Method for measuring the surface interfacial tension of a porous membrane

Abstract

The application provides a solid surface tension and solid-liquid interfacial tension measurement method suitable for porous membranes, which is based on a traditional maximum bubble method, utilizes initial pressure of a bubble generated by compressed gas penetrating a porous membrane infiltrated by an infiltrating liquid or initial pressure of a droplet generated by a non-infiltrating pressurized liquid penetrating a dry porous membrane, respectively measures penetrating pressure of a polar liquid, a non-polar liquid, a calibration liquid and a to-be-measured liquid, and brings into a corresponding formula to calculate to obtain solid surface tension and solid-liquid interfacial tension of the porous membrane. The method can reflect the surface interfacial tension of the internal pore wall surface of the porous membrane, avoids the problem that pore structures are inconsistent when different liquids are infiltrated, has the advantages of being simple and easy to implement and having a wide application range, and can provide key information for research and development detection work of applications such as membrane filtration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of interface chemistry, and relates to the determination of solid surface tension and solid-liquid interfacial tension, in particular to a determination method suitable for porous membranes and capable of determining the solid surface tension and solid-liquid interfacial tension of the pore wall surface inside the porous membranes. BACKGROUND

[0002] Contemporary separation technology is transitioning from traditional energy medium driven technology (such as rectification) to material medium driven technology. Membrane filtration technology, as a heavy material medium driven separation technology, has the characteristics of significant energy saving. In recent years, it has been widely used in the technical iteration and upgrading of chemical, pharmaceutical, food, electronic, energy and other industries, and its annual output value has reached 277.3 billion yuan (2019). The properties of porous membranes and their interaction properties with the filtered liquid will affect the performance of the membrane separation process. The solid surface tension of the porous membrane reflects the interaction between the surface molecules of the porous membrane, i.e. the surface free energy, which has a significant impact on the anti-pollution performance of the porous membrane (i.e. the decline in the flux of the filtered liquid due to the pollution of the porous membrane by particles, colloids, oil droplets, etc. in the filtered liquid) (Nat Commun. (2022) 13, 7334). The solid-liquid interfacial tension between the solid surface of the porous membrane and the filtered liquid reflects the ease with which the liquid wets the membrane surface, which has a significant impact on the flux of the filtered liquid through the porous membrane (Research (2019) 2019, 1). Therefore, the determination of the solid surface tension and solid-liquid interfacial tension of the porous membrane is of great significance to the research and application of the porous membrane.

[0003] Currently, the methods for measuring the surface interfacial tension mainly include image analysis methods (such as pendant drop method, spinning drop method, drop volume method, constrained sessile drop method, etc.) and mechanical analysis methods (such as hanging piece and ring method, capillary rise method, maximum bubble method, etc.). The image analysis method uses liquid drop observation, which can only measure the solid surface and can only give local information, while researchers are generally more concerned about the overall and internal pore wall surface interfacial tension of the porous membrane. In the mechanical analysis method, the hanging piece and ring method is generally only suitable for measuring dense solids. Although the capillary rise method has also developed a technical solution for measuring porous powders (Chemical Research and Application (2011) 23.1364). However, this method generally needs to measure the height, volume or speed of the liquid rising in the capillary, and the thickness of the porous membrane is generally only microns, making it very difficult to achieve the above measurement process. In addition, one of the major shortcomings of this method is that the pore structure of the test liquid and the calibration liquid is difficult to keep consistent, resulting in poor measurement accuracy. The maximum bubble method is generally used to measure the surface tension of the liquid, and its principle is as follows: Figure 1The capillary containing gas is contacted with the liquid to be measured, pressure is provided to make the bubble escape from the capillary, the required maximum pressure of the process is measured, and the bubble radius is calculated to determine the surface tension of the liquid. However, the surface tension of solid and the solid-liquid interfacial tension cannot be measured by the currently available instruments based on the maximum bubble method. SUMMARY

[0004] The present application aims to provide a method for measuring the solid surface tension and the solid-liquid interfacial tension of porous membrane. The method is an improved method based on the maximum bubble method, which can effectively measure the solid surface tension and the solid-liquid interfacial tension of the internal pore wall of porous membrane by using the characteristics of porous membrane that can withstand air flow impact, and can measure the wetting liquid and non-wetting liquid, and provides at least the advantages to be described later.

[0005] The technical solution of the present application is as follows:

[0006] (1) For the measurement of wetting liquid, the porous membrane is fully wetted in the liquid to be measured, and is placed in a membrane cell. The structure of the membrane cell is such that only two sides of the porous membrane placed therein are connected to the outside, and the remaining part is kept airtight. One side of the porous membrane is connected to a compressed gas cylinder, and the pressure on one side of the membrane is gradually applied by adjusting the combination of pressure reducing valve. The other side is connected to a liquid tank containing water through a conduit. When the gas bubble starts to escape from the liquid tank, the breakthrough pressure P on the upstream side of the porous membrane is recorded.

[0007] (2) For the measurement of non-wetting liquid, the porous membrane is fully dried, and is placed in a membrane cell. The structure of the membrane cell is such that only two sides of the porous membrane placed therein are connected to the outside, and the remaining part is kept airtight. One side of the porous membrane is connected to the liquid to be measured, and the pressure on the liquid to be measured is gradually applied by the combination of liquid pump and valve. When the liquid droplet starts to flow out from the other side, the breakthrough pressure P on the upstream side of the porous membrane is recorded.

[0008] For the measurement of the solid surface tension of porous membrane, several typical liquids are used to wet the solid surface respectively, and then calculation is performed. Currently, various models have been proposed, such as OWRK (Owens, Wendt, Rabel, Kaelble) model, Acid-base model, Schultz model, Zisman model, etc. The present application only takes the most commonly used OWRK model as an example, and other models differ in the types of liquid and calculation method, but the method of the present application is still applicable.

[0009] The OWRK model generally uses a polar liquid such as water and a non-polar liquid such as diiodomethane for measurement, so that the breakthrough pressures P 极 and P 非极When gas / liquid permeates through the porous membrane under pressure, the capillary force of the liquid / gas in the pore channel needs to be overcome. The capillary force mainly depends on the pore diameter and the wettability of the liquid to the pore wall surface, and the measurement of the wettability needs the known pore diameter. As shown in Figure 2 , for the irregular through hole across the two sides of the filter membrane, according to Pascal's law, the capillary force required for the gas / liquid to permeate through the hole comes from the pore throat, which is generally located inside the porous membrane. The appearance of the bubble / drop should be in a state of allowing permeation at the largest through hole of the porous membrane, and the state is not affected by the type of liquid. Therefore, a standard liquid with known wettability can be used to calibrate the pore diameter, and a liquid with good wettability to the porous membrane material is generally selected as the calibration liquid, and the permeation pressure is recorded as P 标 . P 极 , P 非极 , P 标 are brought into equations (1), (2), in which γ 极 , γ 非极 , γ 标 are the surface tension parameters of the liquid, the values of which can be obtained by querying the database of standard liquids or using existing technologies such as the maximum bubble method. The simultaneous equations (1), (2) can be solved to obtain the dispersion part and the polar part of the solid surface tension γ s of the solid, and then the solid surface tension γ s of the porous membrane is obtained through equation (3).

[0010]

[0011]

[0012]

[0013] For the measurement of the solid-liquid interfacial tension of the porous membrane, the permeation pressure P 测 of the liquid to be measured needs to be measured, and the solid-liquid interfacial tension γ sl can be calculated according to Young's equation and the surface tension of the solid:

[0014]

[0015] The present application includes the following beneficial effects:

[0016] (1) The method of the present application can measure the solid surface tension of the pore wall surface inside the porous membrane and the solid-liquid interfacial tension;

[0017] (2) The method of the present application can be used to measure both wetting liquids and non-wetting liquids;

[0018] (3) The method can measure porous membrane morphologies such as tubular, sheet, folded, capsule, hollow fiber, and multi-channel, and only the membrane cell pattern needs to be adjusted;

[0019] (4) The method can measure porous membranes made of common materials such as organic, metal, and ceramic materials;

[0020] (5) In the method, the test liquid and the calibration liquid both pass through the largest pore of the porous membrane, thereby ensuring the consistency of the pore structure during the two measurement processes and improving the measurement accuracy;

[0021] (6) The method is close to the filtration process of the porous membrane and is more suitable for actual application scenarios;

[0022] (7) The method is simple to operate, low in cost, and convenient for rapid detection. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A process diagram for measuring the surface tension of a liquid by the maximum bubble method;

[0024] Figure 2 A process diagram for gas passing through the pores of a porous membrane immersed in a test liquid;

[0025] Figure 3 A ten-time solid surface energy test repeatability diagram for stainless steel metal porous membranes, alumina ceramic porous membranes, acetate fiber organic porous membranes, and polyvinylidene fluoride organic porous membranes in each embodiment;

[0026] Figure 4 A ten-time solid-liquid interfacial tension test repeatability diagram for stainless steel metal porous membranes, alumina ceramic porous membranes, acetate fiber organic porous membranes, and polyvinylidene fluoride (PVDF) organic porous membranes and deionized water in each embodiment; DETAILED DESCRIPTION

[0027] The application will be further described in detail below through specific embodiments, which can enable a person skilled in the art to more fully understand the application, but in no way limit the application.

[0028] Example 1

[0029] The solid surface tension of stainless steel porous membrane (pore size 2 μm) and the interfacial tension with deionized water were measured. The porous membrane was immersed in deionized water, diiodomethane and GQ-16 (provided by Nanjing Gaoguan Functional Material Technology Co., Ltd. as a calibration liquid) respectively for 5 min. The wetted membrane was loaded into a membrane cell, the air release valve on the upstream side of the membrane was opened, the compressed gas cylinder was opened, and the degree of opening of the air release valve was gradually adjusted to make the pressure reading on the upstream side of the membrane gradually increase. When bubbles were observed escaping from the water tank on the downstream side of the membrane, the pressure reading at that time was recorded as the breakthrough pressure of the liquid. The breakthrough pressures of deionized water, diiodomethane and GQ-16 were 36.8, 18.3 and 14.6 kPa respectively. The surface tension and its dispersion part and polarity part of deionized water were 72.8, 21.8 and 51.0 mN / m respectively. The surface tension and its dispersion part and polarity part of diiodomethane were 50.8, 50.8 and 0 mN / m respectively. The surface tension of GQ-16 was 16.0 mN / m. The solid surface tension of the stainless steel porous membrane was calculated to be 46.5 mN / m, and the interfacial tension with water was 6.2 mN / m.

[0030] Example 2

[0031] The solid surface tension of aluminum oxide ceramic porous membrane (pore size 0.1 μm) and the interfacial tension with deionized water were measured. The porous membrane was immersed in deionized water, diiodomethane and GQ-16 respectively for 5 min. The wetted membrane was loaded into a membrane cell, the air release valve on the upstream side of the membrane was opened, the compressed gas cylinder was opened, and the degree of opening of the air release valve was gradually adjusted to make the pressure reading on the upstream side of the membrane gradually increase. When bubbles were observed escaping from the water tank on the downstream side of the membrane, the pressure reading at that time was recorded as the breakthrough pressure of the liquid. The breakthrough pressures of deionized water, diiodomethane and GQ-16 were 180.0, 320.2 and 356.1 kPa respectively. The surface tension and its dispersion part and polarity part of deionized water were 72.8, 21.8 and 51.0 mN / m respectively. The surface tension and its dispersion part and polarity part of diiodomethane were 50.8, 50.8 and 0 mN / m respectively. The surface tension of GQ-16 was 16.0 mN / m. The solid surface tension of the aluminum oxide ceramic porous membrane was calculated to be 28.1 mN / m, and the interfacial tension with water was 20.0 mN / m.

[0032] Example 3

[0033] The solid surface tension and the interfacial tension with deionized water of the cellulose acetate organic porous membrane (pore size 1 μm) were measured. The porous membrane was immersed in deionized water, diiodomethane and GQ-16 respectively for 5 minutes, and then the immersed membrane was installed in a membrane cell. The air release valve on the upstream side of the membrane was opened, and the compressed gas cylinder was opened. The opening degree of the air release valve was adjusted gradually to make the pressure on the upstream side of the membrane gradually increase. When bubbles were observed to escape from the water tank on the downstream side of the membrane, the pressure reading at that time was recorded as the breakthrough pressure of the liquid. The breakthrough pressures of deionized water, diiodomethane and GQ-16 were 138.9, 127.7 and 49.3 kPa respectively. The surface tension and its dispersion and polarity components of deionized water were 72.8, 21.8 and 51.0 mN / m respectively. The surface tension and its dispersion and polarity components of diiodomethane were 50.8, 50.8 and 0 mN / m respectively. The surface tension of GQ-16 was 16.0 mN / m. The solid surface tension of the cellulose acetate organic porous membrane was calculated to be 58.1 mN / m, and the interfacial tension with water was 13.0 mN / m.

[0034] Example 4

[0035] The solid surface tension and the interfacial tension with deionized water of the polyvinylidene fluoride (PVDF) organic porous membrane (pore size 1 μm) were measured. The measurements of diiodomethane and GQ-16 were the same as in the previous example. For the measurement of non-wetting deionized water, the dry porous membrane was installed in a membrane cell. The liquid tank on the upstream side of the membrane was connected to a liquid tank containing the liquid to be measured. A diaphragm pump was used to press the liquid into the membrane cell through the pipeline. The opening degree of the lateral pipeline ball valve was adjusted to make part of the liquid return to the liquid tank and the pipeline pressure gradually increase. When liquid droplets were observed to flow out of the water tank on the downstream side of the membrane, the pressure reading at that time was recorded as the breakthrough pressure of deionized water. The breakthrough pressures of deionized water, diiodomethane and GQ-16 were 65.2, 80.4 and 31.4 kPa respectively. The surface tension and its dispersion and polarity components of deionized water were 72.8, 21.8 and 51.0 mN / m respectively. The surface tension and its dispersion and polarity components of diiodomethane were 50.8, 50.8 and 0 mN / m respectively. The surface tension of GQ-16 was 16.0 mN / m. The solid surface tension of the polyvinylidene fluoride organic porous membrane was calculated to be 44.2 mN / m, and the interfacial tension with water was 77.5 mN / m.

[0036] Although the preferred embodiments of the present application have been described above with reference to the accompanying drawings, the present application is not limited to the above-described specific embodiments, and the above-described specific embodiments are merely illustrative and not restrictive. A person of ordinary skill in the art can make many specific changes to the present application without departing from the spirit of the present application and the scope of protection of the claims, and these all belong to the scope of protection of the present application.

Claims

1. A method for measuring the surface interfacial tension of a porous membrane, characterized by: (1) using compressed gas to contact the upstream side of the porous membrane which is wetted by a wetting liquid, the downstream side is covered by the wetting liquid; or using pressurized non-wetting liquid to contact the upstream side of the dry porous membrane, the downstream side is covered by dry gas; (2) gradually increase the pressure of the compressed gas or non-wetting liquid on the upstream side of the porous membrane until bubbles escape from the downstream side of the membrane or liquid droplets flow out, at this time, the pressure on the upstream side of the membrane is recorded as the breakthrough pressure; (3) respectively measure the breakthrough pressure of polar liquid, non-polar liquid, calibration liquid and the liquid to be measured, and record P 极 , P 非极 , P 标 , P 测 , through simultaneous solution of formula (1) , wherein γ 非极 , γ 标 are the surface tension parameters of the liquid, the values can be obtained by querying the database of standard liquids or using the maximum bubble method, and the polar part of the solid surface tension of the pore wall surface of the porous membrane and the dispersion part are calculated, and the sum of the two is the solid surface tension γ s , which is brought into formula (4) to calculate the solid-liquid interfacial tension γ sl between the pore wall surface of the porous membrane and the liquid to be measured.

2. The method of measuring the surface interfacial tension of a porous membrane according to claim 1, wherein Suitable pore size of the porous membrane is 0.02-100 μm, suitable material is metal, ceramic, polymer, glass material, and suitable shape is tube, sheet, folded, capsule, hollow fiber, and multi-channel.

3. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The compressed gas in step (1) includes any gas that does not chemically react with the porous membrane and the liquid, has low solubility, and is stable in its own nature.

4. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The wetting liquid in step (1) refers to any liquid that has a contact angle less than 90° with the porous membrane, and the non-wetting liquid refers to any liquid that has a contact angle greater than 90° with the porous membrane.

5. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The wetting in step (1) includes any means that can fill the porous membrane pores with the wetting liquid.

6. The method of measuring the surface interfacial tension of a porous membrane according to claim 1, wherein In step (1), the rest of the porous membrane should be sealed except for both sides to allow the gas or liquid on one side to be transmitted to the other side only through the membrane.

7. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The pressure control method of the compressed gas in step (2) includes any means using a gas pressure reducing valve combined with a valve to adjust.

8. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The pressure control method of the pressurized liquid in step (2) includes any means using a liquid pump combined with a valve to adjust.

9. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The polar liquid in step (3) is a standard polar liquid required for the solid surface tension calculation model, and the non-polar liquid is a standard non-polar liquid required for the solid surface tension calculation model.

10. The method of claim 1, wherein the porous membrane is a polycarbonate membrane. The calibration liquid in step (3) includes any liquid that has a contact angle less than 20° with the porous membrane material.

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