Polarized and depolarized dynamic light scattering of a rodlike polyelectrolyte in a strong acid

Unusual dynamic light scattering behavior of poly(benzoxazole), a stiff backbone rodlike polymer, has been found in methane sulfonic acid/methane sulfonic acid anhydride. A very rapid, angle-independent decay mode characterized the short-time autocorrelation functions al various levels of added salt, sodium methane sulfonate, in both polarized and depolarized dynamic light scattering experiments. In some ways, the behavior qualitatively resembles the long-predicted ''plasmon'' mode, which has never been seen in more conventional polyelectrolyte systems. However, calculations based on a point charge model are inconsistent with the plasmon mode, even allowing for the high viscosity of the methane sulfonic acid solvent. The absence of angle dependence means that the rapid decay mode cannot be explained by the diffusion of oligomers. The meaning of the rapid, angle-independent decay mode remains unclear.