a camera device 5, a sample platform adjusting device 2, and a support 4 arranged on the base 1; a sample platform 3 arranged on the upper end of the sample platform adjusting device 2, which is used to place a solid phase or a transparent test chamber 14; a suspended support platform 20 arranged by the support 4, and a liquid adding device 17 fixed on the suspended support platform 20, and the liquid adding device 17 is arranged below the end surface object 10; At least one of the sample platform adjusting device 2 and the suspended support platform 20 is provided with a horizontal moving shaft, and the moving direction is perpendicular to the observation direction of the camera device 5; a computer 6, and the camera device 5 and the liquid adding device 17 are connected to the computer 6 through a cable 13.

[0042] In this embodiment, both the sample platform adjustment device 2 and the suspended support platform 20 are equipped with horizontal moving axes, the direction of which is perpendicular to the camera observation direction. The sample platform adjustment device 2 includes tilt adjustment, with a maximum tilt angle of 45 degrees. The horizontal moving axis of the suspended support platform 20 is equipped with tilt adjustment, with a maximum tilt angle of 45 degrees. The suspended support platform 20 is also equipped with a vertical moving axis. The movement of the moving platform and the moving axis can be manual or electric. The movement of the electric moving platform and the moving axis is controlled by application software running on the computer 6 or application software running on an independent control panel. The liquid addition device 17 is loaded with a fluid phase (liquid phase 1, gas G, or liquid phase 2) that forms a fluid bridge. The liquid addition device 17 can be manually controlled or electrically controlled. The liquid addition operation of the electrically controlled liquid addition device 17 is controlled by application software running on the computer 6 or application software running on an independent control panel. The liquid dispensing device 17 is (directly) fixed to the suspended support platform 20. The liquid dispensing device 17 is connected to a liquid dispensing needle 10, the outlet of which is either downward or upward through bending. The outlet end face of the liquid dispensing needle 10 is used as an end effector. The end face of the end effector can be circular, elliptical, egg-shaped (conical), or a near-circular polygon, with a diameter or effective diameter between 0.1 and 10 mm.

[0043] Example 3: This example describes the measurement of the dynamic contact angle of a water droplet on a protective film surface. The device is as follows: Figure 2 As shown, the system includes a base 1, on which a background light source 11, a platform adjustment device 2, an optical platform 16, and an inverted "L"-shaped support 4 are sequentially mounted. The sample platform adjustment device 2 has a vertical up-and-down adjustment axis 12, a horizontal adjustment axis 18, and a sample platform 3. The optical platform 16 has a camera device 5. The support 4 has a suspended support platform 20, on which a horizontal adjustment axis 15 and an up-and-down adjustment device 7 are mounted. The adjustment direction of the horizontal adjustment axis 15 is perpendicular to both the direction of gravity and the direction of camera observation. The up-and-down adjustment device 7 has a liquid addition device 17, which includes a liquid addition (motor) drive device 8, a syringe 9, and a liquid addition needle 10. The camera device 5 and the liquid addition drive device 8 are connected to a computer 6 via a cable 13. The liquid addition needle 10 is located above the sample platform 3. The center lines or center normals of the background light source 11, the sample platform 3, and the camera device 5 are adjusted to be on the same plane.

[0044] The motor and camera device 5 in the liquid addition drive device 8 are controlled by corresponding software on a computer.

[0045] During the experiment, the syringe 9 of the liquid addition device 17 is filled with purified water for measurement. The liquid addition needle 10 is a straight cylindrical metal needle with an outer diameter of 2.7 mm. The sample 14 is placed on the sample platform 3, and the vertical up-and-down movement adjustment axis 12 of the platform adjustment device 2 is adjusted so that the sample to be measured appears in the bottom area of ​​the image window (see...). Figure 3 (a) Adjust the vertical position of the up-down adjustment device 7 and the horizontal position of the horizontal movement adjustment axis 15 so that the needle outlet appears in the image window, its horizontal position is located in the middle-left area of ​​the image, and the lower outlet is about 2-4 mm above the sample surface; the software control device 17 forms a suspended water droplet of about 4 μL at the lower port of the needle 10, and then the recording is started. Adjust the vertical position of the up-down adjustment device 7 so that the top and bottom of the water droplet (Apex) contacts the sample surface, and continue to move downward to squeeze the fluid bridge about 0-0.5 mm before stopping the up-down adjustment. Then, manually operate the horizontal movement adjustment axis 15 to slowly and evenly move the liquid injection needle from left to right until a significant movement is observed at the bottom contact line of the fluid bridge or the movement reaches the required range, then stop the movement and stop the recording. Open the recording and use the generalized Laplace-Young equation method to calculate the recorded image. Figure 3 Images of the fluid bridge at different stages are given: (a) before the start of horizontal movement; (b) before the fluid bridge shape is severely deformed and the position of the left contact line shifts; (c) just before the end of the movement. Figure 4 The calculation results are presented. The horizontal axis in the figure represents the number of frames in the recorded video, equivalent to the progress time. The left vertical axis represents the contact angle value, and the right vertical axis represents the horizontal position values ​​of the left and right three-phase contact points on the sample surface at the fluid bridge interface. Curves 1-4 represent the right contact angle value, left contact angle value, and the horizontal position values ​​of the right and left three-phase contact points, respectively. Figure 4The curve of the right side shows that the contact angle value is very close to 122.5 degrees before the movement starts. The contact angle value of the right side changes from the start of the movement and increases to about 130 degrees when the three-phase contact point position (3PCP-R) of the right side changes. Then, as the 3PCP-R continuously changes, the contact angle basically fluctuates around 125 degrees with a fluctuation range of about 2 degrees up and down, and occasionally re-approaches 129-130 degrees. 125 degrees corresponds to the advancing contact angle value, and the peak value close to 130 degrees is the maximum advancing contact angle value. The situation of the left side is significantly different: the three-phase contact point position (3PCP-L) of the left side basically remains unchanged at the start of the movement, but the contact angle value continuously and rapidly decreases. About to the 160th image, the 3PCP-L value starts to change slowly, and the left side contact angle has decreased to about 33 degrees at this time. About to the 190th image, the 3PCP-L value starts to move obviously, and the left side contact angle has decreased to about 31 degrees at this time. After that, the 3PCP-L value continuously and continuously changes, and the corresponding contact angle value fluctuates around 32.5 degrees with a fluctuation range of about 1.5 degrees, and the lowest value is about 29 degrees. Therefore, it can be determined that 32.5 degrees corresponds to the receding contact angle value, and the lowest receding contact angle value is about 29 degrees. The contact angle hysteresis (CAH) = 125 - 32.5 = 92.5 degrees can be calculated from the advancing contact angle value and the receding contact angle value. The difference is large, which means that the dynamic mobility of the droplet on this sample surface is very poor, and a relatively large force needs to be applied to make the movement occur. If only the static contact angle of about 120 degrees presented by the sample surface is evaluated, it is difficult to recognize its true surface properties. Such a sample surface is basically impossible to measure the dynamic contact angle by the tilting table method, even if the volume of the droplet is increased to nearly 100 ul. This is confirmed by the corresponding tilting table experiment. This embodiment embodies the advantages of the method of the present application.

[0046] Example 4: This embodiment is the measurement of the dynamic contact angle of a water droplet on a sample surface, including the measurement of static and / or initial contact angle, advancing contact angle, receding contact angle, and CAH. The measurement device is similar to that of Example 3, but the horizontal movement adjustment shaft 15 is replaced by a motor-driven automatic movement shaft controlled by software. During the experiment, the syringe 9 of the liquid feeding device 17 was filled with pure water for measurement, and the liquid feeding needle tube 10 was a straight cylindrical metal needle tube with an outer diameter of 1.50 mm; the sample 14 was placed on the sample platform 3, and the platform vertical up-down movement adjustment shaft 12 provided by the platform adjustment device 2 was adjusted so that the sample to be measured position appeared in the bottom area of the image window (see Figure 5); the vertical position of the up-and-down adjustment device 7 and the horizontal position of the horizontal movement adjustment shaft 15 are adjusted so that the needle tube outlet appears in the image window, and its position is located in the upper left area of the image (see Figure 5 ), and the position to be measured on the sample surface is located directly below the needle tube by adjusting the horizontal movement adjustment shaft 18 of the platform. A hanging water droplet of about 3.5ul is formed at the lower end of the needle tube 10 by the software control device 17. The vertical position of the up-and-down adjustment device 7 is continuously adjusted so that the hanging droplet slowly approaches the sample surface and comes into contact with the sample surface, and then continues to be pressed downward by a certain amplitude (about 0-0.5mm, see Figure 5 ). The movement speed of the horizontal movement adjustment shaft 15 is set to 1mm / min, the maximum movement amplitude is 0.7mm, the measurement method of recording and calculating at the same time is selected, and the measurement is started, and then the button is clicked to start the horizontal movement adjustment shaft 15 to move to the right side of the image. After the movement stops, the measurement calculation and recording are also stopped.

[0047] Figure 6 The image at the end of the movement is shown, Figure 7 The graph showing the relationship between the left and right contact angle values and the corresponding three-phase contact coordinate point position and (progress) time is shown. The left coordinate axis shows the left and right contact angle values, the right coordinate axis is the corresponding left and right three-phase contact coordinate point position value, and the x-axis is the measurement time. The whole measurement process lasts about 65 seconds. From Figure 8It can be seen that at the beginning of the movement, the contact angle values of both sides are almost the same, and the value (100.8 degrees) corresponds to the static / initial contact angle value. After the horizontal Y-movement adjustment shaft starts to move, the contact angle value of the right side represented by curve 1 begins to rise, and the contact angle value of the left side represented by curve 2 begins to decrease. Curves 1 and 2 correspond to the advancing and receding contact angle values, respectively. Curve 3 corresponds to the three-phase contact point position value of the right side (advancing side), and its value changes (slowly increases) from the beginning of the horizontal Y-movement adjustment shaft movement and continues until the end of the movement / measurement. Curve 4 corresponds to the three-phase contact point position value of the left side (receding side), and its value remains basically unchanged from the beginning of the horizontal Y-movement adjustment shaft movement until about 28 seconds, and then begins to change (slowly increases) and continues until the end of the movement / measurement. The change speed of the right side from about 30 seconds is very close to that of the left side. The contact angle value of the right side (advancing side) increases with the increase of its corresponding three-phase contact point position value, and then remains basically constant. This basically unchanged stable value, 105.7 degrees, corresponds to the advancing contact angle value. The contact angle value of the left side (receding side) continues to decrease from the beginning of the movement, while its corresponding three-phase contact point position value remains basically unchanged. This state represents a "pinned" state of the contact line, which is a phenomenon commonly encountered on most actual sample surfaces. Only when the force exceeds a certain limit, can this "pinned" state be overcome, and the contact line begins to slide. In this process, the contact angle value continues to decrease, and the force (tension) increases. At about 28 seconds, the above-mentioned "pinned" state is overcome, and the three-phase contact point position of the left side begins to change (slowly increases), and the contact angle value of this side begins to remain basically unchanged. This basically constant contact angle value, 82.0 degrees, corresponds to the receding contact angle value. Thus, for this sample surface, the following results are obtained: Static / initial contact angle value: 100.8 degrees; Advancing contact angle value: 105.7 degrees; Receding contact angle value: 82.0 degrees; Contact angle hysteresis (CAH): 105.7 - 82.0 = 23.7 degrees; During the movement, the fluctuation range of the advancing contact angle value and the receding contact angle value is related to the uniformity of the sample surface. For a sample surface with good uniformity, the values can be quite stable. For a sample surface with poor uniformity, due to the contact and interaction of the fluid bridge with the surface at different positions during movement on the sample surface, the differences in surface properties (non-uniformity / homogeneity) must be reflected in the contact angle values, resulting in fluctuations in the latter. Figure 8The advancing contact angle curve shows slight fluctuations at 2-3 positions, but the retreating contact angle curve fluctuates very little and remains basically stable. The advancing and retreating contact angle values ​​reflect the different chemical properties of the sample surface (polar / non-polar components, hydrophilic / hydrophobic components, surface roughness microstructure, etc.).

[0048] If the movement in one direction ends ( Figure 8 (The image shows movement to the right). The movement direction can be reversed to continue the measurement, which is equivalent to re-scanning the sample area that has already been scanned. Comparing the results of the two measurements allows for analysis of the measurement repeatability. Good repeatability indicates that the sample surface is largely unaffected by the measurement process; conversely, poor repeatability indicates that the measurement process caused changes in the properties of the sample surface and / or the fluid used in the fluid bridge.

[0049] Compared with Example 3, the fluctuation range of the contact angle value obtained in this example is smaller. This is related to the properties of the sample surface itself, as well as the use of the automatically controlled horizontal movement adjustment shaft 15.

[0050] In summary, this invention expands the measurement functions and application scope of ordinary optical video contact angle measuring instruments, providing a simple, accurate, and widely applicable method for measuring the dynamic contact angle of liquids on solid surfaces using image analysis. Furthermore, the device of this invention is characterized by its simple structure, high availability, ease of maintenance, and low requirements for the measurement environment.

Claims

1. A method for measuring the dynamic contact angle of a liquid on a solid surface, characterized in that: Includes the following steps: Step 1: Construct the test system, which includes a first liquid phase, a fluid phase, and a solid phase. The fluid phase is either a gas phase or a second liquid phase that is incompatible with the first liquid. Step 2: Immerse the surface of the solid phase to be tested, facing upwards or downwards, in the environmental phase, wherein the environmental phase is one of the first liquid phase, the gas phase, or the second liquid phase; Step 3: Place an end face object on the surface to be tested, with both the end face of the end face object and the surface to be tested immersed in the same environmental phase; Step 4: Adjust the relative distance and position between the end face object and the surface of the solid phase, and distribute the fluid to form a fluid bridge through the liquid dispensing device, so as to form a longitudinal fluid bridge between the end face of the end face object and the surface of the solid phase; the fluid to form the fluid bridge is the first liquid phase or the fluid phase. Step 5: Observe the fluid bridge from the side using a camera device to obtain an image of the fluid bridge interface contour; Step 6: Controllably move the horizontal position of the end face object and / or the solid phase surface to apply a lateral dragging force to the fluid bridge, causing the fluid bridge to deform and causing the contact perimeter line between the fluid bridge and the solid phase surface to move or be about to move. Step 7: Record the change of the fluid bridge interface contour image over time, and analyze and calculate the image to obtain the relationship between the contact angle value and the corresponding three-phase contact point position value over time. Step 8: Determine the static contact angle, initial contact angle, forward contact angle, backward contact angle, and contact angle hysteresis value based on the changes in the contact angle value over time or the position of the three-phase contact points.

2. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: The steps for analyzing and calculating the image can be implemented in any of the following ways: recording the video first and then calculating, calculating in real time, or recording the video while calculating in real time.

3. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: The application of the lateral drag force is achieved by individually moving the horizontal position of the end face object or by individually moving the horizontal position of the sample surface.

4. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: The liquid addition device contains a fluid for constructing a fluid bridge, wherein the fluid bridge is formed in one of the following ways: (1) First, a fluid droplet is formed on the end face of the object or on the surface of the solid phase, and then the fluid droplet is brought into contact with another surface by adjusting the relative distance to form a fluid bridge; (2) First, adjust the distance between the end face object and the solid phase surface, and then fill the distance with the fluid that forms the fluid bridge through the liquid addition device to directly form the fluid bridge.

5. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 4, characterized in that: During the formation of the fluid bridge, the horizontal position of the sample surface and / or end face object is simultaneously changing, and the direction of the change is perpendicular to the observation direction of the camera device.

6. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 4 or 5, characterized in that: The end face object is a liquid injection needle tube, which is connected to the liquid injection device; by controlling the liquid injection device to form a fluid droplet of appropriate volume at the outlet end of the liquid injection needle tube, the fluid bridge is constructed.

7. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: The angle between the direction of the lateral drag force and the direction of gravity is not less than 45 degrees.

8. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: The angle between the placement direction of the solid phase surface to be tested and the horizontal plane does not exceed 45 degrees.

9. The method for measuring the dynamic contact angle of a liquid on a solid surface according to claim 1, characterized in that: During the measurement process, only one or more images of the fluid bridge interface profile are saved and / or calculated to obtain approximate dynamic contact angle measurement results.

10. An apparatus for implementing the measurement method according to any one of claims 1 to 9, characterized in that, include: Base (1); The background light source (11), camera device (5), sample platform adjustment device (2) and bracket (4) are set on the base (1); The sample platform (3) is set at the upper end of the sample platform adjustment device (2). The sample platform (3) is used to place the solid phase or the transparent test chamber (14). The suspended support platform (20) is provided by the bracket (4), and a liquid adding device (17) is fixed on the suspended support platform (20). An end face object (10) is provided below the liquid adding device (17). At least one of the sample platform adjustment device (2) and the suspended support platform (20) is provided with a horizontal moving axis, the moving direction of which is perpendicular to the observation direction of the camera device (5); The computer (6), the camera device (5) and the liquid dispensing device (17) are connected to the computer (6) via a cable (13).

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