Scattering studies of self‐assembling processes of polymer blends in spinodal decomposition

Structure self‐assembling in the spinodal decomposition (SD) of polymer blends in its late stage has been explored for a near‐critical mixture of polybutadiene and polyisoprene by a time‐resolved light scattering technique, with a particular emphasis on the time evolution of the interface structure. By analysis of a scaled structure factor F ( x, t ) ≡ I ( q, t ) q m ( t ) 3 over wide ranges of a reduced scattering vector x ≡ q / qm ( t ) and time, it was found relevant to divide the late stage of SD into two stages, I and II. Here, I ( q, t ) denotes the scattered intensity as a function of the scattering vector q and time t . In the intermediate stage preceding the late one, F ( x, t ) became sharper with its peak at x = 1 increasing with t . However, as time elapsed, F ( x, t ) turned out to be universal for t , first in the range of x smaller than about 2 and then over the entire range of x accessible by the present experiment. The time interval in which the former occurred is defined as late stage I and the one in which the latter was realised is called late stage II. In late stage I, the average thickness of phase‐phase interfaces decreases towards an equilibrium value and the time evolution of the interfacial area density Σ ( t ) does not scale with q m ( t ), i.e. the exponents γ and α in the power laws Σ ( t ) ~ t − γ and q m ( t ) ~ t − α do not coincide (actually, α < γ ). Late stage II corresponds to the process in which these exponents become equal and the interface thickness reaches equilibrium. Such conditions probably ensure the establishment of a complete dynamical scaling law in the SD process.