Synthesis And Property Study Of A Dual CO₂/N₂-light Stimuli-responsive Surfactant Containing AZO Phenyl Group

Stimuli- responsive surfactants, stimuli-responsive surface-active particles, and their smart systems have been received increasing interest in recent years. The surface activity of these functional chemicals can be controled on damond, which will influence the micro and macro properties of the system. The responsive surfactants can be used reversibly, cleanly, and importantly without changes in composition or thermodynamic conditions. This exciting field has economic and environmental implications for reducing surfactant usage, waste and process remediation costs. C urrently, a variety of triggers has been reported, typically including electrochemistry, light irradiation, p H, temperature, magnetic-field intensity etc. Among these triggers CO₂ is low cost, environmentally benign, easily removed. Light irradiation is another superior trigger without the need to add chemicals, and the wavelength, polarization direction and intensity of the light can be easily controlled.Currently, many attempts have been reported on single stimuli- responsive surfactants, while dual or multiple stimuli- responsive surfactants is less documented. For example, the reversible transformation of CO₂/N₂ switchable surfactant relies on its hydrophilic group, while the hydrophobic part is short of regulation.Therefore the wettability and interfacial tension can’t be controlled faintly.In this paper, photosensitive azo phenyl group is introduced to the structure of CO 2/N₂ switchable surfactants, which enable an extra control over the hydrophobic part of the surfactant by UV or visible light. A series of CO₂/N₂-light dual stimulI-responsive surfactants bave been successfully synthesized. Dual control over interfacial and bulk solution properties can be achieved using the surfactants. And the dual responsivity of self-assembly aggregates of the mixture of the surfactants with other convient surfactants or nanoparticles are also studied.Dual CO₂/N₂-light stimulus- responsive foa ms can be fabricated using the responsive sur factant in aqueous solut ion. The C O2/N₂ switchablility of t he foa m is depending on the conversion between tertiary a mines and surface active bicarbonate salts by bubbling CO₂ and N₂. The foams could also be readily decomposable and regenerated while exposed to UV and blue light alternately.A dual stimuli- responsive reversible change of fluid viscosity with CO₂ and photo triggers can be prepared by addition of the dual stimulli-responsive surfactant into the classic CTAB-NaSal worm micellar system. On one hand, the viscosity of CTAB-NaSal-AZO ternary system can be repeatedly and reversibly switched be tween high viscosity（268.07 Pa*s） and low viscosity（0.02 Pa*s）, while CO₂ is cyclically bubbled into and removed from the solution and the cryo-TEM further confirmed the transformation of micellar structure from worm micelles to spherical micelles. On the other hand, reversible viscosity change can occur as well upon light irradiation, however, the micellar structure transformed from worm micelles to vesicles, which can attribute to the reversible trans-cis photoisomerization of the surfactant.Dual stimulli-responsive surface active nanoparticles can be achieved by interacting with CO₂/N₂-light dual stimuli- responsive surfactant and nanoparticles. CO₂/N₂-light dual stimuli-responsive Pickering emulsions can be formed by the partilces. The Pickering emulsion can be reversibly transformed between stable and unstable at ambient temperature rapidly via the N₂/CO₂ trigger, and on the other hand a reversible change in droplet size and rheological properties of the emulsion can occur upon light irradiation without changing the particle/surfactant concentration and undergoing demulsification/ re-homogenization cycles.Coffee-ring effect can be regulated by UV/blue light irradiation or CO₂/N₂ using negatively charged polystyrene nanoparticles in combination with a trace amount of the stimuli-responsive surfactant. The viscosity and stability of polystyrene nanoparticles can be changed by UV/blue light irradiation or CO₂/N₂, which leads to revisible change of droplet evaporation deposition pattern between ring and plate.