Mass transfer interfacial stability, effect

Immobilization onto a solid support, either by surface attachment or lattice entrapment, is the more widely used approach to overcome enzyme inactivation, particularly interfacial inactivation. The support provides a protective microenvironment which often increases biocatalyst stability, although a decrease in biocata-lytic activity may occur, particularly when immobilization is by covalent bonding. Nevertheless, this approach presents drawbacks, since the complexity (and cost) of the system is increased, and mass transfer resistances and partition effects are enhanced [24]. For those applications where enzyme immobilization is not an option, wrapping up the enzyme with a protective cover has proved promising [21]. 

The gas/liquid and liquid/liquid systems are relevant to biomedical and engineering applications. The large interfacial area in foams, macro- and microemulsions is suitable for rapid mass transfer from gas to liquid or liquid to gas in foams and from one liquid to another or vice versa in macro- and microemulsions. The formation and stability of these systems may be influenced by the chain length compatibility which may also influence the flow through porous media behavior of these systems. Therefore, the present communication deals with the effect of chain length compatibility on the properties of monolayers, foams, macro- and microemulsions. An attempt is made to correlate the chain length compatibility effects with surface properties of mixed surfactants and their flow behavior in porous media in relation to enhanced oil recovery. 

The choice of a phase volume ratio for the two-phase bioconversion was made after examining the modulating effects of this parameter on the en me activity, stability, and enantiospecificity. The volume fraction of the organic phase in a two-liquid phase system may modulate the biohydrolysis of GPE in two ways. Firstly, different phase volume fractions may cause different interfacial areas due to altered degrees of emulsification under the same mixing condition, which may change the mass-transfer rate of the substrate to the aqueous phase as well as that of the product to the organic phase. Secondly,... 

Marangoni effects] nonequilibrated phases/local mass transfer leads to local changes in surface tension and stability analysis yields stable interfacial movement. 

In the next paper Surfactants Effects on Mass Transfer in Liquid-Liquid Systems Dr Alcina Mendes (Imperial College, UK) reviews the work done by herself and co-workers on the effect of surfactants on mass transfer in binary and ternary liquid-liquid systems. The selected organic-aqueous interfaces has been visualised during the mass transfer process in the presence of ionic and non-ionic surfactants. Results obtained in laboratory and under microgravity conditions are reported. The most significant finding is that surfactants in some cases can induce or increase convection. The latter enhance the mass transfer rate as compared to the Pick s law. The latter means that surfactants can be used to manipulate interfacial stability and particularly in space applications. 

Emphasizing equilibrium phenomena, flow, transport, and stability, Intcrfacial Phenomena Equilibrium and Dynamic Effects, Second Edition presents a concise and current summary of the fundamental principles governing interfacial interactions. This new edition features updated and expanded topics in every chapter. It highlights key experimental techniques that have expanded the scope of our understanding, such as in mass transfer, microstructure determination in colloidal dispersions, and surfactant-polymer interactions. 

Finally, we consider the effect of interfacial turbulences, which are due to mass transfer across the phase boundaries, on the stability of emulsion films. Experimentally, the diffusion transfer of alcohols, acetic acid, and acetone has been studied [549,550]. The observed destabilization of the films can be attributed to the appearance of Marangoni instability [494]. The latter manifests itself through the growth of capillary waves at the interfaces, which eventually can lead to film rupture. Lin and Brenner [521] examined the role of the heat and maSs transfer in an attempt to check the hypothesis of Holly [551] that the Marangoni instability can cause the rupture of tear films. Their analysis was extended by Castillo and Velarde [552], who accounted for the tight coupling of the heat and mass transfers and showed that it drastically reduces the threshold for Marangoni convection. 

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