Photoresponsive Oil/water Interface Regulated By Azobenzene Surfactants

Inspiration of nature has been the source of scientific exploration,and a great scientific challenge in the field of soft matter is how to create responsive materials,which can dynamically and"adaptively"change their structure and function on demand,in response to the stimulation of environmental changes.Especially those smart materials that can be switched between"open"and"off"state,have been a major scientific focus for decades.Environmental stimuli-responsive smart materials can dynamically change their structure and function on demand,in response to stimuli generated by environmental changes(including temperature,p H,salt,light,electricity,magnetic field,etc.),and play an important role in biomedicine,optical system,oil mining and other fields.However,there are many challenges to building and developing smart systems.On the one hand,each component of the smart material system plays the structural,functional or responsive role,respectively,and thus the composition and structure of the system are complex,as well as the preparation technology and regulation mechanism.On the other hand,due to the hydrophobicity of some specific components,their functionality in water is weakened or even lost,which limits the development and application of smart aqueous system.Environmental stimuli-responsive surfactants can open the molecular"switch"with the change of environmental conditions,and change the molecular structure,resulting in changes in the surface interface performance and the self-assembly structure accordingly.Using stimuli-responsive surfactants and their self-assembled micelles to stabilize and regulate functional components and interfaces,it can not only regulate the structure and properties of functional aqueous system through environmental stimuli,endowing the system with responsiveness,but also reduce the complexity of the system,making the construction and regulation of smart system easier.In this work,we designed and synthesized three new surfactants and amphiphilic molecules containing azobenzene group.Azobenzene surfactants are typical photo-responsive surfactants,and light is an efficient,harmless,non-invasive environmental stimulus that does not change the composition of the system.are used Through changing the molecular structure of azobenzene surfactants in situ by light,adjust the molecular stacking and arrangement,and then regulate the oil/water interface and the self-assembled micelles,so as to control the structure and properties of micro/nano aqueous systems by p H,light and other environmental stimuli.These studies include the control of the interphase interfacial curvature of the perfluorohexane-heptane-water(H/F/W)three-phase complex emulsion by p H and light dual-stimuli response,to achieve topological conformation transition;{Mo₁₃₂}soft-oxometallates(SOMs)colloids were constructed by micellar template method,and the particle size and electrochemical properties of SOMs were regulated in situ by light;The transformation of the swelling behaviour of polyelectrolyte microgels were induced by micellization of surfactants inside microgels,and the in situ swelling of microgels was further controlled by light.The research work includes:(1)Design and synthesis of novel photoresponsive azobenzene surfactants:a polyamine head and azobenzene containing non-ionic surfactant,C₁₀Azo N₃,and a series of imidazole head and azobenzene containing cationic surfactant,C_mAzo IMB(m=0,2,4,6,8).The correctness of the molecular structure was characterized by ¹H NMR,¹³C NMR and ESI-MS.(2)The p H and photo dual stimuli-responsive surfactant,C₁₀Azo N₃,was used to change the interfacial tension between heptane-water,so as to control the interfacial curvature of heptane-perfluorohexane-water(H/F/W)three-phase complex emulsion,making the reversible conversion of the emulsion between H/F/W double emulsion,Janus emulsion and F/H/W double emulsion by p H variation and light.The results showed that with the addition of C₁₀Azo N₃ induced the conversion from H/F/W double emulsion through Janus emulsion to F/H/W double emulsion.The p H variation and UV/Blue light irradiation induced the change of the interfacial tension of heptane-water and thus the change of the interfacial curvature of the complex emulsion,which further realized the reversible transition between Janus emulsion and F/H/W double emulsion.(3)Based on azobenzene surfactant(C₁₀Azo N₃)micelles as template and anion{Mo₁₃₂}as oxometallate unit,a UV-responsive surfactant-POM composite colloids,soft-oxometallates(SOMs),was prepared by electrostatic adsorption.The size and stability of the C₁₀Azo N₃ micelle template and SOMs were controlled by adding cyclohexane and changing the concentration ratio of C₁₀Azo N₃ and{Mo₁₃₂},while the size of the C₁₀Azo N₃ micelles and SOMs were reduced by UV irradiation.It was found that the presence of C₁₀Azo N₃ had no effect on the redox potential of Mo^V/Mo^VI in{Mo₁₃₂}clusters,but the cyclic voltammetry current decreased significantly after UV irradiation,suggesting that UV might be a switch of electrochemical activity of SOMs.(4)Through ion exchange,a series of imidazole headgroup and azobenzene containing cationic surfactant,C_mAzo IMB(m=0,2,4,6,8),made the negatively charged microgel,p(NIPAM-MAA)MG,with light responsiveness.Adding azobenzene surfactants,microgels underwent a phase transition process of expansion,contraction,precipitation and re-stabilization.The critical micelle concentration(cmc)of surfactants had an important effect on the swelling behavior of microgels during the swell-contraction transition,and the formation of micelles inside the microgel induced the contraction of microgels.Under UV/blue light irradiation,the reversible contraction-expansion transition of the surfactant-microgel complex was controlled.A simple osmotic pressure model of polyelectrolyte microgels was established to explain and predict the swelling behavior of polyelectrolyte microgels under UV/blue light induced by azobenzene surfactants.