Fluctuaton mediated phase separation in polymer blends near the limit of metastability

摘要

The evolution of the structure factor of off-critical polyolefin (polymethylbutylene/polyethylbutylene) blends quenched from the homogeneous state to states near the limit of metastability was studied by small angle neutron scattering. The Cahn-Hilliard-Cook theory was used to organize the data in terms of three time-independent parameters that depend on the scattering vector, q: S_0(Q), THE INITIAL STRUCTURE FACTOR, s_T(q), the terminal structure factor, and R(q), a kinetic parameter than indicates the time scale for the transformation from S_0(q) to S_t(q). These three parameter than indicates the time scale for the transformation from S_0(q) to S_t(q). These three parameters change systematically with quench depth. Changes in the structure factor S(q,t) are only observed in the q values smaller than a critical scattering vector, q_c. At small quench depths, q_c is obtained because R(q)->0 as q->q_c. At deeper quenches, q_c is obtained because S_t(q)->S_0(q) as q->q_c. Scattering characteristics at q