Liquid Concentration Measurement Based on Liquid Contact Angle

Abstract

Different concentrations of the same liquid or liquids with different solutes have different surface tensions. The macroscopic phenomenon is that they have different wetting effects on the same solid surface. The liquid contact angle can describe the wetting effect. Therefore, this paper proposes a method for measuring the liquid concentration using the liquid contact angle. A glass plate with a hydrophobic layer and an angle-measuring device forms the detection part. The glass plate is placed horizontally, and the solution to be tested is dropped on the surface of the glass plate. Solutions with different concentrations have different liquid-solid interfacial tension and liquid-gas interfacial tension, resulting in different liquid contact angles, which can achieve rapid and accurate measurement of solution concentration. Experiments show that the liquid contact angle of ethanol solution decreases with the increase of liquid concentration. Different volumes of ethanol solutions with the same concentration have substantially the same liquid contact angle. This experimental method has the advantages of being simple and easy to operate, having a wide range of applications, not easily limited by the type of detection solution, having a large concentration measurement range, having less sample usage, free from electromagnetic interference, and having real-time online detection.