Perfluorohexanone fire extinguishing microcapsule as well as preparation method and application thereof

Abstract

The invention relates to the technical field of microfluidics, and discloses a perfluorohexanone fire extinguishing microcapsule as well as a preparation method and application thereof. An internal phase fluid, an intermediate phase fluid and an external phase fluid are transmitted through an internal phase flow channel, an intermediate phase flow channel and an external phase flow channel respectively, and the internal phase flow channel, the intermediate phase flow channel and the external phase flow channel are sequentially communicated and intersected to form a first shear point and a second shear point; the inner-phase fluid in transmission is sheared into uniform single-emulsion droplets by the intermediate-phase fluid through the first shear point and then sheared into uniform double-emulsion droplets by the outer-phase fluid through the second shear point, and finally, curing treatment is performed through ultraviolet irradiation to obtain the fire-extinguishing microcapsule. The microcapsule with a thin shell chemical structure is prepared on the basis of a micro-control flow technology, the three-phase flow velocity is adjusted, the liquid drop particle size with the optimal effect is found out, the photosensitive microcapsule with the uniform and controllable size is developed, and meanwhile, a resin-based material provides guidance for research of a microcapsule wall material.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, specifically to a perfluorohexanone fire extinguishing microcapsule based on microfluidic dual emulsification technology, its preparation method, and its application. Background Technology

[0002] Perfluorohexanone (PFH) is a highly promising fire extinguishing agent with low toxicity, environmental friendliness, high fluorination degree, and good fire extinguishing effect. It can be widely used in fire prevention in computer rooms, data centers, aviation, ships, vehicles, libraries, oil and gas production facilities, and other locations. However, because its heat of vaporization is only 1 / 25 that of water, while its vapor pressure is 25 times that of water, it is easily volatile and vaporized, making it difficult to store, transport, and apply.

[0003] Traditional methods for preparing perfluorohexanone fire extinguishing microcapsules primarily utilize polymerization, but this approach suffers from two significant drawbacks. Existing technologies, such as Chinese invention patent CN115487459, disclose a method for preparing perfluorohexanone microcapsules; a master's thesis from Nanjing University of Science and Technology, "Research on Microencapsulation Technology of Perfluorohexanone Fire Extinguishing Agents," describes the preparation of linear polyurethane microcapsules with perfluorohexanone as the core material using interfacial polymerization; and Chinese invention patent CN119680143 specifies that the amount of perfluorohexanone used is 70-90% of the total mass of all raw materials (perfluorohexanone, difunctional isocyanate monomer, organic solvent, emulsifier, crosslinking agent, and initiator) excluding water. However, the usual method is to use polymerization to prepare the microcapsules. According to the microscopic images, it can be found that the particle size distribution of the prepared microcapsules is uneven. On the other hand, perfluorohexanone is unstable and easily vaporized. Moreover, the polymerization method requires heating to cause the material to polymerize, which seriously reduces the encapsulation rate of perfluorohexanone and makes the fire extinguishing microcapsules produced have poor fire extinguishing effect.

[0004] Therefore, the technical problems to be solved in this application are how to produce perfluorohexanone fire extinguishing microcapsules without raising the temperature and how to make the microcapsules uniform in size, in order to adopt a new process for preparing perfluorohexanone fire extinguishing microcapsules. Summary of the Invention

[0005] To solve or partially solve the above-mentioned technical problems, the present invention provides perfluorohexanone fire extinguishing microcapsules based on microfluidic dual emulsification technology and their preparation method, which can achieve the preparation of perfluorohexanone microcapsules with uniform size and high coverage.

[0006] To achieve the above objectives, this invention provides a method for preparing perfluorohexanone fire extinguishing microcapsules based on microfluidic dual emulsification technology, comprising the following steps:

[0007] S1. At room temperature, the inner phase fluid, intermediate phase fluid and outer phase fluid are transported through the inner phase flow channel, intermediate phase flow channel and outer phase flow channel respectively. The inner phase flow channel and the intermediate phase flow channel are connected and intersected to form the first shear point. The inner phase flow channel and the outer phase flow channel are connected and intersected to form the second shear point. The transported inner phase fluid is first sheared into a uniform single emulsion droplet by the intermediate phase fluid at the first shear point, and then sheared into a uniform double emulsion droplet by the outer phase fluid at the second shear point.

[0008] S2. The output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel are merged, the merged flow is collected to obtain a mixed liquid, and then solidified by ultraviolet light irradiation to obtain perfluorohexanone fire extinguishing microcapsules.

[0009] Wherein: the inner phase fluid is perfluorohexanone; the intermediate phase fluid is composed of a mixture of cyclotrimethylolpropane methyl acetal acrylate, tricyclodecanediethanol diacrylate and isooctyl acrylate; and the outer phase fluid is composed of a mixture of water and polyvinyl alcohol.

[0010] As a further preferred embodiment of the present invention, the volume ratio of cyclotrimethylolpropane methyl acetal acrylate, tricyclodecanediethanol diacrylate and isooctyl acrylate in the intermediate phase fluid is 0.7:0.3~0.5:0.1~0.2, and more preferably 0.7:0.4:0.11; and / or, the ratio of water and polyvinyl alcohol in the external phase fluid is 100mL:3~6 g, and more preferably 100 mL:5 g; and / or, the wavelength of the ultraviolet light is 405nm, and the curing time is 1~10s.

[0011] In the preparation method of this invention, the pressure difference between the three phase fluids needs to be controlled by velocity matching to ensure that "the inner phase fluid in transit is first sheared into uniform monoemulsion droplets by the intermediate phase fluid at the first shear point, and then sheared into uniform biemulsion droplets by the outer phase fluid at the second shear point." This is crucial for ensuring stable production of biemulsion droplets. As a further preferred embodiment of this invention, the flow rate of the inner phase fluid is 10-20 mL / h; and / or, the flow rate of the intermediate phase fluid is 7-10 mL / h; and / or, the flow rate of the outer phase fluid is 15-20 mL / h. More specifically, the flow rate of the inner phase fluid is 13 mL / h, the flow rate of the intermediate phase fluid is 7 mL / h, and the flow rate of the outer phase fluid is 17 mL / h.

[0012] As a further preferred embodiment of the present invention, the inner diameters of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel are selected from 0.05~0.2 cm respectively.

[0013] According to a second aspect of the present invention, the present invention also provides a method for preparing perfluorohexanone fire extinguishing microcapsules, which are obtained by the above-described preparation method.

[0014] According to a third aspect of the present invention, the present invention also provides the application of perfluorohexanone fire extinguishing microcapsules in fire extinguishing.

[0015] According to a fourth aspect of the present invention, the present invention also provides a microfluidic dual emulsification device, which includes a reaction chip. The reaction chip is composed of an inner phase channel, an intermediate phase channel, and an outer phase channel forming a microfluidic structure. The inner phase channel and the intermediate phase channel are conductively intersected to form a first shear point, and the inner phase channel and the outer phase channel are conductively intersected to form a second shear point. The output ends of the inner phase channel, the intermediate phase channel, and the outer phase channel converge to form a confluence point. The first shear point, the second shear point, and the confluence point are arranged sequentially along the transmission direction of the inner phase channel.

[0016] As a further preferred technical solution of the present invention, it also includes an inner phase fluid storage tank, an intermediate phase fluid storage tank and an outer phase fluid storage tank respectively connected to the output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel, and a flow controller is provided between the inner phase fluid storage tank and the inner phase flow channel, between the intermediate phase fluid storage tank and the intermediate phase flow channel and between the outer phase fluid storage tank and the outer phase flow channel.

[0017] As a further preferred technical solution of the present invention, a pressure pump is also included, wherein the inner phase fluid storage tank, the intermediate phase fluid storage tank and the outer phase fluid storage tank are all connected to the pressure pump through a venting pipeline.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0019] (1) This invention prepares microcapsules with thinner shell chemical structures based on microfluidic technology. By adjusting the three-phase flow rate, the optimal droplet size is found, and a photosensitive microcapsule with uniform and controllable size is developed. At the same time, resin-based materials provide guidance for the research of microcapsule wall materials.

[0020] (2) The preparation method provided by this invention can precisely control the microcapsule structure according to specific needs. By adjusting the core-shell ratio through adjusting pressure, flow rate, etc., perfluorohexanone microcapsules with different core-shell ratios can be obtained. Moreover, the microcapsules prepared by the method of this invention have very uniform particle size. Specifically, microcapsules of different sizes can be prepared by changing chips with different diameter flow channels according to needs. The special core-shell structure of the microcapsules can effectively encapsulate perfluorohexanone in a flame-retardant polymer shell. This structure can significantly inhibit the volatilization of perfluorohexanone and protect it from the effects of light, temperature, and humidity in the environment, thereby extending its effective storage period.

[0021] (3) The microcapsules prepared by the present invention based on microfluidic technology can be easily integrated into materials of various forms. Whether they are made into flexible fire extinguishing patches, fire extinguishing ropes that can be routed with cables, or directly mixed into coatings for spraying, they can provide efficient fire protection for various small, enclosed or special spaces without significantly changing the original equipment structure.

[0022] (4) The microscale structure of the microfluidic reactor of the present invention can greatly improve the mixing and heat transfer efficiency, which is especially important for processing materials with low boiling point and easy volatility such as perfluorohexanone. It can effectively avoid premature volatilization or decomposition of fire extinguishing agent due to local overheating during the production process. Attached Figure Description

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is a schematic diagram of the piping of the microfluidic device used to prepare perfluorohexanone microcapsules in Example 1 of the present invention;

[0025] Figure 2 This is a schematic diagram of the pipeline of the reaction chip of the microfluidic device for preparing perfluorohexanone microcapsules in Example 1 of the present invention;

[0026] Figure 3 This is a high-speed photograph of the process of preparing microcapsules using microfluidic equipment in Embodiment 2 of the present invention;

[0027] Figure 4 This is a microscopic image of the perfluorohexanone microcapsules after they have been completely dried in Example 2 of this invention;

[0028] Figure 5 This is a high-speed photograph of the process of preparing microcapsules using microfluidic equipment in Embodiment 3 of the present invention;

[0029] Figure 6 This is a microscopic image of the perfluorohexanone microcapsules after they have been completely dried in Example 3 of this invention;

[0030] Figure 7 This is a scanning electron microscope image of the perfluorohexanone microcapsules in Example 2 of the present invention;

[0031] Figure 8 The infrared analysis curve of the microcapsules in Experimental Example 2 of this invention;

[0032] Figure 9 This is the total ion chromatogram of the microcapsules sampled at 150°C during headspace injection in Experiment Example 2 of this invention.

[0033] The diagram is labeled as follows: 100, reaction chip; 101, outer phase flow channel; 102, intermediate phase flow channel; 103, inner phase flow channel; 104, first shear point; 105, second shear point; 106, confluence point; 200, external liquid supply mechanism; 201, pressure pump; 202, venting pipeline; 203, outer phase fluid storage tank; 204, intermediate phase fluid storage tank; 205, inner phase fluid storage tank; 206, flow controller.

[0034] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0036] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0037] In this invention, the terms "perfluorohexanone microcapsules" and "microcapsules" are used interchangeably.

[0038] Example 1:

[0039] like Figure 1 and Figure 2 As shown, this embodiment provides a microfluidic dual emulsification device, which includes a reaction chip 100 and an external liquid supply mechanism 200. The external liquid supply mechanism 200 outputs an inner phase fluid, an intermediate phase fluid, and an outer phase fluid to the reaction chip 100 for microfluidic dual emulsification treatment.

[0040] The reaction chip 100 comprises an inner phase channel 103, an intermediate phase channel 102, and an outer phase channel 101, forming a microfluidic structure. The inner phase channel 103 and the intermediate phase channel 102 intersect in a cross shape to form a first shear point 104. The inner phase channel 103 and the outer phase channel 101 intersect in a cross shape to form a second shear point 105. The output ends of the inner phase channel 103, the intermediate phase channel 102, and the outer phase channel 101 converge to form a confluence point 106. The first shear point 104, the second shear point 105, and the confluence point 106 are sequentially arranged along the transport direction of the inner phase channel 103. The confluence point 106 can be directly used as an output port or connected separately to an output pipeline to output the microfluidically dual-emulsified mixture. The output mixture is collected by a liquid collection assembly equipped with an ultraviolet irradiation mechanism. Figure 2 The middle arrow indicates the direction of fluid flow within each channel.

[0041] The external liquid supply mechanism 200 includes an inner phase fluid storage tank 205, an intermediate phase fluid storage tank 204, and an outer phase fluid storage tank 203, which are respectively connected to the output ends of the inner phase flow channel 103, the intermediate phase flow channel 102, and the outer phase flow channel 101. Flow controllers 206 are provided between the inner phase fluid storage tank 205 and the inner phase flow channel 103, between the intermediate phase fluid storage tank 204 and the intermediate phase flow channel 102, and between the outer phase fluid storage tank 203 and the outer phase flow channel 101. The flow controllers 206 are used to regulate the flow rate of each phase fluid. In practical applications, by adjusting the flow rate, the size of the microcapsules, the shell thickness, and the core size can be adjusted.

[0042] The external liquid supply mechanism 200 also includes a pressure pump 201 that provides power for the transmission of each phase fluid. The inner phase fluid storage tank 205, the intermediate phase fluid storage tank 204, and the outer phase fluid storage tank 203 are all connected to the pressure pump 201 through a venting pipe 202. The pressure pump 201 provides air pressure through the venting pipe 202, so that the corresponding fluids in the inner phase fluid storage tank 205, the intermediate phase fluid storage tank 204, and the outer phase fluid storage tank 203 are continuously output under air pressure. In practical applications, each of the inner phase fluid storage tank 205, the intermediate phase fluid storage tank 204, and the outer phase fluid storage tank 203 can be internally pressurized by a separate pressure pump 201, or a single pressure pump 201 can be used for unified internal pressurization. In this case, only the pressure of the venting pipe 202 needs to be adjusted accordingly.

[0043] In one specific embodiment, the vent pipe 202 has a diameter of 0.5 cm, a length of 3 m, and is made of polytetrafluoroethylene (PTFE). The inner phase flow channel 103, the intermediate phase flow channel 102, and the outer phase flow channel 101 all use PTFE pipes with an inner diameter of 0.1 cm and a length of 20 cm.

[0044] Example 2

[0045] This embodiment describes a method for preparing perfluorohexanone fire extinguishing microcapsules using the microfluidic dual emulsification device described in Example 1 above, as follows:

[0046] (1) Perfluorohexanone was used as the internal phase fluid and stored in the internal phase fluid storage tank; cyclotrimethylolpropane methyl acetal acrylate, tricyclodecanediethanol diacrylate and isooctyl acrylate were mixed in a volume ratio of 0.7:0.4:0.11 to prepare the intermediate phase fluid and stored in the intermediate phase fluid storage tank; water and polyvinyl alcohol were mixed in a ratio of 100 mL:5 g to prepare the external phase fluid and stored in the external phase fluid storage tank.

[0047] (2) The pressure pump is started to deliver air pressure to the inner phase fluid storage tank, the intermediate phase fluid storage tank, and the outer phase fluid storage tank, so that the inner phase fluid, intermediate phase fluid, and outer phase fluid are respectively introduced into the inner phase flow channel, the intermediate phase flow channel, and the outer phase flow channel for transmission. Under the control of the flow controller, the flow rate of the inner phase fluid is 13 mL / h, the flow rate of the intermediate phase fluid is 7 mL / h, and the flow rate of the outer phase fluid is 17 mL / h. In the reaction chip, the inner phase fluid in transmission is first sheared into uniform single emulsion droplets by the intermediate phase fluid at the first shear point, and then sheared into uniform (O / O / W type) double emulsion droplets by the outer phase fluid at the second shear point. The high-speed camera image is shown below. Figure 3 As shown;

[0048] (3) At the end of the reaction chip, the output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel are merged. The mixed solution obtained by the merging flows out from the liquid outlet to the liquid collection component. After being irradiated with ultraviolet light (wavelength is 405nm, curing time is 3s), it reacts under the action of the ultraviolet photoinitiator trimethylbenzoyl-diphenylphosphine oxide. The intermediate phase is cured to form a shell, which encapsulates the inner phase fluid to form microcapsules.

[0049] (4) After collection is complete, wash the microcapsules multiple times with deionized water until they are fully dispersed and there are no other impurities. Then dry them at 40°C for 12 hours.

[0050] Example 3:

[0051] The only difference from Example 2 is that the flow rate of the inner phase fluid is 18 mL / h, the flow rate of the intermediate phase fluid is 8 mL / h, and the flow rate of the outer phase fluid is 20 mL / h. This example utilizes a reaction chip to generate dual emulsion droplets; its high-speed camera image is shown below. Figure 5 As shown.

[0052] Comparative Example 1:

[0053] The only difference from Example 3 is that the flow rate of the inner phase fluid is 18 mL / h, the flow rate of the intermediate phase fluid is 8 mL / h, and the flow rate of the outer phase fluid is 25 mL / h. Compared to Example 3, in this comparative example, due to the increased flow rate of the outer phase fluid, the corresponding pressure increases, causing a mismatch between the pressure of the inner phase fluid and the flow rate of the outer phase fluid. This results in an excessively large pressure difference at the shear point, generating negative pressure that pushes the inner phase liquid back into the storage tank, forming backflow, thus preventing the normal formation of double emulsion droplets.

[0054] Experimental Example 1: Observation using an optical electron microscope

[0055] The size, surface morphology, and internal structure of the perfluorohexanone microcapsules prepared in Examples 2 and 3 were observed using an optical electron microscope. The microscopic observation results of the cured perfluorohexanone microcapsules prepared in Examples 2 and 3 are shown below. Figure 4 and Figure 6 As can be seen from the figure, the sample size is uniform. The size of the microcapsule in Example 2 is 0.097±0.001 mm. The microcapsule prepared in Example 2 contains a liquid sphere of perfluorohexanone. The microcapsule prepared in Example 3 by adjusting the three-phase flow rate contains three liquid spheres of perfluorohexanone. Its core-shell ratio is greater than that of the microcapsule prepared in Example 2.

[0056] Experimental Example 2: Scanning Electron Microscopy Characterization

[0057] The microcapsules prepared in Example 2 were characterized by electron microscopy. The scanning results are shown in the figure. Figure 7 The perfluorohexanone microcapsules prepared in this embodiment have a distinct core-shell structure with uniform shell thickness. The microcapsules are perfectly spherical with smooth outer shell surfaces and no defects such as cracks, holes, or dents.

[0058] Experimental Example 3: Infrared Spectroscopic Characterization

[0059] The microcapsule samples from Example 2 were characterized by infrared spectroscopy, and the results are shown in the figure. Figure 8 In addition to the characteristic peaks of the shell, the 1770~1800 cm⁻¹ peaks can also be clearly observed. -1 The C=O peak at 1100-1300 cm⁻¹ and the peak at 1100-1300 cm⁻¹ -1 The strong CF peak indicates that perfluorohexanone was successfully encapsulated inside the microcapsule.

[0060] Experimental Example 4: Headspace-Gas Chromatography-Mass Spectrometry Detection

[0061] The original microcapsule sample from Example 2 was analyzed by headspace gas chromatography-mass spectrometry (HCGC-MS). The total ion flux of the THF diluent was as follows: Figure 9 Perfluorohexanone was measured at 1.470 min.

[0062] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing perfluorohexanone fire extinguishing microcapsules based on microfluidic double emulsion technology, characterized by, It comprises the following steps: S1, at room temperature, the inner phase fluid, the intermediate phase fluid and the outer phase fluid are respectively transmitted through the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel, wherein the inner phase flow channel and the intermediate phase flow channel are in communication and intersect to form a first shear point, the inner phase flow channel and the outer phase flow channel are in communication and intersect to form a second shear point, the inner phase fluid in transmission is first sheared by the intermediate phase fluid into uniform single emulsion droplets at the first shear point, and then sheared by the outer phase fluid into uniform double emulsion droplets at the second shear point; S2, the output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel are converged, the converged mixed liquid is collected and subjected to solidification treatment by ultraviolet light irradiation to obtain perfluorohexanone fire extinguishing microcapsules; The inner phase fluid is perfluorohexanone; the intermediate phase fluid is composed of cyclotrimethylolpropane formal acrylate, tricyclodecane dimethanol diacrylate and isooctyl acrylate; and the outer phase fluid is composed of water and polyvinyl alcohol.

2. The method for preparing perfluorohexanone fire extinguishing microcapsules based on microfluidic double emulsion technology according to claim 1, characterized in that, The volume ratio of cyclotrimethylolpropane formal acrylate, tricyclodecane dimethanol diacrylate and isooctyl acrylate in the intermediate phase fluid is 0.7:0.3-0.5:0.1-0.2; And / or, the ratio of water and polyvinyl alcohol in the outer phase fluid is 100 mL:3-6 g; And / or, the wavelength of the ultraviolet light is 405 nm, and the solidification time is 1-10 s.

3. The method for preparing perfluorohexanone fire extinguishing microcapsules based on microfluidic double emulsion technology according to claim 1, characterized in that, The flow rate of the inner phase fluid is 10-20 mL / h; And / or, the flow rate of the intermediate phase fluid is 7-10 mL / h; And / or, the flow rate of the outer phase fluid is 15-20 mL / h.

4. The method for preparing perfluorohexanone fire extinguishing microcapsules based on microfluidic double emulsion technology according to claim 1, characterized in that, The flow rate of the inner phase fluid is 13 mL / h, the flow rate of the intermediate phase fluid is 7 mL / h, and the flow rate of the outer phase fluid is 17 mL / h.

5. The process for the preparation of perfluorohexanone fire extinguishing microcapsules based on the double microfluidic emulsification technique according to any one of claims 1 to 4, characterized in that, The inner diameter of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel is 0.05-0.2 cm.

6. A process for the preparation of perfluoroketone fire extinguishing microcapsules, characterized in that, The preparation method of any one of claims 1-5 is adopted.

7. The perfluorohexanone fire extinguishing microcapsules of claim 6 are used in fire extinguishing.

8. A microfluidic double emulsification device for use in the method of claim 1, wherein, It comprises a reaction chip, which comprises a microfluidic structure composed of an inner phase flow channel, an intermediate phase flow channel and an outer phase flow channel, wherein the inner phase flow channel and the intermediate phase flow channel are in communication and intersect to form a first shear point, the inner phase flow channel and the outer phase flow channel are in communication and intersect to form a second shear point, and the output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel are converged to form a convergence point, wherein the first shear point, the second shear point and the convergence point are sequentially arranged along the transmission direction of the inner phase flow channel.

9. The microfluidic double emulsification device of claim 8, wherein, It also comprises an inner phase fluid storage pool, an intermediate phase fluid storage pool and an outer phase fluid storage pool connected to the output ends of the inner phase flow channel, the intermediate phase flow channel and the outer phase flow channel respectively, and a flow controller is arranged between the inner phase fluid storage pool and the inner phase flow channel, between the intermediate phase fluid storage pool and the intermediate phase flow channel, and between the outer phase fluid storage pool and the outer phase flow channel.

10. The microfluidic double emulsification device of claim 9, wherein, It also comprises a pressure pump, and the inner phase fluid storage pool, the intermediate phase fluid storage pool and the outer phase fluid storage pool are connected to the pressure pump through an air pipe.

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