JPH0743334A - Interface potential-measuring device - Google Patents

Abstract

PURPOSE:To measure the interface potential of a sample in a suspension state under simple setting with good reproducibility and high accuracy as compared with a conventional ultrasonic vibration potential measuring method. CONSTITUTION:Frequency variable vibration generating means 2, 11 for forming standing waves due to pressure waves are provided to a container 1 storing a suspension S and a pair of electrodes 3a, 3b are provided in the container 1. The electrodes 3a, 3b are arranged at the nodal positions of the standing waves due to the vibration generating means so as to be mutually separated by the odd number of nodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interfacial potential measuring device for measuring electrical information of a solid-liquid interface formed between a surface of a solid sample in a liquid and the liquid.

[0002]

2. Description of the Related Art Conventional methods for measuring the potential of a solid-liquid interface are as follows.
The electrophoretic method and the streaming potential method are known as typical ones.

The electrophoretic method is a method suitable for measuring the electric potential at the solid-liquid interface of a sample in which solid particles and the like are dispersed in a liquid to form a suspension, and the suspension to be measured is predetermined. In the state of being housed in the container, electric energy is applied through the electrodes arranged in the container, and the potential is obtained from the moving speed of particles.

On the other hand, the streaming potential method applies mechanical energy to a solid sample and a liquid filled in a container so as to cause a relative motion between a solid to be measured and a liquid, and thereby to generate a solid. It is a method for measuring the electrical output generated due to the flow motion of a liquid, and is used for measuring a sample that is unlikely to be in a suspension state due to sedimentation or the like.

As a method for measuring the potential at the solid-liquid interface in a suspension, in addition to the electrophoresis method, conventionally, a sample suspension contained in a container is irradiated with ultrasonic waves of a constant frequency to solidify. A method is also known in which relative motion is applied to the liquid interface to generate an ultrasonic vibration potential, and an electrode is arranged at an odd multiple of its half wavelength to measure the potential.

[0006]

Among the conventional methods for measuring the interfacial potential, the electrophoretic method suitable for the measurement in the suspension state uses the electroosmotic flow in the sample, the generation of Joule heat, or the electrode decomposition reaction. Since there are many interfering factors such as the above, the measurement becomes complicated, and the conventional ultrasonic vibration potential measurement has the following drawbacks.

That is, since the electrode is arranged at a position related to the wavelength of the ultrasonic wave by utilizing the ultrasonic vibration of a constant frequency, the potential is required unless the temperature of the liquid is fixed to a certain temperature and the wavelength is controlled. Not only can't be taken out correctly, but also various measures must be taken with hardware and software to remove the influence of the reflected wave from the wall surface of the container. There is a drawback in that processing also requires a complicated device.

On the other hand, the streaming potential method suitable for measuring a sample which is unlikely to be a suspension has a drawback that the measurement result greatly depends on the shape of the sample and the filling state in the container. That is, it is easy to cause a difference in the flow state depending on the magnitude of the pressure loss, so that the measurement results are likely to vary, and the difference in the pressure term is difficult to occur depending on the sample,
There is also a problem that the measurement accuracy deteriorates.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to enable a wide range of samples to be measured without being limited to the type of a sample in a suspension state. To provide an interfacial potential measuring device capable of easily measuring a solid-liquid interface without requiring complicated condition setting and signal processing at the time of measurement, as compared with the conventional ultrasonic vibration potential measuring method. is there.

A second object of the present invention is to provide an interfacial potential measuring device which can always obtain stable measurement data for a sample which is unlikely to be in a suspension state, regardless of the shape of the sample or the filling state. Especially.

[0011]

A structure for achieving the above-mentioned first object will be described with reference to FIG. 1 which is an embodiment drawing, and a first invention contains a sample suspension. And a vibration generating means (for example, piezoelectric element 2 and its drive circuit 11) with variable frequency for generating a standing wave by pressure wave in the liquid in the container 1, and a pair arranged in the container 1. Electrodes 3a, 3b of the respective electrodes 3a, 3b
Are characterized by being arranged at the positions of the nodes of the standing wave formed in the container by the vibration generating means 2 and 11, respectively, and at the positions separated by an odd number of nodes from each other.

The structure for achieving the above-mentioned second object will be described with reference to FIG. 4 which is an embodiment drawing. In the second invention, a container 101 for containing a liquid and the container 101 are provided. Sample holding means 120 for filling and holding the solid sample to be measured in the liquid inside, pressure wave applying means for applying a pressure wave to the liquid inside the container 101 (for example, piezoelectric element 102 and oscillator 111 for driving it), and its pressure Wave imparting means 102, 11
It is characterized by including a pair of electrodes 103a and 103b that are arranged opposite to each other with the solid sample to be measured sandwiched therebetween in the traveling direction of the pressure wave by 1.

[0013]

The first aspect of the present invention is to solve all the problems in the conventional method of measuring the ultrasonic vibration potential by adding a standing wave to the suspension in the container 1.

That is, by changing the frequency of the vibration generating means, no matter what the temperature of the suspension in the container 1 or other vibration conditions may be, the standing wave is generated in the suspension in the container 1. Can be generated. The wavelength of the standing wave can be determined by the distance between the vibrating surface and the reflecting surface within the container 1, and the positions of the electrodes 3a and 3b can be defined according to this wavelength. The standing wave is not affected by the reflected wave, does not require data processing due to the progress of the wave, and can respond to changes in the sample temperature by changing the frequency, thus achieving the intended purpose.

On the other hand, the second aspect of the present invention is intended to eliminate the drawbacks of the prior art by causing the relative motion of the solid-liquid interface by a pressure wave instead of the conventional flow of the liquid. .

That is, by applying a pressure wave in a state where the solid sample held by the sample holding means is immersed in the liquid, a stable solid-liquid state is obtained irrespective of the shape of the solid sample or the holding or filling state. Relative motion at the interface can be obtained, and by arranging the electrodes 103a and 103b orthogonally to the traveling direction of this pressure wave, highly accurate and stable data can be obtained.

[0017]

1 is a block diagram of an embodiment of the first invention.
The suspension S to be measured is contained in the container 1. In container 1,
A piezoelectric element 2 is mounted on one side surface thereof, and the piezoelectric element 2 is connected to a drive circuit 11 having a variable oscillation frequency so that it can vibrate at a variable frequency. Then, due to the vibration of the piezoelectric element 2, a stationary ultrasonic wave is generated in the suspension S in the container 1 as described later.

In the container 1, a pair of electrodes 3a and 3b are arranged at positions where nodes of the standing wave by the piezoelectric element 2 are formed, and at positions where an odd number of nodes of the standing wave are opened. A potential difference associated with the electrokinetic phenomenon is detected by the electrodes 3a and 3b, and the detection result is taken into the computer 12 via an appropriate measuring circuit and an AD converter (neither is shown).

Another piezoelectric element 4 is mounted on the side surface of the container 1 facing the piezoelectric element 2. The piezoelectric element 4 causes the sound pressure of a standing wave in the suspension S generated by the vibration of the piezoelectric element 2. At the same time as is measured, the standing wave is monitored, and the result is taken into the computer 12.

The container 1 includes a thermometer 5, a conductivity meter 6, and a PH.
A total of 7 and a viscometer 8 are attached, and the measurement result by each of these measuring devices is incorporated in the computer 12. Further, a buret 9 and a temperature controller 10 are attached to the container 1, and the buret 9 and the temperature controller 1 are attached.
0 operates by the control signal from the computer 12,
The state and temperature of the suspension S in the container 1 such as pH and viscosity can be controlled.

That is, the computer 12 takes in the outputs of the piezoelectric element 4, the thermometer 5, the conductivity meter 6, the PH meter 7 and the viscometer 8, and suspends the suspension in the container 1 by the vibration of the piezoelectric element 2. A control signal is issued to the drive circuit 11 to appropriately adjust the frequency of the piezoelectric element 2 so that a standing wave is formed in the liquid S,
In addition, in addition, a control signal is issued to the buret 9 and the temperature controller 10 to adjust the measurement environment of the suspension S.

Here, the wavelength of the standing wave formed by the vibration of the piezoelectric element 2 can be determined from the distance between the vibrating surface of the piezoelectric element 2 of the container 1 and the reflecting surface facing the vibrating surface. Then, from the monitoring result of the ultrasonic wave by the piezoelectric element 4, the ultrasonic wave of this wavelength is generated in the suspension S to form a standing wave, and the piezoelectric element is tracked according to the change of the parameter including the suspension temperature. The frequency of 2 is adjusted.
As a result, a standing wave is always formed in the suspension S in the container 1. The electrodes 3a and 3b are arranged at the positions of the nodes of the standing wave determined in this way, and are spaced from each other by an odd number of the nodes.

In the computer 12, the electrodes 3a,
From the detection result of the potential difference due to the electrokinetic phenomenon from 3b,
The zeta potential is calculated by the method described later, and the calculation result is displayed on the display 13 or printed on the printer 14.

Next, the principle of measuring the zeta potential according to the above embodiment will be described. First, the oscillating potential will be described. When periodic vibration is applied to a system in which particles are dispersed in an electric field solution, the movement of the particles and the ionic atmosphere surrounding the particles is deviated due to the electrophoretic delay effect. Since the relaxation time until the ion atmosphere returns to its original state is finite, polarization occurs due to the asymmetric effect, and the particles and the ion atmosphere form an electric dipole. At this time, if the cycle of vibration is much longer than the relaxation time, periodic polarization that vibrates with the cycle of vibration occurs. Therefore, if a pair of electrodes is installed at a distance of an odd multiple of a half wavelength in the traveling direction of the pressure wave, an AC potential having the same frequency as the pressure wave can be measured. This is called an oscillating potential. Figure 2 shows how particles are polarized in a sound field.

The theoretical treatment of such an oscillation potential is Smol
It is shown by the following equation (1) by chowski.

[0026]

[Equation 1]

This equation is basically the same as the equation for the sedimentation potential, and the gravitational acceleration at the sedimentation potential is simply replaced by the acceleration due to the pressure wave. Where E is an oscillating potential, P is pressure, φ is particle volume fraction, ρ ₂ and ρ ₁ are solute and solvent densities, ε ₀ and ε are vacuum permittivity and solvent permittivity, respectively. λ ₀ is the conductivity of the solvent,
ζ is the zeta potential, and η is the viscosity of the solvent.

Smolchowski considers a single particle, and in the case of a dilute solution, the interaction between particles is negligible, and the movement of particles follows Stokes' law, and the velocity of the liquid moved by the pressure wave is u, If the relative velocity of particles is v, the particle radius is a, and the time axis is t,

[0029]

[Equation 2]

It becomes When the distance x is taken in the traveling direction of the pressure wave, the velocity u of the liquid is U, the velocity amplitude is U, the frequency of the pressure wave is f,
The wavelength is λ _f

[0031]

[Equation 3]

It is expressed as follows. From equations (2) and (3),

[0033]

[Equation 4]

It becomes Considering that the dispersed system behaves as a group of electric dipoles as a whole, the total potential Φ is

[0035]

[Equation 5]

It becomes Here, N is the number of dipoles per unit volume, and m is the dipole moment. Also,

[0037]

[Equation 6]

And m is

[0039]

[Equation 7]

It is represented by Where f (χα) is Henry
Is called a correction function of, and f when χα → 0
When (χα) → 2/3, χα → ∞, f (χα) → 1. Also, χ is the reciprocal of the Debye length (electric double layer thickness δ). When δ << a is acceptable, χα >> 1, that is, f (χα) ≈1. Therefore, with x = λ / 2, from (4) to (8)

[0041]

[Equation 8]

Is obtained. Φ _E represents the maximum value of the amplitude of the potential appearing between a pair of electrodes separated by a half wavelength.
Equation (1) is obtained with E = Φ _E. (1) was solved for a dilute solution and cannot be applied to a concentrated system because the interaction between particles is ignored. Therefore, the cell model theory of Livine et al. Is applied to the concentrated system, and the term of interparticle interaction is added to the equation (1), and the equation is modified as the equation (12).

[0043]

[Equation 9]

Γ (χα, φ) is a term of electrical interaction between particles, and Ω (φ) is a term of hydrodynamic interaction. Equation (12) is expressed under the condition of χα >> 1.

[0045]

[Equation 10]

Can be approximated by When measuring the oscillating potential, it is desired that the relative motion in the liquid has an ideal shape due to the pressure wave. One possible method is to create a force field by standing waves.

The standing wave is generated when one traveling wave and the reflected wave from the plane wall overlap each other, but vibrations having the same phase appear at all places, and at a position of an odd multiple of a half wavelength from its end. The amplitude is 0, which is the maximum at even-numbered positions. These points are called the standing wave node and the antinode, respectively.

The condition for forming a standing wave is complicated by a plurality of factors such as the type and temperature of the medium through which the pressure wave propagates, the frequency of the pressure wave, and the distance between the vibrating surface and the reflecting surface. However, since a standing wave can be created as long as the traveling wave and the reflected wave overlap, other factors can be solved collectively by making the frequency variable. That is, a standing wave is established by setting the frequency so that the distance between the vibrating surface and the reflecting surface is an odd multiple of ¼ wavelength.

Even in the standing wave, the particles and the ionic atmosphere surrounding the particles still form electric dipoles due to the electrophoretic delay effect. Therefore, if a pair of electrodes is installed between nodes having an odd number of amplitudes apart, the oscillating potential can be measured. However, it should be noted that in this case 2P of pressure is applied. FIG. 3 shows how particles are polarized in a standing wave.

In the first embodiment described above, the point to be particularly noted is that the container 1 is formed by the piezoelectric element 2 whose vibration frequency appropriately changes based on the drive signal from the drive circuit 11 according to the control signal from the computer 12. The ultrasonic oscillating potential UVP is measured in the state where a standing wave is always formed in the suspension S in the suspension S, so that the temperature of the suspension S can be changed as in the conventional ultrasonic potential measurement method. Highly accurate UVP measurement can be performed without strictly controlling the ultrasonic wave propagation conditions and without considering the influence of reflected waves.

Next, an embodiment of the second invention will be described with reference to FIG. In the embodiment of the second aspect of the invention, the solid sample B which is difficult or unsuspendable in the liquid is placed in the liquid L filled in the container 101 while being held by the sample holder 120. Get burned.

The piezoelectric element 10 is provided on one side of the container 101.
2 is attached, coaxial with this, and
The piezoelectric element 104 is also mounted on the opposite side surfaces of the container 101. Further, these central axes coincide with the central axis of the sample holder 120 described above.

One of the piezoelectric elements 102 irradiates the liquid L in the container 101 with a pressure wave of ultrasonic waves in response to a signal supplied from the oscillator 111. In addition, the other piezoelectric element 104
Receives this pressure wave and outputs an electric signal corresponding to the pressure. This output is imported into the computer 112.

Inside the container 101, there are a pair of electrodes facing each other in a posture perpendicular to the direction of travel of the pressure wave and at a predetermined distance in the direction of travel of the pressure wave so as to sandwich the sample holder 120 therebetween. 103a and 103b are provided to detect the potential difference due to the electrokinetic phenomenon due to the pressure wave from the piezoelectric element 102. This detection result is also incorporated in the computer 112.

The container 101 has a thermometer 105 and a conductivity meter 1
06, a PH meter 107, and a viscometer 108 are attached, the state of the liquid L in the container 101 is measured by these, and the measurement result is also taken into the computer 112.

A buret 109 and a temperature controller 110 are also attached to the container 101, and these are configured to operate based on a control signal from a computer 112.

In the computer 112, the electrodes 103a and 103b attached to the container 101 and the piezoelectric element 1 are attached.
The signal from 04 and the signals from other measuring devices are input to calculate the zeta potential based on the theory described later, and the parameters such as the temperature and the pH in the container 101 are set within an appropriate range. To control. Information such as the zeta potential obtained by the computer 112 is displayed on the display 113 or printed on the printer 114.

To give a concrete example of the structure of the sample holder 120, an example suitable for the case where the solid sample T is a tube, fiber, plate, pellet, marble or the like is shown in FIG.

In this example, the sample holder 120 has a cylindrical shape, and the solid sample T is filled and held therein. Then, mesh-shaped electrodes 103a and 103b are attached to both ends thereof, and these also serve as a lid. Here, the mesh-shaped electrodes 103a and 103b need to be finely opened so that the sample T does not spill, and at the same time, it is necessary to consider so that the mesh does not interfere with the transmission of pressure waves. For example, when a pressure wave of ultrasonic waves having a frequency of 200 KHz is generated by the piezoelectric element 102, its wavelength is about 7.5 mm, and in this case, the wire diameter is 0.5 m.
In a mesh using lines of about m, if the opening is about the same as the diameter of the line, the waves will wrap around due to the diffraction phenomenon, so that there is almost no obstacle due to the presence of the mesh. Therefore, by appropriately selecting the wavelength of the pressure wave and the mesh according to the size of the sample T, the measurement can be sufficiently performed.

The point to be noted in the above-described second embodiment of the present invention is that the pressure wave is formed by the ultrasonic wave by the piezoelectric element 102, whereby an effective pressure wave can be obtained with a small amount of electric power. be able to.

Now, the measurement principle of the second embodiment of the present invention will be described below, and it will be clarified that the potential difference between the electrodes 103a and 103b can be converted into the zeta potential of the sample.

The potential ψ of the diffusion double layer can be expressed by the Summation type of the ion species contained in the system, assuming that the free ions having point charges follow the Poisson-Boltzman distribution. That is,

[0063]

[Equation 11]

It can be expressed as ε _i is the permittivity in the diffusion double layer,
z _i is the ionic valency, e is the elementary charge, n _i is the ion density, k
Is the Boltzmann constant, T is the temperature, and the symmetric electrolyte (z
_i = -z _i = z, in the case of n _i = -n _i = n) can be written as the following equation.

[0065]

[Equation 12]

When the thickness of the electric double layer is sufficiently thin, the interface can be regarded as a flat plate, and the Laplacian ∇ ² ψ is set as d ² ψ / dx ² with the distance from the solid surface as x, and integration is performed. Is obtained.

[0067]

[Equation 13]

However,

[0069]

[Equation 14]

Where ψ ₀ is the Stern potential. Debye-
When the Huckel approximation (zeψ ₀ << kT) holds,

[0071]

[Equation 15]

Therefore, ψ is simplified as follows.

[0073]

[Equation 16]

The surface charge density σ is expressed by the following equation from the theorem of electrostatics.

[0075]

[Equation 17]

Solve this

[0077]

[Equation 18]

It is The zeta potential ζ obtained by the electrokinetic phenomenon is not the potential on the Stern surface but the potential on the sliding surface, but in many cases it is handled as ψ ₀ = ζ due to the complexity of the electric double layer. .

Ueda et al. Succeeded in extracting a streaming potential having the same characteristics as a sound wave or an ultrasonic wave by using a pressure that periodically changes by the sound wave or the ultrasonic wave using a glass capillary tube and a dilute solution. The phenomenon was named U-effect I.

The electrokinetic phenomenological theoretical consideration of this phenomenon is as follows. In the solid-liquid layer, it is assumed that the liquid existing between solids can be regarded as the liquid existing in the capillaries, and the solid-liquid layer is regarded as an assembly of capillaries.

Now, consider a single capillary as shown in FIG. 6 and assume that its radius is r and its length is l. If the surface charge of the capillary wall is neutralized by an electric double layer of thickness δ,
According to Hel-mholtz's theory of molecular capacity, the charge quantity q is

[0082]

[Formula 19]

It becomes ε ₀ is the permittivity of vacuum, ε _r is the permittivity of liquid, and ζ is the zeta potential. When pressure wave vibration is applied in the direction of the arrow in FIG. 5 to cause relative motion at the solid-liquid interface, the pressure of the pressure wave is ω, the angular velocity of vibration, and t
Can be expressed as P ₀ sin ωt. If the wave displacement is x,

[0084]

[Equation 20]

Where ρ is the density of the liquid and c is the velocity of the pressure wave. On the other hand, the charge transfer amount I due to vibration is

[0086]

[Equation 21]

It is Assuming that the potential difference generated during the distance 1 is E and the specific conductivity of the liquid is λ, according to the law of 0hm,

[0088]

[Equation 22]

Therefore, from (23) to (26),

[0090]

[Equation 23]

It becomes Further, assuming that σ << r, the equation of motion in the sliding surface of the electric double layer of the pipe wall is assumed to be such that the pressure term and the viscosity term are balanced.

[0092]

[Equation 24]

It can be expressed as Here, η is the viscosity of the liquid.
Eliminating δ from (24), (27), (28),

[0094]

[Equation 25]

Is obtained. Φ _E represents the maximum value of the amplitude of the electric potential, and if treated as E = Φ _E , this equation is the same as the equation of the streaming potential.

[0096]

As described above, according to the first aspect of the present invention, the vibration generating means having a variable frequency forms a standing wave in the suspension in the container, and the standing waves are mutually located at the nodes. A pair of electrodes are provided with an odd number of nodes separated from each other, and the electrodes are configured to detect the potential difference associated with the electrokinetic potential phenomenon in the suspension. While taking advantage of the above, it is not necessary to strictly control the temperature of the suspension and other ultrasonic propagation conditions compared to the conventional ultrasonic vibration potential measurement method, and it is necessary to consider the influence of reflected waves. Is eliminated, and the signal processing is relatively simplified, and electrical information at the interface of the suspension can be obtained more easily. Further, according to the configuration of the first aspect of the present invention, there is also an advantage that analysis can be performed using temperature as a parameter.

According to the second aspect of the invention, for a solid sample which is difficult to be suspended, it is immersed in a liquid while the sample holder is filled and held, and the relative motion of the solid-liquid interface is given a pressure wave. Since it is configured to be generated by, the relative motion of the solid-liquid interface is much more stable than the conventional streaming potential method, there is no variation in data due to the sample shape and filling state, and it is highly accurate and reproducible. It became possible to obtain stable data. In addition, since the batch type measurement is performed in the second invention, the amount of the liquid is small,
There is also an advantage that the parameters can be relatively easily changed to perform the measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the first invention.

FIG. 2 is an explanatory diagram showing how particles are polarized in a field when a pressure wave propagates in a suspension.

FIG. 3 is an explanatory diagram showing how particles are polarized in a standing wave.

FIG. 4 is a configuration diagram of an embodiment of the second invention.

FIG. 5 is an external view showing a specific configuration example of the sample holder 120.

FIG. 6 is an explanatory diagram for conducting an electrokinetic theory theoretical consideration of U-effect I.

[Explanation of symbols]

 1, 101 Container 2, 4, 102, 104 Piezoelectric element 3a, 3b, 103a, 103b Electrode 5,105 Thermometer 6,106 Conductivity meter 7,107 PH meter 8,108 Viscometer 9,109 Burette 10,110 Temperature Controller 11 Drive circuit 111 Oscillator 12,112 Computer 120 Sample holder

Claims (2)

[Claims] 1. A device for measuring an electric potential existing at a solid-liquid interface in a suspension in which solid particles are dispersed in a liquid medium, and a container for containing a sample suspension, The container is provided with a vibration generating means with a variable frequency for creating a standing wave due to a pressure wave in the liquid in the container, and a pair of electrodes arranged in the container. At the node of the standing wave formed in
An interfacial potential measuring device, characterized in that the interfacial potential measuring devices are arranged at positions separated from each other by an odd number of nodes. 2. A device for measuring an electric potential existing at a solid-liquid interface of a solid material which is difficult to disperse in a liquid due to precipitation or the like, the container containing the liquid, and the object to be measured in the liquid in the container. The sample holding means for filling and holding the solid sample, the pressure wave applying means for applying a pressure wave to the liquid in the container, and the solid sample to be measured are arranged to face each other in the traveling direction of the pressure wave by the pressure wave applying means. An interfacial potential measuring device comprising a pair of electrodes.