AOT microemulsions: droplet size and clustering in the temperature range between the supercooled state and the upper phase boundary

Abstract

The main focus of this work is the investigation of the mechanism of droplet aggregation and the droplet structure of water–AOT (sodium bis(2-ethyl hexyl) sulfosuccinate)–decane microemulsions between the supercooled state and the upper phase boundary by means of SAXS. We study the temperature dependent droplet structure and size in detail at compositions of droplet volume fractions ϕ = 0.1–0.4 and water/AOT molar ratios of ω = 5–40. We found a change in droplet size at varying temperatures and explain our results by the change of the effective droplet surface covered by an AOT molecule (between the two phase boundaries) and by macro-phase separated water ice below a certain supercooling temperature. We monitor the continuous change of droplet interaction by means of a phenomenological structure factor combining hard sphere interactions with a Lorentzian function accounting for droplet density fluctuations in the system. We analyse the droplet aggregates in dependency on ϕ and ω leading to a better understanding of droplet aggregation with increasing temperature.