CN102914490A - Solid-liquid contact angle measuring method in non-transparent or sealed space - Google Patents

Abstract

The invention relates to a method for measuring a liquid contact angle in non-transparent or sealed space. An optical imaging method in the prior art is replaced by the nuclear magnetic resonance imaging technology; through directly collecting a magnetic resonance signal of a liquid with nuclear spin quantum number of 1/2 of atomic nucleus number, a liquid section passing through an axis of a gas-liquid interface is imaged; and then through fitting an axis section curve of an image and through further measurement or calculation, a solid-liquid contact angle is obtained. As nuclear magnetic resonance imaging has no requirement on optical transparency of a research system, the defect that the traditional solid-liquid contact angle measuring method based on optical imaging only can measure solid-liquid contact angles in transparent and open space is eliminated. The method for measuring the liquid contact angle in the non-transparent or sealed space, provided by the invention, is especially suitable for researches on solid/liquid interface phenomenon in non-transparent environments or sealed systems.

Description

Measurement method of solid-liquid contact angle in opaque or closed space

【Technical field】

The invention relates to the technical field of measurement, in particular to a solid-liquid contact angle measurement method for characterizing wettability of materials.

【Background technique】

Wettability is an important surface property of solids, and it has important applications in ore flotation, building material coatings, anti-corrosion and waterproofing, etc. Due to its important position in scientific research and practical application, the study of solid surface wettability has always been a hot topic in the field of physical chemistry. Among them, contact angle measurement, as the most basic component of wettability research, is of great value to theoretical research and production practice in the field of surface/interface science.

With the advancement of technology and the deepening of research, a variety of methods for measuring contact angle have been developed, such as Wilhelmy hanging plate method, pendant drop method, bubble capture method and so on. Due to the advantages of easy operation and other advantages, the pendant drop method is the most widely used in the measurement of contact angle. Its main principle is to obtain the shape image of the micro-droplet on the solid surface through optical imaging, and through the fitting analysis of the droplet profile, finally get contact angle value. Most current contact angle measuring instruments are based on this principle.

However, since this method is based on optical imaging, it is bound to require that the contact angle measurement must be carried out in a transparent and open system. In practical applications, various wetting behaviors often occur in opaque or closed conditions, such as the measurement of the surface tension of harmful liquids, fluid control in liquid transportation pipelines, microfluidic systems, etc., which are all wetting properties. However, due to the opacity and closure of the system itself, traditional contact angle measurement methods cannot be applied to this type of research, which has caused great obstacles to the theoretical development and practical application of surface interface science.

For example, polytetrafluoroethylene and polyamide are commonly used liquid pipeline transportation materials, and the wetting state of the liquid in the pipeline has an important influence on the fluid parameters and transportation efficiency. Therefore, obtaining the contact angle of the fluid in the pipeline plays an important role in understanding the state of the fluid and further regulating the fluid. However, due to the opacity of the material, it is impossible to understand the wetting state of the liquid in the pipe by using traditional optical methods.

Therefore, a new technology is urgently needed to realize the research on liquid wettability in opaque and closed systems.

【Content of invention】

The technical problem to be solved by the invention is to develop a method capable of measuring the solid-liquid contact angle inside an opaque or closed space.

The invention provides a method for measuring the internal contact angle of an opaque or closed solid-liquid system, wherein the solid is made of a non-ferromagnetic material, the liquid contains an atomic nucleus whose nuclear spin quantum number is equal to 1/2, and the space formed by the solid Filled with said liquid and air, said method comprising:

S1 Place the solid-liquid system into the sample cavity of the nuclear magnetic resonance imager;

S2 Pre-image the liquid in the solid-liquid system sample from at least one direction, and compare and analyze the images to determine the position and direction of the liquid-gas interface and the center point of the liquid-gas interface;

S3 From at least one direction, on a plane perpendicular to the direction of the liquid-gas interface and passing through the center point of the liquid-gas interface, perform nuclear magnetic resonance imaging on the liquid in the solid-liquid system sample, and compare and analyze the images to obtain The cross-sectional view of the central axis of the liquid passing through the liquid-air interface;

S4 Obtain the axial profile curve of the solid-liquid and liquid-gas interface according to the profile;

S5 Fit the axial section curve, and obtain the solid-liquid contact angle through measurement or calculation.

The solid can be composed of any non-ferromagnetic material, such as glass, polytetrafluoroethylene, polyamide, or other non-ferromagnetic materials.

The liquid may be selected from aqueous liquids, oily liquids or water-oil mixtures. Wherein the aqueous liquid can be water, or an aqueous solution, or a liquid soluble in water, including alcohols and the like. Oily liquids can be organic compounds such as alkanes, aromatic hydrocarbons, esters, fatty acids, etc.; water-oil mixtures refer to liquids formed by mixing water and various organic compounds. layered form.

The opaque space may be a closed or open space, and the space may be of any shape, such as a tube, a cone, and the like.

In step S5 of the method, the fitting is in the form of polynomial fitting, circle fitting or ellipse fitting.

The measurement or calculation of the solid-liquid contact angle can be carried out by the angle measurement method or the height measurement method.

The process of fitting and measuring or calculating can be carried out by contact angle fitting and measuring software.

The existing contact angle fitting and measurement software includes Drop Shape Analysis System (Krüss, Germany), Surftens (SURFTENS Universal, Germany), SCA20 (Dataphysics, Germany), etc.

The beneficial effect of the present invention is that: compared with the contact angle measurement method based on optical imaging, the present invention uses nuclear magnetic resonance as an imaging means, utilizes the unique internal imaging function of nuclear magnetic resonance technology, not only can measure the contact angle in a conventional transparent or open space system The solid-liquid contact angle can also measure the solid-liquid contact angle in opaque or closed space systems. The scope of application is broadened, for the actual environment that is more in line with the characterization of liquid wettability.

【Description of drawings】

Fig. 1 is a flow chart of the method for measuring solid-liquid contact angle according to the present invention.

Figure 2 shows a comparison of optical imaging and MRI imaging of opaque spaces.

Fig. 3 is a diagram of imaging of opaque spaces of different shapes using the method of the present invention.

Figure 4 is a schematic diagram of the measurement of contact angle using circular fitting.

【Detailed ways】

Magnetic resonance imaging (MRI) technology is a technology that obtains images of the internal structure of objects by detecting the electromagnetic waves emitted by hydrogen nuclei with an external gradient magnetic field. Magnetic resonance is a physical phenomenon first reported by Block and Purcell in 1946 and applied to spectroscopy. Then in the early 1970s, P. C. Lauterbur and P. Mansfield made a breakthrough in the field of MRI, which laid the foundation for the successful application of MRI.

In recent years, nuclear magnetic resonance imaging technology has developed very rapidly and has become more mature and perfect. Due to its good non-destructive and non-invasive properties, magnetic resonance imaging technology has been widely used in various fields such as medical diagnosis, oil exploration, and material characterization.

From the point of view of imaging principle, nuclear magnetic resonance imaging technology directly collects the magnetic resonance signals of hydrogen nuclei, and does not require any optical transparency of the research system, so it is very suitable for solid/liquid interface phenomena in opaque environments and closed systems. Research.

The inventor took the study of the wettability of water in polytetrafluoroethylene tubes and polyamide tubes as an example to illustrate the principle of wettability characterization under opaque conditions. In the present invention, we have successfully realized the imaging of liquids in opaque polytetrafluoroethylene and polyamide pipelines by taking advantage of the advantages of magnetic resonance imaging technology in opaque conditions, and by analyzing and measuring the interface curves in the images, In this way, the contact angle value that is difficult to obtain by optical methods can be obtained.

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

FIG. 1 is a flowchart of a method for measuring solid-liquid contact angle according to the present invention. As can be seen from the figure, the measurement process mainly includes the following five steps:

The first is step S1. Put the solid-liquid system sample into the sample cavity of the MRI instrument. The appearance and shape of the solid interface can be any shape and shape, and no special treatment is required for the sample before the experiment. Since the calculation of the contact angle is realized by measuring the angle between the gas-liquid interface and the solid-liquid interface, no matter how complicated the interface shape is, as long as the curve shape of the gas-liquid and solid-liquid interface can be accurately obtained, it can be obtained by fitting Calculate the contact angle value.

In step S2, pre-image the liquid in the solid-liquid system sample from at least one direction, and compare and analyze the images to determine the position and direction of the liquid-air interface and the center of the liquid-air interface. In order to measure accurately, it is necessary to obtain the axial profile curves of the solid-liquid and gas-liquid interfaces.

When the space shape and surface topography are regular, or the space is a transparent space, it is relatively easy to judge the liquid axis section curve, which can be judged by naked eyes, and the imaging parameters can be set directly according to the space shape. Therefore, the liquid can be imaged from only one direction, the imaging process is relatively simple, and the desired image can be obtained only once.

However, when the space is opaque, because the internal conditions of the space are not clear, it is necessary to perform pre-imaging first, and compare and analyze the images to determine the position, direction and center of the liquid-gas interface. It may be necessary to image from multiple directions to get accurate and suitable results.

Then, in step S3, since the position and direction of the liquid-gas interface and the center of the liquid-gas interface have been determined, the parameters of the nuclear magnetic resonance imager can be adjusted at this time, so as to be perpendicular to the liquid-gas interface and pass through the liquid-gas interface from at least one direction. In the plane of the center point (that is, the plane passing through the central axis of the liquid), NMR imaging is performed on the liquid in the solid-liquid system sample, and the images are compared and analyzed to obtain a cross-sectional view of the liquid passing through the central axis suitable for further analysis .

Afterwards, in step S4, accurate axis profile curves of the solid-liquid and liquid-gas interfaces can be obtained according to the obtained profile.

Finally, in step S5, the axial section curve is fitted, and the solid-liquid contact angle is obtained through measurement or calculation.

In the following specific examples, the inventor takes the wettability research of water and dodecane in glass nuclear magnetic tubes, polytetrafluoroethylene tubes and polyamide tubes as examples to illustrate the measurement of solid-liquid contact angles in solid-liquid systems, that is, liquid wettability The principle of representation.

Instruments and materials

The liquid was imaged by NMI20-Analyst magnetic resonance imaging analyzer produced by Suzhou Numai Electronic Technology Co., Ltd.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the solid-liquid interface curve in the NMR images.

Solid: polytetrafluoroethylene tube ( Φ 12, about 3.5 cm in length); polyamide tube ( Φ 12, about 3.5 cm in length); glass NMR tube ( Φ 5 and Φ 15).

Liquids: Secondary deionized water; dodecane.

Example 1

Solid-liquid system preparation: Use acetone, ethanol and secondary deionized water to ultrasonically wash the PTFE tube for 15 minutes, dry it for later use; inject the secondary deionized water into the PTFE tube, calculate according to the diameter of the tube Inject the amount of water, and control the amount of water so that the height of the water column in the pipe is not greater than 2 cm.

The control of the height of the liquid is to meet the requirements of the equipment used in this experiment for the height of the sample. It should be understood that this parameter can be adjusted appropriately when using other solid-liquid systems, spaces with different shapes, or measuring on other nuclear magnetic resonance imagers. without affecting the scope of the present invention.

Nuclear magnetic resonance imaging: Put the water-polytetrafluoroethylene tube system vertically into the nuclear magnetic resonance imager, select the z-axis or x-axis as the imaging direction, and the magnetic field strength is 0.5 T. The multi-layer spin echo sequence is used as the imaging sequence. The waiting time of repeated sampling was 1000 ms, and the accumulation times were 32 times, and the water in the Teflon tube was imaged.

Liquid axis profile curve: adjust the brightness and contrast of the image, and obtain the water-PTFE and air-water phase interface curves from the figure.

Fitting and measurement calculation: The water-polytetrafluoroethylene and air-water phase interface was fitted by the contact angle measurement software SCA20 (Dataphysics, Germany), and the contact angle was measured, and the contact angle of water in the pipeline was obtained as 107.5 ±1.1°.

Example 2

The procedure is similar to Example 1 except that a polyamide tube is used instead of a polytetrafluoroethylene tube.

The water-polyamide and air-water phase interfaces were fitted by the contact angle measurement software SCA20 (Dataphysics, Germany), and the contact angle was measured, and the contact angle of water in the pipeline was obtained to be 69.4 ± 1.9°.

Example 3

The procedure was similar to Example 1 except that dodecane was used instead of secondary deionized water. During the MRI process, the waiting time for repeated use was 500 ms.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the dodecane-polytetrafluoroethylene and air-dodecane phase interface, and the contact angle was measured, and the contact angle of dodecane in the pipeline was 45.7 ±2.0°.

Example 4

The procedure was similar to Example 2 except that dodecane was used instead of secondary deionized water. During the MRI process, the waiting time for repeated use was 500 ms.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the dodecane-polyamide and air-dodecane phase interface, and the contact angle was measured, and the contact angle of dodecane in the pipeline was 41.3 ± 3.6 °.

Example 5

Except using Φ 5 NMR tubes instead of polytetrafluoroethylene tubes, the steps are similar to Example 1.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the water-glass and air-water phase interfaces, and the contact angle was measured, and the contact angle of water in the pipeline was obtained to be 24.3 ± 2.7°.

Example 6

The procedure was similar to Example 5 except that dodecane was used instead of secondary deionized water. During the MRI process, the waiting time for repeated use was 500 ms.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the dodecane-glass and air-dodecane phase interface, and the contact angle was measured, and the contact angle of dodecane in the pipeline was 24.5 ± 2.8° .

Example 7

Except using Φ 15 nuclear magnetic tubes instead of Φ 5 nuclear magnetic tubes, the steps are similar to embodiment 5.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the water-glass and air-water phase interfaces, and the contact angle was measured, and the contact angle of water in the pipeline was obtained to be 29.1 ± 5.6°.

Example 8

The procedure was similar to Example 7 except that dodecane was used instead of secondary deionized water.

The contact angle measurement software SCA20 (Dataphysics, Germany) was used to fit the dodecane-glass and air-dodecane phase interfaces, and the contact angle was measured, and the contact angle of dodecane in the pipeline was obtained to be 33.7 ± 6.3° .

Embodiment 1-4 is to the measurement of solid-liquid contact angle under opaque condition; Embodiment 5-8 is to the measurement of solid-liquid contact angle under transparent condition. It can be seen that the contact angle measurement method based on nuclear magnetic resonance imaging of the present invention does not require any transparency of solids, which greatly broadens the research scope of liquid wettability.

In order to illustrate the superiority of the solid-liquid contact angle measurement method based on nuclear magnetic resonance imaging in the present invention compared with the existing optical imaging method, the inventors carried out optical imaging and nuclear magnetic resonance imaging respectively on the water in the polytetrafluoroethylene tube . The obtained images are shown in Fig. 2, where a) is an optical imaging image; b) is an MRI image.

It can be clearly seen from the figure that due to the opacity of the PTFE tube, it is difficult to understand the wetting behavior of water in the PTFE tube by traditional optical methods, but it can be clearly observed by magnetic resonance imaging that the wetting behavior of water in the PTFE tube Wetting state in vinyl tubing. Therefore, the method of the present invention can effectively overcome the defect that the optical imaging method cannot be imaged in an opaque space, and is especially suitable for measuring the solid-liquid contact angle in an opaque space, thereby helping to understand the wettability of a liquid to a solid in an opaque space.

Figure 3 shows the images obtained by using nuclear magnetic resonance imaging to image water in a Φ 5 cylindrical glass nuclear magnetic tube (a) and a conical glass container (b).

It can be seen that the method of the present invention has no limitation on the shape of the space, which can be cylindrical, conical, or any other shape. The image in the figure clearly reflects the hydrophilic nature of the glass.

Figure 4 illustrates a schematic diagram of the measurement of the contact angle θ by employing a circle fit.

Above, we have successfully realized the imaging of liquids in opaque polytetrafluoroethylene and polyamide pipes and transparent glass nuclear magnetic tubes by taking advantage of the advantages of magnetic resonance imaging technology in opaque conditions, and by analyzing the The interface curve is analyzed and measured to obtain the contact angle value which is difficult to obtain by optical methods. Therefore, the method of the present invention has no requirements on whether the space is transparent or the shape of the space is regular, which greatly expands the application range of solid-liquid contact angle measurement and liquid wettability characterization.

The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (8)

1. method that is used for solid-liquid contact angle in measurement for opaque or the enclosure space, wherein solid is made of nonferromugnetic material, and liquid contains the atomic nucleus that nuclear-spin quantum number equals 1/2, is filled with described liquid and air in the described space, and described method comprises:

S1 places the solid-liquid system sample to the sample cavity of NMR imaging instrument;

S2 carries out pre-imaging from least one direction to the liquid the described solid-liquid system sample, and to the image comparison analysis, to determine liquid gas interface position, direction and liquid gas interface center;

S3 is from least one direction, on the plane perpendicular to described liquid gas interface and the described liquid gas interface central point of mistake, liquid in the described solid-liquid system sample is carried out Magnetic resonance imaging, and to the image comparison analysis, cross the sectional view of liquid gas interface central shaft to obtain liquid;

S4 obtains the axle center section curve of solid-liquid and liquid gas interface according to described sectional view;

S5 carries out match to described axle center section curve, and by measuring or calculating, obtains solid-liquid contact angle.

2. method according to claim 1, wherein, described solid is made of the material that is selected from glass, teflon, polyamide.

3. method according to claim 1, wherein, described liquid is selected from waterborne liquid, oil-based liquid or water-oil mixture.

4. method according to claim 1, wherein, described opaque space is sealing or open space.

5. method according to claim 1, wherein, the shape in described space comprises tubular, taper.

6. method according to claim 1, wherein, among the step S5, described fitting of a polynomial, circle match or the ellipse fitting of fitting to.

7. method according to claim 1, wherein, among the step S5, the measurement of solid-liquid contact angle or calculate and adopt goniometry or amount supreme people's court to carry out.

8. method according to claim 1, wherein, step S5 adopts contact angle match and Survey Software to carry out.

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