Self vesicle fusion process

Considerations of the packing parameter concept of Israelachvili et al. [1] suggest that double-chain surfactants, which form the basis of measurements described in this article, cannot readily form spherical micelles. With double-chain surfactants, a more likely aggregate structure is the formation of bilayer vesicles, which can be also thought of as a dispersed lamellar phase (La) as such the vesicular dispersed form is likely to be preferentially formed at low concentrations ( 1 mmol dm-3) of surfactant. Furthermore, it is necessary to consider the possibility, unlike in the case of micelles, that such vesicles, formed by self-assembly of surfactant monomers, will not be thermodynamically stable. The instability is then likely to be in the direction of growth to a thermodynamically-stable lamellar phase from the vesicles. This process will be driven, at least initially, by fusion of two vesicles. 

To date there appear to be no equations available to describe the corresponding situation in vesicle systems. One reason for this is that the equilibrium state of vesicles is still not clearly established. Many systems are unstable and the usual transition is to return (by fusion of vesicles) to a lamellar state from which the vesicle system is often formed in the first place, which can be a very slow process. However, this is certainly not always the case. The problem of vesicle stability has been discussed in general terms by Luisi who suggests the following as some of the criteria for establishing whether or not a self-assembly system is at chemical equilibrium ... 

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