Gibbsite systems for confocal microscopy studies

Abstract

This thesis describes the synthesis of large (fluorescent) gibbsite platelets and their phase behaviour studied by optical observations of Bragg reflections, polarized light microscopy, and confocal laser scanning microscopy. Large gibbsite platelets (500-700 nm) were synthesized via two different methods; the seeded growth method, in which small platelets are stepwise grown to larger sizes and the direct growth method, in which large platelets are obtained in a one-step synthesis. These platelets were either sterically stabilized with N-modified polyisobutylene or coated with silica. A fluorescent dye was successfully incorporated in both systems, and the resulting platelets were suitable for confocal microscopy studies. The phase behaviour of both systems was analyzed using observations of optical Bragg reflections and polarized light microscopy. For silica coated platelet dispersions phase separation was not observed. However, phase separation was observed for dispersions of sterically stabilized gibbsite; both in systems of fluorescent and non-fluorescent platelets. Confocal studies of this system reveal that the platelets form stacks which have a preferential orientation. However, long range positional order is not observed and therefore it is assumed that a columnar nematic phase is observed.