Formation of BaSO4 fibres with morphological complexity in aqueous polymersolutions

BaSO4 fibres with morphological complexity were formed in aqueous solution with polyacrylate and partially monophosphonated poly(ethyleneoxide)-block- poly(methacrylic acid) additives by a simple precipitation reaction. For po lyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2+:polymer molar ratio (R). At S = 60 t o 80, and R = 3 to 14, highly anisotropic crystalline fibres consisting of bundles of BaSO4 nanofilaments were formed after several weeks, although th e yield was low. The nanofilaments were also organized into cone-shaped agg regates at S = 80, and at lower R values these formed higher-order structur es that consisted of multiple cone-on-cone assemblies with remarkable self- similarity. Increasing the supersaturation produced ovoid or cross-shaped d endritic particles for the ran-e of molar ratios studied. In contrast, BaSO 4 crystallisation in the presence of a partially phosphonated block copolym er gave a high yield of BaSO4 fibres up to 100 mum in length, and consistin g of co-aligned bundles of 30 nm-diameter defect-free single-crystal nanofi laments with a uniform growth tip. A model for the defect-free growth of Ba SO4 nanofilaments in aqueous polymer solutions based on amorphous precursor particles, vectorially directing forces and van der Waals attraction is pr oposed.