Dynamic microprobing of viscoelastic polymer properties

Scanning force microscopy (SFM) was used to probe the micromechanical prope rties of polyisoprene rubbers, polyurethanes, polystyrene and polyvinylchlo ride. Applicability of the SFM cantilevers for microprobing is presented as a convenient method for materials selection. The Hertzian model of elastic contacts was used to obtain Young's modulus at contact frequencies range 0 .05-367 Hz. The absolute values of the elastic modulus were correlated with the known properties of bulk materials, with no frequency dependence detec ted for glassy polyvinylchloride and polystyrene in air. The time dependenc e of the Young's modulus of rubber and polyurethanes followed the Williams- Landel-Ferry relationship, with parameters known for bulk materials. For PV C in water, a significant reduction of the elastic modulus and strong time- dependency were recorded. This behaviour can be related to the lower local glass transition temperature because of a plastification effect of solvent molecules on the uppermost polymer layer. (C) 2000 Society of Chemical Indu stry.