Micromechanical resonators as a tool for polymer characterization

The aim of this Ph.D. project was the evaluation of micromechanical resonators like cantilevers and strings as analytical tools for characterization of polymers. Spray coating was used as the technique to coat one side of the micromechanical resonators with polymer. Process optimization of different spray coating parameters was carried out with two polymer-solvent systems to obtain homogeneous films with uniform thickness and low roughness. Full factorial experimental design was employed to identify the most important parameter among the crucial parameters of spray coating such as nozzle-substrate distance, the temperature of the substrate and the speed of the spraying nozzle. Micromechanical string resonators were successfully developed as an analytical tool for sensitive and fast thermal characterization of polymers with only a few nanograms of sample. Both the glass transition (T_g) and sub-T_g transition of different polymers were detected and confirmed by conventional thermal polymer characterization techniques. An analytical model was derived to validate the resonance frequency response of the polymer coated microstrings during heating cycles. The resonance frequency change provided the quasi-static T_g of polymers while the quality factor change provided the frequency dependent shift of T_g to higher temperature. Microcantilevers were successfully employed as a platform for fast estimation of polymer degradation rate with minute amount of sample compared to conventional techniques. A detailed investigation of enzymatic degradation of poly (D, L-lactide) was done in buffered proteinase K solution. The influence of concentration of the enzyme solution, pre-hydration in buffer, surface morphology and adsorption time of enzymes on the rate of degradation was studied. The bulk degradation rate estimated from the experimental results and model simulation of multilayered cantilever structures matched well with values reported in literature. The basic understanding of the spray coating process and the newly developed approaches of microstrings and microcantilevers as analytical tools show promising potential for investigation of different polymers and pharmaceutical systems.