Hypothesis -Hydrogen-bonding capacities of polar nonaqueous media significantly affect selfassembly behaviours of surfactants in these media.Introduction -Glycerol, a nonaqueous hydrogen-bonding solvent, is widely used in industrial formulations due to its desirable physical properties. Surfactants are ubiquitous in such applications; however, surfactant self-assembly in glycerol is not well understood.Methods -The microscopic structure of the gel phase was studied using a series of imaging techniques: polarised light microscopy (PLM), confocal laser scanning microscopy (CLSM), and environmental scanning electron microscopy (ESEM). The rheological properties of the gel were studied using viscometry and oscillation rheology measurements. Further nanostructural characterisation was carried out using small-angle neutron scattering (SANS).Results -We have observed the unexpected formation of a microfibrillar gel in SDS and glycerol mixtures at a critical gelation concentration (CGC) as low as ~ 2 wt%; such SDS gelation has not been observed in aqueous systems. The microscopic structure of the gel consisted of microfibres some mm in length and with an average diameter of D ~ 0.5 μm. The fibres in the gel phase exhibited shear-induced alignment in the viscometry measurements, and oscillation tests showed that the gel was viscoelastic, with an elastic-dominated behaviour. Fitting to SANS profiles showed lamellar nano-structures in the gel microfibres at room temperature, transforming into cylindrical-micellar solutions above a critical gelation temperature, T CG ~ 45 o C.Conclusions -These unprecedented observations highlight the markedly different selfassembly behaviours in aqueous and nonaqueous H-bonding solvents, which is not currently well understood. Deciphering such self-assembly behaviour is key to furthering our understanding of self-assembly on a fundamental level.

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Understanding morphological transformations upon temperature-induced mesophase transitions offers mechanistic insights into the self-assembly process. We have recently reported the unexpected formation of a microfibrillar lamellar gel in SDS-glycerol mixtures above a critical gelation concentration (CGC) as low as ~2 wt%. The gel phase comprised a fibrillar structure on the microscale and a lamellar structure on the nanoscale. Here, the nanoscopic structure of the gel as a function of temperature was probed with small-angle neutron scattering (SANS). The gel underwent a gel-to-fluid transition at a critical gelation temperature, T GC = 45 • C, forming cylindrical micelles at elevated temperatures. Upon cooling, a hexagonal phase formed at ~T GC , evident from the SANS Bragg peaks. This hexagonal phase upon the fluid-to-gel transition sheds light on the gelation mechanism, in which self-assembled SDS micelles undergo a cylindrical-to-lamellar morphological transition via a hexagonal phase. This unprecedented observation also highlights the complexity of self-assembly in nonaqueous hydrogenbonding rich media.

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