CN108680466B - Liquid water absorption research method based on liquid core column lens - Google Patents

Liquid water absorption research method based on liquid core column lens Download PDF

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CN108680466B
CN108680466B CN201810480318.2A CN201810480318A CN108680466B CN 108680466 B CN108680466 B CN 108680466B CN 201810480318 A CN201810480318 A CN 201810480318A CN 108680466 B CN108680466 B CN 108680466B
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孟伟东
普小云
夏燕
陈艳
魏利
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Yunnan University YNU
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Abstract

The invention discloses a liquid water absorption research method based on a liquid core column lens. Injecting hygroscopic liquid into the lower part of the liquid core area of the cylindrical lens, and enabling the upper end opening to be in contact with humid air; adjusting the position of the detector to enable the monochromatic collimated light beam to clearly image on the CMOS/CCD surface after passing through the liquid core column lens; the concentration of the moisture absorption liquid changes after continuously absorbing moisture in the humid air, so that the refractive index changes, and an image received by the image detector is not a sharp thin line any more, but a dispersed image with a certain width; and according to the image widths at different positions at different moments, the changes of the corresponding solution concentration and moisture content along with time and space positions are obtained, and the moisture absorption capacity of the corresponding moisture absorption liquid is obtained. The method of the invention describes the moisture absorption process in a visual way, and can obtain the concentration gradient, the water absorption capacity and the moisture absorption rate of the moisture absorption liquid solution and the microscopic transport information of moisture molecules in the moisture absorption liquid. The research method of the invention is also suitable for researching the liquid absorption process of the greenhouse gas.

Description

Liquid water absorption research method based on liquid core column lens
Technical Field
The invention belongs to the technical field of research on microscopic moisture absorption processes by using an optical method, and particularly relates to a quick, accurate and visual liquid water absorption research method based on a liquid core column lens.
Background
Humidity, like temperature, has a significant impact on human health and comfort. The overlarge air humidity not only affects the living environment of people, but also seriously affects the quality of products such as food, precision electronic instruments, optical imaging systems and the like. The problem of air humidity control is more and more emphasized by people, and various dehumidification technologies are widely concerned and developed. The liquid dehumidification technology is increasingly applied to various dehumidification environments due to the advantages of large air handling capacity, no pollution, environmental friendliness, easiness in humidity control, capability of fully utilizing low-grade heat sources and the like. Examples of the liquid moisture absorber which is often used include ethylene glycol, glycerin, calcium chloride, lithium chloride, and ionic liquid. The liquid dehumidification process is a complex heat transfer and mass transfer process, and basic data of a liquid dehumidification system suitable for multiple environmental conditions, high efficiency, high energy conservation and high performance are very lacking. However, the liquid dehumidification technology can be applied to many occasions, so that the intensive research on the water absorption of the liquid is necessary. At present, the water absorption research is mainly to weigh the moisture absorption samples respectively at different times through a balance according to the mass change conditions of the moisture absorption liquid under different environments (temperature, humidity and the like). The research of obtaining physical parameters such as water absorption capacity, water absorption rate and the like by weighing the change of liquid mass before and after the water absorption process is a macroscopic research. The traditional method can not directly obtain the microscopic transport information (such as water absorption conditions, diffusion coefficients, concentration gradients of solutions and the like at different positions) of water and gas molecules in the hygroscopic liquid.
Before the present invention is put forward, a plurality of liquid core column lens imaging methods are carried out to research the relevant work of the aspects of liquid refractive index spatial distribution, liquid diffusion and the like in a liquid core. The liquid core column lens is designed according to the different focusing point positions of parallel light after passing through the column lens filled with different liquids and the special concentration spatial resolution capability of the column lens, and a method for measuring the liquid concentration (refractive index) and the liquid phase diffusion coefficient is provided. A liquid-core column lens is used for rapidly measuring liquid phase diffusion coefficient-refractive index spatial distribution transient measurement method [ J ] ("Physics report", 2015,64(11), 114205-1-114205-7); the method is characterized in that a double-liquid core column lens which has the advantages of good imaging quality, no spherical aberration or small spherical aberration in wide concentration (refractive index) and adjustable aplanatic position as required is designed for improving the precision and accuracy of measuring the refractive index and the liquid phase diffusion coefficient, a new method for measuring the diffusion coefficient is provided by utilizing the characteristics of the double-liquid core column lens, the liquid phase diffusion coefficient is measured based on the double-liquid core column lens, and the like observation height measuring method [ J ], ('optical science report', 2018,38(1), 0112002-1-0112002-7).
Conventionally, the mass change of the hygroscopic liquid of the hygroscopic sample under different environments (temperature, humidity, etc.) is respectively weighed by a balance at different times. The research of obtaining physical parameters such as water absorption capacity, water absorption rate and the like by weighing the change of the liquid mass before and after the water absorption process is a macroscopic research, and cannot directly obtain microscopic transport information (such as water absorption conditions, diffusion coefficients, concentration gradients of solutions and the like) of water vapor molecules in the moisture absorption liquid. The microscopic states of molecules can be obtained by X-ray diffraction, neutron scattering, Raman spectroscopy and the like which can obtain various molecular states in the microscopic world, but are limited by factors such as instruments, environments, technical conditions and the like, so that many experimental methods cannot directly obtain the physicochemical processes concerned by people, and are not suitable for moisture absorption research. Therefore, it is necessary to develop a method for investigating water absorption properties, which can solve the above problems.
Disclosure of Invention
The invention aims to provide a microscopic, accurate and visual liquid water absorption research method based on a liquid core column lens.
The invention is realized by the following processes:
A. injecting moisture absorption liquid into the lower end of the liquid core, sealing the upper end of the liquid core to isolate the liquid core from air, adjusting the position of the detector to enable the monochromatic collimated light beam to form a thin and sharp bright line with the same width on the CMOS/CCD surface after passing through the liquid core column lens, and opening the upper end seal to enable the moisture absorption liquid to be naturally exposed to air with certain relative humidity, wherein t is the time when t is 0;
B. the concentration of the hygroscopic liquid changes after the hygroscopic liquid continuously absorbs the moisture in the air, so that the refractive index changes, and an image received by the image detector is not a sharp thin line any more, but a dispersed image with a certain width, namely a hygroscopic image;
C. preparing mixed solution with different concentrations, injecting the mixed solution into the liquid core column lens, obtaining dispersion images with different widths at a fixed observation position, and measuring the relationship between the image width and the solution concentration;
D. according to the moisture absorption images at different moments, the spatial distribution condition of the moisture in the liquid core at the moment can be intuitively obtained, and the moisture absorption process can be seen.
The method can describe the moisture absorption process in a microscopic form, directly obtain microscopic transport information of water vapor molecules in the moisture absorption liquid, and obtain the concentration gradient, the water absorption capacity, the moisture absorption rate and the like of the moisture absorption liquid solution. Meanwhile, the research method is also suitable for researching the liquid absorption process of the greenhouse gas. The method better solves the problem that the traditional method for weighing the mass change of the liquid before and after the water absorption process through a balance can only study the water absorption process from the macroscopic aspect. Particularly, by combining the advantages of high spatial resolution capability and sensitivity, good aplanatic effect and adjustable aplanatic position (concentration/refractive index) in a wider refractive index range of the lens with the double liquid core columns, the water absorption capacity, the water absorption rate and the like can be quickly and accurately measured according to concentration spatial distribution information reflected by an image after water absorption obtained by the CMOS image acquisition system. Meanwhile, by utilizing the spatial and temporal distribution of the solution concentration after the moisture absorption of the moisture absorption liquid, the diffusion coefficient of water in the moisture absorption liquid can be calculated according to the previously proposed equal-refractive-index thin layer moving method, the transient-refractive-index spatial distribution method and the equal observation height method. And establishing the relation between the diffusion coefficient and the moisture absorption capacity.
Drawings
FIG. 1 is a schematic diagram of the structure of an experimental device used in the invention based on a new method for researching water absorption of a liquid core column lens;
in the figure: the system comprises a laser 1, an attenuator 2, a plane mirror 3, a microscope 4, a pinhole 5, a lens 6, a slit plate 7, a double-liquid-core column lens 8, an image acquisition system 9-CMOS (CCD), an image acquisition display system 10 and monochromatic parallel light 11.
In the figure, laser with lambda of 589.0nm is attenuated by an attenuation sheet, passes through a spatial filter and a collimating lens to generate monochromatic collimated light, the monochromatic collimated light is vertically incident on a liquid core column lens after being limited by the width of a slit, and a CMOS (CCD) image acquisition system connected with a computer is used for observing the moisture absorption process in real time and acquiring images after moisture absorption.
FIG. 2 is a photograph of a moisture absorption image of pure ethylene glycol;
in the figure, (a) is an imaging picture without water absorption; (b) the image is formed after water absorption for 4 hours.
FIG. 3 is a schematic diagram of liquid core cylindrical lens refraction law imaging;
in the figure, 1 denotes the current injection index of refraction n in the wickcThe solution is accurately imaged on a CMOS observation detector; 2 denotes the refractive index n of the front liquid corei<ncWhen the solution is observed on a CMOS detector, the width of the diffusion image is AC (namely sigma)i) The angle between the light ray and the main optical axis is thetai(ii) a 3 denotes the refractive index n of the front liquid corei>ncThe solution of (A) is observed as a diffuse image on the detector CMOS, again with a width of AC (i.e. sigma)i) The angle between the light ray and the main optical axis is thetai；
FIG. 4 is a graph of refractive index versus spherical aberration for various liquid core liquids;
in the figure, when the rear liquid core is selected from solutions having refractive indices n' of 1.4486, 1.4454, 1.4406, 1.4358 and 1.4316, the spherical aberration can be eliminated at the positions of pure ethylene glycol (n ═ 1.4306), 95% ethylene glycol (n ═ 1.4275), 90% ethylene glycol (n ═ 1.4225), 85% ethylene glycol (n ═ 1.4175) and 80% ethylene glycol (n ═ 1.4126), respectively.
FIG. 5 is a visual concentration profile of glycol water uptake at different times;
FIG. 6 is an image width on a fixed observation plane when different concentrations (refractive indices) of liquid are injected into the front wick;
in the figure, a fixed observation plane position (glycol clear focus position) ncThe refractive indexes of the liquid injected into the liquid core lens of other images are (a) n-1.4306, (b) n-1.4298, (c) n-1.4291, (d) n-1.4260, (e) n-1.4232, (f) n-1.4078, and (g) n-1.3993.
FIG. 7 is a graph of refractive index versus image width obtained from experimental and theoretical calculations;
FIG. 8 is a visual concentration profile of glycol water uptake at different times;
FIG. 9 is a model view of water absorption diffusion;
FIG. 10 is an image of water absorption diffusion at different times;
in the figure, the fixed viewing plane position is located at the index thin layer (i.e., the finest "waist" of the image) nc＝1.4295。
Detailed Description
The invention is further described with reference to the accompanying drawings, but the invention is not limited in any way and any variations or modifications based on the teachings of the invention are within the scope of the invention. As shown in fig. 1 to 10, the present invention includes:
A. injecting moisture absorption liquid into the lower end of the liquid core, sealing the upper end of the liquid core to isolate the liquid core from air, adjusting the position of the detector to enable the monochromatic collimated light beam to form a thin and sharp bright line with the same width on the CMOS/CCD surface after passing through the liquid core column lens, and opening the upper end seal to enable the moisture absorption liquid to be naturally exposed to air with certain relative humidity, wherein t is the time when t is 0;
B. the concentration of the hygroscopic liquid changes after the hygroscopic liquid continuously absorbs the moisture in the air, so that the refractive index changes, and an image received by the image detector is not a sharp thin line any more, but a dispersed image with a certain width, namely a hygroscopic image;
C. preparing mixed solution with different concentrations, injecting the mixed solution into the liquid core column lens, obtaining dispersion images with different widths at a fixed observation position, and measuring the relationship between the image width and the solution concentration;
D. according to the moisture absorption images at different moments, the spatial distribution condition of the moisture in the liquid core at the moment can be intuitively obtained, and the moisture absorption process can be seen.
The specific operation method in the step C is as follows:
a. preparing mixed solutions with different concentrations, measuring the refractive indexes of the mixed solutions, and fitting the relation between the refractive indexes and the concentrations of the mixed solutions;
b. injecting prepared solutions with different refractive indexes into the liquid core column lens at a fixed observation position, measuring the width of an image on an observation system, fitting the relationship between the image width and the refractive index, and substituting the image obtained by the experiment into the fitting relational expression to obtain the corresponding refractive index;
c. parallel light with the width of 2h is incident on the liquid core column lens, and when the liquid core column lens is injected with refractive index ncWhen the liquid is in the liquid state, the focal length of the liquid core column lens is fcWhen the refractive index of the injected liquid in the lens core is niWhen the liquid is in the liquid state, the focal length of the liquid core column lens is fiThe angle between the emergent ray and the main optical axis is thetaiAt fcWidth of sigma imaged on a fixed observation planei；fi、∑iAnd thetaiThere are the following geometrical relationships
Figure BDA0001665423620000061
Fitting the relation between the refractive index and the image width under the condition of refraction law imaging according to the formula (1), and substituting the experimental image into the fitting relation formula to obtain the refractive index at the corresponding position under the condition of refraction law imaging;
e. and (c) obtaining the relation between the image width and the concentration according to the relation between the refractive index and the concentration in the step (a) and the relation between the image and the refractive index, wherein the relation between the image width and the refractive index is preferably calculated by the method introduced in the step (c) under the condition that the fitting relational expression obtained by the experimental method in the step (b) and the relational expression obtained by calculation are similar.
The hygroscopic solution is formed by using hygroscopic liquid as a solvent and water as a solute, the corresponding solution concentration C (Z, t) at the time t is obtained according to the hygroscopic image width at different positions Z according to the one-to-one correspondence among the solution concentration, the refractive index and the image width, and the mass of the absorbed water in the region from the position Z to the position Z plus delta Z is expressed as follows:
Δms＝M0*C(Zi)*S*ΔZ， (2)
wherein S is the cross-sectional area corresponding to the selected volume element, i.e. the cross-sectional area of the front liquid core, Δ Z is the height of the volume element, M0Is the molar mass of water;
from equation (2), it can be seen that the mass of water absorbed at position Z is a function of the cross-sectional area, volume element and solution concentration, at Z0To ZiThe absorbent system at a certain moment in time has an absorbent capacity expressed as:
Figure BDA0001665423620000071
calculating the total water absorption capacity of the unit volume of the hygroscopic liquid or the water absorption capacity in a certain time period, and obtaining the average moisture absorption rate and the moisture absorption rate in a certain time period according to the relation between the water absorption capacity of the unit volume of the hygroscopic liquid and the time, namely the ratio m of the water absorption capacity in the unit volume to the time0And/t is taken as a parameter index of moisture absorption capacity.
For an unsteady one-dimensional diffusion system along the Z axis, the concentration of the diffusion solution at the Z position at the time t is set as C (Z, t), and according to the Fick second law followed by the unsteady diffusion process, C (Z, t) satisfies the following differential equation,
Figure BDA0001665423620000072
c (Z, t) is the concentration at position Z at time t; d is the diffusion coefficient; depending on the initial and boundary conditions, the solution of equation (4) can be expressed as,
Figure BDA0001665423620000073
in the formula Cs、C0The concentrations of water at and away from the interface, respectively.
According to the spatial and time distribution of the solution concentration after the moisture absorption of the moisture absorption liquid, the diffusion coefficient of water in the moisture absorption liquid can be calculated according to an equal-refractive-index thin layer moving method, a transient-refractive-index spatial distribution method and an equal observation height method.
The invention is based on the new method of the research of the water absorption of the liquid core column lens, the application of the double liquid core column lens can be expanded by using the double liquid core column lens as a water absorption measuring pool and a main imaging element, the application of the liquid core column lens system to measure the liquid phase diffusion coefficient can be perfected and expanded, and the foundation can be laid for the research of the solid dissolution and the liquid absorption of greenhouse gases.
The method better solves the problem of the traditional method that the change of the liquid mass before and after the water absorption process is weighed by a balance, and the research of obtaining physical parameters such as water absorption capacity, water absorption rate and the like is a macroscopic research. The method can describe the water absorption process in a microscopic form, directly obtain microscopic transport information of water molecules in the moisture absorption liquid, and obtain the concentration gradient, the water absorption capacity, the water absorption rate and the water absorption mechanism of the moisture absorption liquid solution. Meanwhile, the method is also suitable for researching the liquid absorption process of the greenhouse gas.
The device has the advantages of simple equipment, automatic, convenient, quick and accurate measurement of the moisture absorption quantity and the moisture absorption rate of the moisture absorption liquid, and the moisture absorption process can be directly seen. The water absorption process can be described in a microscopic form by diffusion, and the microscopic transport information of water vapor molecules in the hygroscopic liquid can be directly obtained, so that the concentration gradient, the water absorption capacity, the water absorption rate and the water absorption mechanism of the hygroscopic liquid solution can be obtained.
Examples
Example 1
Measuring the relationship between the concentration (refractive index) of the ethylene glycol solution and the image width
1.1 fitting a Linear relationship between concentration and refractive index of an aqueous solution of ethylene glycol
For the water absorption process, the concentration change of water is mainly studied, so that glycol aqueous solutions with different concentrations (molar concentrations) are prepared by using glycol with different concentrations as a solvent and pure water as a solute, and after a refractive index (as shown in table 1) is measured by an abbe refractometer (with an accuracy of 0.0002), a linear relationship is fitted between the concentration of the glycol aqueous solution and the refractive index:
c-649.6787 n +929.5325, (correlation coefficient R)2＝0.999)。 (6-1)
TABLE 1 refractive index of different molarity waters in ethylene glycol
Figure BDA0001665423620000081
Similarly, the data of the molar concentration and the refractive index of water are shown in tables 6-2, 6-3, 6-4 and 6-5 respectively by using ethylene glycol solutions with different concentrations as solvents. And respectively fitting the corresponding relationship between the concentration and the refractive index, and satisfying the following formulas:
95％EG:C＝－662.9946n+946.3851，(R2＝0.9992), (6-2)
90％EG:C＝－686.8354n+976.9940，(R2＝0.9985), (6-3)
85％EG:C＝－708.8904n+1005.3443，(R2＝0.9993), (6-4)
80％EG:C＝－778.6301n+1099.7185，(R2＝0.9981), (6-5)
1.2 relationship between refractive index n of solution and image Width ∑
Taking a pure ethylene glycol solution as an example, the refractive index n' of the liquid core liquid after the selection is 1.3974, and the relationship between the refractive index and the image width is obtained through experiments and theoretical calculation respectively. And fixing the position of the CMOS at the position of the glycol clear imaging. The prepared 24 groups of solutions with different concentrations are respectively placed in the front liquid core, and the image width is measured. Only a portion of the imaged image is listed as shown in fig. 6.
The width data of the measured images are shown in Table 2, the functional relationship between the fitted width and the refractive index is shown as (7-1), and the fitted curve is shown as a small square in FIG. 7:
n＝-0.4785×10-4x Σ +1.4306, (correlation coefficient R)2＝0.9994). (7-1)
TABLE 2 relationship of refractive index to image width (Experimental method)
Figure BDA0001665423620000091
Through the geometrical optics theory, the image width and the refractive index data are obtained through calculation, the functional relation between the image width and the refractive index data is fitted to satisfy the formula (7-2), and the fitting curve is shown as a black solid line in FIG. 7:
n＝-0.4799×10-4×Σ+1.4306，(R2＝1). (7-2)
it can be seen from fig. 7 and equations (7-1) and (7-2) that the experimental method and the theoretical calculation method are very close to each other in the functional relationship between the measured image width and the refractive index, and the experimental method is complicated in the measurement process, so that the experimental method can be replaced by the theoretical calculation method. In the following, when measuring the water absorption of solutions of 95% ethylene glycol, 90% ethylene glycol, 85% ethylene glycol and 80% ethylene glycol, the functional relationship between the refractive index and the image width was calculated by a theoretical calculation method. The functional relation obtained by fitting the specific refractive index and the image width data is as follows:
95％EG:n＝-0.4546×10-4×Σ+1.4273,(R2＝1) (7-3)
90％EG:n＝-0.4599×10-4×Σ+1.4225,(R2＝1) (7-4)
85％EG:n＝-0.4548×10-4×Σ+1.4175,(R2＝1) (7-5)
80％EG:n＝-0.4524×10-4×Σ+1.4126,(R2＝1) (7-6)
example 2
Method for measuring water absorption capacity of glycol solutions with different concentrations based on liquid core column lens
Under the conditions of measuring 20 +/-1 ℃ and relative humidity RH of 80 +/-3% by using the device shown in the figure 1, 4.4ml of pure ethylene glycol is injected into the liquid core in front of the double-liquid-core column lens, the upper end of the liquid core lens is sealed, and the liquid core lens is stood for 30 minutes to reduce the turbulence caused by the injection. And (3) opening the upper end seal of the liquid core column lens to enable the liquid core column lens to be in contact with air, wherein the time t is marked as 0. At intervals, images were collected and recorded after water absorption, as shown in fig. 5. In the early stage of water absorption, due to the hydrophilic effect at the edge of the cylindrical lens, the liquid surface of an image is concave obviously, and the image width is difficult to accurately judge; and the water absorption capacity is small, which easily causes a large error in the calculation of the water absorption capacity. Therefore, the water absorption image after 20h is selected for calculation, and the water absorption capacity of the ethylene glycol is measured by a focal plane imaging method. The mode of directly measuring the water absorption by a balance and the mode of measuring by a focal plane imaging method based on the liquid core column lens form a control group. The balance and the device for measuring the water absorption capacity by the focal plane method are placed in the same experimental environment (the temperature and the relative humidity are the same), and after standing for 30min to reduce the turbulence caused by liquid injection, the seal is simultaneously uncovered, and the time t is recorded as 0.
2.1 Water absorption of pure ethylene glycol at different times
The calculation results of the water absorption by the liquid-core rod lens focal plane imaging method are shown in row 2 of table 3. The water uptake was measured directly on a balance as shown in row 3 of table 3. It can be seen from the table that the water absorption calculated by the double liquid core column lens focal plane method is closer to the water absorption measured by a balance, the relative error between the two is within 5 percent, and the method is stable and reliable in water absorption measurement.
TABLE 3 Water absorption of pure ethylene glycol at different times
Figure BDA0001665423620000111
2.2 Water absorption Capacity of different concentrations of ethylene glycol at different times
The water absorption capacity of the ethylene glycol with different concentrations in 20h-30h is respectively measured by the same method, the measurement results are respectively shown in the following table 4, and the relative errors of the measurement results of the two measurement methods are smaller. Comparing the data in the table, it can be seen that as the concentration of ethylene glycol is reduced, the mass of water in the air absorbed in the same time is reduced, i.e. the water absorption capacity is gradually reduced.
TABLE 4 Water absorption of ethylene glycol of different concentrations at different times
Figure BDA0001665423620000112
As can be seen from the calculation results in tables 3 and 4: in the same time, the relative error between the measurement result of the double liquid core column lens and the measurement result of the balance is within 5 percent and within an allowable error range. The method can realize the visualization of the water absorption process, can see the concentration change caused by water absorption in real time, and can study the liquid water absorption process from the microscopic aspect.
2.3 moisture absorption Capacity of different concentrations of ethylene glycol at different times
In the ratio m of water absorption per unit volume to time0The t is taken as a moisture absorption capacity parameter index, corresponding moisture absorption capacity can be calculated according to the water absorption capacity of the ethylene glycol with different concentrations in 20h-30h, and the measurement results are respectively shown in the following table 5. Comparing the data in the table, it can be seen that the moisture absorption capacity gradually decreases as the concentration of ethylene glycol is continuously decreased.
TABLE 5 Water absorption of ethylene glycol of different concentrations at different times
Figure BDA0001665423620000121
As can be seen from the calculation results in table 5: the higher the concentration, the stronger the moisture absorption capacity in the same time.
Example 3
The diffusion coefficients of ethylene glycol with different concentrations in the moisture absorption process are calculated by taking an equal-refractive-index thin-layer moving method as an example. The same experimental environment as the water absorption measurement was adopted, and the room temperature was controlled to 20 ℃. + -. 1 ℃ and the relative humidity RH was 80%. + -. 3%. And selecting a liquid thin layer close to the refractive index of the liquid to be detected to clearly image the liquid thin layer. And (3) by utilizing an equal-refractive-index thin layer moving method, the brightest and sharpest image is formed at the selected refractive-index thin layer, the change rule of the position along with time is observed and recorded, the slope is obtained by fitting, and the diffusion coefficient is calculated.
3.1 relationship between concentration of ethylene glycol solution and refractive index
When the diffusion coefficient is measured by using an equal refractive index thin layer moving method, the concentration corresponding to the selected thin layer needs to be known, and the qualitative relation between the water absorption capacity and the diffusion coefficient is mainly researched, so that glycol aqueous solutions with different concentrations are prepared from 0-100% by using water as a solute and glycol as a solvent, the corresponding refractive index is measured by using an Abbe refractometer (the precision is 0.0002), the data is shown in a table 6, and the relation between the concentration (mass fraction) of the fitted solution and the refractive index can be expressed as follows:
c-10.0581 n +14.4023, (correlation coefficient R)2＝0.9997). (8)
TABLE 6 correlation between refractive index and concentration of water using ethylene glycol as solvent
Figure BDA0001665423620000131
3.2 diffusion coefficients of different concentrations of ethylene glycol and Water in air
Pure ethylene glycol is taken as an example, and an aplanatic liquid with the refractive index of 1.4486 is put into the rear liquid core. Putting 4.4ml of glycol solution into the lower end of the front liquid core, sealing the upper end of the column lens, standing for 30 minutes to reduce turbulence caused by liquid injection, and then opening the seal to enable the glycol solution to be in contact with air, and recording the time when t is 0. Selecting a thin refractive index layer adjacent to the ethylene glycol solution (n is selected)cThree index layers 1.4295, 1.4292, 1.4296) and the CMOS detector is fixed in position where the selected index layers are clearly imaged, and multiple sets of experimental measurements are made. From 190min, the movement of the recording sheet position Z with time t was observed every 5min, as shown in fig. 10.
Thin layer n of selected refractive indexc1.4295, substituting (8) formula C-10.0581 n + 14.4023-0.024,in the diffusion during water absorption, it is considered that water molecules are concentrated and then diffused into ethylene glycol, and therefore, the concentration of water near the interface is approximately considered to be constant, that is, Cs in the formula (5) is 1. For pure glycol absorption, formula C 00. The change relationship between the time t and the position Z of the glycol and the air which are contacted for 190min-310min is measured experimentally, and the measured data is shown in Table 7. Fitting position Z and time
Figure BDA0001665423620000141
The relationship of (a) yields:
Figure BDA0001665423620000142
according to the formula (9), the diffusion coefficient D between pure ethylene glycol and water in the air in the water absorption process can be obtainedEG＝1.32×10-6cm2/s。
TABLE 7 Iso-refractivity film position time-varying data at different times
Figure BDA0001665423620000143
The diffusion coefficients of pure ethylene glycol, 95% ethylene glycol, 90% ethylene glycol, 85% ethylene glycol, 80% ethylene glycol and water in the air were measured, respectively, using the above experimental calculation method. No relevant literature data was found, so multiple sets of experiments were performed for each concentration to determine whether the measurement results were stable, and the measurement results are shown in table 8, with only some of the data listed. The results of multiple experiments in the table are analyzed, and the diffusion coefficient measured by using a semi-infinite-length diffusion model based on an equal-refractive-index thin-layer method is stable.
TABLE 8 measurement of diffusion coefficient of water in air with different glycols
Figure BDA0001665423620000151
Note: diffusion coefficient in the table has the unit 10-6cm2/s
The results of the calculations in table 8 show that: (1) the diffusion coefficient is larger with increasing concentration, i.e. the larger the concentration gradient; (2) the diffusion coefficient and the water absorption capacity are qualitatively combined for analysis, and the larger the diffusion coefficient is, the stronger the water absorption capacity is, and the more the water absorption capacity is.

Claims (3)

1. A liquid water absorption research method based on a liquid core column lens is characterized by comprising the following steps:
A. injecting moisture absorption liquid into the lower end of the liquid core, sealing the upper end of the liquid core to isolate the liquid core from air, adjusting the position of the detector to enable the monochromatic collimated light beam to form a thin and sharp bright line with the same width on the CMOS/CCD surface after passing through the liquid core column lens, and opening the upper end seal to enable the moisture absorption liquid to be naturally exposed to air with certain relative humidity, wherein t is the time when t is 0;
B. the concentration of the hygroscopic liquid changes after the hygroscopic liquid continuously absorbs the moisture in the air, so that the refractive index changes, and an image received by the image detector is not a sharp thin line any more, but a dispersed image with a certain width, namely a hygroscopic image;
C. preparing mixed solutions with different concentrations, injecting the mixed solutions into the liquid core column lens, obtaining diffusion images with different widths at a fixed observation position, and measuring the relationship between the image width and the solution concentration;
D. according to the moisture absorption images at different moments, the spatial distribution condition of the moisture in the liquid core at the moment can be intuitively obtained, and the moisture absorption process is seen;
the specific operation method in the step C is as follows:
a. preparing mixed solutions with different concentrations, measuring the refractive indexes of the mixed solutions, and fitting the relation between the refractive indexes and the concentrations of the mixed solutions;
b. injecting prepared solutions with different refractive indexes into the liquid core column lens at a fixed observation position, measuring the width of an image on an observation system, fitting the relationship between the image width and the refractive index, and substituting the image width obtained by an experiment into a fitting relational expression to obtain the corresponding refractive index;
c. parallel light with the width of 2h is incident on the liquid core column lens, and when the liquid core column lens is injected and foldedRefractive index of ncWhen the liquid is in the liquid state, the focal length of the liquid core column lens is fcWhen the refractive index of the injected liquid in the lens core is niWhen the liquid is in the liquid state, the focal length of the liquid core column lens is fiThe angle between the emergent ray and the main optical axis is thetaiAt fcWidth of sigma imaged on a fixed observation planei；fi、∑iAnd thetaiThe following geometrical relationships exist:
Figure FDA0002922640580000011
fitting the relation between the refractive index and the image width under the condition of refraction law imaging according to the formula (1), and substituting the experimental image width into the fitting relation formula to obtain the refractive index at the corresponding position under the condition of refraction law imaging;
e. obtaining the relation between the image width and the concentration according to the relation between the refractive index and the concentration in the step a and the relation between the image width and the refractive index, wherein the relation between the image width and the refractive index is preferably calculated by the method introduced in the step c under the condition that the fitting relational expression obtained by the experimental method in the step b and the step c is similar to the calculated relational expression;
the method for calculating the water absorption capacity comprises the following specific steps: the hygroscopic solution is formed by using hygroscopic liquid as a solvent and water as a solute, the corresponding solution concentration C (Z, t) at the time t is obtained according to the hygroscopic image width at different positions Z according to the one-to-one correspondence among the solution concentration, the refractive index and the image width, and the mass of the absorbed water in the region from the position Z to the position Z plus delta Z is expressed as follows: Δ ms＝M0*C(Zi)*S*ΔZ，(2)；
Wherein S is the cross-sectional area corresponding to the selected volume element, i.e. the cross-sectional area of the front liquid core, Δ Z is the height of the volume element, M0Is the molar mass of water;
from equation (2), it can be seen that the mass of water absorbed at position Z is a function of the cross-sectional area, volume element and solution concentration, at Z0To ZiThe absorbent system at a certain moment in time has an absorbent capacity expressed as:
Figure FDA0002922640580000021
2. the method for studying water absorption of a liquid-core column lens-based liquid according to claim 1, wherein: calculating the total water absorption capacity of the unit volume of the hygroscopic liquid or the water absorption capacity in a certain time period, and obtaining the average moisture absorption rate and the moisture absorption rate in a certain time period according to the relation between the water absorption capacity of the unit volume of the hygroscopic liquid and the time, namely the ratio m of the water absorption capacity in the unit volume to the time0And/t is taken as a parameter index of moisture absorption capacity.
3. The method for studying water absorption of a liquid-core column lens-based liquid according to claim 1, wherein: according to the spatial and time distribution of the solution concentration after the moisture absorption of the moisture absorption liquid, the diffusion coefficient of water in the moisture absorption liquid can be calculated according to an equal-refractive-index thin layer moving method, a transient-refractive-index spatial distribution method and an equal observation height method.
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