Dual-switchable Responsiveness Of 11-benzylselanyl Undecanoate

Switchable surfactants have reversible molecular self-assembly?mesoscale?and solution phase behavior?macroscale?owing to reversible changes in the molecular structure triggered by external stimulus.Not only are switchable surfactants great prospective in colloidal interface chemistry,manufacturing advanced materials,and life science,but also they provide an effective path towards to orderly-functional and intelligent assemblies.To realize the controlled self-assemblies of switchable surfactants in the multiple-stimulus environment,the dual?multiple?-switchable surfactants therefore receive constant attention from researchers.In this paper,we described a redox and pH dual switches-responsive anionic surfactant,11-benzylselanyl undecanoate?BSeU^-M⁺?,in which the Se atom serves as a redox-sensitive center,and the carboxylate serves as a pH-sensitive center.We had done research on its dual-switchable properties have been studied,and the main experimental results and conclusions were summarized as following:?1?Dual-switchable responsive interfacial properties of BSeU^-M⁺Selenium powder,benzyl bromide,and 11-bromoundecanoic acid were used as raw materials to prepare 11-benzylselenoundecanoic acid?BSeUH?.it was neutralized with N,N-dimethyl monoethanolamine?DMEA?to synthesize an anionic surfactant,ammonium11-benzylselanyl undecanoate?BSeUA?,which was characterized by fourier transform infrared spectroscopy?FT-IR?,nuclear magnetic resonance spectroscopy?¹H NMR?and electrospray ionization mass spectrometry?ESI-MS?,respectively.Using 50 mmol·L^-1 DMEA aqueous solution as a solvent,the Krafft temperature of BSeUA dropped below 25°C;the critical micelle concentration?cmc?of BSeUA at 25°C is 5.09×10^-3 mol·L^-1 measured by conductivity and 4.95×10^-3 mol·L^-1 measured by fluorescence spectroscopy.After oxidization of H₂O₂?or bubbling CO₂ for 20 min?,the surface tension and D80/H₂O interfacial tension of0.01 mol·L^-1?C>cmc?BSeUA increased from 48.11 mN·m^-1,8.06 mN·m^-1 to 64.30 mN·m^-1,31.03 mN·L^-1(or 67.06 mN·m^-1,40.10 mN·L^-1),respectively,consequently its foaming and emulsification abilities both disappeared;while after reduction of N₂H₄·H₂O?or bubbling N₂at 60?for 2 h?,the surface tension and D80/H₂O interfacial tension of it both decreased to the initial values and its foaming and emulsification abilities both reappeared.It was found that,under the stimuli of Redox,the selenium-containing group can be reversibly switched between hydrophobic selenide?-Se-?and hydrophilic selenoxide?-Se=O?by alternately adding H₂O₂ and N₂H₄·H₂O,and the typical single-head-single-tail amphiphilic molecular reversibly converted into a hydrophilic Bola-type molecular structure,consequently its surface activity was turned on or off;under the stimuli of CO₂/N₂,the CO₂-sensitive group can be reversibly switched between carboxylate?-COO^-?and carboxylic acid?-COOH?,consequently its surface activity was turned on or off.The dual-switchable responsive behaviors of surface/interfacial tension,foaming and emulsification abilities could cycle reversibly over five times at least,thus Redox and CO₂ dual-switchable responsive interfacial properties of BSeUA were achieved.?2?Dual-switchable responsiveness of wormlike micelles?WLMs?based on BSeU^-M⁺A highly viscoelastic fluid was fabricated by mixing potassium 11-benzylselanyl undecanoate?BSeUK?and 3-?N,N-Dimethylpalmityl ammonio?propanesulfonate(C₁₆DSB)with a stoichiometric ratio of 1:1 in 75 mmol·L^-1 guanidine hydrochloride?Gu?solution,which was systematically characterized with rheology measurements and cryo-TEM,proving that the fluid was based on wormlike micelles?WLMs?self-assembled by surfactants.Results showed that,by alternately adding H₂O₂ and Na₂SO₃,100 mmol·L^-1 WLMs could be reversibly switched between gel and sol.Moreover,by alternately adding H₂SO₄ and NaOH to change the pH from 9.47 to 7.16,WLMs could undergo the transformation from a gel-like fluid to an emulsion.The addition of H₂O₂ induced the transition of the selenium-containing group in BSe UK from its reduced form?selenide?to its oxidized form?selenoxide?transition,thereby resulting in a transition of the aggregates from an entangled WLM to small spherical ones.The decrease in pH induced the transition of BSeUK from its dissociated form?surfactant?to an insoluble fatty acid form?nonsurfactant?,with the consequent loss of viscoelasticity and the transformation from a gel-like fluid to an emulsion.In addition,the reversible change of WLMs viscosity could cycle over three times,thus a kind of Redox and pH dual-switchable responsive WLMs was achieved.