Pressure dependence of thickness and refractive index of thin PMMA-films investigated by surface plasmon and optical waveguide spectroscopy

Total internal reflection (TIR) and attenuated total reflection (ATR) measu rements in the Kretschmann configuration have been performed at 25 degrees C with poly(methyl methacrylate) (PMMA) films (of ca. 2.5 mu m thickness) s pincoated on top of a 50 nm thick gold layer, as a function of the applied hydrostatic pressure, ranging from p = I . 10(5) to 1050 . 10(5) Pa. The an alysis of guided optical modes allows for the separate determination of the refractive index n and the thickness d of the polymer films as a function of pressure. The pressure media in contact with the PMMA films were water, ethanol, and methanol. Thermodynamic theories for the density of solids and fluids in combination with the Lorentz-Lorenz equation for their optical p roperties fit the experimental data quite well.