Additives-induced smart micelles and photorheological response in the cationic surfactant solutions

In this paper, we report the rheological properties of the photorheological fluid by using steady state test and frequency sweep measurement. The fluids are consisted of the cationic surfactant (3-hexadecyl-2-hydroxypropyltrimethylammonium bromide, R16HTAB), sodium salicylate (NaSal) and commonly photosensitive aromatic compound (sodium trans-ortho-methoxycinnamic acid, trans-NaOMCA). Initially, systems of R16HTAB/trans-NaOMCA and R16HTAB/NaSal in basic solution are able to self-assemble into long wormlike micelles, inspiring a high viscoelasticity of the sample. After adding NaSal (or NaOMCA) to the R16HTAB/NaOMCA (or R16HTAB/NaSal) aqueous solution, the viscosity of the mixed solution was reduced. All systems containing NaOMCA show photoresponsive character. Under ultraviolet light, OMCA undergoes a photoisomerization from trans form to cis form, which changes the molecular packing at the micellar interface, shortens the length of the wormlike micelles to decrease the viscosity of the systems.