Lipid-water interfacial free energy

A special group of lipids that possess both hydrophilic and hydrophobic (lipophilic) parts are termed as amphiphiles or amphipathics and are also referred to as surfactants. They adsorb at surfaces or interfaces and change the interfacial free energy associated with the building of an interface. A surfactant molecule consists of two distinct chemical groups (i) the head which is hydrophilic (water-loving) and (ii) the tail which is hydrophobic (water-fearing). 

It turns out that such terms have the correct order of magnitude and the expected behaviour, which can be verified by using electrostatic models to compute the derivative in Eq. (16). It is thus highly plausible that the strong interfacial adsorption of the chaotropic anions both affects the intra-bilayer free energy and contributes to the osmotic pressure in ways that have not been quantified until now. The work described here demonstrated that the level of existing theory for lipid bilayers and for the structure and thermodynamics of the water-lipid interface in the presence of ions is very unsatisfactory. Further progress with this model system can only be achieved if more theoretical work is carried out, probably assisted by computer simulation, to elucidate what happens at these important interfaces in the presence of electrolytes. 

Properties of Component Phases The composition and physicochemical properties of both the oil and aqueous phases influence the size of the droplets produced during homogenization (52). Variations in the type of oil or aqueous phase will alter the viscosity ratio, ri ,/ri(-, which determines the minimum size that can be produced under steady-state conditions. The interfacial tension of the oil-water interface depends on the chemical characteristics of the lipid phase, e.g., molecular structure or presence of surface-active impurities, such as free fatty acids, monoacylglycerols, or diacylglycerols. These surface-active hpid components tend to accumulate at the oil-water interface and lower the interfacial tension, thus lowering the amount of energy required to disrupt a droplet. 

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