Methods of contact angle measurements as a tool for characterization of wettability of polymers

Many problems related to the quality of protective coatings for more sophisticated applications can be solved on the basis of the wettability of their surfaces measurements. The equilibrium (static) or dynamic contact angle (CA) of solids can be measured and the sessile drop method or Wilhelmy method are usually applied. In the sessile drop method CA is measured optically. The measured values of static CA are influenced by evaporation of the liquid, absorption of the liquid by porous substrate (e.g. paper, building material) and other chemical or physical interactions occurring on the solid surface. The Wilhelmy method is based on the measurements of the force which is needed to overcome the resistance of the liquid as the solid plate with known wetted length is immersed in or withdrawn from the liquid of known surface tension. The precision of the contact angle measurements by Wilhelmy method is higher as compared with the sessile drop method. Very important factor highly influencing the quality of CA measurements is the proper selection of applied liquids which should be selected according to the applied measuring method. The careful selection of the method of CA measurements is a crucial factor influencing the possibility of practical application of the results of wettability measurements.