Time-resolved small-angle neutron scattering study of spinodal decomposition in deuterated and protonated polybutadiene blends. I. Effect of initial thermal fluctuations

Abstract

Time-resolved small-angle neutron scattering (SANS) experiments have been performed on the self-assembling process of a binary mixture of deuterated polybutadiene and protonated polybutadiene at the critical composition. This mixture has an upper critical solution temperature type of phase diagram with the spinodal temperature at 99.2 °C. Specimens held in the single-phase state at an initial temperature (Ti) were quenched to a point inside the spinodal phase boundary at a final temperature (Tf) to induce phase separation via spinodal decomposition (SD). In order to examine the effect that thermal concentration fluctuations have on SD, three different initial temperatures, Ti=102.3 °C, 123.9 °C, and 171.6 °C, were chosen while Tf was fixed at −7.5 °C. The time-dependent SANS structure factor, S(q,t;Tf), showed clear scattering peaks corresponding to the early and intermediate stages of SD. The time changes in the wave number qm(t;Tf) and the intensity Sm(t;Tf) at the peak of S(q,t;Tf) followed different paths depending on the initial temperature. This fact evidences a definite effect of thermal concentration fluctuations on SD (i.e., a significant ‘‘memory’’ effect). A critical test of the linearized Cahn–Hilliard–Cook theory led to the conclusion that this theory can describe satisfactorily the early stage SD in the deep-quench region.