Aggregation in a high internal phase emulsion observed by SANS and USANS

Date

2006

Authors

Zank, Johann
Reynolds, Philip
Jackson, Andrew
Baranyai, Krisztian
Perriman, Adam
Barker, John G
Kim, Man-Ho
White, John

Journal Title

Journal ISSN

Volume Title

Publisher

Elsevier

Abstract

As part of a wider study into high internal phase emulsions, we have prepared and studied by SANS and USANS the structure of an unstable emulsion consisting of 90% by volume saturated ammonium nitrate dispersed as micron-scale droplets in hexadecane, stabilised by the surfactant Pluronic L92. Similar emulsions produced using polyisobutylene-based surfactants, reported earlier, are highly stabilised by a significant number of surfactant rich reverse micelles a few nanometres in diameter in the oil phase. The aqueous-oil droplet interfaces are coated with a monolayer of surfactant, while a very small amount of surfactant is aggregated into micron-scale surfactant-rich objects. In contrast, the Pluronic emulsion contains an insignificant number of reverse micelles and a complex multilayered interface between oil and aqueous phases. Now, the great majority of added surfactant is in the form of micron scale, fractally linked, blocks of lamellar phase at the aqueous-oil droplet interfaces. The lamellar phase can be characterised by the Bragg peaks observed in three different isotopic contrasts by SANS. We attribute the shear instability of the Pluronic emulsion to the more hydrophilic nature of the surfactant which causes both depletion of reverse micelles in the oil phase, and aggregation into the blocks of lamellar phase.

Description

Keywords

Keywords: Emulsions; Micelles; Monolayers; Nanotechnology; Paraffins; Phase shift; Surface active agents; Ammonium nitrate; Hexadecane; Internal phase emulsion; Isotopic contrasts; Ammonium compounds Emulsion; Lamellar phases; Small angle neutron scattering; Ultra small angle neutron scattering

Citation

Source

Physica B

Type

Journal article

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2037-12-31