Preparation And Properties Of Selenium-containing Anionic Surfactant

The interfacial properties and self-assembly in the bulk solution of stimuli-responsive surfactants can be reversibly switched by external stimuli,such as pH,CO₂,redox,light and magnetic.Among redox-responsive surfactants,the focus has been on ferrocene-based surfactants and surfactants containing a disulfide bond.However,novel redox-responsive surfactants have rarely been covered so far.Here,a selenium-containing anionic surfactant,sodium 11-?benzylselany?undecyl sulfate?BSe AS?has been synthesized based on unique redox property of selenium.The redox stimuli-response of BSeAS at interface and spontaneous vesicles based on its mixtures with N,N,N,-trimethyldodecan-1-aminium bromide?DTAB?has been investigated.More importantly,the dual stimuli-response of the wormlike micelles?WLMs?based on BSeAS combination with N,N,N?,N?-tetramethyl-1,2-ethanediamine?TMEDA?has been systematically investigated.The main contents and conclusions are summarized as following.?1?Synthesis of BSeAS and its redox propertiesBSeAS was synthesized by three steps process.Molecular structures and transition in molecular structures with oxidization and reduction have been confirmed with NMR and ESI-MS.At 25 ?,with 0.1 mol�L-1?CH₃?4N+Br-as solvent,the critical micellar concentration?cmc?of BSe AS is 0.16 mmol�L-1 and surface tension at cmc??cmc?is 48.22 mN�m-1.BSeAS shows high interfacial activity?good foaming/emulsification properties?.After oxidization with H₂O₂,BSeAS converts into a bola-type surfactant?BSeAS-Ox?due to the formation of a new hydrophilic group?selenoxide?and its interfacial activity decline greatly?cmc,2.04 mmol�L-1,?cmc,62.81 mN�m-1,almost no foaming/ emulsification properties?.After reduction with Na₂SO₃,the BSeAS-Ox converts into BSeAS.Such conversion is reversible.?2?The redox response of vesicles in the aqueous mixtures of BSeAS and DTABMixing BSeAS and DTAB aqueous solution with total surfactants concentration?CT=10-2 mol�L-1?at 40 ? can spontaneously form vesicles at various molar fractions?X1=0.1⁰.7,X1 refers to molar fractions of BSeAS?.Dynamic light scattering and Transmission electron microscopy indicate that the average radius of vesicles firstly decreases and then increases with the increasing X1 and varies from 48 nm to 75 nm.The salinity-tolerance property of vesicles based on different X1 was investgated and it shows that the stability of vesicles is excellent when X1 is fixed at 0.3 and the vesicles still exist in 2 mol�L-1 Na₂SO₄ aqueous solution.Then the redox response of vesicles based on X1=0.3 was determined.Vesicles can be disrupted after addition of H₂O₂ due to the formation of BSeAS-Ox.After addition of Na₂SO₃,Vesicles can be re-formed because of the reduction of BSeAS-Ox.By adding H₂O₂ and Na₂SO₃ alternately,the reversible transformation of vesicles to spherical micelles can be achieved,and the average radius of vesicles is almost unchanged in five number of cycles.?3?The CO₂/N₂ and redox response of wormlike micelles?WLMs?in the aqueous mixtures of BSeAS and TMEDAMixing 200 mmol�L-1 BSeAS and 100 mmol�L-1 TMEDA in molar ratio of 2:1 at 25 ? can form a water-like fluid?¹ mpa�s?.when CO2 is bubbled into the water-like fluid,a transparent,viscoelastic fluid WLMs?⁸300 mpa�s?can be formed as verified by Cryo-TEM.The WLMs can be ruptured?¹ mpa�s?and re-formed?⁸300 mpa�s?by the alternate addition of H₂O₂ and N₂H₄�H₂O,because of a transition in the structure between selenoxide?Se=O?and selenide group?Se-C?as confirmed by 1H NMR and Se77 NMR.The WLMs also show a reversible response to the bubbling and removal of CO₂,reflecting a transition between a viscoelastic fluid?⁸300 mpa�s?and a water-like fluid?¹ mpa�s?due to the reversible transition of TMEDA and protonated TMEDA as confirmed by 1H NMR.