Optical Probe Study of Solutionlike and Meltlike Solutions of High Molecular Weight Hydroxypropylcellulose

Document Type

Conference Proceeding

Publication Date


Publication Title

Scattering from Polymers: ACS Symposium Series


Quasi-elastic light scattering spectroscopy spectra of optical probes diffusing in hydroxypropylcellulose (HPC):water (1,2) are well-described as a sum of two modes, here described as 'fast' and 'slow'. There are correlations between the experimental parameters that characterize spectra and system properties including probe radius and polymer concentration; these correlations separate probe behavior into distinct small-probe and large-probe regimes. For the two probe-size regimes, the fast and slow modes can be grouped into three physical regimes, namely a long time scale regime for the large-probe slow mode, an intermediate time scale regime for the small-probe slow mode and the large-probe fast mode, and a broad time scale regime for the small-probe fast mode. Physical interpretations for the three physical regimes are proposed. The probe diameter separating small-probe and large-probe behavior is the same at all polymer concentrations, consistent with hydrodynamic models for polymer dynamics, but inconsistent with models that assume the existence of a transient gel pseudolattice in solution. It has previously been reported that the zero-shear viscosity of HPC solutions shows a sharp change, at transition concentration c+, in the functional form of its concentration dependence, from a stretched exponential at lower concentration to a power law at higher concentrations. We observe a sharp transition in the concentration dependence of mode parameters at the same concentration c+, supporting the interpretation that the transition is physically real, and not an artifact of the fitting process.