ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Explicit expressions have been derived for the two curvature constants k1 and k2 that mainly influence the size and shape, respectively, of generally shaped micelles (triaxial tablets with a thickness〈width〈length). It is found that geometrical packing constraints, together with an unfavorable hydrocarbon/water interfacial tension γhc/w, give rise to a large and positive contribution to both k1 and k2 that increases with the micellar thickness (equivalent to surfactant tail length) as well as with γhc/w. The constant k1 that mainly influence the size of the micelles may be brought down by electrostatics to values where rather small micelles are able to form. However, electrostatics also have a tendency to increase the constant k2 that mainly affects the length-to-width ratio of the micelles so that the smaller micelles are predicted to be rather disklike, i.e., with a low length-to-width ratio. In addition, residual head group effects as well as the free energy contribution due to the hydrocarbon chains may influence the micellar size and shape. In particular, it is demonstrated that mixing of two surfactants reduces k2 and promotes the formation of elongated micelles with a large length-to-width ratio whereas k1, and thus the overall size of the micelles, is only slightly influenced. The effect of mixing is predicted to increase with increasing asymmetry between the surfactants mixed in the micelles with respect to head group size and charge number as well as hydrophobic tail volume. © 2000 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1289885
Permalink
