Jasper L. Dickson

Synthesis and properties of semifluorinated block copolymers containing poly(ethylene oxide) and poly(fluorooctyl methacrylates) via atom transfer radical polymerisation

Abstract Amphiphilic block copolymers of poly(ethylene oxide) (PEO) and poly(fluorooctyl methacrylates) were synthesised by atom transfer radical polymerisation of semifluorinated methacrylates such as 1H,1H-perfluorooctyl methacrylate, and 1H,1H,2H,2H-perfluorooctyl methacrylate using PEO macroinitiators. The use of mono- and difunctional initiator led to AB and ABA block copolymers with controlled molecular weights. The linear time dependence of ln([M]0/[M]) is consistent with a controlled polymerisation i.e. first-order in monomer concentration. Various block copolymers could be prepared by varying the ratio of monomer to macro-initiator. The copolymers self-assembled in chloroform to form micelles, which was evidenced by dynamic light scattering and transmission electron microscopy. Different morphologies of spheres and rods were observed by changing the copolymer composition. In addition, these surfactants lower the interfacial tension between water and supercritical carbon dioxide to stabilise water-in-carbon dioxide emulsions.

Water-in-carbon dioxide emulsions stabilized with hydrophobic silica particles

W/C emulsions were stabilized using hydrophobic silica particles adsorbed at the interface, resulting in average droplet diameters as low as 7.5 microm. A porous cross-linked shell was formed about a hydrophilic (colloidal and fumed) silica core with a trifunctional silylating agent, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethyoxysilane, to render the particles CO(2)-philic. The stability of emulsions comprising equal weights of CO(2) and water was assessed with visual observations of settling fronts and the degree of emulsion coalescence, and the average drop size was measured by optical microscopy. The effect of CO(2) density on both emulsion stability and droplet size was determined quantitatively. The major destabilizing mechanism of the emulsions was settling, whereas Ostwald ripening and coalescence were not visible at any density, even over 7 days. Flocculation of the settling droplets did not occur, although gelation of the emulsions through particle interactions resulted after longer periods of time. CO(2)-philic particles offer a new route to highly stable W/C emulsions, with particle energies of attachment on the order of 10(6)kT, even at CO(2) densities as low as 0.78 g ml(-1). At these low densities, surfactants rarely stabilize emulsions as the result of poor surfactant tail solvation.