JPS5818157A - Zeta potential measuring device - Google Patents

Abstract

PURPOSE:To measure a zeta potential continuously with high accuracy over a wide measuring range, by changing the pressure of circulated fluid periodically and measuring an AC potential difference generated between electrodes provided at upper-stream packing layer. CONSTITUTION:Powder or fibrous solid sample is packed in a packing layer 1 and liquid is circulated from a liquid vessel 9 through a circulating flow path 17. When the liquid is packed in the path 17, a vibrator 6 is oscillated. When a pressure change is caused in a liquid due to vibration, an AC liquid potential E is generated between electrodes 2 and only AC components are synchronously rectified at a synchronizing rectifier 11 and outputted to an operation device 15. A liquid pressure P and conductivity lambda are inputted to the device 15 to obtain a zeta potential zeta. Thus, the zeta potential can continuously be measured with high accuracy over a wide measuring range without being affected with the drift.

Description

[Detailed description of the invention] The present invention relates to a zeta potential measuring device.

One of the methods for measuring zeta (zero potential), which represents the charge state at the solid-liquid interface, is the streaming potential method. The zeta potential is determined by measuring the potential difference that occurs between the electrodes when a liquid permeates through this packed layer, that is, the flowing potential.In conventional devices, the liquid is made to flow in a certain direction at a constant pressure. However, since there is a drift due to the contact potential between the electrode and the liquid and the irregular potential between the electrodes, it is difficult to expect improvement in measurement accuracy when measuring samples with small zeta potentials or near equipotentials. In particular, as the ionic strength of the flowing liquid increases, the generated potential becomes smaller and the proportion of drift increases, resulting in further loss of accuracy.In this way, devices that measure DC potential have a narrow measurement range. There was a drawback.

In addition, due to such asymmetric potential, calculation of zeta potential requires changing the pressure of the fluid continuously in one direction, recording the flowing potential at this time on an X-Y recorder, etc., and calculating the relationship between the potential and pressure. This method has the disadvantage that it must be performed from a gradient or the streaming potential must be measured at pressures at at least two or more points. Furthermore, due to this drawback, if you want to measure the change in zeta potential when changing the properties of the liquid such as pH or ionic strength, it is difficult to measure continuously and easily, as it requires a lot of effort such as changing the liquid. could not.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional art, an object of the present invention is to provide a zeta potential measuring device that can measure zeta potential with high precision and continuously over a wide measurement range without being affected by drift due to contact potential or irregular potential. Our goal is to provide the following.

In order to achieve the above object, the present invention comprises a circulation channel, a pump, etc., means for circulating the fluidized liquid from the fluidized liquid container to the packed bed, means for applying periodic pressure changes to the fluidized liquid, and the above-mentioned. A zeta potential measuring device is provided with a means for measuring the pressure of the flowing liquid flowing into the photoreceptor layer, and is provided in the upstream photoreceptor layer when the pressure of the circulating liquid changes periodically. The device is characterized in that it is configured to determine the zeta potential by measuring the AC potential difference generated between the electrodes.

The principle of alternating current zeta potential measurement of this invention will be explained below.

When a liquid is poured into a layer filled with powder or the like and the flow is considered, the layer can be approximately regarded as an aggregate of thin tubes. The principle diagram shown in Figure 1 is a model of one of the thin tubes, and shows the relationship between the flow of liquid and ions and the polarity of the electrode 22 when the solid 21 is negatively charged. . When a liquid flows in one direction, the flow of ions remains steady, and a constant potential difference occurs between the electrodes (Figure 1 (~). Furthermore, when the liquid flows in the opposite direction, a constant potential difference with different polarity occurs. A potential difference is generated (Fig. 1 ■)). Therefore, when a liquid whose pressure P changes periodically is caused to flow, an alternating current potential difference is generated. This potential difference is the streaming potential E, and its relationship with periodically changing pressure is shown in FIG. C in Figure 2 is the change in streaming potential E when the zeta potential is negative;
The figure shows changes when the zeta potential is positive.

From the above, by flowing a liquid whose pressure changes periodically, the flowing potential can be extracted as an alternating current voltage.

On the other hand, the relationship between the zeta potential (0) and the streaming potential E is expressed by the following formula.

η: Viscosity coefficient of liquid λ: Electrical conductivity of liquid e: Dielectric constant of liquid Therefore, if η and l are constant, the zeta potential is λ and E%
It can be determined by measuring P.

On the other hand, the zeta potential can also be determined by measuring the flowing current I flowing between the electrodes. In this case, the relationship with I is expressed by the following formula.

Here, C is the number of interelectrode tests including the filling layer.

Hereinafter, an embodiment of the present invention will be described based on the drawings. This embodiment is a zeta potential measuring device configured to measure a flowing potential and obtain a zeta potential based on equation (1). The configuration diagram is shown below.

The flowing potential measuring tank 16 includes a filling layer 1 for filling a solid sample such as powder, and a pair of electrodes 2 provided in the direction in which the liquid flows. FIG. 4 shows an enlarged cross-sectional view of the filled layer 1. The electrode 2 has a shape with a large number of small holes having a diameter of about IW to allow liquid to flow. As for the material of the electrode, platinum or silver plated with silver chloride is used.

The filter paper 6 is for preventing the solid sample filled in the packed layer 1 from flowing out. In order to flow and circulate the fluid in the fluid fluid container 9 through the packed bed 1, a circulation channel 17 is provided which communicates the fluid fluid container 9 with the fluid fluid container 16. The inflow path of the flowing potential measuring tank 16 is provided with a vibrator 5 that gives vibration to the flowing liquid and a pressure sensor 4 that measures the pressure of the flowing liquid. The pump 7 is for sucking up the fluid from the fluid container 9' and making it flow. The pulp 8 provided in the flow path communicating the inflow side and the outflow side of the circulation flow path 17 is used for flow rate adjustment. The vibration device 6 is the oscillator 1
6.

The pressure sensor 4 is connected to a pressure sensor power supply and rectifier 12, and is rectified to become a reference signal for the synchronous rectifier 11 and is also introduced to the arithmetic unit 15 as a signal indicating the liquid pressure. The output of the potential difference generated between the electrodes 2 is output by a synchronous rectifier 11.
It is connected to the.

Note that an impedance conversion circuit is included at the stage before the synchronous rectifier 11. In the synchronous rectifier 11, the alternating current signal generated between the electrodes 2 is synchronously rectified using the output signal of the pressure sensor 4 as a reference signal. The conductivity measuring device 14 measures the conductivity of the fluid from the electrical resistance of the fluid, and the measurement is performed by dipping the conductivity measurement electrode 10 into the fluid.

The arithmetic device 15 outputs each of the synchronous rectifier 11, the pressure sensor power supply/rectifier 12, and the conductivity measuring device 14,
That is, a signal corresponding to the pressure P1 and conductivity λ of the liquid flowing potential E1 is input, and the zeta potential ζ is calculated based on equation (1).

In the above structure, the packed layer 1 is filled with a powdery or fibrous solid sample, and the fluid is circulated from the fluid container 9 through the circulation channel 17. The flow rate at this time is determined in consideration of the liquid permeability determined by the particle size of the solid sample to be filled. When the liquid is spilled into the circulation channel 17, the vibration device 6 is vibrated. The pressure of the flowing liquid is rectified by vibration and output to the arithmetic unit t15. Also,
The pressure P1 and conductivity λ of the flowing liquid are input to the calculation device 15, and the zeta potential ζ is determined.

The measurement of the flowing potential may be performed by applying vibration after filling the packed layer 1 with the liquid, stopping the driving of the pump 7 and stopping the flow of the liquid. Further, the signal from the oscillator 13 may be used as a reference signal for synchronously rectifying the signal generated between the electrodes 2. Furthermore, as a means of imparting vibration to the liquid,
The vibration may be generated by a mechanical structure consisting of a crank mechanism, or the pump itself may generate pulsating flow.

Furthermore, when measuring the zeta potential based on equation (2), it can be done by lowering the input impedance of the synchronous rectifier 11 and measuring the flowing current (2).

As described above, according to the present invention, since the alternating current flowing potential is measured, it is not affected by the drift caused by the contact potential between the electrode and the liquid or the uneven potential between the electrodes, and a circuit that compensates for such drift can be created. The configuration is simple without the need for any additional equipment. In addition, since it is not affected by drift, it is possible to increase the measurement sensitivity when the ionic strength of the liquid is high, or when the pH of the liquid is very high or very low, and even under conditions where there is little generation of streaming potential. Zeta potential can be measured with high precision for measurements such as .

In addition, a zeta potential measuring device can be obtained that can easily carry out measurements using the same solid sample while changing liquid properties, such as pH and electrolyte concentration, and can also measure changes over time and has a wide measurement range. Since the flow potential can be directly connected to changes in the pressure of the liquid, the data can be input directly into a computer to calculate the zeta potential, which simplifies the measurement.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the zeta potential measurement principle of this invention, Fig. 2 is an output waveform diagram of liquid pressure P and streaming potential E in this measurement principle, and Fig. 3 is the configuration of an embodiment of this invention. 4 are enlarged cross-sectional views showing the filling layer 1 of this embodiment. 1...Filled layer 2...Electrode 4.
... Pressure sensor 5 ... Vibrator 6 ...
...Electromagnet 7...Pump 9...
... Fluid liquid container 10 ... Conductivity measurement electrode 911 ...
...Synchronous rectifier 12...Power supply and rectifier for pressure sensor 16...
... Oscillator 14 ... Conductivity measuring device 15 ... Arithmetic device 16 ... Flowing potential measuring tank 17 ... Circulating flow path Patent applicant Co., Ltd. Shimadzu Corporation

Claims (1)

[Claims] A flowing potential measurement tank consisting of a packed layer of a solid sample, a flowing liquid container, and a pair of electrodes sandwiching the packed layer and provided in the flow direction of the flowing liquid, the flowing liquid being flowed into the packed layer and the above-mentioned A device for measuring zeta potential from a flowing potential generated between electrodes, comprising means for circulating the flowing liquid from the flowing liquid container to the packed bed, means for applying periodic pressure changes to the flowing liquid, and the packed bed. means for measuring the pressure of the flowing liquid flowing into the bed, and determining the zeta potential by measuring the alternating current potential generated between the electrodes when the pressure of the flowing liquid changes periodically. The constructed zeta potential measuring device.