Effect of Impurity Molecules on the Low-Temperature Vibrational Dynamics of Polyisobutylene: Investigation by Single-Molecule Spectroscopy

I. Yu. Eremchev, A. V. Naumov, Yu. G. Vainer, and L. Kador

2009, in: The Journal of Chemical Physics J. Chem. Phys. (2009) Bd.: 130 Hnr.: 18 S.: 184507-1 - 184507-5

Abstract:
The influence of impurity chromophore molecules — tetra-tert-butylterrylene (TBT) and dibenzo-anthanthrene (DBATT) — on the vibrational dynamics of the amorphous polymer polyisobutylene (PIB) has been studied via single-molecule spectroscopy. The measurements were performed in the temperature region of 7 – 30 K, where the interaction of the chromophores with quasilocalized low-frequency vibrational modes (LFMs) determines the observed spectral line broadening. The analysis of the individual temperature dependences of the linewidths for a large number of single probe molecules yielded effective frequency values of those LFMs which are located near the respective chromophores. In this way the distributions of the LFM frequencies were measured for the two systems, and they were found to be similar. Moreover, they are in good agreement with the vibrational density of states as measured in pure PIB by inelastic neutron scattering. This allows us to conclude that, at least in the case of PIB, doping with low concentrations of the nonpolar and neutral molecules TBT and DBATT does not affect the vibrational dynamics of the matrix markedly.