Formation of BaSo₄ fibres with morphological complexity in aqueous polymer solutions

BaSO4 fibres with morpho- logical complexity were formed in aque- ous solution with polyacrylate and par- tially monophosphonated poly(ethyle- neoxide)-block-poly(methacrylic acid) additives by a simple precipitation reac- tion. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2á:polymer molar ratio (R). At Sà 60 to 80, and Rà 3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although the yield was low. The nanofilaments were also organ- ized into cone-shaped aggregates at Sà 80, and at lower R values these formed higher-order structures that consisted of multiple cone-on-cone assemblies with remarkable self-similarity. Increasing the supersaturation produced ovoid or cross-shaped dendritic particles for the range of molar ratios studied. In con- trast, BaSO4 crystallisation in the pres- ence of a partially phosphonated block copolymer gave a high yield of BaSO4 fibres up to 100 mm in length, and consisting of co-aligned bundles of 30 nm-diameter defect-free single-crys- tal nanofilaments with a uniform growth tip. A model for the defect-free growth of BaSO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is proposed.

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