Using adhesion to probe viscoelasticity of polymer film surfaces: A quartz crystal microbalance study

Abstract: We have used a quartz crystal microbalance to monitor the adhesion of small particles to the surface of polystyrene films. This technique is shown to provide a signature of viscoelastic relaxation processes at the polymer surface. For Mn values less than 104 and greater than 105, this signature occurs at a temperature ∼ 12.5 K above the measured bulk glass transition temperature, Tg. For intermediate values of Mn however, the relaxation signature occurs at temperatures as low as 7 K above the bulk Tg. This observation suggests a slight decrease in the Tg value near the polymer surface. A model incorporating the effects of enrichment of polymer chain ends at the free surface was considered and found to provide a quantitative description of the data.