Influence of pressure on fast dynamics in polyisobutylene

Influence of pressure on fast dynamics and elastic properties in polyisobutylene is studied using Raman, Brillouin and neutron scattering spectroscopy. Analysis of the results shows that the boson peak frequency increases with pressure stronger than the longitudinal sound velocity measured by Brillouin scattering. Moreover, the boson peak intensity decreases under pressure stronger in Raman scattering than in neutron scattering suggesting a decrease in the light-to-vibrations coupling coefficient C(ν). The strong decrease of the microscopic peak intensity under pressure in Raman spectra supports this suggestion. We argue that variations in C(ν) might be related to amplitude of structural fluctuations. We speculate that change in disorder and/or overall density under pressure is the main cause for the observed variations.