A hydrogel surface zeta potential testing device and working method thereof

Abstract

The present invention discloses a hydrogel surface Zeta potential testing device and a working method thereof, which belong to the technical field of functional polymer material performance testing. It includes a fixed bracket, a high-level container, a low-level container, a sample storage device, a pressure difference detection device, a digital source meter and a circulation pump; the high-level container is installed on the fixed bracket; the circulation pump is arranged in the low-level container; the high-level container and the low-level container are filled with electrolyte solution; the height of the sample storage device is between the high-level container and the low-level container; the sample to be tested is placed in the sample storage device, and the electrolyte solution circulates between the high-level container, the low-level container and the sample storage device. The present invention has a reasonable structural design, low cost, and simple operation. It can obtain relatively accurate results while saving a lot of manpower and material resources, and realizes a simple and rapid measurement method for characterizing the electrochemical properties of the surface of macroscopically large-volume hydrogels, filling the gap in this regard.

Description

Technical Field

[0001] The invention belongs to the technical field of functional polymer material performance testing, and specifically relates to a hydrogel surface Zeta potential testing device and a working method thereof. Background Art

[0002] In the field of nanoscience, the Zeta potential can be used to understand the dispersion mechanism of molecules or particles in detail, which is crucial for electrostatic dispersion control. Zeta potential can be used to measure the solid-liquid interface electrical properties of dispersed system particles, to measure the interface electrical properties of emulsion droplets, and to determine the isoelectric point and study the mechanism of interfacial reaction processes. At present, for hydrogels that can generate electricity by evaporation, the size of the flow potential plays a decisive role in the efficiency of power generation.

[0003] Using porous media materials with micro-nano channels for solar interfacial evaporation will cause water to flow in the micro-nano material channels under a certain pressure. When water or other electrolyte solutions move in their channels, an electric current will be generated, which is called streaming current. At the same time, due to the accumulation of charged ions in the electrolyte solution at both ends of the porous medium, an electric potential difference is generated, which is called streaming potential. Generally speaking, there are two main forms of streaming potential. The first is due to the charge on the solid surface. Even in pure water, because water molecules are polar, water molecules will continuously dissociate H + , while a single H + Often cannot exist alone, will re-combine with water molecules to form hydronium ions (H3O + ). Since water is electrically neutral, there must be an equal number of negatively charged particles. These charged particles combine with the charged solid surface to form a double electric layer on the surface and generate Zeta potential at the solid-liquid shear interface.

[0004] Zeta potential refers to the potential of the shear surface and is an important indicator for characterizing the stability of colloidal dispersions. Most particles dispersed in solvents obtain surface charges mainly by ionization of surface groups or adsorption of charged particles. This charge will attract surrounding charges of opposite signs in the solvent, forming a double layer at the junction of the two phases, which is the so-called double layer model - Stern double layer. This model divides the double layer into two parts - Stern layer and diffusion layer. The Stern layer is a compact layer composed of a layer of charges adsorbed on the surface of the particles. Ions of opposite signs are distributed in a diffuse state outside the Stern layer, which is called the diffusion layer. The potential at the interface sliding surface between the diffusion layer and the external solution is the so-called Zeta potential.

[0005] At present, the main methods for measuring Zeta potential include electrophoresis, coprecipitation, ultrasound and streaming potential. In electrophoresis, charged particles move to the electrode with opposite charge under the action of an external electric field, and their movement speed is proportional to the size of the Zeta potential. By measuring the electrophoretic speed of particles in a specific electric field, the Zeta potential can be obtained. However, this method is cumbersome to measure; it is limited to powder or suspension samples, and has very high requirements on the concentration and particle size of the suspension, and is not suitable for gel samples with ion movement. For hydrogels prepared by coprecipitation, the operation is difficult and it is often difficult to obtain accurate values. The Zeta potential measured by the ultrasonic method is relatively accurate, but it is also limited by the sample volume and has a high cost, which does not conform to the concept of sustainable development.

[0006] The streaming potential method is relatively simple and convenient to operate, has wide applicability, and is low in cost. It can also obtain the Zeta potential of macroscopic solid surfaces of almost all sizes. The Zeta potential of the hydrogel surface in this experiment can be calculated using the Helmholtz-Smoluchowski (HS) equation: Where ξ is the Zeta potential of the hydrogel in the electrolyte solution (mV); ΔE is the streaming potential generated at both ends of the hydrogel microchannel after the electrolyte flows through the hydrogel microchannel (mV); ΔP is the hydraulic pressure difference generated at both ends after the electrolyte solution flows through the hydrogel microchannel (Pa), and the ratio of ΔE to ΔP is called the streaming potential coefficient; η is the solution viscosity (Pa·s); ε is the dielectric constant of the electrolyte (F·m -1 );K L is the conductivity of the electrolyte solution (S·m -1 ), which can be directly measured by a conductivity meter. Zeta potential is an important electrochemical property of this type of hydrogel, but its value is often difficult to obtain directly, so it is indirectly measured by streaming potential method.

[0007] Many researchers have studied the actual operation of measuring Zeta potential using the streaming potential method. Currently, Zeta potential testing devices are mostly used in papermaking, civil engineering and water conservancy, ultrafine materials, etc. Such devices are relatively expensive, complex in structure, and the measurement process is very cumbersome. However, there are few testing devices for the Zeta potential of macroscopic solid surfaces such as hydrogels that can evaporate and generate electricity. Summary of the invention

[0008] In order to solve the above problems, the purpose of the present invention is to provide a hydrogel surface Zeta potential testing device and a working method thereof, which have reasonable structural design, low cost, and simple operation, and can obtain relatively accurate results while saving a lot of manpower and material resources, thereby realizing a simple and rapid measurement method for characterizing the electrochemical properties of macroscopically large-volume hydrogel surfaces, filling the gap in this regard.

[0009] The present invention is achieved through the following technical solutions:

[0010] The invention discloses a hydrogel surface Zeta potential testing device, comprising a fixed support, a high-position container, a low-position container, a sample storage device, a pressure difference detection device, a digital source meter and a circulation pump; the high-position container is installed on the fixed support; the circulation pump is arranged in the low-position container; the high-position container and the low-position container contain electrolyte solution; the height of the sample storage device is between the high-position container and the low-position container;

[0011] The sample storage device comprises a sample chamber for accommodating the hydrogel, a first mesh electrode and a second mesh electrode are fixed at two ends of the sample chamber respectively, the first mesh electrode and the second mesh electrode are connected to the positive and negative electrodes of the digital source meter through wires respectively; an upper pressure measuring joint and a liquid outlet joint are arranged at the upper end of the sample storage device, a lower pressure measuring joint and a liquid inlet joint are arranged at the lower end of the sample storage device, the upper pressure measuring joint, the liquid outlet joint, the lower pressure measuring joint and the liquid inlet joint are all connected to the sample chamber; the upper pressure measuring joint and the lower pressure measuring joint are respectively connected to the differential pressure detection device; the liquid inlet joint is connected to the outlet of the high-level container, the inlet of the high-level container is connected to the circulation pump, and the inlet of the low-level container is connected to the liquid outlet joint; the electrolyte solution circulates between the high-level container, the low-level container and the sample storage device.

[0012] Preferably, the sample storage device also includes a cap and a base, the cap is detachably connected to the upper end of the sample chamber through a cap thread, and the base is detachably connected to the lower end of the sample chamber through a base thread; the upper pressure measuring joint and the liquid outlet joint are arranged on the cap, and the lower pressure measuring joint and the liquid inlet joint are arranged on the base.

[0013] Further preferably, the cap is provided with an upper wire passing hole for the wire to pass through, and the base is provided with a lower wire passing hole for the wire to pass through.

[0014] Further preferably, a blocking device is filled between the wire and the upper wire hole and between the wire and the lower wire hole.

[0015] Further preferably, a sealing ring is provided between the cap and the sample chamber, and between the base and the sample chamber.

[0016] Preferably, both the high-position container and the low-position container are made of transparent materials.

[0017] Preferably, the height of the fixing bracket is adjustable.

[0018] Preferably, the first mesh electrode and the second mesh electrode are copper electrodes.

[0019] Preferably, the circulation pump is a liquid circulation pump.

[0020] The working method of the hydrogel surface Zeta potential testing device disclosed in the present invention comprises:

[0021] The plug-shaped hydrogel to be tested fills the sample chamber and is fixed between the first mesh electrode and the second mesh electrode; several groups of electrolyte solutions with different concentrations are prepared and filled to nearly fill the lower container; the height of the upper container is adjusted by a fixed bracket so that its bottom is slightly higher than the top of the sample storage device; there is a pressure difference between the upper container and the sample storage device, and the electrolyte solution enters from the liquid inlet joint under the action of siphon, fills the sample chamber, and is discharged from the liquid outlet joint and flows into the lower container, and the electrolyte is circulated in the entire test device under the action of a circulation pump;

[0022] Measurement of streaming potential coefficient: After the electrolyte solution circulates for a period of time and reaches stability, a digital source meter is used to measure the streaming potential difference before and after flowing through the plug-shaped hydrogel to be tested. At the same time, the pressure difference detection device can also be used to obtain the hydraulic pressure change value at the upper and lower ends. Several groups of data within a stable period of time are recorded and the average value is taken;

[0023] Calculation of streaming potential coefficient: Wherein, ΔE is the average value of the streaming potential generated at both ends of the plug-shaped hydrogel microchannel after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested, and ΔP is the average value of the hydraulic pressure difference generated at both ends of the plug-shaped hydrogel microchannel after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested;

[0024] Zeta potential calculation: Where ξ is the Zeta potential of the hydrogel in the electrolyte solution; ΔE / ΔP is the streaming potential coefficient C measured above; η is the viscosity of the NaCl solution; ε is the dielectric constant of the NaCl solution; K L It is the conductivity of the electrolyte solution, which is directly measured by a conductivity meter.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The present invention discloses a hydrogel surface Zeta potential testing device, in which there is a pressure difference between a high-level container and a sample storage device. After the electrolyte solution enters and fills the sample chamber under the action of a siphon, it is discharged from the liquid outlet joint and flows into the low-level container. The electrolyte is circulated in the entire testing device under the action of a circulation pump. The liquid passes through the sample to be tested from bottom to top in the sample storage device to reduce the influence of gravity on the pressure difference. The device has a simple structure and a reasonable design, and can be tested conveniently and quickly, saving time and effort, while avoiding measurement errors caused by human operation. At the same time, a pressure difference detection device and a digital source meter are integrated to achieve an integrated test of further obtaining the Zeta potential value by measuring the flow potential coefficient of the hydrogel surface.

[0027] Furthermore, the sample storage device is a split structure, and each part is connected by threads, the connection is tight and easy to disassemble, the sealing performance is good, and it is convenient to load and clean the internal test samples.

[0028] Furthermore, the cap is provided with an upper wire hole for the wire to pass through, and the base is provided with a lower wire hole for the wire to pass through, so as to facilitate wiring.

[0029] Furthermore, a sealing device is filled between the wire and the upper wire hole and the lower wire hole to ensure that the overall device has good air tightness and stable internal pressure.

[0030] Furthermore, sealing rings are provided between the cap and the sample chamber, and between the base and the sample chamber, which further improves the sealing performance of the device.

[0031] Furthermore, both the high-level container and the low-level container are made of transparent materials, which facilitates observation of the liquid level.

[0032] Furthermore, the first mesh electrode and the second mesh electrode are copper electrodes with good electrical conductivity.

[0033] Furthermore, the circulation pump uses a liquid circulation pump with small pulsation, so that the electrolyte solution can circulate continuously in the device, saving energy. At the same time, it avoids complex operations such as additional manual constant pressure, greatly improving work efficiency; in addition, it also reduces the fluctuation of the flow potential on the surface of the hydrogel, ensuring the stability and reliability of the test results.

[0034] The working method of the hydrogel surface Zeta potential testing device disclosed in the present invention is easy to operate, does not rely on the operator's experience and skill level, saves a lot of manpower and material resources, and can obtain relatively accurate results, thus realizing a simple and rapid measurement method for characterizing the electrochemical properties of macroscopically large-volume hydrogel surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0036] Figure 2 This is an exploded view of the sample storage device;

[0037] Figure 3 It is a schematic diagram of the overall structure of the sample storage device;

[0038] Figure 4 It is a schematic front view of the structure of the sample storage device;

[0039] Figure 5 The Zeta potential of the hydrogel in NaCl solutions of different concentrations measured in Test Example 1;

[0040] Figure 6 It is the streaming potential of the hydrogel measured in Test Example 2 under different hydraulic pressure differences in deionized water.

[0041] In the figure: 1 is a fixed bracket, 2 is a high-level container, 3 is a low-level container, 4 is a sample storage device, 5 is a differential pressure detection device, 6 is a digital source meter, 7 is a cap, 8 is a second mesh electrode, 9 is a sample chamber, 10 is a first mesh electrode, 11 is a base, 12-1 is an upper pressure measuring joint, 12-2 is a lower pressure measuring joint, 13-1 is a liquid outlet joint, 13-2 is a liquid inlet joint, 14-1 is an upper wire hole, 14-2 is a lower wire hole, 15-1 is a cap thread, and 15-2 is a base thread. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings, the contents of which are intended to explain the present invention rather than to limit it:

[0043] like Figure 1 , is a hydrogel surface Zeta potential testing device of the present invention, comprising a fixed support 1, a high-level container 2, a low-level container 3, a sample storage device 4, a pressure difference detection device 5, a digital source meter 6 and a circulation pump; the high-level container 2 is installed on the fixed support 1; the circulation pump is arranged in the low-level container 3; the high-level container 2 and the low-level container 3 are filled with electrolyte solution; the height of the sample storage device 4 is between the high-level container 2 and the low-level container 3.

[0044] like Figure 2 , 3 The sample storage device 4 comprises a sample chamber 9 for accommodating the hydrogel, and the two ends of the sample chamber 9 are respectively fixed with a first mesh electrode 10 and a second mesh electrode 8, and the first mesh electrode 10 and the second mesh electrode 8 are respectively connected to the positive and negative electrodes of the digital source meter 6 through wires; the upper end of the sample storage device 4 is provided with an upper pressure measuring joint 12-1 and a liquid outlet joint 13-1, and the lower end of the sample storage device 4 is provided with a lower pressure measuring joint 12-2 and a liquid inlet joint 13-2, and the upper pressure measuring joint 12-1, The liquid outlet joint 13-1, the lower pressure measuring joint 12-2 and the liquid inlet joint 13-2 are all connected to the sample chamber 9; the upper pressure measuring joint 12-1 and the lower pressure measuring joint 12-2 are respectively connected to the pressure difference detection device 5; the liquid inlet joint 13-2 is connected to the outlet of the high-level container 2, the inlet of the high-level container 2 is connected to the circulation pump, and the inlet of the low-level container 3 is connected to the liquid outlet joint 13-1; the electrolyte solution circulates between the high-level container 2, the low-level container 3 and the sample storage device 4.

[0045] In a preferred embodiment of the present invention, the sample storage device 4 also includes a cap 7 and a base 11, the cap 7 is detachably connected to the upper end of the sample chamber 9 through a cap thread 15-1, and the base 11 is detachably connected to the lower end of the sample chamber 9 through a base thread; the upper pressure measuring joint 12-1 and the liquid outlet joint 13-1 are arranged on the cap 7, and the lower pressure measuring joint 12-2 and the liquid inlet joint 13-2 are arranged on the base 11.

[0046] Preferably, the cap 7 is provided with an upper wire hole 14 - 1 for the wire to pass through, and the base 11 is provided with a lower wire hole 14 - 2 for the wire to pass through.

[0047] Preferably, a blocking device is filled between the wire and the upper wire hole 14 - 1 and between the wire and the lower wire hole 14 - 2 .

[0048] Preferably, sealing rings are provided between the cap 7 and the sample chamber 9 , and between the base 11 and the sample chamber 9 .

[0049] In a preferred embodiment of the present invention, the high-level container 2 and the low-level container 3 are both made of transparent materials.

[0050] In a preferred embodiment of the present invention, the height of the fixing bracket 1 is adjustable.

[0051] In a preferred embodiment of the present invention, the first mesh electrode 10 and the second mesh electrode 8 are copper electrodes.

[0052] In a preferred embodiment of the present invention, the circulation pump is a liquid circulation pump.

[0053] When the hydrogel surface Zeta potential testing device of the present invention is working:

[0054] The plug-shaped hydrogel to be tested fills the sample chamber 9 and is fixed between the first mesh electrode 10 and the second mesh electrode 8; several groups of electrolyte solutions of different concentrations are prepared and filled to nearly fill the low-level container 3; the height of the high-level container 2 is adjusted by fixing the bracket 1 so that its bottom is slightly higher than the top of the sample storage device 4; there is a pressure difference between the high-level container 2 and the sample storage device 4, and the electrolyte solution enters from the liquid inlet joint 13-2 under the action of siphon, fills the sample chamber 9, and is discharged from the liquid outlet joint 13-1 and flows into the low-level container 3. The electrolyte is circulated in the entire test device under the action of the circulation pump;

[0055] Measurement of streaming potential coefficient: After the electrolyte solution circulates for a period of time and reaches stability, the digital source meter 6 is used to measure the streaming potential difference before and after flowing through the plug-shaped hydrogel to be tested. At the same time, the pressure difference detection device 5 can also obtain the hydraulic pressure change value at the upper and lower ends. Several groups of data within a stable period of time are recorded and the average value is taken;

[0056] Calculation of streaming potential coefficient: Wherein, ΔE is the average value of the streaming potential generated at both ends of the plug-shaped hydrogel microchannel after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested, and ΔP is the average value of the hydraulic pressure difference generated at both ends of the plug-shaped hydrogel microchannel after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested;

[0057] Zeta potential calculation: Where ξ is the Zeta potential of the hydrogel in the electrolyte solution; ΔE / ΔP is the streaming potential coefficient C measured above; η is the viscosity of the NaCl solution; ε is the dielectric constant of the NaCl solution; K L It is the conductivity of the electrolyte solution, which is directly measured by a conductivity meter.

[0058] The present invention will be further explained below with specific embodiments:

[0059] In this embodiment, the fixed bracket 1 adopts an iron frame with a lifting function; the high-level container 2 adopts a beaker with a capacity of 500ml and a minimum scale of 50ml, which is suspended and fixed by an iron frame that can be freely raised and lowered; a square acrylic plexiglass water tank is placed below as a low-level container 3, with a size of approximately 40*20*40 (cm).

[0060] The core device is the sample storage device 4 located in the middle, which consists of three parts: the cap 7, the sample chamber 9 and the base 11. The cap 7 is connected to the sample chamber 9 through the cap thread 15-1, and the second mesh electrode 8 is fixed; the base 11 is connected to the sample chamber 9 through the base thread 15-2, and the first mesh electrode 10 is fixed. Among them, the middle sample chamber 9 is a cylinder with a diameter of 35mm, a height of 95mm and a thickness of 5mm. The length of the liquid inlet joint 13-2 extending from the bottom of the base 11 and the liquid outlet joint 13-1 at the top of the cap 7 are both 20mm. The upper and lower extended columnar pressure measuring joints 12-1 and lower pressure measuring joints 12-2 on the side for connecting the digital differential pressure gauge are also 20mm long, which are used to measure the pressure difference ΔP before and after passing through the hydrogel microchannel to be tested. A small column extends outward from the side of the cap 7 and the base 11, and an overflow hole with a diameter of 10 mm is opened at the center to stabilize the water level. The two raised columns and the two joints of the HT-1890 digital differential pressure gauge are sealed and connected with rubber hoses to measure the change in the pressure difference before and after the hydrogel sample to be tested passes through. The sample storage device 4 and the beaker, the sample storage device 4 and the water tank, and the beaker and the water tank are all connected with rubber hoses.

[0061] The hydrogel sample to be tested is fixed between the first mesh electrode 10 and the second mesh electrode 8, and a wire is welded to each of the first mesh electrode 10 and the second mesh electrode 8. A small hole with a diameter of 4 mm is opened at the same radial position on the outer surface of the base 11 and the cap 7 as the upper wire hole 14-1 and the lower wire hole 14-2. The other end of the wire located at the electrode extends outward through the small hole and is respectively connected to the positive and negative electrodes of the digital source meter 6 to measure the flow potential ΔE flowing through the two ends of the microchannel; the digital source meter 6 adopts the Keithley 2450 digital source meter. In order to ensure the good airtightness of the overall device, after the wiring is completed, the wires at the upper wire hole 14-1 and the lower wire hole 14-2 can be wrapped with raw tape to seal them so that the internal pressure is stable.

[0062] Take a small amount of NaCl electrolyte of a certain concentration and put it in a beaker. Insert the external pipe of the conductivity meter into the solution to directly obtain the conductivity value K of the NaCl solution at that concentration. L .

[0063] Zeta potential test method

[0064] This test method can be used to measure the Zeta potential value of macroscopic solid surfaces of almost all sizes, including hydrogels, films, quartz sand, soil, etc. The specific operation process is as follows:

[0065] 1) Sample filling

[0066] The height of the beaker above is controlled by adjusting the iron stand so that its bottom is slightly higher than the top of the sample storage device 4 on the right. When in use, first fix the first mesh electrode 10 between the base 11 and the sample chamber 9 through the base thread 15-2, and then pour the suspension prepared in advance for this experiment, which has been stirred but not yet precipitated, into the sample chamber 9. After the suspension is filtered through the mesh, it will gradually form a plug-shaped hydrogel. Then, the second mesh electrode 8 is covered on the surface of the hydrogel and fixed by the cap thread 15-1. The plug-shaped hydrogel to be tested is filled and fixed between the two mesh electrodes, ensuring that the cap 7 and the sample chamber 9 and the base 11 and the sample chamber 9 are tightly connected.

[0067] 2) Solution preparation

[0068] Prepare five groups of electrolyte solutions (NaCl solutions) of different concentrations and fill them nearly to the bottom water tank, so that the solution can circulate in the whole device under the action of a low-power liquid pump;

[0069] 3) Measurement of streaming potential coefficient

[0070] After the electrolyte solution (NaCl solution) circulates for a period of time and reaches stability, the two wires passing through the wire hole 14-1 and the lower wire hole 14-2 on the outer surface of the cap 7 and the base 11 are connected to the positive and negative electrodes of the digital source meter 6 respectively, and the flow potential difference ΔE before and after flowing through the plug-shaped hydrogel to be measured is measured; at the same time, the two rubber hoses of the digital differential pressure gauge are connected to the upper pressure measuring joint 12-1 and the lower pressure measuring joint 12-2 on the side of the cap 7 and the base 11 respectively, and the pressure difference ΔP before and after flowing into the hydrogel microchannel is measured. 20 sets of data within a stable period of time are recorded and the average value is taken. Finally, the formula The streaming potential coefficient C can be obtained.

[0071] 4) Conductivity measurement

[0072] A small amount of five groups of electrolyte solutions (NaCl solutions) of different concentrations prepared in step 2) were extracted and measured respectively. In the same time period as the above-mentioned flow potential coefficient measurement, 20 groups of data were measured by the conductivity meter and the average value was taken to finally obtain the average conductivity value K L ;

[0073] 5) Zeta potential calculation

[0074] The streaming potential coefficient C and conductivity K L Substituting into the Helmholtz-Smoluchowski (HS) equation: The Zeta potential value of the hydrogel surface in this experiment can be calculated. The above operation steps can be used to measure the Zeta potential values ​​of macroscopic solids of almost all sizes, including hydrogels, films, quartz sand, soil, etc., in different electrolyte solutions, so as to characterize their surface electrochemical properties.

[0075] Zeta potential test example

[0076] In order to further understand the device and test method of the present invention and verify the feasibility and convenience of the present invention, the following will be described in detail through test examples 1 and 2. Among them, test example 1 is the Zeta potential of PIC hydrogel in NaCl solutions of different concentrations. Test example 2 is the Zeta potential streaming potential of deionized water flowing through the surface of PIC hydrogel under different pressure differences.

[0077] Test Example 1

[0078] The Zeta potential of the specially prepared PIC hydrogel in NaCl electrolytes of different concentrations was determined by using the device of the present invention and following the above device and operating steps. The PIC hydrogel is cross-linked by poly (sodium p-styrene sulfonate) (PNaSS) and poly (3-methyl 2-methyl propylene acrylamide-ammonium chloride) (PMPTC) at a molar ratio of 1:1, and is precipitated into a film by a coprecipitation method. The mass fractions of the NaCl solutions used are: 0, 2%, 4%, 6%, and 8%, respectively. Sample filling, solution preparation, flow potential coefficient measurement, and conductivity measurement are performed in the order of the above steps. Finally, the Zeta potential of the PIC hydrogel in NaCl electrolytes of different concentrations is calculated, and the external open circuit voltage value V of the PIC hydrogel is additionally measured. oc For comparison, Figure 5As shown. It can be found that when the evaporative power generation PIC hydrogel is placed in a NaCl solution, the voltage sign is reversed as the solution concentration increases. The direction of the electrodes is not changed during this process, the bottom electrode is the positive electrode, and the top electrode is the negative electrode. Therefore, to illustrate that the surface charge of the PIC hydrogel is reversed in the NaCl solution, the device of the present invention can be used to verify that the change trend of the Zeta potential in salt water is exactly the same as V oc On the contrary, when the PIC hydrogel is immersed in pure water, due to the evaporation of the top, the ions at the bottom will move upward with the water flow. In pure water, what moves with the water flow is a small amount of OH- and H3O dissociated from the water. + The channels with negative charges on the surface will repel OH- with the same charge, and attract positively charged counterions into the channels. This hydroelectricity phenomenon caused by the movement of positive charges is called p-type. When the PIC hydrogel is immersed in salt water, a large number of ions pass through the polyelectrolyte brush channels. Through molecular dynamics simulation, it is found that PNaSS is more likely to attract Na + , and due to the presence of benzene rings, PNaSS has harder "bristles". This will lead to excess Na + Being bound between the "bristles", the charge sign on the channel surface is reversed, that is, it appears positive. At this time, the channel will attract negatively charged counterions to enter. We call this power generation caused by the movement of negative charges n-type. Therefore, when there are a large number of ions in the channel and the transport direction of water does not change, the sign of the generated streaming potential will be reversed. The Zeta potential of the PIC hydrogel surface measured by the present invention is consistent with the theory and has a high accuracy.

[0079] Test Example 2

[0080] The device of the present invention is used, and the good linear fitting relationship between the flow potential ΔE and the hydraulic pressure difference ΔP generated after deionized water flows through the surface of the PIC hydrogel is verified according to the above device and operating steps, ensuring the accuracy of the device of the invention in the subsequent measurement of Zeta potential. Among them, the preparation method of the PIC hydrogel is the same as that of test example 1. The different pressure difference values ​​are 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa, and 0.5MPa. The sample is first filled according to the above steps, and then the solution here is replaced with a deionized water solution. Further, when measuring the flow potential coefficient, by changing the different heights of the beaker relative to the sample storage device 4, after stabilization for a period of time, five different pressure differences are used and 20 groups of data are recorded under each pressure difference and the average value is taken to obtain the average pressure difference ΔP; at the same time, 20 groups of flow potential values ​​corresponding to each of the five different pressures are measured, and the average potential difference ΔE is obtained after taking the average value. The average potential difference ΔE and the average pressure difference ΔP obtained in the above process are fitted to observe whether the fitting is good, such as Figure 6As shown. It can be found that as the hydraulic pressure difference gradually increases, the streaming potential difference across the two ends of the PIC hydrogel also increases linearly, and it is verified that the two have a good fit, close to a straight line, and the slope of the straight line is the desired streaming potential coefficient C. Therefore, the streaming potential coefficient of the PIC hydrogel surface measured by the present invention is consistent with the theory, which provides a reliable basis for the accuracy of the subsequent measurement and calculation of its Zeta potential value in deionized water.

[0081] The above is only part of the embodiments of the present invention. Although some terms are used in the present invention, the possibility of using other terms is not excluded. The use of these terms is only for the convenience of describing and explaining the essence of the present invention. It is contrary to the spirit of the present invention to interpret them as any additional restrictions. The above is only to further illustrate the content of the present invention with examples for easier understanding, but it does not mean that the embodiments of the present invention are limited to this. Any technical extension or re-creation made according to the present invention is protected by the present invention.

Claims

1. A hydrogel surface Zeta potential testing device, characterized in that: The invention comprises a fixed support (1), a high-level container (2), a low-level container (3), a sample storage device (4), a pressure difference detection device (5), a digital source meter (6) and a circulation pump; the high-level container (2) is installed on the fixed support (1); the circulation pump is arranged in the low-level container (3); the high-level container (2) and the low-level container (3) contain electrolyte solution; the height of the sample storage device (4) is between that of the high-level container (2) and the low-level container (3); The sample storage device (4) comprises a sample chamber (9) for accommodating a hydrogel, a first mesh electrode (10) and a second mesh electrode (8) are respectively fixed at two ends of the sample chamber (9), and the first mesh electrode (10) and the second mesh electrode (8) are respectively connected to the positive and negative electrodes of a digital source meter (6) through wires; an upper pressure measuring joint (12-1) and a liquid outlet joint (13-1) are provided at the upper end of the sample storage device (4), and a lower pressure measuring joint (12-2) and a liquid inlet joint (13-2) are provided at the lower end of the sample storage device (4); the upper pressure measuring joint (12-1), the outlet joint (13-1) and the liquid inlet joint (13-2) are respectively connected to the positive and negative electrodes of a digital source meter (6) through wires; The liquid port joint (13-1), the lower pressure measuring joint (12-2) and the liquid inlet joint (13-2) are all connected to the sample chamber (9); the upper pressure measuring joint (12-1) and the lower pressure measuring joint (12-2) are respectively connected to the differential pressure detection device (5); the liquid inlet joint (13-2) is connected to the outlet of the high-level container (2), the inlet of the high-level container (2) is connected to the circulation pump, and the inlet of the low-level container (3) is connected to the liquid outlet joint (13-1); the electrolyte solution circulates between the high-level container (2), the low-level container (3) and the sample storage device (4); The height of the fixing bracket (1) is adjustable; The circulating pump is a liquid circulating pump; The first mesh electrode (10) and the second mesh electrode (8) are copper electrodes; The sample storage device (4) further comprises a cap (7) and a base (11); the cap (7) is detachably connected to the upper end of the sample chamber (9) via a cap thread (15-1), and the base (11) is detachably connected to the lower end of the sample chamber (9) via a base thread; an upper pressure measuring joint (12-1) and a liquid outlet joint (13-1) are arranged on the cap (7), and a lower pressure measuring joint (12-2) and a liquid inlet joint (13-2) are arranged on the base (11); The working method of the hydrogel surface Zeta potential testing device comprises: The plug-shaped hydrogel to be tested fills the sample chamber (9) and is fixed between the first mesh electrode (10) and the second mesh electrode (8); a plurality of groups of electrolyte solutions of different concentrations are prepared and filled almost to the bottom of the lower container (3); the height of the upper container (2) is adjusted by means of a fixed bracket (1) so that the bottom of the upper container (2) is slightly higher than the top of the sample storage device (4); there is a pressure difference between the upper container (2) and the sample storage device (4), and the electrolyte solution enters through the liquid inlet joint (13-2) under the action of siphon, fills the sample chamber (9), and is discharged from the liquid outlet joint (13-1) and flows into the lower container (3), and the electrolyte is circulated in the entire test device under the action of a circulation pump; Measurement of streaming potential coefficient: After the electrolyte solution circulates for a period of time and reaches stability, a digital source meter (6) is used to measure the streaming potential difference before and after flowing through the plug-shaped hydrogel to be tested. At the same time, the pressure difference detection device (5) can also be used to obtain the hydraulic pressure change values ​​at the upper and lower ends. Several groups of data within a stable period of time are recorded and the average value is taken; Calculation of streaming potential coefficient: ; Wherein, ΔE is the average value of the streaming potential generated at both ends after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested, and ΔP is the average value of the hydraulic pressure difference generated at both ends after the electrolyte solution flows through the plug-shaped hydrogel microchannel to be tested; Zeta potential calculation: ; where ξ is the Zeta potential of the hydrogel in the electrolyte solution; ΔE / ΔP is the streaming potential coefficient C measured above; η is the viscosity of the NaCl solution; ε is the dielectric constant of the NaCl solution; K L It is the conductivity of the electrolyte solution, which is directly measured by a conductivity meter.

2. The hydrogel surface Zeta potential testing device according to claim 1, characterized in that: An upper wire hole (14-1) for the wire to pass through is provided on the cap (7), and a lower wire hole (14-2) for the wire to pass through is provided on the base (11).

3. The hydrogel surface Zeta potential testing device according to claim 2, characterized in that: A blocking device is filled between the wire and the upper wire hole (14-1) and between the wire and the lower wire hole (14-2).

4. The hydrogel surface Zeta potential testing device according to claim 1, characterized in that: Sealing rings are provided between the cap (7) and the sample chamber (9), and between the base (11) and the sample chamber (9).

5. The hydrogel surface Zeta potential testing device according to claim 1, characterized in that: The high-position container (2) and the low-position container (3) are both made of transparent materials.

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