Microemulsions possess promising electrolyte capacity due to their constituent polar and nonpolar regions. Using fluorescence, the behavior of multiple small molecules, including ionic (rhodamine 6g, r6g), polar(coumarin 153, c153), and amphiphilic (laurdan), were studied in these complex fluids. All probes investigated were found to associate with the surfactant region despite their structural differences. In fact, the r6g and c153 were in close enough proximity to exhibit FRET, highlighting the nonselective nature of the microemulsion environment. While the hydration of the surfactant layer was found to increase linearly with water addition, this trend did not mirror the rotational dynamics of c153 and r6g. Specifically, fluorescence anisotropy results show that the probes’ rotational time decreases until the water content reaches 60%, but the rotational time increases after further dilution. This stiffing of the surfactant layer at higher water content potentially correlates to a more significant change in the microemulsion structure away from being bicontinuous. Overall, these studies elucidate not only the capability of these microemulsions to host a range of small molecules in the surfactant layer but also probe the larger solution structure of these heterogeneous fluids

Fluorescence studies of small molecule dynamics in toluene/polysorbate-20/water microemulsions

ACS Fall 2021

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