30. effects of ethanol on aot/n-heptane reverse micelle systems

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Agile - CaliBaja Center for Resilient Materials & Systems
Faculty Advisor(s): Olivia A. Graeve

Primary Student
Name: Robyn Elizabeth Ridley
Email: reridley@ucsd.edu
Phone: 858-246-0146
Grad Year: 2020

As the use of reverse micelles for nanoparticle synthesis has become more prevalent, we seek to better understand the effects of solvent miscibility on surfactant self-assembly by studying the effects of ethanol on sodium bis (2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in heptane. Using dynamic light scattering (DLS) to measure reverse micelle size, three distinct behavior regimes and a point of destabilization have been identified with regards to the amount of ethanol in the system. Comparisons to literature are made to hypothesize the structures present in these systems and the conditions resulting in reverse micelle destabilization. In low ethanol content systems, ethanol-to-surfactant ratio w = 0 - 20, DLS reveals narrow size distributions which are qualitatively consistent with those of known reverse micelle systems. In this regime it has also been found that the average reverse micelle size decreases with increased ethanol content. For midrange ethanol content, w = 30 - 40, DLS measurements have bimodal distributions indicative of a change in self-assembled surfactant morphology from spherical reverse micelles to elongated prolate structures. At w = 50, DLS measurements have multimodal size distributions across three orders of magnitude (nm to μm) revealing a lack of order in the system characteristic of reverse micelle system destabilization. In high ethanol content systems, w = 60 - 80, DLS gives wide, positive skew size distributions which suggests a departure from symmetric surfactant aggregations. It was also found that there is no increase to average assembly size with additional ethanol in this regime, signifying a threshold exists beyond which ethanol adds to bulk solvent without interacting with AOT self-assembly structures. Overall, our preliminary results give evidence of AOT micellization despite solvent miscibility and indicate that significant interactions between ethanol and AOT dictate surfactant aggregate shape and size.

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