6533b7dcfe1ef96bd1271d23

RESEARCH PRODUCT

Nucleation phenomena in polymeric systems

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Materials formed from long flexible macromolecules differ from their small-molecule analogs, because corresponding collective length scales are distinctly larger and many dynamical phenomena are very much slower; in addition, the variation of chain length N yields a control parameter that leaves intermolecular forces invariant, but allows a stringent test of theories. These concepts are exemplified in a discussion of nucleation barriers for symmetrical polymer (A, B)-mixtures (chain lengths NA = NB = N) near the critical temperature Tc, and for symmetrical block copolymers near the (fluctuation-induced) first order transition between the disordered melt and the lamellar mesophase. While in the latter case for N → ∞ the transition becomes second-order and the order of magnitude of the nucleation barrier vanishes as N−13, for the polymer mixtures it increases as N12 in the mean-field critical regime. Experiments and simulations, however, both show that very long chains are needed to fully reach this mean-field critical regime. For asymmetrical block copolymers {f=NA(NA+N)≠12} the nucleation barrier scales as N12|f−12|5.