Study On CO₂-responsive Viscoelastic Fluid Constructed Based On Ionic Liquid And Its Responsivenes

Viscoelastic fluids are the smart materials with the reversible viscoelasticity regulated by the introduction and removal of CO2,and have excellent properties of intelligent controlling and clean recycles.Thus viscoelastic fluids have promising application.Recently,the viscoelastic fluids with CO2 response were constructed by introducing the CO2 responsive materials,such as amines or carboxylates with CO2 response.However,amines are generally organic solvents with high volatility and toxicity,which is harmful to the ecological environment.The carboxylates have CO2 response irreversibly,which make it difficult to be recycled.Therefore,the cleaner and reversible viscoelastic fluids regulated by CO2 were necessary to be investigated.As we all known,ionic liquids are the green materials with lower volatility and low toxicity,and have applied widely in the greener and sustainable development.In this work,the two kinds of ionic liquid with CO2 response were synthesized respectively,and were combined with tyltrimethylammonium bromide(TTAB),forming viscoelastic fluids.The CO2 responsive behavior of viscoelastic fluids were evaluated and the CO2 responsive mechanism was also discussed.Firstly,ionic liquid surfactant TMG-OA was prepared by direct neutrallzation reaction between 1,1,3,3,3-tetramethylguanidine(TMG)and oleic acid(HOA).It was demonstrated that TMG-OA had good stability.Besides,by the test of pH and nuclear magnetic hydrogen resonance(1H NMR),it was found that TMG-OA also had CO2 switchable behavior,which was induced by the reversible transformation between TMG-OA and HO A.Then,the viscoelastic fluid TMG-OA/TTAB with CO2 response was prepared by combining TMG-OA with the cationic surfactant TTAB.The CO2-responsive viscoelastic behavior of TMG-OA/TTAB was demonstrated by rheological and dynamic light tests,and the CO2-regulated mechanism of TMG-OA/TTAB was analyzed by 1H NMR,pH and Cryo-TEM.It was found that the viscoelastic fluid TMG-OA/TTAB with the the structure of worm micelle was formed by the electrostatic interaction between TMG-OA and TTAB.After bubbling CO2,the carboxylate group of TMG-OA was protonated,which destroyed the electrostatic interaction between TMG-OA and TTAB.Meanwhile,the emulsion was formed by the emulsification of oleic acid.Under the addition of N2/heating,the emulsion could be transformed into viscoelastic fluid with the structure of worm micelle.Secondly,to obtain viscoelastic fluid with thermal stability,the polyionic liquid PNIPAM-P(TMG-DA)with CO2 and temperature response was synthesized.It was decomposed that PNIPAM-P(TMG-DA)had good stability,reducing the volatilization of CO2-responsive solvent,TMG.The excellent CO2 response of PNIPAM-P(TMG-DA)was demonstrated by pH,and the reversible transformation of the micro-structure from individual aggregates to string aggregates induced by CO2 was also detected by TEM.In addition,the temperature response of PNIPAM-P(TMG-DA)was demonstrated by the changes of hydraulic radius at different temperatures,and it was measured that the sensitive temperature ranges was between 35 ℃ and 50℃.Then polyionic liquid PNIPAM-P(TMG-DA)was combined with cationic surfactant TTAB to prepare viscoelastic fluid PNIPAM-P(TMG-DA)/TTAB.With the help of rheological and pH dynamic light scattering(DLS)test,it was found that PNIPAM-P(TMG-DA)/TTAB had excellent CO2 response behavior and thermal stability.The CO2 responsive mechanism of viscoelastic fluid PNIPAM-P(TMG-DA)/TTAB was investigated by 1H NMR,pH and TEM.It was concluded that the short rod-like network structure was generated by the electrostatic interaction between TTAB and PNIPAM-P(TMG-DA)to improve the viscosity of system.After bubbling CO2,the increasing hydrophobicity of PNIPAM-P(TMG-DA)was induced by protonation.Meanwhile,the long and dense network structure was formed under the synergistic action of TTAB,causing increasing viscosity of PNIPAM-P(TMG-DA)/TTAB.When bubbling CO2 constantly,the some precipitate was separated out from the solution,the short rod-like network was destroyed,inducing decreasing viscosity.Besides,under the addition of N2/heating,the aggregate of solution system was transformed from the state contained rod-like and globular to the stable state short rod-like.