in-Plane Stress Measurement in Polymer Coatings As Induced By Vapor Sorption/Desorption Processes

The aim of this work is the design, set up and test of an apparatus which allow to measure the in-plane stress that arise in polymer coatings below the glass transition temperature (Tg) as result of vapor sorption/desorption processes and its evolution in time. The in plane stress is measured using beanding beam cantilever technique. The experiments were performed on polystyrene coatings at different temperatures, conditioning the system in n-pentane or toluene vapor at prescribed rate of change of vapor fugacity. From the stress state, the change in the volume of polymer coating as induced by the sorption/desorption process was obtained. Through the non-equilibrium lattice fluid model (NELF) information for volume dilation in the system was used to estimate the amount of vapor sorbed/desorbed in the coating and the results were compared with those obtained by means of corresponding sorption/desorption experiment in mibrobalance devices.