阅读说明：本技术 一种表面电荷的测量方法和测量装置 (surface charge measuring method and device ) 是由 吴昊 弗里德里希·穆盖莱 周国富 于 2019-09-17 设计创作，主要内容包括：本发明公开了一种高效便捷的表面电荷的测量方法和测量装置。该测量方法包括以下步骤：在待测疏水绝缘层上设置导电液体,将电极层与待测疏水绝缘层连接,电极层和导电液体等电位连接,测量导电液体的接触角θ<Sub>t</Sub>,由接触角θ<Sub>t</Sub>得到待测疏水绝缘层上表面电荷的电荷密度。整个测量系统内导电液体和电极层处于等电势的状态,疏水绝缘层携带束缚电荷后对导电液体产生的电驱动力使得导电液体在疏水绝缘层表面的润湿状态形成新的平衡,接触角随之发生变化。本方法在不施加外加电压的情况下,利用疏水绝缘层表面润湿性的改变即实现了测量,更加快速便捷,适用于需要面扫描的场景,可以在不借助于复杂昂贵的仪器设备的情况下完成测量工作。(The invention discloses a high-efficiency and convenient surface charge measuring method and device. The measuring method comprises the following steps: arranging conductive liquid on the hydrophobic insulating layer to be measured, connecting the electrode layer with the conductive liquid in an equipotential manner, and measuring the contact angle theta of the conductive liquid t From the contact angle theta t And obtaining the charge density of the surface charge on the hydrophobic insulating layer to be detected. The conductive liquid and the electrode layer in the whole measuring system are in an equipotential state, and the electric driving force generated on the conductive liquid after the hydrophobic insulating layer carries bound charges enables the wetting state of the conductive liquid on the surface of the hydrophobic insulating layer to form new balance, so that the contact angle changes. The method realizes measurement by using the change of the surface wettability of the hydrophobic insulating layer under the condition of not applying external voltage, is quicker and more convenient, is suitable for scenes needing surface scanning, and can finish measurement without using complex and expensive instruments and equipment.)

1. A method of measuring surface charge, comprising the steps of:

Arranging conductive liquid on a hydrophobic insulating layer to be detected, connecting an electrode layer with the hydrophobic insulating layer to be detected, connecting the electrode layer with the conductive liquid in an equipotential manner, and measuring a contact angle theta of the conductive liquid_tFrom said contact angle theta_tAnd obtaining the charge density of the surface charge on the hydrophobic insulating layer to be detected.

2. The method for measuring surface charge according to claim 1, wherein the charge density of the surface charge on the hydrophobic insulating layer to be measured is calculated by the following formula:

Wherein C is the capacitance of the hydrophobic insulating layer to be detected, gamma_l/vAs surface tension of liquid-third phase, contact angle θ₀Is the contact angle of the conductive liquid on the hydrophobic insulating layer in the absence of surface charges.

3. The method of claim 2, wherein the contact angle θ is_tAnd the contact angle theta₀Measured in an oily atmosphere.

4. The method for measuring surface charge according to claim 1, wherein the volume of the conductive liquid is 0.01 to 20 μ L.

5. The method for measuring surface charge according to any one of claims 1 to 4, wherein the thickness of the hydrophobic insulating layer to be measured is 10nm to 5 mm.

6. The method of claim 1, further comprising moving the conductive liquid along a measurement path through a contact angle θ_tAnd obtaining the distribution of the charge density of the surface charge on the hydrophobic insulating layer to be measured along the measuring path through the change on the measuring path.

7. A surface charge measuring device, comprising:

the electrode layer is used for being connected with the hydrophobic insulating layer to be detected;

The electrode probe is used for communicating the conductive liquid arranged on the hydrophobic insulating layer to be detected;

Wherein the electrode probe and the electrode layer are connected in an equipotential manner.

8. The apparatus of claim 7, further comprising an image acquisition system for measuring the contact angle.

Technical Field

The invention relates to the technical field of material testing, in particular to a method and a device for measuring surface charges.

Background

The surface of the hydrophobic insulating layer may in some cases (e.g. after contact with an aqueous solution) generate a bound charge that may be present for a long time, either spontaneously or by artificial treatment. This stable surface bound charge in turn causes the hydrophobic insulating 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 surface bound charges capable of stabilizing existence) can cause a device to generate a surface potential spontaneously under the condition that an applied electric field is zero, and the controllability of the applied electric field on the function of the device is influenced, so that the device is failed. For example, in an electrowetting display, if bound charges are generated on the surface of the hydrophobic insulating layer, the ink in the pixel cells cannot flow back or the flow back is incomplete. On the other hand, in other fields such as micro-nano fluid, biological protein surface adsorption, water energy collection and the like, stable surface bound charges can be effectively utilized. Therefore, the measurement of the bound charges on the surface of the hydrophobic insulating layer and the resulting surface potential is of great significance in many related fields.

One method currently used to measure bound charges on the surface of a hydrophobic insulator is kelvin probe force microscopy. Kelvin probe force microscopy is a method of measuring the surface potential by electrostatic forces between the probe and the sample. The direct-current bias voltage is applied to the feedback loop to offset the potential of the surface of the sample, and the stress of the probe is monitored to measure the potential value and distribution of 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. However, the measurement process requires the use of an atomic force microscope, which is a complex and expensive device, and thus is difficult to be applied to a portable rapid measurement scenario.

To address this deficiency, arn g. The main principle is to measure the value of the voltage at the maximum of the contact angle, i.e. the surface binding potential, by measuring the response of the contact angle of a drop of liquid on the surface of a hydrophobic insulating layer to an applied voltage (Banpurkar AG, Sawan Y, Wadhai S M, et al. Spontanoraw electric selection of fluoropolymers-water interfaces under the same by electric heating [ J ]. Farad semiconductors, 2017,199: 29-47). Furthermore, the value of the surface charge was obtained by further performing calculations based on models of Prins and Verheijen (Verheijen H J, Prins M W J. reversible electrolytic and bridging of charge: model and experiments [ J ]. Langmuir,1999,15(20): 6616-6620). The method does not need expensive instrument equipment such as an atomic force microscope, and the numerical value of the surface binding potential at the minimum value of the contact angle can be visually seen through the variation trend of the contact angle along with the applied voltage in the measurement process. However, the measurement time of the method is long, and the measurement of a certain point on the surface needs to apply a complete triangular wave to the liquid drop on the point, and a set of variable contact angle data is acquired to obtain the final result. Meanwhile, the measurement precision also depends on the speed and the step length of the voltage change, the slower the voltage change is, the shorter the step length is, the more accurate the result is, however, the measurement efficiency is also greatly reduced.

Therefore, it is necessary to provide a method for measuring bound charges on the surface of a hydrophobic insulating layer with high efficiency and convenience.

Disclosure of Invention

The invention aims to provide a high-efficiency and convenient surface charge measuring method and a measuring device.

According to a first aspect of the present invention, there is provided a method of measuring surface charge, comprising, according to an embodiment of the present invention, the steps of:

arranging conductive liquid on the hydrophobic insulating layer to be measured, and arranging electrode layerConnecting with hydrophobic insulating layer to be measured, connecting electrode layer with conductive liquid at equal potential, and measuring contact angle theta of conductive liquid_tFrom the contact angle theta_tAnd obtaining the charge density of the surface charge on the hydrophobic insulating layer to be detected.

Among them, the electrode layer may be a conductive film or a conductive flat plate, and non-limiting examples of materials thereof are metal, metal oxide, graphene, carbon nanotube, and the like. The conductive liquid may specifically be electrolyte liquid, ionic liquid, liquid metal, nano metal solution, etc., and may be, for example, NaCl solution, KCl ionic liquid, liquid mercury, nano silver paste. The hydrophobic insulating layer to be tested may be any hydrophobic insulating material with a surface charge including, but not limited to, low surface energy fluoropolymer materials, such as amorphous fluoropolymer materials, non-limiting examples of which are: PTFE, PDMS, Teflon AF, Cytop, Hyflon.

The invention has the beneficial effects that:

in the method for measuring the surface charge, the conductive liquid is used as an upper electrode, the electrode layer is used as a lower electrode, the conductive liquid and the electrode layer in the whole measuring system are in an equipotential state after the two electrodes are connected in an equipotential manner, and in the state, the electric driving force generated on the conductive liquid after the hydrophobic insulating layer carries bound charges enables the conductive liquid to form new balance in the wetting state of the surface of the hydrophobic insulating layer, and the contact angle changes along with the change. The electric driving force generated by the conductive liquid is different according to the different charge density of the bound charges, and accordingly, the contact angle of the conductive liquid on the surface of the hydrophobic insulating layer is different. Contact Angle θ through a conductive liquid on a surface charged hydrophobic insulating layer_tAnd combining the Young's equation to obtain the charge density of the surface charge. The method realizes the measurement of the surface charge by utilizing the change of the surface wettability of the hydrophobic insulating layer under the condition of not applying an external voltage. The measurement of the charge density of the surface charge of a certain point to be measured on the surface of the hydrophobic insulating layer can be realized by measuring the contact angle of the conductive liquid only once in the whole measurement process, compared with the method for measuring the asymmetry of the electrowetting response provided by Banpurkar, the method is quicker and more convenient, and simultaneously,The method is suitable for scenes needing surface scanning, and measurement can be completed without the aid of complex and expensive instruments and equipment.

According to the embodiment of the invention, the charge density of the surface charge on the hydrophobic insulating layer to be detected is calculated by the following formula:

Wherein C is the capacitance of the hydrophobic insulating layer to be measured, and gamma_l/vAs surface tension of liquid-third phase, contact angle θ₀Contact angle theta of conductive liquid on hydrophobic insulating layer without surface charge₀I.e. the contact angle is the contact angle that would be produced if the same conductive liquid were placed on a hydrophobic insulating layer of the same nature as the one to be tested (except for the absence of surface charge). Typically, when the measurement process is carried out in air or other atmosphere, the third phase is an air phase, i.e. γ_l/vIs the liquid-gas surface tension.

According to an embodiment of the invention, the contact angle θ_tand contact angle theta₀Can be measured in an oily atmosphere. The oily atmosphere refers to an oil component which is used in an oil environment to place a sample to be measured in a measurement process in the oil environment, and the oil component used in the oil environment is preferably an oil component which can enable a contact angle measurement value of a conductive liquid to be as close to 180 degrees as possible when the same type of hydrophobic insulating layer sample without bound charges is measured, and specifically includes but is not limited to silicone oil. That is, the conventional gas phase is replaced with an oil phase as a liquid phase of the conductive liquid and a third phase outside the solid phase of the hydrophobic insulating layer, γ in the above formula_l/v(liquid-third phase surface tension) also corresponding to the measurement of gamma_l/o(surface tension of the conductive liquid and the oil phase),The corresponding detection is carried out in the oil phase, the contact angle change response is more sensitive, and therefore the measurement value of the surface charge is more accurate.

according to an embodiment of the invention, the volume of the conductive liquid is 0.01-20 μ L.

If the volume of the conductive liquid is too small, the measurement is inconvenient to carry out; if the volume of the conductive liquid is too large, the conductive liquid is obviously influenced by gravity, so that the error of the measurement result is large. The volume of the conductive liquid is controlled to be 0.01-20 mu L, so that the measurement can be carried out smoothly, and the measurement accuracy can be considered.

According to the embodiment of the invention, the thickness of the hydrophobic insulating layer to be tested is 10nm-5 mm.

according to an embodiment of the invention, further comprising moving the conductive liquid along the measurement path through the contact angle θ_tAnd obtaining the distribution of the charge density of the surface charge on the hydrophobic insulating layer to be measured along the measuring path through the change on the measuring path.

By moving the conductive liquid, the contact angle condition of each position on the surface of the hydrophobic insulating layer is collected, and the charge density condition of the surface charge of each measuring point is obtained by the Young equation, so that the measurement of the surface charge distribution of the hydrophobic insulating layer is realized.

According to a second aspect of the present invention, there is provided a surface charge measuring device, according to an embodiment of the present invention, comprising:

the electrode layer is used for being connected with the hydrophobic insulating layer to be detected;

The electrode probe is used for communicating conductive liquid arranged on the hydrophobic insulating layer to be detected;

Wherein, the electrode probe and the electrode layer are connected in an equipotential manner.

according to an embodiment of the present invention, the surface charge measuring apparatus further includes an image acquisition system for measuring the contact angle. The image acquisition system can be a system comprising a light source and an image acquisition device, wherein the light emitted by the light source irradiates the conductive liquid on the hydrophobic insulating layer to be detected, and the image of the conductive liquid arranged on the surface of the hydrophobic insulating layer to be detected is acquired by the image acquisition device. A non-limiting example of an image capture device may be a camera lens including a microlens.

According to the embodiment of the invention, the surface charge measuring device further comprises an image processing system, and the positions of three-phase contact points and the like are determined through analysis of the obtained images, so that the contact angle of the conductive liquid is obtained.

According to the embodiment of the invention, the device for measuring the surface charge further comprises a movable sample stage and/or a movable electrode probe stage, and automatic scanning measurement of contact angles of the conductive liquid on different positions of the surface of the hydrophobic insulating layer is realized through the movement of the sample stage and/or the electrode probe stage, so that the measurement of the surface charge distribution of the hydrophobic insulating layer is realized.

drawings

Fig. 1 is an operation diagram of a surface charge measuring apparatus according to an embodiment of the present invention.

Fig. 2 is a three-phase contact line force balance diagram of the three-phase boundary of a conductive droplet on a surface charge measuring device in accordance with one embodiment of the present invention.

Fig. 3 is an experimental result of a comparative experiment of another embodiment of the present invention.

Detailed Description

The conception, the specific structure, and the technical effects produced by the present invention will be clearly and completely described in conjunction with the embodiments below, so that the objects, the features, and the effects of the present invention can be fully understood. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.