Abstract
Crystallization in concentrated aqueous solutions of the alcohol ethoxylate diblock copolymers C11E40, C15E39 and C17E40 (where C = methylene or methyl and E = oxyethylene) has been investigated using small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS) and rheology. It is shown that the gel phase formed in these materials has body-centred cubic (bcc) symmetry, and that the bcc structure can be macroscopically oriented by large amplitude oscillatory shear. At concentrations above about 55 wt.-% copolymer, crystallization of the poly(oxyethylene) block occurs at low temperatures, and the effect of crystallization from the oriented bcc structure of a 70 wt.-% solution is examined using SAXS/WAXS. Crystallization induces a second phase separation, i.e. the semicrystalline lamellar structure resulting from poly(oxyethylene)-block crystallization is incommensurate with the oriented bcc structure, with which it coexists at low temperatures. However, crystallization produces an unoriented lamellar structure. WAXS indicates that the poly(oxyethylene) in the diblock copolymer crystallizes in its usual (helical) form.
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