Using adhesion to probe viscoelasticity of polymer film surfaces: A quartz crystal microbalance study
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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 M(n) values less than 10(4) and greater than 10(5), this signature occurs at a temperature approximately 12.5 K above the measured bulk glass transition temperature, T(g). For intermediate values of M(n) however, the relaxation signature occurs at temperatures as low as 7 K above the bulk T(g). This observation suggests a slight decrease in the T(g) 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.
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