JP6867678B2 - Zeta potential measuring device - Google Patents

Description

The present invention relates to a zeta potential measuring device that ultrasonically measures a zeta potential representing the potential of a "sliding surface" in which a liquid flow begins to occur in an electric double layer formed around fine particles in a solution.

The surface of colloidal particles dispersed in a solution is often positively or negatively charged. For example, it is considered that the colloidal particles can be stably dispersed in water due to the repulsive repulsion between the negatively charged colloidal particles. The state of the surface potential of the colloidal particles is often evaluated by a parameter called the zeta potential shown in FIG. This zeta potential can be considered as the potential on the surface of colloidal particles (strictly speaking, the Stern potential). Zeta potential is a very important property not only in colloid science and surface chemistry, but also in food and biology. Analyzing the zeta potential on the surface of the colloidal particles as the degree of charge of the colloidal particles is a very effective method for grasping the dispersion stability of the colloidal particles.

As a method for measuring the zeta potential, various methods including a microscope method and an electrical method are known. In the microscopy method, the movement of fine particles due to the application of an electric field is considered based on the descent of fine particles at the interface of the fine particle layer. However, microscopy can count particles when they are present at fairly low concentrations that are large enough to be resolved by a light microscope, but nanoparticlees measure the rate at which the entire sedimentation interface descends. , The zeta potential is not measured by analyzing each fine particle individually.

The most widely used method today as a method for directly measuring the zeta potential by individually analyzing individual particles is electrophoretic light scattering (ELS, Electrophoretic Light) that combines the principles of dynamic light scattering. Scattering) method. In this ELS method, laser light is irradiated, the scattering amplitude of laser light from each fine particle is captured as a change in time, and the mobility of each fine particle due to electric field application is calculated by making full use of a technique called heterodyne detection. , It is a method to obtain the average zeta potential from it.

However, since this ELS method is a technique for optically reading the velocity of fine particles dispersed in a solution, it is difficult in principle to measure a highly emulsified solution that does not transmit light. This often forces the solution to be significantly diluted to allow sufficient light transmission when attempting to measure the zeta potential of a highly emulsified solution.

That is, if only the zeta potential in the dilute solution is known, it is possible to measure by the ELS method without significant dilution. However, many solutions that are practical materials are often used in a high concentration state and an optically highly emulsified state. Therefore, when diluted, the diluted solution cannot be said to capture the original state, and in many cases, dispersion stabilization due to dilution is erroneously observed. Therefore, there has been a demand for a technique for measuring the zeta potential of a concentrated solution as it is without dilution.

As a technique for measuring the zeta potential using ultrasonic waves in which light transmission is not a problem, instead of the optical method such as the ELS method described above, the ultrasonic vibration potential (CVP (Colloid Vibration Potential)) method and the ultrasonic vibration potential (CVP) method are used. , Electrokinetic Sonic Amplitude (ESA) is known (Non-Patent Document 1).

In the CVP method, the colloidal particles dispersed in the solution are irradiated with ultrasonic waves to vibrate the colloidal particles. For example, when negatively charged colloidal particles vibrate in water due to ultrasonic irradiation, the colloidal particles move to the right, for example, by ultrasonic wave irradiation. Then, the positive charge around the colloidal particles is biased to the opposite left. Therefore, a large amount of positive charges are collected on the left side of the colloidal particles, and a large amount of negative charges are collected on the relatively right side. As a result, a distorted electric double layer is formed around the colloidal particles. Therefore, the vibration of the colloidal particles by ultrasonic waves induces a dipole moment. Since ultrasonic waves are coarse and dense waves, the dipole moments are gathered and oriented at a position away from the transmitter of the ultrasonic waves applied to the colloidal particles, and a macroscopic dipole moment, that is, an electric field is formed.

The formation of the electric field, the particle surface conduction current I _S to the surface of the colloidal particles are induced, the compensation current I _n occurs to compensate it. The zeta potential measuring apparatus, the particle surface conduction current I _S, the zeta potential is calculated by measuring a compensation current I _n.

Thus, the CVP method, the fine particles dispersed in the solution by irradiation with ultrasonic waves by vibrating the fine particles, the induced vibrations particle surface conduction current I _S, the zeta potential by detecting the compensation current I _n It is calculated (Non-Patent Document 1).

In the ESA method, an AC voltage is applied to the charged fine particles from the outside to vibrate the fine particles, and an acoustic signal (sound pressure fluctuation) generated by the vibration is detected. Then, the zeta potential is calculated from the magnitude of the detected acoustic signal and the magnitude of the applied AC electric field (Non-Patent Document 1).

Further, the present inventors have published a conventional technique for measuring the particle size of fine particles dispersed in a solution by ultrasonic waves (Patent Document 1). In this prior art, the first scattering amplitude Ψ based on the propagation time t of the ultrasonic pulse and the observation time T with respect to the motion of the fine particles by receiving the ultrasonic pulse irradiated and scattered by the settling fine particles in the solution. (T, T) is generated. Then, the first scattering amplitude Ψ (t, T) is Fourier-transformed in the direction of the propagation time t to generate the second scattering amplitude Ψ (f, T) which is a function of the frequency f and the observation time T, and the first scattering amplitude Ψ (f, T) is generated. 2 The amplitude r (f, T) and the phase θ (f, T) are calculated based on the real part and the imaginary part of the scattering amplitude Ψ (f, T), respectively. Next, the particle size of the fine particles is calculated based on the amplitude r (f, T) and the phase θ (f, T).

International Publication No. 2016/129399 (published on August 18, 2016)

Shinichi Taketa, "Particle Size Distribution and Zeta Potential Measurement in Concentrated Slurry", Journal of Powder Engineering Vol.41 No.3 Page 190-196 (2004.03.10)

However, the CVP method as described above detects a minute current when calculating the zeta potential from ultrasonic waves, uses various parameters from this minute current, and calculates the zeta potential through a complicated calculation process. is there. Therefore, there are many problems such as time-consuming measurement, need to prepare various parameters, and poor measurement accuracy. For this reason, it is difficult to say that it is a method that is generally easy to accept, and it has not been put into practical use.

Further, in the ESA method, the zeta potential is calculated by performing complicated calibration from the relationship between the AC voltage applied to the fine particles and the sound pressure of the acoustic signal due to the vibration of the fine particles. Therefore, it is difficult to use because it requires complicated calibration, and it has not been put into practical use.

As a result, it seems that users often use the ELS method while limiting the measurement target of the zeta potential to dilute solutions. Above all, the above-mentioned microscopy method does not analyze individual fine particles individually, so that the accuracy of zeta potential measurement is low and effective in a realistic solution system such as when various types of fine particles are mixed. It is hard to say that it is a technology. The basic problem of the ELS method is that the ELS method is a technology that optically reads the velocity of fine particles dispersed in the solution, so in the case of a highly emulsified solution that does not transmit light, the ELS method is basically a measurement method. It is difficult to do.

The prior art described in Patent Document 1 discloses a configuration for calculating the particle size of fine particles in a solution, and does not suggest the present invention for measuring the zeta potential on the surface of fine particles dispersed in a solution. ..

One aspect of the present invention is a zeta potential measuring device capable of easily and accurately measuring the zeta potential of fine particles dispersed in a solution in a high concentration state or an optically highly emulsified state with a simple configuration. The purpose is to realize.

In order to solve the above problems, the zeta potential measuring device according to one aspect of the present invention applies an electric field to the charged fine particles along the electric field application direction in order to run the charged fine particles in the liquid. Based on the device, the ultrasonic receiver that receives the scattered ultrasonic pulses that are applied to the fine particles to which the electric field is applied, and the ultrasonic pulse received by the ultrasonic receiver, in the electric field application direction. A zeta that calculates the zeta potential of the fine particles based on the migration rate calculator that calculates the migration rate of the fine particles along the line by the dynamic ultrasonic scattering method and the migration rate of the fine particles calculated by the migration rate calculator. It is characterized by being provided with a potential calculator.

According to this feature, the moving speed of the fine particles along the electric field application direction is calculated by the dynamic ultrasonic scattering method. Therefore, unlike the CVP method, various parameters for converting ultrasonic waves to an electric field are unnecessary, and unlike the ESA method, it is not necessary to calibrate the relationship between AC voltage and sound pressure. As a result, the zeta potential of the fine particles dispersed in the solution can be easily measured with a simple configuration.

In the zeta potential measuring device according to one aspect of the present invention, it is preferable that the ultrasonic pulse irradiates the fine particles along a direction intersecting the electric field application direction.

According to the above configuration, the arrangement of the electric field applyer and the ultrasonic irradiator can be compactly configured.

In the zeta potential measuring device according to one aspect of the present invention, the electric field applyer applies a sinusoidal AC electric field to the fine particles, the dynamic ultrasonic scattering method includes a phase mode method, and the fine particles are microparticles or sub particles. It preferably contains micron particles.

According to the above configuration, it is suitable for measuring the zeta potential of microparticles or submicron particles.

In the zeta potential measuring device according to one aspect of the present invention, the electric field strength of the sinusoidal AC electric field is 2.0 (V / cm (volt / centimeter)) or more, and the sinusoidal wave corresponding to the sinusoidal AC electric field. The signal period is preferably 1 second or more and 30 seconds or less.

When the electric field strength of the sinusoidal signal is less than 2.0 (V / cm), the migration speed of the fine particles is low, the migration of the fine particles is difficult to observe, and the measurement accuracy is lowered. If the period of the sinusoidal signal applied to the fine particles exceeds 30 seconds, the fine particles will either settle completely or the measurement will take too long, which is not preferable. When the period T of the sinusoidal signal is smaller than 1 second, the pulse repetition time (PRT, Pulse Repetition Time) needs to be 1 ms or less in order to follow a high frequency, which is not preferable.

In the zeta potential measuring device according to one aspect of the present invention, it is preferable that the electric field applyer applies a square wave AC electric field to the fine particles, and the dynamic ultrasonic scattering method includes a complex correlation function method.

According to the above configuration, it is suitable for measuring the zeta potential of nanoparticles.

In the zeta potential measuring device according to one aspect of the present invention, the electric field strength of the square wave AC electric field is 1 (V / cm) or more and 10 (V / cm) or less, and the square wave signal corresponding to the square wave AC electric field. The period of is preferably 1 second or more and 30 seconds or less.

When the complex correlation function method is applied in the region where the electric field strength of the square wave signal is less than 1 (V / cm), the migration speed of the fine particles is slow, so the vibration point of the vibration of the complex correlation function due to the migration of the fine particles is long. Shift to the side. Therefore, it is difficult to actually measure the migration rate depending on the relaxation time of the fine particles, which is not preferable. If the electric field strength of the square wave signal exceeds 10 (V / cm), fine particles collected near the positive electrode or the negative electrode of the electric field applyer are aggregated, which is not preferable.

If the period of the square wave signal exceeds 30 seconds, the movement of the fine particles becomes one-way, and the fine particles 8 accumulate on the positive electrode or the negative electrode of the electric field applyer, and as a result, the fine particles tend to aggregate, which is not preferable. If the period of the square wave signal is less than 1 second, the complex correlation function cannot be constructed, which is not preferable.

In the zeta potential measuring device according to one aspect of the present invention, it is preferable that the liquid is a suspension.

According to the above configuration, the zeta potential of the fine particles dispersed in the liquid can be measured even if the liquid is highly emulsified as compared with the dynamic light scattering (DLS) method.

According to one aspect of the present invention, there is an effect that the zeta potential of the fine particles dispersed in the solution can be easily measured with a simple structure.

It is a schematic diagram which shows the schematic structure of the zeta potential measuring apparatus which concerns on embodiment. The specific configuration of the zeta potential measuring device is shown, (a) is a front sectional view, (b) is a plan view, and (c) is a side view of a main part. It is a figure for demonstrating the electrophoresis cell provided in the zeta potential measuring apparatus, (a) is a figure which shows assembly structure, (b) is a plan view, (c) is the said zeta potential measurement. It is a figure which shows the relationship with the transducer provided in the apparatus. It is a figure for demonstrating the procedure for calculating the zeta potential of the fine particle by the migration rate of the fine particle calculated based on the ultrasonic pulse which was scattered by irradiating the fine particle to which an electric field was applied. (A) and (b) are diagrams showing the relationship between the polarity of the voltage applied by the electric field applyer and the migration direction of the fine particles. (A) and (b) are diagrams showing the relationship between the polarity of the voltage applied by the electric field applyer and the migration direction of the fine particles. It is a figure which shows the measurement method using the sinusoidal alternating current method by the zeta potential measuring apparatus, (a) corresponds to the electric field applied to the fine particle in a liquid by the electric field applyer provided in the zeta potential measuring apparatus. It is a graph which shows the AC voltage, (b) is a graph which shows the migration rate of a fine particle, and (c) is a figure which shows the analysis result which shows the velocity field of the said fine particle analyzed by the phase method. (A) to (f) are graphs showing the dependence of the migration motion of fine particles on the applied voltage by the sinusoidal AC method. (A) to (f) are graphs showing the dependence of the migration motion of fine particles on the electric field period by the sinusoidal AC method. It is a figure which shows the measurement method using the rectangular wave AC method by the zeta potential measuring apparatus, (a) corresponds to the electric field applied to the fine particle in a liquid by the electric field applyer provided in the zeta potential measuring apparatus. It is a graph which shows the rectangular wave voltage, (b) is a graph which shows the migration rate of a fine particle, and (c) is a figure which shows the analysis result which shows the rate of the said fine particle analyzed using FD-DSS. (A) to (f) are graphs showing the dependence of the migration motion of fine particles on the applied voltage by the square wave AC method. (A) to (f) are graphs showing the dependence of the migration motion of fine particles on the electric field period by the square wave AC method. It is a graph which shows the pH dependence of the zeta potential of the said fine particles. It is a graph which shows the particle size dependence of the zeta potential of the said fine particles. It is a graph for demonstrating the sample concentration dependence of the zeta potential of the said fine particles. It is a graph which shows the zeta potential of a mullite particle. It is a graph which shows the surfactant concentration dependence of the zeta potential of the polydivinylbenzene crosslinked body. It is a graph which shows the particle concentration dependence of the zeta potential of the polydivinylbenzene crosslinked body. It is a figure which shows the state of the surface potential of a colloidal particle.

(Overview)
Today, various dispersion systems such as solid fine particle dispersion systems, emulsions, and microbubbles are used regardless of whether they are solids, liquids, or gases. In evaluating the characteristics of such a dispersion system, it is an important issue to develop a technique for evaluating the characteristics of the dispersion system as it is in the solution without diluting or drying the solution (sample) in which the dispersion system is dispersed. ..

In response to such needs, the present inventors have developed a high-frequency dynamic ultrasonic scattering (DSS) method. This DSS method can be said to be an ultrasonic version of the ELS method that analyzes the motion of fine particles suspended in a solution as it is by using light. Compared with the ELS method using light, the DSS method has the advantage that it can be used even when the solution is highly emulsion and does not allow light to pass through because it uses ultrasonic waves. Initially, even when using a high-frequency ultrasonic longitudinal wave transducer of 20 megahertz, the application was limited to relatively large particle analysis of several to several tens of micrometer, but the recently developed frequency domain dynamic super With the advent of the ultrasonic scattering (FD-DSS) method (complex function method), the lower limit of its application has dramatically improved to fine particle analysis of about 30 nanometers.

The present inventors have developed various new technologies using ultrasonic pulses such as the time domain DSS method, the phase-mode DSS method (phase mode method), the FD-DSS method, and the active mode method. It was. For example, by analyzing not only the amplitude of the ultrasonic pulse but also the phase, it is possible to analyze the spatial image even though it is a spectral analysis method. It also realizes position-dependent analysis (imaging) of characteristics.

Unlike the ultrasonic spectroscopy method (absorption method), which also uses ultrasonic pulses, these methods have a major feature in that the motion state of individual fine particles can be individually evaluated in real time. That is, the Brownian motion of nanoparticles suspended in a solution and the motion mode identification and quantification of the sedimentation velocity of the microaggregates can be performed, and the dispersion stability analysis of fine particles has been realized from this.

(Rough configuration of zeta potential measuring device 1)
Against this background, in the embodiment of the present invention, the zeta potential of fine particles dispersed in a solution in an optically highly emulsified state such as a high concentration state can be easily and accurately obtained with a simple configuration. A zeta potential measuring device that is an electrophoretic ultrasound scattering (ESS) method that employs the principle of the dynamic ultrasonic scattering method for the purpose of realizing a zeta potential measuring device that can measure well. To propose. The concept is briefly described as shown in FIG.

FIG. 1 is a schematic view showing a schematic configuration of the zeta potential measuring device 1 according to the embodiment. The running state of the fine particles 8 in the suspension 7 is directly and quantitatively read using an ultrasonic pulse. As a result, the zeta potential can be obtained from the migration speed of the fine particles 8 accompanying the application of an electric field. In FIG. 1, only one fine particle 8 is described for easy explanation of the operating principle, but in reality, a large number of fine particles 8 are dispersed in the suspension 7.

The zeta potential measuring device 1 includes an electrophoresis cell 9 containing a suspension 7 in which a large number of fine particles 8 are dispersed, and a zeta potential measuring device 1 along the Z direction (electric field application direction) for running the fine particles 8 in the suspension 7. It is provided with an electric field applyer 2 that applies an electric field to the fine particles 8. The electric field applyer 2 has a positive electrode 12 and a negative electrode 11.

The zeta potential measuring device 1 is irradiated with ultrasonic pulses along an oblique direction intersecting the Z direction to the fine particles 8 which are migrating by applying an electric field by the electric field applyer 2, and the ultrasonic pulses scattered by the fine particles 8 are applied. A transducer 3 (ultrasonic transmitter / receiver) for receiving is provided. In FIG. 1, the transmission and reception of ultrasonic waves are performed by one transducer 3, but the transmission and reception may be performed by separate transducers (ultrasonic transmitter and ultrasonic receiver).

The zeta potential measuring device 1 includes an analyzer 6. The analyzer 6 has a migration speed calculator 4 and a zeta potential calculator 5. The migration speed calculator 4 calculates the migration speed of the fine particles 8 along the Z direction, which is the electric field application direction, by the dynamic ultrasonic scattering method based on the ultrasonic pulse received by the transducer 3. The zeta potential calculator 5 calculates the zeta potential of the fine particles 8 based on the migration speed of the fine particles 8 calculated by the migration speed calculator 4.

This method uses the frequency domain analysis of ultrasonic pulses (frequency domain dynamic ultrasonic scattering (FD-DSS) method (complex function method)), which has been developed by the present inventors, from nanoparticles. It is possible to obtain information on fine particles in all particle size ranges at the same time with one technique, including microaggregates or nanoparticles.

Here, the frequency domain analysis is not a spectrum analysis of the frequency domain that evaluates the magnitude of the Fourier amplitude, but a method based on a complex time correlation function decomposed into frequency components. We have achieved great results.

In addition, the phase mode DSS method (phase mode method) has been newly developed, and it is possible to analyze the field of fine particle electrophoresis (having spatial information as well as time) due to electric field application in real time.

Further, the fine particles 8 can be analyzed as they are in the suspension 7, and of course, it is not necessary to dilute the sample as long as the ultrasonic waves can propagate regardless of whether it is a cloudy solution or a concentrated solution. .. Since the migration state of the fine particles 8 can be directly probed in real time, it is also effective in a system in which various fine particles 8 are mixed. The principle and practical examples are described below.

2A and 2B show a specific configuration of the zeta potential measuring device 1, FIG. 2A is a front sectional view, FIG. 2B is a plan view, and FIG. 2C is a side view of a main part. 3A and 3B are views for explaining an electrophoresis cell 9 provided in the zeta potential measuring device 1, FIG. 3A is a diagram showing an assembly configuration, FIG. 3B is a plan view, and FIG. 3C is a plan view. It is a figure which shows the relationship with the transducer 3 provided in the zeta potential measuring apparatus 1.

The zeta potential measuring device 1 uses an electrophoresis cell 9, a cell holder 10 for holding the electrophoresis cell 9, and an ultrasonic pulse transducer 3, as shown in FIGS. 2 and 3. These electrophoresis cell 9, cell holder 10, and transducer 3 are liquids that have a small ultrasonic attenuation and play a role of acoustic matching such as in water so that the positions of the transducer 3 and the electrophoresis cell 9 can be freely changed. Placed inside.

There is also a method in which an ultrasonic matching material made of glass or plastic is provided between the transducer 3 and the fine particles (sample) 8 in the electrophoresis cell 9 to bring the transducer 3 into contact with the ultrasonic matching material. However, in this case, a coupling medium for not forming an air layer with respect to the transducer 3 in contact with the ultrasonic matching material is required, which may cause an error depending on the degree of contact. Therefore, the electrophoresis cell 9, the cell holder 10, and the transducer 3 are preferably arranged in a liquid such as water in order to create a situation in which ultrasonic waves propagate stably.

As shown in FIG. 2C, the ultrasonic pulse emitted from the transducer 3 is incident diagonally with respect to the migration direction of the fine particles 8 accompanying the application of the electric field, and is post-based on the obtained oblique migration speed. Calculate the migration direction component with and analyze it.

In the electrophoresis cell 9, a Teflon (registered trademark) tape 15 is wound around the metal cell 13, and a rubber ring 17, a polystyrene film 18, and a platinum material 16 sandwiched between the metal cell 14 and the metal cell 13 are screwed together. It is fixed and assembled by a screw 19 inserted into the hole 20. The platinum material 16 constitutes the positive electrode 12 and the negative electrode 11 of the electric field applyer 2.

(Flow of analysis of migration speed)
An electric field is applied to both ends of the electrophoresis cell 9 containing the suspension 7 in which the fine particles 8 are dispersed by the electric field applyer 2. Then, the migration speed of the fine particles 8 traveling toward the positive electrode 12 or the negative electrode 11 is detected by the dynamic ultrasonic scattering method, depending on the potential of the surface of the fine particles 8. FIG. 4 shows the flow of a series of analyzes for measuring the migration rate of the fine particles 8.

FIG. 4 is a diagram for explaining a procedure for calculating the zeta potential of the fine particles 8 based on the migration speed of the fine particles 8 calculated based on the ultrasonic pulses scattered by irradiating the fine particles 8 to which an electric field is applied. is there.

The migration speed of the fine particles 8 calculated based on the ultrasonic pulse incident obliquely with respect to the electric field application direction is defined as _vDSS . By dividing this migration speed v _DSS by the direction cosine corresponding to the obliquely incident angle θ1, the migration speed calculator 4 converts the migration speed v _{DSS into the migration speed v obs} of the electric field application direction component (X direction). ..

In this method, it is possible to evaluate a plurality of migration velocities having information on the sample depth (Y direction) by one measurement by making the best use of the characteristics of the ultrasonic pulse. Therefore, the migration velocity v _obs per pulse propagation time, the migration speed calculator 4 is converted to the migration speed v _obs is the functional form of the depth Y in the sample. Thus, the analysis to calculate the migration speed v _obs apparent due to the electric field application is completed.

In addition to the components derived from the surface charge of the fine particles 8, the electroosmotic flow component peculiar to the electrophoresis cell 9 is involved in the migration of the fine particles 8. Therefore, an analysis is performed to separate the electroosmotic flow component from the apparent migration rate _volts. Various equations have been proposed for the analysis of electroosmotic flow components, but as a widely accepted theory, Mori and Okamoto's theory (Yuyuki Mori, 1980, microscopic electrophoresis of the flow in a rectangular cell) Analysis, flotation, 27 (4), 171) are known. An example of the formula for _{obtaining the} migration rate vobs based on this theory is shown below.

Here, x represents the cell width direction, y represents the depth direction (z is the direction between the electrodes), and the center of the sample is the origin. The cell width is 2a and the cell depth is 2b.

Also,

Is.

According to the above (Equation 1), the electroosmotic flow component can be analyzed in consideration of the width, depth, and height of the electrophoresis cell 9. The above (Equation 1) is an example, and it is possible to calculate using another equation depending on the situation.

Migration velocity v _p of the particles 8 was obtained by separating from the migration speed v _obs apparent electroosmotic flow components, by normalizing the magnitude of the electric field previously prepared E (V / m) Electrophoretic mobility μ. Generally, the zeta potential ζ can be calculated from the electrophoretic mobility μ, the permittivity ε, and the viscosity η. The formula used differs depending on the particle size of the fine particles 8 and the thickness of the electric double layer. (Henry, DC, 1931, The Cataphoresis of Suspended Particles. Part 1 --The Equation of Cataphoresis, Proc. R. Soc. Lond, A 133). An example of the equation is shown below.

Here, μ is the particle velocity standardized by the applied electric field, f (κa) is the Henry coefficient, ε _r is the relative permittivity of the solvent, ε ₀ is the dielectric constant of the vacuum, η is the viscosity of the solvent, and ζ is the zeta potential to be obtained. Is.

(Equation 2) is used when the electric double layer is much smaller than the particle size. (Equation 3) is used when the electric double layer is much larger than the particle size. (Equation 3) represents the theory connecting the two polar sources.

(Etrophoresis of fine particles 8 by applying an electric field)
5 and 6 show an embodiment in which the migration of the fine particles 8 correctly follows the application of the electric field by the electric field applyer 2, and the fine particles 8 are running toward the appropriate electrodes according to the sign of the surface charge of the fine particles 8. Shown in. 5 (a) and 5 (b) are diagrams showing the relationship between the polarity of the voltage applied by the electric field applyer 2 and the migration direction of the fine particles 8. 6 (a) and 6 (b) are diagrams showing other relationships between the polarity of the voltage applied by the electric field applyer 2 and the migration direction of the fine particles 8.

Here, a sample in which silica particles having a particle diameter of 3 micrometers as fine particles 8 are dispersed in a 1 mM (mol) KCl aqueous solution is used. It is known that these silica particles are positively charged on the acidic side and negatively charged on the basic side with the isoelectric point as a boundary. A measurement example of pH = 9 on the basic side is shown in FIG. 6, and a measurement example of pH = 3 on the acidic side is shown in FIG. At pH = 9, the surface of the fine particles 8 is negatively charged, and it can be confirmed that the particles migrate to the positive electrode 12 side. On the contrary, at pH = 3, it can be confirmed that the positively charged fine particles 8 migrate to the negative electrode 11 side.

(Sine wave AC method)
FIG. 7 is a diagram showing a measurement method using the sinusoidal AC method by the zeta potential measuring device 1, and FIG. 7A shows fine particles in the suspension 7 by the electric field applyer 2 provided in the zeta potential measuring device 1. It is a graph which shows the AC voltage corresponding to the electric field applied to 8, (b) is the graph which shows the migration rate of the fine particle 8, and (c) is the rate of the fine particle 8 analyzed by using the phase mode DSS method. It is a figure which shows the analysis result which shows the field.

The electric field applyer 2 applies a sinusoidal AC voltage to the charged fine particles 8 in the electrophoresis cell 9. In the experiment, the distance between the electrodes is set to 3 cm. Then, the transducer 3 irradiates the migrating fine particles 8 with an AC voltage with an ultrasonic pulse, and receives the ultrasonic pulses scattered by the migrating fine particles 8.

Next, the migration rate calculator 4 is based on the phase mode DSS method (phase mode method), and is scattered by the traveling fine particles 8 and received by the transducer 3 from the ultrasonic pulse, and the velocity field of the moving fine particles 8 ( The spatiotemporal image of the velocity) is analyzed, and the migration velocity of the fine particles 8 is calculated.

The phase mode DSS method is an analysis method that utilizes the phase part rather than the amplitude part of the signal in the setup of the DSS method, and is instantaneous (in the shortest possible time allowed by the pulse repetition time, for example, 0.01 seconds). ) It is a means to analyze the motion velocity of fine particles. Particle motion velocity data holding position information can be obtained hourly in a short time.

Specifically, it is possible to lock in to the main frequency of the broadband ultrasonic pulse (for example, the frequency that gives the peak amplitude) and calculate the fine particle motion velocity data from the phase difference of the signal component (Ayumi Nagao, Mariko Kohyama, Tomohisa Norisuye, and Qui Tran-Cong-Miyata, Journal Of Applied Physics 105, 023526, 2009).

On the other hand, in the conventional correlation function method, a stable amplitude for a certain period of time (for example, about 10 minutes) is recorded, and a highly accurate motion velocity evaluation is performed by constructing the correlation function. However, when the state changes from moment to moment, such as the sedimentation of fine particles, the state changes during the integration, so the conventional correlation function method is not suitable. The phase mode DSS method makes it possible to obtain the instantaneous particle velocity in real time. That is, when a sinusoidal AC electric field is applied, it is extremely effective to use the phase mode DSS method.

After that, the zeta potential calculator 5 calculates the zeta potential of the fine particles 8 based on _{the migration speed vobs of the fine particles 8 calculated by the migration speed calculator 4.} Specifically, the zeta potential calculator 5, as described above with reference to FIG. 4, to calculate the migration speed v _p of the particles 8 by separating the electro-osmotic flow component from the migration speed v _obs. Then, the zeta potential calculator 5 calculates the electrophoretic mobility μ by normalizing the migration velocity v _p in the electric field of magnitude E (V / m). Next, the zeta potential calculator 5 calculates the zeta potential ζ based on the electrophoresis mobility μ, the dielectric constant ε, and the viscosity η.

8 (a) to 8 (f) are graphs showing the dependence of the migration motion of the fine particles 8 corresponding to the applied electric field by the sinusoidal AC method.

FIG. 8A shows an example in which the electric field strength Epp (pp represents peak to peak) applied to the fine particles 8 is 3.3 (V / cm (volts / centimeters)). d) indicates the migration speed of the fine particles 8 measured at an electric field strength Epp of 3.3 (V / cm). FIG. 8 (b) shows an example in which the electric field strength Epp is 16.7 (V / cm), and FIG. 8 (e) shows the migration of the fine particles 8 measured at the electric field strength Epp of 16.7 (V / cm). Indicates speed. FIG. 8 (c) shows an example in which the electric field strength Epp is 33.4 (V / cm), and FIG. 8 (f) shows the migration of the fine particles 8 measured at the electric field strength Epp of 33.4 (V / cm). Indicates speed.

As can be seen from FIG. 8D, when the electric field strength Epp is 3.3 (V / cm), the contribution of fluctuation to the migration rate is larger than that of the average migration component. When the electric field strength Epp applied to the fine particles 8 is less than 2.0 (V / cm), the migration speed of the fine particles 8 is further reduced, and the migration of the fine particles 8 becomes difficult to observe. That is, when the electric field strength Epp is less than 2.0 (V / cm), the contribution of fluctuation to the migration rate becomes larger than that of the average migration component. The electric field strength Epp applied to the fine particles 8 varies depending on the viscosity of the solution and the distance between the electrodes, but in the case of a general solution, the electric field strength Epp applied to the fine particles 8 is 2.0 (V / cm). The above is preferable, and more preferably 3.0 (V / cm) or more because accurate measurement can be performed.

Considering the influence of the electric field strength on the sample, it is preferable to shorten the application time when the electric field strength is large. Measured for 3 minutes under the conditions of electric field strength Epp = 3.3 (V / cm) for 30 seconds, Epp = 16.7 (V / cm) for 10 seconds, and Epp = 33.4 (V / cm) for 10 seconds. However, there were no problems such as damage to the fine particles 8 (sample). Further, even if the electric field was continuously applied for 3 hours at Epp = 6.7 (V / cm), there was no problem such as damage to the sample.

9 (a) to 9 (f) are graphs showing the dependence of the migration motion of the fine particles 8 on the electric field period by the sinusoidal AC method.

FIG. 9A shows an example in which the period T of the electric field applied to the fine particles 8 is 1 second, and FIG. 9D shows the migration speed of the fine particles 8 measured in the period T of the electric field in 1 second. FIG. 9B shows an example in which the electric field period T is 2 seconds, and FIG. 9E shows the migration speed of the fine particles 8 measured in the electric field period T of 2 seconds. FIG. 9 (c) shows an example in which the electric field cycle T is 5 seconds, and FIG. 9 (f) shows the migration speed of the fine particles 8 measured in the electric field cycle T of 5 seconds.

If the period T of the electric field applied to the fine particles 8 exceeds 30 seconds, the fine particles 8 either settle completely or the measurement takes too long, which is not preferable. Further, when the period T of the electric field is slow enough to exceed 30 seconds while applying a high voltage of 100 V or more to the fine particles 8, the fine particles 8 are affected by the turbulent flow generated in the suspension 7 in the electrophoresis cell 9. It is not preferable because the migration rate profile may not be measured correctly.

In order to accurately determine the migration speed of the fine particles 8 in the period T of the applied electric field, a plurality of measurement pulses (for example, 1000 pulses or more) are required, and the shorter the period T of the electric field, the shorter the pulse repetition time (PRT). Become. Experimentally, when the period T of the applied electric field is smaller than 1 second, the pulse repetition time (PRT) needs to be 1 ms or less, which is not preferable in terms of processing time and ultrasonic reverberation. That is, the period T of the applied electric field is preferably set to 1 to 30 seconds.

(Square wave AC method)
FIG. 10 is a diagram showing a measurement method using the rectangular wave AC method by the zeta potential measuring device 1, and FIG. 10A shows the fine particles 8 in the suspension 7 by the electric field applyer 2 provided in the zeta potential measuring device 1. It is a graph which shows the rectangular wave voltage corresponding to the electric field applied to, (b) is a graph which shows the migration rate of the fine particle 8, and (c) is the rate of the fine particle 8 analyzed by using the FD-DSS method. It is a figure which shows the analysis result which shows the field.

In the above-mentioned example of the sinusoidal AC method, a sinusoidal AC electric field is applied and the migration state of the fine particles 8 accompanying the sinusoidal AC electric field is observed. However, the present invention is not limited to this. In some cases, application of a square wave AC electric field based on a square wave that switches the positive and negative properties at regular intervals (square wave AC method) is effective.

It is possible to effectively use the sine wave AC method and the square wave AC method depending on the measurement situation, such as in the case of large microparticles (or aggregates) or in the case of fine particles that easily aggregate with time when an electric field is applied. is there. For example, microparticles having a relatively large particle size settle quickly and their states change from moment to moment, so a phase mode dynamic ultrasonic scattering method that can acquire motion information in real time is effective. On the other hand, in the case of nanoparticles, a stable signal can be recorded over a long period of time, so if you want to measure information on small particles with sufficient statistical accuracy, you can build a complex correlation function of a stable time signal. The present inventors have found that FD-DSS is preferable.

The present inventors have found that the phase-mode DSS method, which enables observation of the velocity field in real time, is particularly effective for observing changes in the state of particle motion due to the application of a sinusoidal AC electric field. This is based on the analysis principle that the phase mode DSS method can acquire information by following the state change of the sample at a sufficiently high speed as described above.

On the contrary, in the case of the square wave AC method in which a constant electric field is applied by a square wave for a certain period of time, the complex correlation function method (frequency domain dynamic ultrasonic scattering (FD-DSS) method) is effective. They found. This is because the FD-DSS method is suitable for analyzing a signal that is relatively stable with respect to time, and is suitable for detecting small fluctuations in the signal. Since the stationary part of the rectangular signal is kept stationary, it is possible to analyze the information of fine particles with sufficient statistical accuracy by constructing a correlation function in that region.

The electric field applyer 2 applies a square wave voltage (square wave AC electric field) to the charged fine particles 8 in the electrophoresis cell 9. Then, the transducer 3 irradiates the moving fine particles 8 with an ultrasonic pulse by applying a rectangular wave voltage, and receives the ultrasonic pulses scattered by the running fine particles 8.

Then, the first scattering amplitude Ψ (t, T) is generated based on the propagation time t of the ultrasonic pulse and the observation time T for the migration of the fine particles 8.

Next, the migration speed calculator 4 Fourier-transforms the first scattering amplitude Ψ (t, T) in the direction of the propagation time t, and the second scattering amplitude Ψ (f, T) is a function of the frequency f and the observation time T. To generate. Then, the migration speed calculator 4 calculates the amplitude r (f, T) and the phase θ (f, T) based on the real part and the imaginary part of the second scattering amplitude Ψ (f, T), respectively. Next, the migration speed calculator 4 obtains a complex correlation function based on the amplitude r (f, T) and the phase θ (f, T). After that, the migration rate calculator 4 calculates the migration rate of the fine particles 8 based on this complex correlation function.

As described above, the migration speed calculator 4 is based on the complex correlation function method, and the velocity field (time and space of velocity) of the moving fine particles 8 is obtained from the ultrasonic pulse scattered by the moving fine particles 8 and received by the transducer 3. Image) is analyzed, and the migration speed of the fine particles 8 is calculated.

After that, the zeta potential calculator 5 calculates the zeta potential of the fine particles 8 based on _{the migration speed vobs of the fine particles 8 calculated by the migration speed calculator 4.} Specifically, the zeta potential calculator 5, as described above with reference to FIG. 4, to calculate the migration speed v _p of the particles 8 by separating the electro-osmotic flow component from the migration speed v _obs. Then, the zeta potential calculator 5 calculates the electrophoretic mobility μ by normalizing the migration velocity v _p in the electric field of magnitude E (V / m). Next, the zeta potential calculator 5 calculates the zeta potential ζ based on the electrophoresis mobility μ, the dielectric constant ε, and the viscosity η.

11 (a) to 11 (f) are graphs showing the dependence of the migration motion of fine particles on the applied voltage by the square wave AC method. Here, the distance between the electrodes is set to 3 cm.

FIG. 11 (a) shows an example in which the electric field strength Epp applied to the fine particles 8 is 2.6 (V / cm), and FIG. 11 (d) is measured at an electric field strength Epp of 2.6 (V / cm). The migration speed of the fine particles 8 is shown. FIG. 11B shows an example in which the electric field strength Epp is 4 (V / cm), and FIG. 11 (e) shows the migration speed of the fine particles 8 measured at the electric field strength Epp of 4 (V / cm). FIG. 11 (c) shows an example in which the electric field strength Epp is 5.4 (V / cm), and FIG. 11 (f) shows the migration of the fine particles 8 measured at the electric field strength Epp of 5.4 (V / cm). Indicates speed.

When the complex correlation function method is applied in a region where the electric field strength Epp applied to the fine particles 8 is less than 1 (V / cm), the migration speed of the fine particles 8 is slow, so that the vibration of the complex correlation function due to the migration of the fine particles 8 The vibration point shifts to the long-time side. Therefore, it is difficult to actually measure the migration rate depending on the relaxation time of the fine particles 8, which is not preferable. The time delay is about 3 seconds in relaxation time.

If the electric field strength Epp exceeds 10 (V / cm), the fine particles 8 gathered in the vicinity of the positive electrode 12 or the negative electrode 11 of the electric field applyer 2 are aggregated, which is not preferable. The electric field strength Epp applied to the fine particles 8 varies depending on the viscosity of the solution and the distance between the electrodes, but in the case of a general solution, the electric field strength Epp applied to the fine particles 8 is 1 (V / cm) -10. (V / cm) is preferable.

In general, it is preferable to determine the applied voltage (electric field strength Epp) so that an appropriate correlation time is secured.

12 (a) to 12 (f) are graphs showing the dependence of the migration motion of the fine particles 8 on the electric field period by the square wave AC method.

FIG. 12A shows an example in which the period T of the electric field applied to the fine particles 8 is 10 seconds, and FIG. 12D shows the migration speed of the fine particles 8 measured when the period T of the electric field is 10 seconds. FIG. 12B shows an example in which the electric field period T is 20 seconds, and FIG. 12E shows the migration speed of the fine particles 8 measured in the electric field period T of 20 seconds. FIG. 12 (c) shows an example in which the electric field cycle T is 30 seconds, and FIG. 12 (f) shows the migration speed of the fine particles 8 measured in the electric field cycle T of 30 seconds.

When the period T of the electric field applied to the fine particles 8 exceeds 30 seconds, the movement of the fine particles 8 becomes one-way, and the fine particles 8 are accumulated in the positive electrode 12 or the negative electrode 11 of the electric field applyer 2, and as a result, the fine particles 8 are aggregated. It is not preferable because it easily occurs.

If the period T of the electric field is less than 1 second, a complex correlation function cannot be constructed, which is not preferable. That is, the period T of the applied electric field is preferably 1 to 30 seconds.

In general, it is preferable to apply a rectangular wave voltage to the fine particles 8 with a short period T while ensuring a sufficient time for the correlation time determined by the applied voltage.

(Measurement result)
FIG. 13 is a graph showing the pH dependence of the zeta potential of the fine particles 8. When the fine particles 8 are silica particles, the zeta potential becomes positive on the low pH side, and the zeta potential approaches zero as the pH increases. Then, when the isoelectric point exceeds pH 3 to around pH 4, the zeta potential becomes negative. In the basic region where the pH is higher, the zeta potential has a larger negative absolute value. When salt is added to this system, the electric double layer of the fine particles 8 is shielded and thinned, so that the negative absolute value of the zeta potential becomes small as shown in FIG. 13, and the graph becomes flat as a whole approaches zero. Become.

Although it is more common to use the Henry formula for the calculation of the electrophoretic mobility, there is no big difference even if the Smoluchowski formula is used in this basic region. From the above, it was shown that the zeta potential can be correctly measured as a function of pH and a function of concentration.

FIG. 14 is a graph showing the particle size dependence of the zeta potential of the fine particles 8. An example of measuring the zeta potential when the fine particles 8 are silica particles having diameters of 30 nanometers, 600 nanometers, and 3 micrometers (3000 nanometers) is shown in FIG. In this way, we have succeeded in obtaining the zeta potential by independently measuring the migration of individual fine particles 8 with respect to fine particles 8 having various sizes such as microparticles, submicron particles, and nanoparticles. In addition, the agreement between the measured value of the zeta potential and the value of the zeta potential described in the literature was also good, demonstrating the effectiveness of the measurement method according to the present embodiment.

FIG. 15 is a graph for explaining the sample concentration dependence of the zeta potential of the fine particles 8. Since the measuring method of the present embodiment does not have a problem of emulsion turbidity of the sample, it is possible to measure a sample having a considerably high concentration as compared with the measuring method using light. The volume fraction dependence of the zeta potential at pH 7 of silica particles having a particle size of 3 micrometers is shown in FIG. Unlike nanoparticles, particles with a diameter of about several micrometers have significant light scattering and are difficult to measure even under dilute conditions of 1% or less. However, it was found that the measurement method according to the present embodiment can measure the electrophoretic mobility and analyze the zeta potential even at a sample concentration of several tens of percent.

FIG. 16 is a graph showing the zeta potential of mullite particles. The pH dependence of the zeta potential of mullite particles is shown in contrast to that of silica particles.

FIG. 17 is a graph showing the dependence of the zeta potential of the crosslinked polydivinylbenzene on the surfactant concentration. FIG. 18 is a graph showing the particle concentration dependence of the zeta potential of the crosslinked polydivinylbenzene.

In addition to the silica particles, the zeta potential of the suspension of mullite particles and polystyrene-based particles dispersed with a surfactant could be measured.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

1 Zeta potential measuring device 2 Electric field applyer 3 Transducer (ultrasonic receiver)
4 Migration rate calculator 5 Zeta potential calculator 6 Analyzer 7 Suspension (liquid)
8 Fine particles 9 Electrophoresis cell 10 Cell holder 11 Negative electrode 12 Positive electrode

Claims (6)

An electric field applyer that applies an electric field to the charged fine particles along the electric field application direction in order to run the charged fine particles in the emulsion.
An ultrasonic receiver that receives ultrasonic pulses scattered by irradiating fine particles in an emulsion to which an electric field is applied, and
Based on the ultrasonic pulse received by the ultrasonic receiver, the migration speed calculator that calculates the migration speed of the fine particles in the emulsion along the electric field application direction by the dynamic ultrasonic scattering method, and
A zeta potential calculator is provided, which calculates the zeta potential of the fine particles in the emulsion based on the migration rate of the fine particles in the emulsion calculated by the migration rate calculator. measuring device. The zeta potential measuring device according to claim 1 , wherein the ultrasonic pulse is applied to the fine particles in the emulsion along a direction intersecting the electric field application direction. The electric field applyer applies a sinusoidal AC electric field to the fine particles in the emulsion,
The zeta potential measuring apparatus according to claim 1, wherein the dynamic ultrasonic scattering method includes a phase mode method. The electric field strength of the sinusoidal AC electric field is 2.0 (V / cm (volt / centimeter)) or more.
The zeta potential measuring device according to claim 3, wherein the period of the sinusoidal signal corresponding to the sinusoidal AC electric field is 1 second or more and 30 seconds or less. The electric field applyer applies a square wave AC electric field to the fine particles in the emulsion,
The zeta potential measuring apparatus according to claim 1, wherein the dynamic ultrasonic scattering method includes a complex correlation function method. The electric field strength of the square wave AC electric field is 1 (V / cm) or more and 10 (V / cm) or less.
The zeta potential measuring device according to claim 5, wherein the period of the square wave signal corresponding to the square wave AC electric field is 1 second or more and 30 seconds or less.

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