Anomalous Spectral Modulation of 4-Aminophthalimide inside Acetonitrile/AOT/ n-Heptane Microemulsion: New Insights on Reverse Micelle to Bicontinuous Microemulsion Transition

Small Molecule Sorting: A Fluorescence Study of Microemulsions

The application of microemulsions to a wide range of industries relies on their ability to solubilize small molecules with vastly different structures. Herein, we use multiple fluorescence techniques to probe ionic (rhodamine 6g, r6g), polar (coumarin 153, c153), nonpolar (diphenylanthracene, DPA), and amphiphilic (laurdan) small molecules in a nonionic, bicontinuous microemulsion of varying hydration. All fluorophores investigated were found to associate with the surfactant region despite their different structures and properties. The hydration of the surfactant layer was found to increase linearly with water addition, but while this initially increases the fluidity of the surfactant layer, fluorescence anisotropy of c153 and r6g indicates a stiffening of the surfactant at water content >60%. This stiffening of the surfactant layer at higher water content correlates with a morphological change in the microemulsion from a bicontinuous structure to droplets. In contrast, the nonpolar DPA shows a change in partitioning as hydration changes, increasing its association with the oil domain. Overall, these studies elucidate not only the capability of these microemulsions to host a range of small molecules in the surfactant layer with tunable position but also the ability to probe the driving force of bulk structural changes in these heterogeneous fluids.

Freestanding organogels by molecular velcro of unsaturated amphiphiles

A simple amphiphile, N-cardanyltaurine amide (NCT) with different degrees of cis-unsaturation in its tail resulted in the formation of strong organogels. Interestingly, this is in contrast to the commonly accepted notion that introducing unsaturation in alkyl chains enhances fluidity in lipid assemblies. The physico-chemical and first-principles DFT calculations confirmed the pegging of 'kinked' unsaturated side chains, where the hydrophobic interlocking as in Velcro fasteners leads to a network of cylindrical micelles, resulting in self-standing organogels. Textural profile analysis and spectroscopic details substantiated the dynamic assembly to resemble a 3D network of gelators rather than being a cross-linked or polymerized matrix of monomers.