Crossover of domain-growth behavior from percolation to cluster regime in phase separation of an off-critical polymer mixture

Takeno, Hiroyuki; Hashimoto, Takeji
August 1997
Journal of Chemical Physics;8/1/1997, Vol. 107 Issue 5, p1634
Academic Journal
Time-resolved light scattering has been used to investigate phase-separation dynamics for off-critical mixtures of polybutadiene (PB) and polyisoprene (PI) with a well defined phase diagram. Percolation-to-cluster transition (PCT) occurs in the course of the phase separation process for an off-critical mixture of the PB and the PI in the shallow quenches covered in this work. Before the onset of PCT occurs, the phase separation dynamics is fast, typically obeying qm⇢t-0.9 and Im∼t2.7 ("percolation regime"), where qm is the scattering vector at the maximum scattered intensity Im . After the onset of PCT the time changes in qm and Im become very slow, and the phase separation process might appear to stop, if we observe the dynamics in a short time scale after the onset of PCT. The behavior corresponds to the results which Hashimoto et al. reported for the off-critical mixtures of poly (styrene-ran-butadiene) (SBR) and PB, and SBR and PI (spontaneous pinning of the domain growth) [J. Chem. Phys. 97, 679 (1992)]. However, it is shown in this paper that the droplets formed after PCT eventually grow according to the scaling law of qm∼t-n and Im∼t3n with n=1/4 to 1/3 ("cluster regime"), if we keep observing the phase separation process in the much longer time scale, beyond the time period over which the domain growth appeared to be pinned. To our knowledge, it is for the first time that such crossover of domain-growth behavior from percolation to cluster regime was observed via the intermittent time period over which the growth kinetics are apparently pinned.


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