Investigation of W/O microemulsion droplets

by contrast variation light scattering

ANUJ SHUKLA^1,2,* and REINHARD H H NEUBERT¹

¹Department of Pharmacy, Institute of Pharmaceutics and Biopharmaceutics,

Martin-Luther-University Halle-Wittenberg, D-06120 Halle/Saale, Germany

²Present address: Lehrstuhl f\"{u}r Physikalische Chemie II

Universit\"{a}t Dortmund, Otto-Hahn-Str. 6 D-44227 Dortmund, Germany

^*Corresponding author. E-mail: anuj.shukla@uni-dortmund.de

Abstract. Dynamic and static light scattering experiments have been

performed at various molar ratios ($\mu$) of water to AOT and

temperatures on water-in-oil (W/O) microemulsions dispersed in

n-heptane, n-octane, and n-nonane. Size and shape fluctuations

of microemulsion droplets are determined with very high

precision because polydispersity influences the characteristic

features of scattering data as well as the hydrodynamic radius with

$\mu$. Self-consistent interpretation of dynamic and static light

scattering data using optical properties and packing consideration

on the basis of the layered sphere model are obtained. The estimated

extent of polydispersity index of 17\% is found, whereas the

polydispersity is independent of the alkane types. The geometrical

parameters, e.g., hydrodynamic radius, area per head group of the

surfactant molecule and thickness of the surfactant layer of

microemulsion droplets are also estimated and compared in three

different $n$-alkane types. The best interpretation of the

temperature dependence of data has shown a transition from spherical

droplets to ellipsoid aggregates with increasing temperature. Axial

ratio increases with increase of temperature and the longer the

alkane the larger is the axial ratio. The parameters describing the

polydispersity and shape change are in agreement with theoretical

and experimental results found in the literature.

Keywords. Microemulsions; static and dynamic light scattering.

PACS Nos 68.05; 78.35