Liquid-fluid contact angle measurements on hydrophilic cellulosic materials

Abstract

Contact angle measurements with captive bubbles have been used to quantify the wettability of different cellulosic materials in contact with pure water or aqueous protein solutions. The application of a new contact angle technique (axisymmetric drop shape analysis) in combination with atomic force microscopy permits new insights into the wetting behaviour of these hydrophilic surfaces. It was found that the unmodified cellulose membrane has a very smooth and homogeneous surface in the water-swollen state. There is almost no hysteresis between the advancing and receding water contact angles. The chemical modification of the cellulose with diethylaminoethyl groups results in a smooth but heterogeneous water-swollen membrane surface with fewer hydrophilic properties. A water-swollen cellulose acetate film was used as a model surface for wetting measurements with buffered protein solutions. It was found that different proteins (human serum albumin, fibrinogen) yielded different contact angles in their adsorbed state; after the adsorption of fibrinogen the contact angle of the pure aqueous buffer solution on the cellulose acetate was lower than the contact angle measured after the adsorption of human serum albumin.