Attempting to extend the database of work reported earlier, the practical adhesion between a glass filler, modified by various silane-coupling agents, and a polystyrene matrix is measured and compared with predictions based on a generalized thermodynamic criterion. Measurements leading to adhesion failure are carried out using the single-particle composite method, in which a rectangular polymer specimen containing a single untreated or silane-treated glass bead is subjected to increasing uniaxial tensile stress until interfacial failure, as observed using a microscope, occurs at one of the poles of the sphere. The results show no difference in adhesion strength between an untreated and a silane-treated glass bead, and the interfacial failure mechanism for the polystyrene composites is markedly different from that observed for previously studied systems. Crazes originate at the particle pole at low values of the applied stress and continue to form along the interface with continued strain. A dye test performed on filled composites confirms that the polystyrene is not wetting the untreated glass beads. More studies must be done to determine the origin of the anomalous failure and wetting behavior. (C) 2003 Wiley Periodicals, Inc.