Study On The Rheo-reactive Kinetics Of Photosensitive Gemini Viscoelastic Micellar Systems

A novel reversible photorhelogical (PR) micelle system was investigated, which was composed of the cationic Gemini surfactant propylene-(dimethyldioctadecylammonium chloride) (18-3-18) and the photoresponsive counter ion,trans-4-phenylazo benzoic acid (trans-ACA). The influences of molar concentration ratio, temperature and pH on the viscosities of micellar systems were investigated, photorheological properties (rheological properties, microrheological properties and interfacial properties) under different irradiation conditions were studied and the rheo-reactive kinetic equation was established. Furthermore, drag-reduction properties of typical micellar systems were investigated. Main conclusions were made as follows:1) The viscoelastic micellar systems could be formed by Gemini 18-3-18 and trans-ACA in certain conditions. The optimum molar ratio of Gemini 18-3-18 and trans-ACA was about 1/1.25. The viscosity of micellar systems increased with increasing [ACA] at the same molar ratio, and the micellar systems showed good viscoelastical properties when [ACA]>6 mM. The optimum conditions were pH=7.0,30℃.2) Gemini 18-3-18/trans-ACA micelle system showed reversible photorheological properties. Initially, the 18-3-18/trans-ACA mixtures with proper compositions formed highly viscoelastic fluids, showing good viscoelasticity, thixotropy and shear thinning properties. After UV irradiation, rheological properties of 18-3-18/ACA micelles changed obviously, exhibiting UV photothinning property, because the trans-ACA was isomerized to cis-ACA. For 18-3-18/ACA (8 mM/10 mM) micelle system, after 1 h 365 nm UV irradiation, the reduction percentage of relative viscosity of the micelle was nearly 90%, and its thixotropy loop disappeared, the rheological properties of UV-irradiated micelle can recover after 10 h 465 nm visible light irradiation. The microrheological properties of systems showed corresponding changes.3) The process rheology could reveal the rheological property changes of micelle along with UV irradiation. For the proper Gemini 18-3-18/trans-ACA micelles, with the UV irradiation, the elastic modulus G’droped quickly while the viscous modulus G" rised. The rheokinetics equation was obtained to characterize the changing process of elastic modulus (G’) and complex viscosity (η*).4) The changes of interfacial viscoelasticity with different condition were investigated. For 20000 times of 18-3-18/trans-ACA (8mM/10mM) dilution, the surface tension increased by 45% while interface dilational modulus decreased by nearly 32% after 1 h UV irradiation, and these interfacial properties could recover after visible light irradiation. It revealed that the solution was a photo-sensitive surfactant solution with reversible interfacial rheological property.5) Gemini 18-3-18/trans-ACA micelle system showed good drag-reduction effect, and its drag-reduction properties decreased obviously after UV irradiation, and the drag reduction properties could be restored after the visible light irradiation.