Influence of bending energetics on the size, shapeand polydispersity of droplet microemulsions
2008 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 316, 15-26 p.Article in journal (Refereed) Published
A theory for ellipsoidal shape fluctuating droplet microemulsions in the presence of excess discrete phase (Winsor I and II) is expounded that combines bending energetics of the amphiphilic monolayer at the droplet interface with thermodynamics of self-assembling solute and amphiphilic molecules. The theory relates the three bending elasticity constants spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant () with interfacial tension, average size and shape and polydispersity of microemulsion droplets. It is demonstrated that the well-known conventional relations become modified as the entropy of self-assembling amphiphilic as well as solute molecules are taken into account, in particular at low values of the effective bending constant . As a result, the average droplet radius 〈R〉 as well as the droplet polydispersity σR/〈R〉 behave consistently in the limit whereas the conventional expressions are recovered in the limit . It is demonstrated that association entropy effects may be quantified by a parameter kS with same dimension and order of magnitude as kc and . kS is found to be always negative and tends to decrease 〈R〉 and to increase σR/〈R〉. Moreover, the average axial ratio of an oblate/prolate fluctuating droplet is found to be a strong function of the bending rigidity (the droplets become increasingly non-spherical with decreasing kc) but is independent of , in contrast to previous investigations where association entropy effects were neglected.
Place, publisher, year, edition, pages
Elsevier, 2008. Vol. 316, 15-26 p.
Self-assembly, Surfactant, Microemulsion, Bending elasticity, Solubilization
IdentifiersURN: urn:nbn:se:kth:diva-58918DOI: 10.1016/j.colsurfa.2007.08.012ISI: 000253710700003OAI: oai:DiVA.org:kth-58918DiVA: diva2:474379
QC 201201242012-01-242012-01-092012-01-24Bibliographically approved