Aggregation energies of nonionic micelles calculated via pair potentials |
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Authors: | N Vila Romeu G Taddei |
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Institution: | (1) Department of Chemistry University of Florence via G. Capponi 9, I-50121 Florence, Italy e-mail: taddei@dada.it, IT |
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Abstract: | The aggregation energies of two different forms of nonionic isolated micelles belonging to a binary oil-in-water system were
calculated by using pairwise central potentials. One of the micelles is an elongated form (the spherocylinder); the other
one is a flat form (the square tablet). The spherocylinder and the square tablet degenerate into the same spherical micelle
at low aggregation numbers, whereas they form elongated cylinders and lamellae, respectively, at very high aggregation numbers.
Both forms are of particular importance in some nematic systems involving a phase transition. The interaction energy among
the polar heads of the amphiphilic molecules was calculated using a central Lennard-Jones potential. The interaction energy
among the hydrocarbon chains in the micelle bulk was calculated via a phenomenological potential model. The calculations were
performed considering a wide range of values of the parameters involved (i.e. polar head diameter, chain length). The entropic
contribution to the aggregation free energy is similar for both micelles, and so their relative stability depends principally
on the aggregation energy. The micelle aggregation energy depends strongly on the aggregation number and other geometrical
parameters for both forms. The present results are consistent with those obtained using the surfactant parameter model, which
permits the evaluation of the elastic bending energy of the micelle membrane for both forms.
Received: 29 March 1999 Accepted in revised form: 28 June 1999 |
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Keywords: | Colloids Amphiphilic aggregates Micelles Aggregation energy |
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