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 diameter) was studied at water-air interfaces in a broad hydrophobicity range (40-90 degrees) using a Wilhelmy him balance. The wettability of surface modified particles was characterized by the determinations of static water contact angles using an optical microscopic method. In the course of the film balance investigations the direction of particles' removal during the collapse was studied visually and surface pressure (II) versus surface area (A) isotherms were obtained from which some important parameters, like collapse pressures, collapse areas and contact angles were calculated. Comparing the measured and calculated values of contact angles with each other and considering the unexpected direction of particles' removal from the interface during the collapse of monoparticulate layer we came to the conclusion (concerning the medium hydrophobicity range) that there should had been an extra force which could hinder the immersion of particles into the water phase. The present conclusion partially supports our earlier investigations of wettability of similarly sized and hydrophobic glass spheres accomplished by a Langmuir film balance. However, the Wilhelmy film balance seems to be more sensitive for the study of wettability of the particles. (C) 1999 Elsevier Science B.V. All rights reserved.