Thin Films and Interfaces at High Pressure

This contribution summarizes the design and implementation of a novel experimental tool for the investigation of thin polymer films and interfacial architectures: a classical surface plasmon spectrometer is combined with a high pressure cell, thus allowing for the optical characterization of polymer layers at pressures up to 200 MPa and over a temperature range of 10° to 120°C. We demonstrate the excellent performance of this combination setup by presenting a few typical results obtained with this instrument. These include, first, the determination of the pressure- and temperature-dependent refractive indices of the pressurizing media used in these studies, i.e., water, methanol, ethanol, and supercritical CO2 (scCO2), the pressure dependence of the glass transition temperature in thin poly(ethylmethacrylate) films, and the pressure-dependent collapse behavior of surface-grafted poly(N-isopropylacrylamide) gels in water. The final example then concerns a further extension of the setup by an electrochemical cell offering investigation of processes like heterogeneous electron transfer reactions at high pressure. We demonstrate by a few results obtained with the electropolymerization of bithiophene that the pressure is not only a thermodynamic variable that determines – just like the temperature – the physical properties of thin films, but it also constitutes an important process parameter during the preparation of polymer coatings.