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 (T_i) were quenched to a point inside the spinodal phase boundary at a final temperature (T_f) 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, T_i=102.3 °C, 123.9 °C, and 171.6 °C, were chosen while T_f was fixed at −7.5 °C. The time‐dependent SANS structure factor, S(q,t;T_f), showed clear scattering peaks corresponding to the early and intermediate stages of SD. The time changes in the wave number q_m(t;T_f) and the intensity S_m(t;T_f) at the peak of S(q,t;T_f) 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.