SMALL-ANGLE NEUTRON-SCATTERING FROM DEUTERATED POLYSTYRENE IN DIOCTYL PHTHALATE SOLUTION UNDER SHEAR

Small-angle neutron scattering measurements were taken from high molecular weight (1.95 x 10(6)) deuterated polystyrene in dioctyl phthalate solution at low concentration (3% weight fraction) under steady shear with rates ranging from the quiescent condition (0 s-1) to 1100 s-1 at room temperature (22-degrees-C). The scattered intensity increased drastically beyond a characteristic shear rate (gamma(c) = 57 s-1) similar to the increase following a temperature drop from the one-phase region (ambient temperature) to the two-phase region in this upper critical solution temperature system. The cloud point is estimated to be a few degrees lower than 14-degrees-C which is the cloud point for protonated polystyrene in dioctyl phthalate at this molecular weight and concentration. On the basis of this analogy, the random-phase approximation (RPA) approach (the Zimm inverse scattering formula) was used along with a swollen radius of gyration in the Debye function to analyze the data and extract a statistical segment length b and a polymer-solvent interaction parameter chi(ps). The segment length was seen to increase slightly, indicating a slight increase in chain volume beyond gamma(c), while the interaction parameter showed a dramatic increase up to the 'spinodal" value gamma(s) = 280 s-1 where the RPA breaks down, therefore giving nonreliable values. This data treatment method has no justification on physical grounds: it is merely a way to quantify our observations since specific models that could explain our data are not available at this time.