JPS5945937B2 - Method for measuring pore diameter of porous membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the pore size of a membrane having micropores.

In general, porous membranes are widely used for the separation, recovery, and purification of various substances.Among these, those with micropores with pore diameters of 1 to several 100 A are used for the concentration and purification of proteins, viruses, colloids, etc. It is used for hemodialysis and body fluid concentration.

By the way, in order to use such a porous membrane for a desired purpose, it is necessary to determine the diameter of its micropores, but all of the methods known so far have low precision and require complicated operations. There were problems such as , and it was not necessarily suitable for practical use.

For example, with the method of direct observation and measurement using an electron microscope, it is almost impossible to measure micropores with a diameter of 200A or less, and mercury intrusion method must be performed under high pressure, which prevents membrane deformation. This has the disadvantage that it cannot be used for the desired purpose.

Furthermore, the method of measuring the amount of permeation of water or air and determining the pore size using the Hagen-Poiseuille equation requires several unverifiable assumptions, making it difficult to ensure accuracy and providing relatively accurate results. Compared to the molecular adsorption method, which provides promising results, this method has the inconvenience of requiring complicated measurements over a long period of time. The present inventors have overcome the drawbacks of such conventional methods, and have made it possible to measure micro/J-L of several hundred amperes or less, which has been difficult to accurately measure, with relatively simple operations. As a result of extensive research to develop a method, we discovered that the pore diameter of a membrane can be accurately measured from the relative permeability differences between different types of salts, and based on this knowledge we have developed the present invention. .

That is, according to the present invention, by measuring the membrane permeation rates of at least two different salt solutions through a porous membrane and comparing the relationship between relative permeability and diffusion coefficient derived therefrom, The pore diameter of the porous membrane can be determined by As the salt solution used in the method of the present invention, a combination of salt solutions having a common anion and different cations is suitable (1).

Examples of such things include a combination of aqueous solutions of at least two salts selected from lithium chloride, sodium chloride, potassium chloride, cesium chloride and calcium chloride, lithium bromide, sodium bromide, potassium bromide, Examples include a combination of aqueous solutions of at least two salts selected from cesium bromide and calcium bromide.
Although it is sufficient to use two types of these salts, one with a relatively large diffusion coefficient and one with a relatively small diffusion coefficient, the measurement accuracy can be further improved by using 3J or more types.

To specifically carry out the present invention, one side of the porous membrane is brought into contact with pure water and the other side is brought into contact with a salt solution, and after a predetermined period of time the salt concentration on the pure water side is adjusted by, for example, electric power. Measurement is performed using conductivity, and the transmittance per unit time for the salt is determined.

Next, under the same conditions except for changing the type of salt solution,
Repeat the same operation to determine the permeability per unit time for another salt. The concentration of the salt solution at this time must be such that it can be easily detected by a conductivity meter or spectrometer, and that the electric conductivity and absorption coefficient of the pure water itself will increase during the measurement time. Considering conditions such as not giving a large error, that the charge of the membrane does not have a large effect on ion permeation, and that the decrease in concentration on the salt solution side due to salt migration does not give a large error to the measurement results, Concentration 0.5-2 mol/t
It is preferable to choose within the range. At this level of concentration,
The amount of salt transferred to the pure water side per hour is 0.001 to 0.0.
The ratio is 5 mol/t. When carrying out this measurement, it is advantageous to carry out the measurement while stirring thoroughly in order to maintain a uniform concentration in the solution. In this way, by repeating the measurement 2 to 3 times every 10 to 15 minutes, the salt permeability can be determined extremely accurately.

It is not necessary to know the absolute value for this transmittance, but it is necessary to know the relative ratio of one of the two or more salts to the other. That's enough. If we plot the relationship on a graph with the relative permeability obtained in this way on the vertical axis and the salt diffusion coefficient on the horizontal axis, we will obtain a straight line corresponding to each pore diameter, but the slope of this straight line is , corresponds to the pore diameter.

For example, the attached drawing is a graph plotting the common logarithm of the diffusion coefficient on the horizontal axis and the common logarithm of the relative permeability on the vertical axis for each of five porous membranes with different pore sizes. Sample A'T! has a slope of 1.
00, 1.32 for sample B with a pore diameter of 100λ, and a pore diameter of 50 (
1.43 for sample C with A, and 2.43 for sample D with pore diameter number x.
24, sample E'C'Ft of 1 to 2 pore diameters was $6.63, and it can be seen that the gradient increases as the pore diameter becomes smaller.

The ion permeation rate of each salt used as a basis for measurement in the method of the present invention is determined not by its atomic weight but by the size of the imen including hydration water, so the relative permeability As a factor that has a correlation with the above, it is necessary to use the diffusion coefficient instead of using the atomic weight or the atomic radius.

The porous membrane whose pore diameter can be measured by the method of the present invention is not particularly limited and may be of any type as long as it does not have functional groups that inhibit smooth ion permeation like ion exchange membranes. .

According to the present invention, even an unskilled person can obtain accurate pore diameter measurements in a short time using a simple device, and since the measurement conditions are close to practical conditions, it is possible to obtain results that are suitable for practical use. It has the advantage of being possible.

Next, the present invention will be explained in more detail with reference to Examples. Example dialysis cell with 4C on each side! Attach IL force-shaped porous membrane (
Effective area 3?2), pure water 100?3 on one side,
100 Cf of salt solution with a concentration of 0.5 mol/t on the other side! L
3 and kept at 20°C for 10 minutes, the amount of each salt passing through the cation 2 was determined by measuring the electrical conductivity of the pure water side.

As the salt in this case, lithium chloride, sodium chloride, potassium chloride, cesium chloride, and calcium chloride were used. In this way, one of the following five types (A-E) of porous membranes was prepared.
The amount of ions passing per minute and the amount of 0.
5 mol/TVC} and the diffusion coefficient are expressed in graphs in common logarithmic units. The results are shown in the drawing.
The diffusion coefficient in this case is as described by R.A. Lopinson et al.
“Electrite Solutions
OlyteSOlutiOns), page 515 (
(1959 edition). A: Jyuragard 2500 membrane (manufactured by Celanese, porous polypropylene membrane, pore size 400X4000λ, membrane thickness 25μ) B: Ultra filter 1 (manufactured by Sartorius, cellulose nitrate porous membrane, pore diameter 100, membrane thickness 350μ) c: Ultra filter 1 ( D: Sarcoplasmic reticulum membrane (T.KOmetaniandMKa
saitJOwnalOfMembraneBlOl
OgyO Vol. 41, pages 295-308) E:
Cellulose acetate membrane (pore size 1 to 2X, membrane thickness 60μ) As is clear from this drawing, the slope of each straight line changes depending on the pore size, and the slope becomes larger as the pore size becomes smaller.

Therefore, by comparing the measured value of the in-material permeation amount obtained with an unknown sample with these data, the pore diameter can be easily determined.

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between the diffusion coefficient of each salt and the amount of membrane permeation in the method of the present invention.

Claims (1)

[Claims] 1 Membrane permeation rates of at least two different salts through a porous membrane having micropores are measured, and determined from the relative membrane permeability derived therefrom and the diffusion coefficients of these salts. A method for measuring the pore diameter of a porous membrane, characterized by determining the pore diameter based on a factor. 2. The method according to claim 1, wherein the at least two different salts share an anion and differ only in cations.