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Phase separation by continuous quenching: similarities between cooling experiments in polymer blends and reaction‐induced phase separation in modified thermosets
Author(s) -
Alig Ingo,
Rüllmann Maximilian,
Holst Marco,
Xu Jianjun
Publication year - 2003
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200350821
Subject(s) - materials science , quenching (fluorescence) , phase (matter) , nucleation , lower critical solution temperature , polymer blend , polymer , epoxy , miscibility , spinodal decomposition , polymer chemistry , isothermal process , upper critical solution temperature , siloxane , thermodynamics , composite material , copolymer , chemistry , organic chemistry , optics , physics , fluorescence
Small angle light scattering (SALS) has been applied to study the phase separation kinetics in a binary polymer mixture of poly(ethyl methyl siloxane) (PEMS) and poly(dimethyl siloxane) (PDMS). The phase separation was induced by cooling an initially homogeneous mixture with well defined cooling rates. The results have been compared to time resolved SALS and microscopy in the course of reaction‐induced phase separation in mixtures of an epoxy resin and polysulfone (PSU). For the critical PEMS/PDMS mixture with an upper critical point it was found in a continuous quenching experiment that the time evolution of the scattered light intensity I(q,t) scales with the cooling rate. The similarity to the scaling behavior of I(q,t) in isothermal experiments after fast quenches (scaled by the quench depth) is discussed. A secondary phase separation was found and has been explained by the competition between the growth of the two phase structure during cooling and the mutual diffusion without the assumption of gelation or vitrification. For the epoxy/PSU mixture with 15% PSU, after the appearance of a bicontinuous structure a secondary phase separation was observed. Mixtures with higher PSU‐contents formed epoxy‐rich droplets in the PSU‐rich matrix by nucleation and growth mechanism. The frustration of the structure growth can be explained by approaching vitrification of one or both phases. The similarity between continuous cooling experiments in blends and the reaction‐induced phase separation have been discussed in the generalized χN vs. composition phase diagram ( N : degree of polymerization, χ : Flory‐Huggms interaction parameter).