阅读说明：本技术 一种快速测量表面束缚电荷密度的方法 (Method for rapidly measuring surface bound charge density ) 是由 周国富 吴昊 弗里德里希·穆盖莱 于 2019-09-17 设计创作，主要内容包括：本发明公开了一种快速测量表面束缚电荷密度的方法,该方法通过在待测束缚电荷膜层的上下表面上分别设置下电极层和上电极,将下电极层接地,对上电极和下电极层进行电性连接,并在上电极和下电极层之间串联负载,而后通过在待测束缚电荷膜层的上表面靠近上电极的位置设置导电液滴,导电液滴在待测束缚电荷膜层的上表面铺展,与上电极接触时,产生电流回路；而后测定导电液滴接触上电极时电流回路中的电流大小,进而可通过预先构建的计算模型计算出待测束缚电荷膜层的表面束缚电荷密度。通过以上方式,本发明可实现对表面束缚电荷密度的快速测量,且所需设备和具体操作简单,无需施加外电压,成本低廉。(The invention discloses a method for rapidly measuring the density of surface bound charges, which comprises the steps of respectively arranging a lower electrode layer and an upper electrode on the upper surface and the lower surface of a bound charge film layer to be measured, grounding the lower electrode layer, electrically connecting the upper electrode layer with the lower electrode layer, serially connecting a load between the upper electrode layer and the lower electrode layer, arranging a conductive liquid drop on the upper surface of the bound charge film layer to be measured, wherein the conductive liquid drop is spread on the upper surface of the bound charge film layer to be measured and generates a current loop when contacting with the upper electrode; and then measuring the current in the current loop when the conductive liquid drop contacts the upper electrode, and further calculating the surface bound charge density of the bound charge film layer to be measured through a pre-constructed calculation model. Through the mode, the method can realize the rapid measurement of the surface bound charge density, and has the advantages of simple required equipment and specific operation, no need of applying external voltage and low cost.)

1. A method for rapidly measuring the density of surface bound charges is characterized by comprising the following steps:

s1, arranging a lower electrode layer on the lower surface of the bound charge film layer to be detected, and arranging an upper electrode on the upper surface of the bound charge film layer to be detected;

s2, grounding the lower electrode layer, electrically connecting the upper electrode with the lower electrode layer, and connecting a load in series between the upper electrode and the lower electrode layer;

s3, arranging a conductive liquid drop on the upper surface of the to-be-tested bound charge film layer close to the upper electrode, wherein the conductive liquid drop is spread on the upper surface of the to-be-tested bound charge film layer and is in contact with the upper electrode to generate a current loop; measuring the current in a current loop when the conductive liquid drop contacts the upper electrode;

s4, calculating the surface bound charge density of the bound charge film layer to be detected through a pre-constructed calculation model;

the calculation model isWherein σ_TIs the surface bound charge density; i.e. i₀The current in the current loop is measured when the conductive liquid drop contacts the upper electrode; r is the resistance of the load; c_DielThe capacitor is a capacitor of a dielectric layer which comprises the bound charge film layer to be detected and is arranged between a solid-liquid interface of the conductive liquid drop on the surface of the bound charge film layer to be detected and the lower electrode layer; a is the solid-liquid interface area of the conductive liquid drop on the surface of the bound charge film layer to be detected.

2. The method for rapidly measuring the density of bound charges on a surface according to claim 1, wherein the conductive liquid droplet is ultrapure water, an aqueous solution, an ionic liquid or a liquid metal.

3. The method for rapidly measuring the density of surface bound charges according to claim 2, wherein the volume of the conductive droplet is 3 μ L to 10mL in step S3.

4. The method for rapidly measuring the density of bound charges on the surface according to claim 1, wherein in step S3, the distance D between the position where the conductive liquid drop is disposed and the upper electrode is smaller than the solid-liquid contact surface radius r of the conductive liquid drop after spreading on the bound charge film layer to be measured, and D > r/2.

5. The method of claim 1, wherein the load has a resistance greater than or equal to 20 times an internal resistance of the current loop.

6. The method of claim 1, wherein in step S1, the bound charge film to be measured is a hydrophobic insulating material layer.

7. The method as claimed in claim 6, wherein the film layer to be measured is a fluoropolymer film layer.

8. The method for rapidly measuring the density of the surface bound charges according to claim 7, wherein the material of the charge film layer to be measured is at least one of PDMS, Teflon AF, Cytop and Hyflon.

9. The method of claim 1, wherein in step S1, the thickness of the bound charge film to be measured is 10nm to 5 mm.

10. The method for rapidly measuring the density of bound charges on the surface according to any one of claims 1 to 9, wherein step S4 further comprises calculating the surface potential of the bound charge film layer to be measured through a calculation model of the surface potential; the calculation model of the surface potential is U_T＝i₀X R, wherein i₀The magnitude of the current in the current loop measured when the conductive droplet contacts the upper electrode, R is the resistance of the load.

Technical Field

The invention relates to the technical field of surface charge density measurement, in particular to a method for rapidly measuring surface bound charge density.

Background

In some cases (e.g. after contact with an aqueous solution), the surface of the hydrophobic insulating material film layer may spontaneously or by human handling generate a long-standing bound (trapped) charge, which in turn may cause the material film layer to develop a surface potential. The existence of the surface bound charges has great influence on the application of the hydrophobic insulating material in various technical fields, and the function of the hydrophobic insulating material has advantages and disadvantages. On the one hand, in the electrowetting field, surface charges (especially stably existing surface bound charges) can cause a device to generate a surface potential spontaneously under the condition that an applied electric field is zero, so that the controllability of the applied electric field on the function of the device is influenced, and the device is failed. For example, in an electrowetting display, if bound charges are generated on the surface of the hydrophobic insulating layer, the problem that the ink in the pixel cells cannot flow back or the flow back is incomplete is caused. On the other hand, stable surface charges can be effectively utilized in many fields such as micro-nano fluids, bio-protein surface adsorption, water energy collection, and the like. Therefore, the measurement of the bound charges on the surface of the hydrophobic insulating film and the surface potential caused by the bound charges are of great significance in various related fields.

The current measurement of bound charges on the surface of a hydrophobic insulating film can be quantified by measuring the asymmetry of the electrowetting response. Such as the Banpurkar, Arun g., et al, "plasma electric selection of fluorine-water interfaces by electric selection," radar dis-cussions 199(2017):29-47. the value of the voltage at the minimum of the contact angle, i.e., the surface binding potential (Trapping) can be measured by measuring the response of the contact angle of a droplet of liquid on the surface of the film to an applied voltage. The value of the surface charge can be calculated by calculation based on models of Prins and Verheijen (Verheijen, H.J.J., and M.W.J.Prins. "Receplolelecetropicting and applying of charge: model and experiments." Langmuir 15.20(1999): 6616-. The advantages of this method are: the magnitude of the surface binding potential at the contact angle minimum can be visualized by the trend of the contact angle as a function of applied voltage. The disadvantages are that: 1) measurement needs to be performed by applying an external voltage of a triangular wave; 2) the measurement time is longer.

Another commonly used method of measuring surface potential is kelvin probe force microscopy. The Kelvin probe force microscope technology is a method for measuring surface potential through electrostatic force between a probe and a sample, and is characterized in that direct-current bias voltage is applied to a feedback loop to offset the potential on the surface of the sample, and the force applied to the probe is monitored to realize the measurement of the potential value and the distribution on the surface of the sample. The advantages of this test method are: the surface scanning of the surface potential can be realized, and the scanning resolution and the scanning precision are high. The disadvantages are that: 1) the test needs to use an atomic force microscope, the equipment is complex, and the counterfeiting is expensive; 2) the measurement range of the surface potential is limited by the bias voltage range available in the instrument, the bias voltage range available by the current atomic force microscope is +/-10V, and if the surface potential exceeds the bias voltage range, the test result cannot be obtained due to overranging. Therefore, a method which is convenient to operate, low in cost and capable of rapidly measuring the surface bound charges is urgently needed.

Disclosure of Invention

In order to achieve the above object, the present invention provides a method for rapidly measuring the density of surface bound charges.

The technical scheme adopted by the invention is as follows: a method for rapidly measuring surface bound charge density, comprising the steps of:

s1, arranging a lower electrode layer on the lower surface of the bound charge film layer to be detected, and arranging an upper electrode on the upper surface of the bound charge film layer to be detected;

s2, grounding the lower electrode layer, electrically connecting the upper electrode with the lower electrode layer, and connecting a load in series between the upper electrode and the lower electrode layer;

s3, arranging a conductive liquid drop on the upper surface of the to-be-tested bound charge film layer close to the upper electrode, wherein the conductive liquid drop is spread on the upper surface of the to-be-tested bound charge film layer and is in contact with the upper electrode to generate a current loop; measuring the current in a current loop when the conductive liquid drop contacts the upper electrode;

s4, calculating the surface bound charge density of the bound charge film layer to be detected through a pre-constructed calculation model;

the calculation model is as follows:wherein σ_TIs the surface bound charge density; i.e. i₀The current in the current loop is measured when the conductive liquid drop contacts the upper electrode; r is the resistance of the load; c_DielThe capacitor is a capacitor of a dielectric layer which comprises the bound charge film layer to be detected and is arranged between a solid-liquid interface of the conductive liquid drop on the surface of the bound charge film layer to be detected and the lower electrode layer; a is the solid-liquid interface area of the conductive liquid drop on the surface of the bound charge film layer to be detected.

The magnitude of the resistance of the load in the circuit directly affects the test current signal. Due to surface bound potential U_T＝i₀X R, wherein i₀Obtaining a current peak value (namely the measured current in a current loop) for a current signal generated when the conductive liquid drop contacts the upper electrode, wherein R is the resistance of the load; theoretically the smaller R, i₀Indicated U_TThe more accurate. However, the load must not be chosen too small, since the response time of the current is well knownIf R is too small, the response time will be very short, and the existing current testing equipment may not capture the corresponding peak value i of the current₀(ii) a In addition, the circuit itself has an internal resistance, i.e. the actual resistance is the sum of the internal resistance of the circuit and the load resistance, and since the internal resistance of the circuit is small and unknown, the resistance of the load generally used is much larger than the internal resistance of the current loop (i.e. R>>R_{Internal resistance of}) Further neglecting the internal resistance of the current loop; the resistance of the load may specifically be greater than or equal to 20 times the internal resistance of the current loop. Of course,if the internal resistance of the current loop is known, this restriction is not present.

Preferably, the conductive liquid droplets are ultrapure water, an aqueous solution, an ionic liquid, or a liquid metal. The aqueous solution may be sodium chloride solution, potassium chloride solution, etc. Preferably, conductive droplets having a conductivity higher than 100. mu.S/cm are used. In the existing surface bound charge density measuring method, the surface bound charge of a hydrophobic insulating film is measured by measuring the asymmetry of electrowetting response for quantification, the test process needs to be carried out in an oil environment, and the surface of the material is oleophilic, so that the material is polluted by oil materials after the test and cannot be used again; this application accessible adopts above electrically conductive liquid drop to measure, avoids placing the constraint charge rete that awaits measuring in oily environment test and lead to the rete pollution.

Preferably, in step S3, the conductive droplet has a volume of 3 μ L to 10 mL.

Preferably, in step S3, a distance D between the installation position of the conductive droplet and the upper electrode is smaller than a solid-liquid contact surface radius r of the conductive droplet after spreading on the bound charge film layer to be tested, and D > r/2.

Preferably, in step S1, the bound charge film layer to be tested is a hydrophobic insulating material layer.

Preferably, the film layer to be tested is a fluoropolymer material film layer. Further preferably, the material of the charge membrane layer to be detected is at least one of PDMS, Teflon AF, Cytop, and Hyflon.

Preferably, in step S1, the thickness of the bound charge film layer to be tested is 10nm to 5 mm.

In step S1, the bottom electrode layer may be any conductive film or plate, and the material thereof may be metal, Indium Tin Oxide (ITO), or two-dimensional conductive material such as graphene; the surface of the electrode layer needs to be flat. And arranging an upper electrode on the upper surface of the bound charge film layer to be detected, wherein the upper electrode cannot cover the whole upper surface of the bound charge film layer to be detected. The upper electrode can be directly attached to the upper surface of the bound charge film layer to be detected or arranged above the upper surface of the bound charge film layer to be detected, and a certain gap is formed between the upper electrode and the bound charge film layer to be detected, but the height of the gap is not higher than that of the conductive liquid drop. The material of the upper electrode can be metal, two-dimensional conductive material, indium tin oxide or heavily doped semiconductor, etc.

Preferably, in step S4, the surface potential of the bound charge film layer to be measured may be further calculated by using a calculation model of the surface potential, where the calculation model of the surface potential is U_T＝i₀X R, wherein i₀The magnitude of the current in the current loop measured when the conductive droplet contacts the upper electrode, R is the resistance of the load.

The beneficial technical effects of the invention are as follows: the invention provides a method for rapidly measuring the density of surface bound charges, which comprises the steps of respectively arranging a lower electrode layer and an upper electrode on the upper surface and the lower surface of a bound charge film layer to be measured, grounding the lower electrode layer, electrically connecting the upper electrode layer with the lower electrode layer, serially connecting a load between the upper electrode layer and the lower electrode layer, arranging a conductive liquid drop at the position, close to the upper electrode, of the upper surface of the bound charge film layer to be measured, wherein when the conductive liquid drop is not in contact with the upper electrode, counter charges caused by the bound charges are all in the lower electrode layer, and when the conductive liquid drop is spread on the upper surface of the bound charge film layer to be measured and is in contact with the upper electrode, the counter charges move from the lower electrode layer to the upper electrode, so that a current; the surface bound charge density of the bound charge film layer to be detected can be calculated through a pre-constructed calculation model by measuring the current in a current loop when the conductive liquid drop contacts the upper electrode. The method can realize the rapid measurement of the surface bound charge density, and has the advantages of simple required equipment and specific operation, no need of applying external voltage and low cost; the problems that in the existing measuring method, the external voltage of a triangular wave needs to be applied and the measuring time is long when the electrowetting asymmetric response method is used for measuring, and the problems that the Kelvin probe force microscope technical equipment is complex and expensive and the measuring range is limited by the internal bias range of the instrument can be solved.

Drawings

In order to more clearly illustrate the technical solution in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly described below.

FIG. 1 is a schematic diagram of the method for rapid measurement of surface bound charge density according to example 1;

FIG. 2 is a partial photograph and equivalent circuit diagram of the conductive liquid drop of FIG. 1 before and after contacting the upper electrode;

FIG. 3 is an equivalent circuit diagram of a calculation model for constructing a surface bound charge density when a conductive liquid droplet contacts an upper electrode in example 1;

FIG. 4 is a graph showing the results of fitting the current model in example 1;

FIG. 5 is a graph showing the results of measuring current signals obtained from samples of different surface bound charge densities in example 2 using the measurement method of example 1 and using a 1.67 M.OMEGA.load with 0.6mol/L NaCl solution as the conductive droplet;

FIG. 6 is a graph showing the results of measuring current signals obtained from samples of different surface bound charge densities in example 2 using the measurement method of example 1 and using a 6.5 M.OMEGA.load with 0.6mol/L NaCl solution as a conductive droplet;

FIG. 7 is a graph of the minimum value of the contact angle of a liquid drop on the surface of a sample measured by the electrowetting asymmetric response method in example 2 as a function of an applied voltage;

FIG. 8 is a graph comparing the results of measuring the binding potential of the sample surface in example 2 using the method of example 1 and the prior art electrowetting asymmetric response method.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.