Aging and Stability of Vesicular Dispersions

Hassan Madani, Eric W. Kaler

Research output: Contribution to journalArticlepeer-review

40 Scopus citations

Abstract

Vesicle dispersions formed by sonication of aqueous dispersions of the synthetic surfactant sodium 4-(r-heptylnonyl)benzenesulfonate (SHBS) have been characterized with quasielastic light scattering (QLS) and electrical conductivity as a function of time. We present evidence that SHBS vesicles grow by means of size disproportionation, wherein surfactant monomers diffuse from small vesicles to large ones. The average size of the vesicles increases with time t as t0 3, and the total number of vesicles decays as t-0,6, while the exponents predicted for diffusion-limited growth are respectively 0.33 and -0.67. Size distribution measurements show that the vesicle population is nearly monodisperse immediately after sonication but becomes polydisperse with age. Vesicle stability and size are strong functions of the sonication process, temperature, and electrolyte concentration. For example, vesicles formed by indirect sonication using a cup sonicator are more stable than those formed by sonication with the sonicator probe in direct contact with solution. Liquid crystals are observed in samples formed by direct sonication seconds after sonication, while they appear 24-48 h after sonication in samples made by indirect sonication. SHBS vesicles are more stable in electrolyte solutions due to reduction of surfactant solubility.

Original languageEnglish (US)
Pages (from-to)125-132
Number of pages8
JournalLangmuir
Volume6
Issue number1
DOIs
StatePublished - Jan 1 1990

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