Synthesis And Properties Of Novel Dual Stimuli-responsive Surfactants

Stimuli-responsive?switchable?surfactants are amphiphiles that can be responsive to an external stimulus which activates changes in molecular structures so that can achieve reversible conversion between “surface-active” and “non-surface-active” state.Currently,there has been a growing interest in smart systems formed by stimuli-responsive surfactants.In recent years,a variety of stimuli-responsive surfactants sensitive to external triggers,such as pH,light irradiation,magnetic field,redox,and CO₂/N₂,have been extensively reported.Triggers of redox are of particular interest because similar processes with oxygen metabolism occur constantly in life entities.Therefore,the development of redox stimuli-responsive surfactants are important for the research of bioscience.Meanwhile,many studies on single stimuli-responsive surfactants have been reported,while dual or multiple stimuli-responsive surfactants are less documented.Single stimuli-responsive surfactants can only achieve one regulation of hydrophilic group or hydrophobic group,while dual stimuli-responsive surfactants can achieve both regulation,therefore the self-organized structure and the interface behavior can be controled precisely,which not only giving surfactant more functional,but also wider application of surfactant in advanced technology.A dual stimuli-responsive surfactant,11-tertiary-amine-1-carbonyl ferrocenyl(C₁₁-N-Fe),was synthesized by introducing ferrocene group into the terminal tail of a tertiary amine surfactant.C₁₁-N-Fe can be reversibly transformed between surface active and inactive state via pH adjustment of the system,and can be reversibly transformed between bola-type and cationic-type surfactant via adding oxidant or through electrochemical reducation reaction.C₁₁-N-Fe hydrochloride has good foaming and emulsifying properties and the stability of foams and emulsions responses to pH and redox.The negatively charged silica nanoparticles can be hydrophobised in situ through electrostatic interaction with C₁₁-N-Fe bicarbonate,then the modified silica nanoparticles can threfore stabilize n-decane-in-water Pickering emulsions.Through bubbling/removing CO₂ of the system or reduction/oxidation of surfactant,the emulsions were almost completely demulsified.Meanwhile,oxidation or reduction of C₁₁-N-Fe bicarbonate resulted in the inversion of CO₂/N₂ trigger.Meanwhile,inversion of CO₂/N₂ trigger can occur after oxidation or reduction of C₁₁-N-Fe bicarbonate,thus stimuli-response time required is significantly reduced.Anthor dual stimuli-responsive surfactant,sodium double-undecyl-diselenidecarboxylate(D₁₁-Se-COONa),was synthesized by introducing selenium into the terminal tail of a sodium carboxylate surfactant.The binary mixed system of such surfactant with cationic surfactant such as CTAB in aqueous solution give birth to a dual stumuli-responsive viscoelastic wormlike micelle through self-assembly,which have both CO₂ and redox responsive properties.On the one hand,the zero shear viscosity of binary system can be transformed between 80 Pa·s and 0.02 Pa·s when bubbling/removing CO₂ of the system alternately.On the other hand,the viscosity of binary system can also be adjusted by adding H2O₂/Na2SO3 into the system alternately,and the reduction processes can be achieved within 4 min.