Characterization of interfaces formed between thin, poly(l-lactic acid) polymer films and quartz crystal microbalance, sensor substrates with high frequency impedance analysis

In the present contribution, the influence of the film/substrate interface on the electrical response of a quartz crystal microbalance, coated with semi-crystalline poly(l-lactic acid) (PLLA), is assessed. Films with thicknesses ranging in the micrometer range (∼5 μm), were prepared on the surface of the quartz crystal microbalance, either by a solvent casting or via a layer-by-layer spin coating process. The samples were annealed either below or above the polymer's glass transition temperature and, subsequently, subjected to temperature ramps between 25 and 115 °C. The electrical response of the coated resonator (the series resonant frequency, the resistance at series resonance, and the quality factor) was recorded during the temperature ramps. From the experimental data, it was concluded that the electrical response of the polymer-coated resonator is governed by the presence of residual stresses, the degree of stiffness of the film/substrate interface, and the presence of residual solvent therein.