Pulse-induced critical scattering and the characterisation of polymer samples
An instrument, developed over the last decade, and now made available, for measuring Pulse-induced Critical Scattering (PICS) intensities, serves a variety of purposes: to explore phase relationships in blends, to aid in refining statistical thermodynamic models for polymer solutions, and to characterise polymer samples. This last aspect is here explored in relation to the high 'tail' of the molecular weight distribution (MWD), which critically affects the slow relaxation to equilibrium of samples in the last stages of manufacture e.g. in die-swell ratios. Polystyrene/cyclohexane solutions are studied and demonstrate the sensitivity of spinodal curves, even greater sensitivity of cloud-point curves, to higher moments of the MWD. Effects due to M+1 are easily observed, which reflect a pattern predicted on mild assumptions from statistical —-thermodynamic models. The general philosophy of characterisation is briefly reviewed. Sensitive techniques which explore the region of undisturbed dimensions and balanced interactions are valuable and complementary to GPC.