Study On The Photo-responsive Rheological Behavior Of The Photosensitive Gemini Cationic Surfactant System

Two Gemini surfactants,propylene bis(octadecyl dimethyl ammonium chloride)(C18-3-Ci8)and ethylene bis(stearamide propylene dimethyl ammonium chloride)(G18(CONHCl)2),were mixed with trans-ortho-methoxycinnamic acid(trans-OMCA)and trans-4-phenylazo benzoic acid(trans-ACA),respectively,and two new types of photosensitive surfactant systems were successfully constructed.The effects of 365nm UV light and 460nm visible light on the rheological properties of the new photosensitive system were investigated.The rheokinetics process of the photosensitive systems during UV irradiation was studied.The microrheological properties of the C18-3-Ci8/trans-OMCA system before and after UV irradiation were studied,and its microstructure was characterized.The main conclusions were made as follows:1)A novel irreversible photothickening system C18-3-C18/trans-OMCA were prepared.Initially,14mM/14mM C18-3-Ci8/trans-OMCA solution was a low-viscosity Newtonian fluid with no thixotropy and viscoelasticity.After UV irradiation,20mL solution transformed into a gel-like viscoelastic fluid with high viscosity,and showed shear thinning characteristics and thixotropy.The steady shear viscosity(200s-1)increased by 20.7 times and the elastic modulus increased by more than 2 orders of magnitude.After UV irradiation,the macromolecular viscosity index and elastic index increased obviously,and the flow index and solid-liquid equilibrium value decreased obviously.The results showed that the viscoelasticity of UV-irradiated solution was significantly enhanced,its liquidity significantly weakened.2)The dynamic changing of the rheological properties of the C18-3-C18/trans-OMCA photothickening systems during UV irradiation were obtained.After the UV lamp opening,the elastic modulus,viscous modulus,and complex viscosity of the system increased rapidly.At the end of illumination,the elastic modulus of 12mM/12mM C18-3-C18/trans-OMCA system increased by more than 60 times.The established rheokinetics model could well describe the experimental data.After UV irradiation,the vesicles transform into wormlike micelles that causes the rheological changes above.The theory of molecular packing parameter could well explain aggregate transition.3)The rheological properties of new reversible photothinning systems Gi8(CONHCl)2/trans-ACA before and after UV/visible light irradiation and the dynamic changing of its rheological properties during UV irradiation were obtained.Before illumination,20mL 8mM/12mM Gi8(CONHCl)2/trans-ACA wormlike micellar system showed high viscoelasticity and obvious shear thinning property,forming a thixotropic loop with stress overshoot.After 1h of UV irradiation,steady shear viscosity(200s-1)decreased by 83.8%,and the elastic modulus and the area of the thixotropic loop decrease obviously.The viscoelasticity of the UV-irradiated micellar system was restored after 3h visible light irradiation.