Slow spinodal decomposition in binary liquid mixtures of polymers. IV. Scaled structure factor for later stage unmixing

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The later-stage spinodal decomposition (SD) of polymer mixtures at deep quenches were investigated by time-resolved light scattering. The scaled structure factor F(x)≡qm (t,T)3I(x) with x≡q/qm (t,T) was analyzed as a function of time t or reduced time τ during the SD at various temperatures T’s, where qm (t,T) is the magnitude of the scattering vector q at which the first-order peak of the scattering intensity profile I(q;t,T) appears. Spectacular features in F(x) were discovered; (i) F(x) at large x is not universal with t but rather increasing with t, implying that the local structure is not scaled with a single length parameter 1/qm (t,T) used for the scaling of the global structure at x≂1, (ii) F(x) shows the second- and the third-order peaks or shoulders at x=2 and 3, and (iii) F(x) exhibits a dynamical crossover from x−n (n≂6) to x−4 with t in the asymptotic behavior at x≳2, as well as a spatial crossover from x−n to x−4 with x at τ in the sufficiently late stage.