The phase transition from L₃ phase to vesicles and rheological properties of a nonionic surfactant mixture system

A sponge phase (L₃ phase) was observed in aqueous solution of a nonionic surfactant polyethylene glycol ether of tridecyl alcohol with the average 3 of ethylene oxide (CH₃(CH₂)₁₂(OCH₂CH₂)₃OH, abbreviated as Trideceth-3) with tetradecyldimethylamino oxide (\( {\mathrm{CH}}_3{\left({\mathrm{CH}}_2\right)}_{13}\overset{\overset{\mathrm{O}}{\uparrow }}{\mathrm{N}}{\left({\mathrm{CH}}_3\right)}_2 \), abbreviated as C₁₄DMAO). The L₃ phase can be transferred to planar lamellar phase after the bilayer was protonated by the formic acid formed through the hydrolysis of methylformate. The addition of surface charge into the nonionic L₃ phase through electrostatic repulsion on the ionic head groups will suppress the Helfrich undulation and induce the transition to planar lamellar phase. The planar lamellar phase can be transformed into multilamellar vesicles under shear. Rheological properties show that both of the storage modulus and the loss modulus of the lamellar phase were increased with the increment of surface charge density. The phase transition from L₃ phase to vesicles was characterized by rheological measurements, ²H NMR spectra, and transmission electron microscope (TEM) observations. To our best knowledge, this is the first example of a controlled phase transition in nonionic surfactant mixtures through protonation and shear forces. The procedure provides a direction on how to achieve phase transition in surfactant solution by changing the conditions and an application of phase transition of controlled materials.