Wetting behaviour of silanized glass microspheres at water-air interfaces:a Wilhelmy film balance study

The wetting behaviour of silanized glass microspheres (75 +/- 5 mu m diamet er) was studied at water-air interfaces in a broad hydrophobicity range (40 -90 degrees) using a Wilhelmy him balance. The wettability of surface modif ied particles was characterized by the determinations of static water conta ct angles using an optical microscopic method. In the course of the film ba lance investigations the direction of particles' removal during the collaps e was studied visually and surface pressure (II) versus surface area (A) is otherms were obtained from which some important parameters, like collapse p ressures, collapse areas and contact angles were calculated. Comparing the measured and calculated values of contact angles with each other and consid ering the unexpected direction of particles' removal from the interface dur ing the collapse of monoparticulate layer we came to the conclusion (concer ning the medium hydrophobicity range) that there should had been an extra f orce which could hinder the immersion of particles into the water phase. Th e present conclusion partially supports our earlier investigations of wetta bility of similarly sized and hydrophobic glass spheres accomplished by a L angmuir film balance. However, the Wilhelmy film balance seems to be more s ensitive for the study of wettability of the particles. (C) 1999 Elsevier S cience B.V. All rights reserved.