SMALL-ANGLE NEUTRON-SCATTERING OF POLY(GAMMA-BENZYL L-GLUTAMATE) IN DEUTERATED BENZYL ALCOHOL

Small-angle neutron scattering has been used to study poly(gamma-benzy l L-glutamate) (PBLG) in deuterated benzyl alcohol (DBA) as the soluti on is brought from the isotropic phase into the gel phase. The results show that an aggregation of PBLG molecules exists up to 80 degrees C even in the isotropic phase and the size of the aggregate does not cha nge with temperature within the isotropic phase for a given concentrat ion. However, the size of the aggregate increases with concentration o r as the gelation threshold is crossed. The measurement of fractal dim ension at intermediate length scales of the aggregates in the isotropi c phase shows that the aggregates are less dense at higher polymer con centrations. But at lower length scales of similar to 50 Angstrom, the mesh size of the aggregates in the isotropic phase decreases with inc reasing polymer concentration. Studies of the fractal dimension of the resultant gels show that the thermal history of the sample in the iso tropic phase influences the gel microstructure. The fractal dimension of the PBLG-DBA gel obtained by a step quench procedure is higher than that of a gel obtained by a sudden quench. We have also observed that the local concentration gradients become sharper as the polymer conce ntration increases in the gel phase.