SU1377680A1 - Method of determining edge angle of wetting between liquids and solid bodies - Google Patents

Abstract

The invention relates to the field of determination of the optic-chemical parameters of liquids and solids, in particular to the determination of the regional angle, pa. between the surface of a solid and the meniscus of the liquid in contact with it at the interface with the gaseous medium by observing the capillary effect. The goal is to improve the accuracy of determining the wetting angle between a solid surface and a liquid that does not wet it by eliminating the error in measuring the geometric dimensions of the capillary. The method includes determining the pressure in the capillary on the material under study. The liquid is passed through the capillary under the action of the hydrostatic pressure of the test liquid. Values of pressures are recorded at the moments of loss of stability of the interface in the inlet and outlet sections of the capillary. The desired value is determined from the ratio of pressures, proportional to the ratio of liquid levels. 3 il. i (L

Description

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The invention relates to the determination of the physicochemical parameters of liquids and solids, in particular to the determination of the contact angle between the surface of a solid and the meniscus and the liquid in contact with it at the boundary with the gas phase by observing the capillary effect.

The purpose of the invention is to increase the accuracy of determining the wetting angle between a solid surface and a liquid that does not wet it by eliminating the error in measuring the geometric dimensions of a capillary cap.

FIG. I shows a measuring structure; 4G.2 - formation of the interface in the inlet section of the capillary under study during the measurement; in fig. 3 - the same, the output section.

The method is carried out as follows.

A relatively wide transparent vessel 1, installed vertically, with a test capillary 3 mounted inside its lower part through a seal 2, slowly pumps liquid 5 through a dropper 4. The appearance of a liquid in the exit section of the capillary 3 is fixed by an optical system 6.

, In the inlet section of the capillary a downwardly convex surface forms. Assuming that this surface is spherical, which is true for thin capillaries, its radius of curvature will be equal to Ri sinoi, where R is the radius of the capillary; at is the angle between the horizontal plane and. tangent to the interface at the point of contact of the liquid with the wall, and oi B - g / 2, where 9 is the wetting angle.

As the vessel is filled with liquid and its level increases, the hydrostatic pressure of the liquid at the interface increases, and the deflection of the interface will increase until it loses its stability (height) and moves down to the exit section of the capillary. The limiting condition for the stability of the interface:

. . P, pgH, 2C. sincxl / K ,,

where b is the surface tension coefficient at the liquid – gas interface;

p is the density of the investigated liquid.

In the general case, in the output section of the capillary, the interface of the phase also forms convexly downward, the curvature of which decreases with increasing hydrostatic pressure in the capillary with a further increase in the liquid level in the vessel until the moment of loss, stability and the beginning of the drip outflow of liquid at its level in the vessel . The ultimate equilibrium condition for this case

Р pgH ,, 26 / Е, -.

Solving the system of equations for yb in view of about 9 - g / 2, we obtain the expression for the magnitude of the wetting angle through the pressure ratio:

PI sin about -

  Have

 Pshi

pgs;

or

0

COS 9

N. / N ,,.

Depending on the degree of wetting of the surface with a liquid, the diameter ti of the height of the capillary under study at the 0th probe, the following options are possible.

1. When the vessel is filled with liquid, the formation of an interface in the inlet

5, the capillary section, the loss of surface stability with and its movement down the capillary until reaching the output section, the stabilization of the interface, the loss of stability at the beginning of the drip flow.

2. Stabilization of the interface in the exit section of the capillary does not occur, and drip begins

5 outflow, stopping without complete emptying of the vessel, with the formation of an interface in the outlet section. The vessel is refilled and the drip flow is recorded when it begins.

 3. When (drip flow occurs, ending with complete emptying of the vessel. Replace the capillary, reducing its height and

2 diameter, until option 1 or 2 is realized and H and Hr are measured.

4. The formation of a phase boundary in the input section did not occur.

walks. Angle 9 g / 2. The method is not operational.

The positive effect from the use of the invention is achieved due to the fact that only two quantities are included in the calculation equation - the levels of liquid in the vessel, which can be measured with high accuracy. The error of HdcTb associated with the effect of the volume of the capillary on the accuracy of pressure determination can be reduced by increasing the volume of vessel 1 and capillary 3.

Claims (1)

Formula of gain The method of determining the wetting angle between liquids and solids, including determining the pressure in the capillary from the material under study, characterized in that, in order to improve the accuracy of determination in the study of liquids that do not wet the surface, by eliminating the error in measuring geometric dimensions the capillary, the liquid is passed through the capillary under the action of the hydrostatic pressure of the test liquid, the pressure values are recorded at the moments of loss of stability of the interface in the input and output sections of the capillary and the pressure value is proportional to the ratio of the liquid levels. Fy