Interactions Between Micron-sized Glass Particles and Poly(dimethyl siloxane) in the Absence and Presence of Applied Load

Abstract

A technique using a scanning electron microscope to view a fine particle in contact with a flat substrate whilst under load and during its removal is described. The particle is attached to an atomic force microscope cantilever so that the magnitude of the load can be estimated directly from the imaged deflection. Interactions between 5 to 60 μm spherical glass particles and cross-linked poly(dimethyl siloxane) were studied in the presence and absence of load. WA was estimated to be 74 mJ/m2 from the size of the contact area in the absence of load. Using highly flexible cantilevers to apply load resulted in large shear displacements and forces, which distorted the contact area and assisted in particle removal. These shear effects were eliminated by using a more rigid cantilever to measure a normal pull-off force for which the interface toughness, Gc , exceeded 950 mJ/m2. The large adhesion hysteresis indicated the presence of chemical bonding, presumed to occur between silanol and siloxane groups. The mode of particle detachment varied significantly with the choice of cantilever, showing evidence of both cohesive failure and interfacial crack propagation. The relevance of these results to the interpretation of AFM data is discussed.