Elastic properties and equation of state for polycarbonate by high-pressure Brillouin spectroscopy

Although the conventional vibrational spectroscopic techniques of Raman and infrared spectroscopy are generally used to analyze the material properties of polymers, the physical and mechanical information that can be obtained through these techniques is very scarce. Since elastic information and equation of state are important for the application of polymers, we carried out Brillouin spectroscopy coupled with a diamond anvil cell. The pressure dependence of elastic properties for an amorphous polycarbonate with and without pressure medium was investigated for pressure up to 11 GPa. A substantial collapse of free volume under the anisotropic pressure was ascertained with the different slopes of elastic constants, Young's moduli, and bulk moduli at low and high pressures. From the Brillouin frequency shifts, we extracted C11 and C12 elastic constants, Young's moduli, shear moduli, bulk moduli, Poisson's ratios, and their pressure dependences. P-V isotherms were then constructed and fitted to two semi-empirical equations of state to extract the isothermal bulk modulus and its pressure derivative.