| Colloidal liquid aphrons (CLA) are surfactant-stabilized droplets (1--50 microns in diameter) of a nonpolar liquid dispersed in a continuous aqueous phase. The small dimensions of CLA provide very large interfacial areas and short diffusion path lengths; consequently interphase solute transfer can often be completed within seconds. The interfacial structure and mass transfer properties of CLA emulsions were investigated in this research. Applications of CLA emulsions in multiphase enzymatic and whole-cell biocatalysis were also developed.; A variety of experimental tools were used to characterize the interfacial structure of CLA emulsions, including freeze fracture transmission electron microscopy, differential scanning calorimetry, small angle x-ray scattering, and Isothermal titration calorimetry. Results indicate the presence of liquid crystalline bilayers surrounding the organic phase in CLA emulsions. These layers are formed by the interaction between the two surfactants used in CLA formulation. The energetics and stoichiometry of the surfactant interaction were measured. A conceptual model of the mechanism stabilizing CLA emulsions was developed.; The mass-transfer properties of CLA emulsions mere measured experimentally using two approaches. The first approach involved the direct measurement of heptanoic acid diffusion from the CLA emulsions into the water phase. The second approach involved indirect measurement via coupling the mass-transfer of the solute (p-tolyl acetate) to a chemical reaction (alkaline hydrolysis). The local mass transfer coefficient of the surfactant shell (KL,shell ) was estimated to be about ∼30 x 10-3 cm/s, which is comparable to KL values for surfactant-free, liquid-liquid systems at an equivalent void fraction (&phis;). The volumetric mass transfer coefficient (KLa) for CLA were 5 to 20 times higher than those for conventional emulsions.; Application of CLA emulsions to enzymatic and whole cell biocatalysis was demonstrated. The dynamic resolution of L,D phenylalanine was carried out in a multiphase system using porcine pancreatic lipase. The CLA emulsions were found to reduce the time required to attain equilibrium by about four-fold over conventional contacting methods. A statistical design of experiment approach was used to identify the major variables affecting equilibrium conversion and enantiomeric excess. The use of CLA emulsions in the biotransformations of cinnemaldehyde by Baker's yeast at high cell densities (250g/L) using a non-toxic solvent (2,2,4 trimethyl pentane) was also studied. The selectivity of this transformation was influenced by the presence of CLA emulsions.; Reversible emulsions formed using novel block-graft copolymeric emulsifiers (Polymethacrylic acid (PMAA)-g-Ethylene Glycol (EG)) were investigated. Such emulsions show considerable promise in multiphase contacting, since the emulsions produced can be maintained stable as long as desired and then coalesced on demand by a small pH change. |
