Morphological Changes from Silica Tubules to Hollow Spheres Controlled by the Intermolecular Interactions within Block Copolymer Micelle Templates

The morphological changes from tubules to large hollow spheres to (micelle-sized) small hollow-spherical silica were realized by polystyrene-block-poly(vinylpyridine) (PS-b-PVP) block copolymer micelle templates by controlling the intermolecular interactions with the corona chains. PS-b-PVP with weak intermolecular interactions among PVP corona chains yields the coexistence of tubules, large hollow spheres, and small hollow spheres. The coexistence of the three phases arises from the direct aggregation of block copolymer micelles during hydrolytic condensation of a silica precursor (tetraethylorthosilicate), as evidenced by transmission electron microscopy. When the degree of intermolecular interactions within the PVP corona blocks is increased by a change in either the degree of quaternization of the PVP blocks or the dielectric constant of the medium, small hollow spherical silica, with size equivalent to the block copolymer micelles, were solely obtained. We believe that this morphological change is due to the fact that the dipole-dipole interactions among quaternized PVP blocks physically cross-link the PVP coronas in micelles resisting the curvature change during the silica condensation.This work was financially supported by the Korea Science and Engineering Foundation (KOSEF) through Acceleration Research funded by the Ministry of Education, Science and Technology (MEST; Grant R17-2007-059-01000-0) and by the NANO Systems Institute through the KOSEF (Grant R15-2003-032-02002-0). We also acknowledge financial support from the MEST through the Brain Korea 21 Program and the World Class University Program (400-2008-0230) at Seoul National University. Additional financial support from the NGNT Project (No. 10024135) supported by the Ministry of Commerce, Industry and Energy is greatly acknowledged