JPH10332621A - Evaluation method for zeta potential and measuring apparatus for zeta potential - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method in which a dynamic electricity phenomenon can be evaluated in a many-sided manner by a method wherein a zeta potential is computed on the basis of data obtained by measuring the dynamic electricity phenomenon of a solid- liquid interface a plurality of numbers of times and the zeta potential is captured as a distribution amount which expresses its electric charge state so as to be processed on the basis of a statistical technique. SOLUTION: A solid sample whose zeta potential is to be measured is filled between an electrode 1 and an electrode 2 inside a cell 10, and a filled layer 3 is formed. A liquid which is made to flow into the cell 10 is housed in a fluid-liquid supply container 11, and the pressure at the inside of the supply container 11 is made higher than atmospheric pressure while valves 17a, 17b at a fluid-liquid receiver container 12 and values 14a, 14c at the supply container 11 are opened and closed. In this state, the liquid inside the supply container 11 flows to the cell 10, and a fluid potential E which is generated in the filled layer 3 is measured by an electrometer 13. The output of the electrometer 13 and outputs of pressure gages 15a, 15b are input to a computer 22 via respective A/D converters 21. Then, a zeta potential ζis found by ζ=k.E/P [where (k) represents a constant] on the basis of a fluid pressure P which is found from the pressure difference between the pressure gages 15a, 15b and on the basis of the fluid potential E. By a computing operation based on a statistical technique, the mode value, the mean value, the standard deviation and the like of distribution amounts are found.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the charge state of a solid-liquid interface by using a zeta potential, and a zeta potential measuring device capable of outputting an evaluation result according to the method.

[0002]

2. Description of the Related Art Conventionally, a zeta potential representing a charge state at a solid-liquid interface has been conventionally obtained as a unique value per measurement. As a method for measuring the zeta potential, a streaming potential method, an electrophoresis method, or the like is generally used, but a commercially available measuring device based on any of these methods can measure an electrokinetic phenomenon with respect to one sample. One zeta potential, which is a unique value, is obtained from one or a plurality of obtained data.

Here, in the conventional apparatus, a plurality of data of the electrokinetic phenomenon are measured for one sample.
The purpose is to improve the accuracy of the measurement by averaging, and the zeta potential as a unique value is obtained as the measurement result. Also, in some conventional devices, parameters obtained during the analysis are displayed as distribution amounts, but this is unavoidably obtained from analysis theory or method, and the display of the distribution amounts is physically It doesn't mean much.

[0004]

By the way, in the measurement of the zeta potential, the semi-fixed adsorbent layer must be symmetrical, and dynamic characteristics must be captured and analyzed using any measurement principle. In addition, the fact that it deals with the adsorption phenomenon that is easily affected by the state of the system, it is inevitable that the dispersion will be larger or smaller. For this reason, when the zeta potential is obtained as a unique value, it is difficult to determine whether a difference between the values is significant. Also,
In some cases, the state or property of an object cannot be represented by only one zeta potential value. For example, in an event that is closely related to the charge state of the interface, there is a significant difference as a phenomenon but no significant difference in the value of zeta potential.

The present invention has been made in view of such circumstances, and a new evaluation criterion can be obtained by using the zeta potential, and the electrokinetic phenomenon at the solid-liquid interface can be more multifacetedly evaluated. It is an object of the present invention to provide a method capable of performing the method and a zeta potential measuring device capable of outputting an evaluation result according to the method.

[0006]

In order to achieve the above object, a method for evaluating zeta potential according to the present invention measures electrokinetic phenomena at a solid-liquid interface a plurality of times independently of each other, and measures each time. The zeta potentials are individually calculated from the data, and the calculated plurality of zeta potentials are regarded as a distribution amount representing the charge state of the solid-liquid interface, and the distribution amount is subjected to a processing based on a statistical method to determine one or more distribution amounts. In the required expression form.

Further, the zeta potential measuring apparatus of the present invention comprises an electrokinetic phenomenon measuring means for measuring an electrokinetic phenomenon at a solid-liquid interface, and an electrokinetic phenomenon which is independently measured a plurality of times by the measuring means. Storage means for storing the phenomenon measurement data, zeta potentials are individually calculated from the stored measurement data, and the plurality of zeta potential calculation results are subjected to predetermined statistical calculations as distribution amounts and output It is characterized by having arithmetic means.

According to the present invention, the solid-liquid interface using the zeta potential is obtained by not grasping the zeta potential as a unique value but as a distribution amount and converting the distribution amount into an appropriate expression form by a statistical method. This makes it possible to perform the evaluation of the state of charge in more detail than in the conventional evaluation based on the zeta potential as a unique value.

Hereinafter, the principle of the present invention will be described with its background. The streaming potential method is taken as an example of the method for measuring the zeta potential. The streaming potential method is a method of obtaining a zeta potential from a ratio (E / P) of a streaming potential E generated when a liquid around a fixed solid flows and a flowing pressure P of the liquid. According to the technical book, in the streaming potential method, a liquid is caused to flow using a plurality of flowing pressures P, and a streaming potential E generated at each of the flowing pressures P is measured. The plot of (PE) is performed, an approximate straight line is obtained from the plot, the (E / P) value is determined, and the value is multiplied by a coefficient that is determined separately to uniquely determine the zeta potential. The way to decide is prescribed.

As described above, when the zeta potential is uniquely obtained by the streaming potential method, if each plot point of the (PE) plot is truly linear as shown in FIG. Although less reproducible results are obtained, if the plot points deviate from the linear positions as shown in FIG. 2, the results are large and the reproducibility is not very good. For example, if one point of data in FIG. 2 is ignored because the error is large, a completely different (E / P) value may be obtained.

Until now, the cause of the deviation of the plot point of the (PE) plot from the straight line has been treated as an experimental error (measurement error). As a method of eliminating such a measurement error problem, the inventor of the present invention continuously measures the flowing potential E while passively changing the flowing pressure P, thereby obtaining the flow resistance existing in the liquid flow path. Has already been proposed that eliminates the delay in detecting the flow pressure corresponding to the pressure loss caused by the above, and can accurately measure the flow pressure P when the respective flow potentials E are obtained (Japanese Patent Laid-Open No. 7-325062).
No.) has been put to practical use. The streaming potential E-
When the flow pressure P is measured, it can be seen that the above measurement error has been eliminated.
E) There are cases where the plot is obtained as a straight line as shown in FIG. 3 and cases where the plot is obtained as a curve as shown in FIG. Further, even for the same sample, if the type of liquid is different, it may be a straight line or a curved line. In these cases, reproducibility is obtained if the conditions are the same, and it is determined that this phenomenon depends on the state of the sample, in other words, on the state of adsorption at the solid-liquid interface.

[0012] Zeta potential is defined as the electrical potential on the sliding surface that occurs when relative motion occurs between the two phases at the solid-liquid interface. The position of the sliding surface is not unique but depends on the adsorbing layer existing at the solid-liquid interface. If this is extended, the position of the sliding surface moves depending on the state of the adsorbing layer even with the same relative movement. That is, in the case of a stable (or should be described as strong) adsorption layer, the position of the sliding surface is constant without being affected by the change in the flow pressure, and the ratio of the generated flow potential to the flow pressure is constant, In the case of a stable (or weak) adsorption layer, it is considered that the position of the sliding surface changes due to the change in the flow pressure, and the ratio of the flow potential to the flow pressure changes. Considering this, the phenomenon that the (PE) plot may be obtained as a straight line or the curve may be obtained depending on conditions can be interpreted as a phenomenon caused by the stability of the adsorption layer. Can be strongly affirmed. Here, each measurement point in the above (PE) plot is a value obtained independently of each other, and is a significant value since it is not obtained by deformation of single data.

Therefore, when the zeta potential is obtained using the differential gradient at each point of the (PE) plot, the zeta potential can be expressed as a value having a distribution as a whole. When the (PE) plot is obtained as a straight line, the distribution of the zeta potential is sharp (see FIG. 6), and the adsorption layer can be said to be stable (strong). Is broad (see FIG. 7), and it can be determined that the adsorption layer is unstable. From this, when using the zeta potential as the amount of distribution obtained by the present invention, as an example, the width of the distribution, or the standard deviation obtained by statistically processing it, is a parameter indicating the stability of the adsorption layer It can be seen that Similarly, the mode value of the distribution of the zeta potential can be a parameter indicating the strength of the charged state at the solid-liquid interface. Can be obtained.

[0014]

FIG. 5 is a block diagram of an embodiment of the present invention, showing an example in which the present invention is applied to a zeta potential measuring device based on the streaming potential method.

A streaming potential measuring cell 10 having a substantially tubular shape as a whole and having a pair of electrodes 1 and 2 disposed opposite to each other has one end communicating with a flowing liquid supply container 11 via a liquid supply pipe 11a. The other end communicates with the fluid receiving container 12 via the liquid receiving pipe 12a. The solid sample whose zeta potential is to be measured is filled between the electrodes 1 and 2 in the cell 10, and the filling layer 3 is formed there.

An electrometer 13 is connected to each of the electrodes 1 and 2, and the electrometer 13 measures a potential difference between the electrodes 1 and 2 due to the flow of the liquid in the packed bed 3, that is, a streaming potential E. You.

The fluid liquid supply container 11 is constituted by a container having a pressure-resistant and airtight structure, and contains therein a liquid to be flowed into the cell 10. Further, a gas passage 14a for introducing a gas (for example, N ₂ ) from a pressure source (not shown) is connected to the supply container 11, and a pressure for flowing the liquid is applied by these. Make up the mechanism. Further, the supply container 11 is provided with a pressure gauge 15a for measuring the internal pressure and a thermometer 16 for measuring the temperature of the liquid.

The gas passage 14a is provided with a gas introduction valve 14b for opening and closing the passage 14a to introduce / stop a gas from a pressure source into the supply container 11. There is provided a branch path 14d provided with an atmosphere release valve 14c for bringing the pressure to atmospheric pressure. Therefore, by closing the atmosphere opening valve 14c and opening the gas introduction valve 14b, a gas higher than the atmospheric pressure from the pressure source can be introduced into the supply container 11,
Conversely, by closing the gas introduction valve 14b and opening the atmosphere release valve 14c, the pressure in the supply container 11 can be made equal to the atmospheric pressure.

The fluid liquid receiving container 12 is also constituted by a container having a pressure-resistant and airtight structure, and a pressure gauge 15b for measuring the internal pressure is provided at an upper portion thereof. An atmospheric release valve 17a for setting the pressure to atmospheric pressure is provided. At the bottom of the receiving container 12, a liquid discharge valve 17b for discharging the liquid in the container 12 is provided. Both the liquid discharge valve 17b and the atmosphere opening valve 17a are closed when the flow potential is measured, and the receiving container 12 is in an airtight state.

The outputs of the electrometer 13 and the pressure gauges 15a and 15b for measuring the pressures in the containers 11 and 12 are digitized by an AD converter 21, respectively.
The data is sampled by the computer 22 every moment. These sampled data are stored in the memory of the computer 22. As will be described later, the computer 22 includes a plurality of flow rates P each obtained from the output difference between the pressure gauges 15a and 15b and the output of the electrometer 13 obtained under each of the flow pressures P, that is, the flow potential E. The zeta potential 個 々 is individually calculated from the data pair (PE) using the known zeta potential calculation formula represented by the following formula (1), and the obtained plurality of calculated values are used as the distribution of the zeta potential 分布. And calculate the distribution mode value, average value,
The standard deviation and the like are calculated, and the result is displayed on the display 23.

Ζ = k ・ E / P (1) where k in the equation (1) is a constant determined by the dielectric constant, viscosity and conductivity of the liquid.

The operation of measuring the flow pressure P and the flow potential E in the above embodiment will be described. First, a predetermined amount of the fluid is stored in the fluid supply container 11 and the fluid supply container 12 is opened to the atmosphere. After the valve 17a is once opened and the air pressure in the container 12 is set to the atmospheric pressure, the air release valve in the fluid supply container 11 is closed with the air release valve 17a and the liquid discharge valve 17b of the fluid supply container 12 closed. 1
4c is closed and the gas introduction valve 14b is opened, so that a constant pressure P
_{Give P.} In this state, the supply container 11, the streaming potential measurement cell 10, and the receiving container 12 communicate with each other in an airtight state, and a pressure difference is generated between the supply container 11 and the receiving container 12. The liquid inside flows toward the cell 10, passes through the inside of the filling layer 3 sandwiched between the electrodes 1 and 2, and flows into the receiving container 12. The flowing potential E generated in the packed bed 3 by the flow of the liquid is measured by the electrometer 13 via the electrodes 1 and 2, and the digital conversion data is taken into the computer 22 as described above.

At the same time, the flow of the liquid causes the amount of liquid in the receiving container 12 to increase at a speed corresponding to the flow velocity of the liquid. The pressure P _C in the receiving container 12 increases by the amount of the liquid in the container 12. Therefore, even if the pressure P _P in the supply container 11 is kept constant, the cell 1
The differential pressure P (= P _P -P _C ) at the two ends of the
It changes passively in accordance with the change in the flow velocity of the liquid flowing therethrough, and there is no deviation between the instantaneous differential pressure P and the streaming potential E.

Now, the computer 22 stores a large number of pairs of accurate data of the flow pressure P and the flow potential E without time lag, as described above. From the pair of data, the zeta potential
Is calculated. Flow pressure P and streaming potential E for each pair
Are significant values because they are measured independently. Zeta potential obtained individually from each data pair ζ
Is information having a distribution indicating the charge state of the solid-liquid interface in the packed layer 3. For example, if 100 pairs of data consisting of the flowing pressure P and the flowing potential E are measured by one measurement, 100 zeta potentials ζ are calculated. At this time, when each data pair is uniformly proportional, the value of each zeta potential と り also takes substantially the same value, and the distribution becomes sharp as illustrated in FIG. In this case, the value of each zeta potential ば ら つ き fluctuates and becomes broad as illustrated in FIG. If this distribution state is represented by, for example, a standard deviation, the value can be a parameter indicating the stability / instability (strong / weak) of the adsorption layer existing at the solid-liquid interface as described above.

Further, if the mode value of each zeta potential ζ is calculated, it can be a parameter representing the strength of the charged state at the solid-liquid interface. Note that the distribution amount of each zeta potential 求 め is obtained as a number distribution, but can be normalized by dividing by the total incremental number. In this case, it is possible to directly compare the respective measurement results. .

In the above embodiment, an example is shown in which the present invention is applied to a zeta potential measuring apparatus based on the streaming potential method. However, the present invention can be applied to a measurement based on the electrophoretic method. is there. However, in this case, if the movement of a large number of particles is regarded as a single phenomenon at a time as in the laser Doppler method and the distribution is determined by analyzing a single data, the interfacial dynamics are independent of each other multiple times. It cannot be said that the electrical phenomenon was measured, and even if distributed data is obtained, the distribution is not a significant data group. Therefore, when the present invention is applied to the measurement based on the electrophoresis method, if the method of measuring the movement of each particle is measured for each of a plurality of particles, and obtained as independent data. The result must be displayed as the amount of distribution of the zeta potential.

[0027]

As described above, according to the present invention, the electrokinetic phenomena at the solid-liquid interface are measured independently of each other a plurality of times, and the zeta potential is calculated individually from the measurement data of each time to obtain a distribution. It is treated as a quantity and subjected to a process based on a statistical method to represent the distribution quantity in one or a plurality of required expression forms. Therefore, the zeta potential, such as the evaluation of the stability / instability of the adsorption layer existing at the solid-liquid interface, etc. Items that could not be evaluated by the conventional method of expressing as a unique value can now be easily evaluated. For example, when the zeta potential is obtained as a unique value by the conventional method, it is considered that this means that an average value when the zeta potential is regarded as a distribution amount is obtained. In this case,
For example, it is difficult to determine whether the difference between the measurement results of two samples is significant, but this is relatively easy when viewed as a distribution amount. In addition, when obtained as a unique value, for example, even if there is no difference between two samples, if there is a difference when expressed as a distribution amount, it can be said that there is a difference between both samples. Many insights can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of the relationship between streaming pressure and streaming potential obtained when measuring zeta potential by the streaming potential method.

FIG. 2 is a graph showing another example of the relationship between streaming pressure and streaming potential obtained when measuring zeta potential by the streaming potential method.

FIG. 3 is a graph showing an example of a relationship between a flowing pressure and a flowing potential measured by a method that hardly causes a measurement error.

FIG. 4 is a graph showing another example of the relationship between the flowing pressure and the flowing potential measured by a method that is unlikely to cause a measurement error.

FIG. 5 is an overall configuration diagram of an embodiment of the present invention.

FIG. 6 is a graph showing an example of a distribution state of zeta potential obtained according to the embodiment of the present invention.

FIG. 7 is a graph showing another example of a distribution state of zeta potential obtained according to the embodiment of the present invention.

[Explanation of symbols]

 1, 2 electrode 3 packed bed 10 flowing potential measuring cell 11 flowing liquid supply container 12 flowing liquid receiving container 13 potentiometer 14a gas passage 14b gas introduction valve 15a, 15b pressure gauge 21 A / D converter 22 computer 23 display

Claims (2)

[Claims] 1. A method for evaluating the charge state of a solid-liquid interface by using a zeta potential, wherein the electrokinetic phenomenon at the solid-liquid interface is
Measured multiple times independently of each other, calculate the zeta potential individually from the measurement data of each time, capture the calculated plurality of zeta potentials as a distribution amount representing the charge state of the solid-liquid interface, and use a statistical method A zeta-potential evaluation method characterized by performing a process based on an expression and expressing the distribution amount in one or a plurality of required expression forms. 2. An electrokinetic phenomenon measuring means for measuring an electrokinetic phenomenon at a solid-liquid interface, and a storage means for storing electrokinetic phenomenon measurement data measured independently a plurality of times by the measuring means. A zeta-potential measuring device including a calculating means for individually calculating a zeta-potential from the stored measurement data, performing a predetermined statistical calculation as a distribution amount of the plurality of zeta-potential calculation results, and outputting the result. .