MEASURING DEVICE FOR CONTROL THE SPREADING DEGREE OF LIQUIDS ON SOLID SURFACE

The course of many technological processes, where various liquids are used, depends on the wetting properties of the latter, ie on the liquids spread intensity on the solids surfaces. The problem of the spreading degree measuring appears in instrument making, mechanical engineering (in conducting capillary control of surface defects), light industry (in controlling the quality of paints, varnishes, inks, etc.), chemical industry (in the manufacture of herbicides), medicine (in creating artificial devices blood circulation), to intensify oil and gas production, etc.

. The proposed method for the case of solid dielectrics is based on the relationship between the dielectric and surface properties of these bodies. The adhesion work on the solid-liquid interface is determined by the dispersion forces of intermolecular interaction and is described by the following dependence [5]: Since the dispersion forces determine the polarization properties of dielectrics, the relationship between the microstructure of the dielectric and the macroscopic surface energy is given in the form [6]: In turn, there is a relationship between the polarization of the molecule and the dielectric constant of the environment. It is described by the Clausius-Mosotti formula [7]: ). From the above dependences derived the equation that reflects the relationship between surface tension and dielectric constant: (4) The obtained dependence includes many constants relating to both microscopic and macroscopic values, which confirms the unambiguous relationship between the dielectric constant of the controlled sample and the surface tensions of the solid and liquid at the interface with the gas [8]. The control of the spreading degree is carried out by measuring of impedance changing of the system "solid-liquid", which is placed between the plates of the capacitor.
To implement the proposed method, a device [9] was developed, which provides measurement and comparison of the measuring system impedance, between the covers of which there is a system "solid-liquid", when the reference and test fluids are spreading. The measurement process is automated with the indication of the results, their recording and processing in dynamic mode. The device design provides fast replacement of investigated surfaces samples, and also protection against influence of external electric fields.
The device block diagram is given in Fig. 1.

Fig. 1. Device block-diagram for measuring wettability degree of solid surface by liquids
The measuring sequence on it provides a following: distilled water falls on a testing solid sample, which is placed between the capacitor plates of the measuring unit 1 by means of a transmission mechanism 4 and a stepper motor 5 from the dispenser 3. The measuring unit 1 protected by a screen 2 and controlled by a computer 8. In an automated mode is determined the dynamics of change in the impedance by Measuring converter 9 of the measuring cell 1 due to wetting and spreading of the liquid drop on the surface, which leads to a change in the total dielectric constant of the space between the capacitor plates. The converted and amplified signal from blocks 9 and 10 is fed to a computer 8, it programmatically processes the signal and builds the change characteristics in impedance over time. After cleaning and drying the solid surface, the test liquid is applied to it and similar measurements are made. Note that the investigated solid must completely cover the working area of the capacitor plates, which simplifies the calculation of the impedance range and increases the accuracy of measurement. As a reference liquid can be not only distilled water, but also other liquids that do not chemically react with a solid. Wetting quality evaluation of liquid and the interaction nature of the system "liquidsolid" is carried out by comparing the curve angle and the scatter degree around the average values of dynamic condenser impedance during the spreading of reference and test fluids. . The device was used to measure the dynamics of impedance change relative to 15 pF calibration capacity for three liquids: distilled water and penetrants "TsZh-1", "TsZh-4" and smoothed time dependences for these liquids are constructed (Fig. 2).

. Time dependences for the change of impedance
It follows from the Fig. 2 that the impedance change curve of reference liquid A has significantly higher steepness, but smaller scatter, and impedance change curves of penetrants B, C are accordingly has less steepness, with bigger dispersion around average values. It can be noted that the best wetting properties have penetrant "TsZh-4", for which the change in impedance has the form of curve C. Thus, reducing the angle and increasing the width of the scatter of the measured values indicate better wetting properties of the liquid, more intense interaction between liquid and solid.
Based on the measurement results, the wetting quality comprehensive assessment of the selected surface with the investigated liquid is obtained. The measuring is carried out by the nature of the impedance change over time, and thus makes it possible to control the spreading dynamics. Both environments are investigated simultaneously: the liquid and the surface of a solid body in their direct contact, and not each in particular.