Effect of temperature on low-frequency Raman scattering from crystalline pentadecaethylene glycol di-n-octadecyl ether

Abstract

Raman spectra have been recorded for a homogeneous sample of pentadecaethylene glycol di-n-octadecyl ether at several temperatures in the range 77–293 K. The crystalline material comprises helical oxyethylene and planar zig-zag n-alkyl blocks in a contiguous structure. Five scattering peaks are found with frequency (ν) dependent on temperature (T). One peak at 88–80 cm^–1 with a linear variation of ν with T is assigned to a lattice mode. The other peaks, with more complex variations of ν with T, are assigned to the longitudinal acoustical mode, LAM-1, of the n-alkyl block (130–125 cm^–1), to the LAM-3 and LAM-1 of the oxyethylene block (46–41 and 18–14 cm^–1) and, with less certainty, to a transverse acoustical mode, TAM-1 (14–10 cm^–1).