Contact angle measurements with constant drop volume. Control of wettability of some materials by physico-chemical treatment

Wetting between different liquids and solids have received tremendous interest from both fundamental and applied points of view. It plays an important role in many chemical technologies, such as oil recovery, lubrication, liquid coating, printing, spray quenching, and lithography [1, 2]. In recent years, there has been an increasing interest in the study of superhydrophobic and superhydrophilic surfaces, due to their potential applications in, for example, self-cleaning, nanofluidics, electrowetting, and nanolithography. Traditional way to study wetting is quantitative measurement of contact angle θ, which characterizes the shape of a liquid drop on a solid surface (or on another liquid) (see Fig. 1) [1, 2].

Currently, the primary method of measuring the contact angle θ is to observe the shape of the drop (volume of the order of 1 µcL) and measure the angle between the drop tangent T and the solid surface at the drop–solid contact point either directly or by calculating it from the drop diameter D and height H. Several methods and apparatuses were developed which permit to investigate wetting over the whole range of contact angles 0○ < θ < 180○ in static and in dynamic regimes. Nevertheless, these methods have some limitations: they are not fast enough, do not allow investigating the anisotropy and homogeneity of wetting, and require special equipment.