Synthesis And Properties Of Erucic Acid Based Ionic Liquid Surfactant

Ionic liquids have excellent characteristics that traditional organic solvents do not possess,such as electrical conductivity,low vapor pressure,non-flammability,thermal stability,and designability.Ionic liquid surfactants have the common characteristics of ionic liquids and surfactants.Based on their good designability,various functionalized ionic liquid surfactants have been designed and synthesized recently.Compared with traditional ionic liquid surfactants,fatty acid ionic liquid surfactants show higher biocompatibility and exhibite better solubility and surface activity than ordinary fatty acid soaps.However,the previous researches mainly focused on short chain fatty acids,and few concerned on the aggregation of these surfactants.Therefore,in this paper,novel ionic liquid surfactants based on ultra-long-chain fatty acid-erucic acid were designed and synthesized,and the aggregation behaviors in solution were investigated by various techniques such as surface tension,rheology,and polarized light microscopy.The main conclusions are summarized as follows:（1）Four erucic acid-based ionic liquid surfactants:erucic acid choline salt（ErCho）,erucic acid benzyl trimethylammonium salt（ErBTA）,erucamide benzoic acid choline salt（ErBCho）,erucamide benzoic acid benzyl trimethylammonium salt（ErBBTA）,were synthesized and their molecular structures were characterized by hydrogen nuclear magnetic spectroscopy and infrared spectroscopy.（2）Micellarization behavior and surface activity of erucic acid-based ionic liquid surfactants in dilute solutions were investigated.The results showed that the CMC of ErCho,ErBTA,ErBCho and ErBBTA were 0.078 mmol·L^-1,0.026 mmol·L^-1,0.0105 mmol·L^-1,and0.0035 mmol·L^-1 respectively.Under the same hydrophobic tail chain,the CMC of the surfactant with benzyltrimethylammonium as counter ion is about 1/3 of that of choline salt.The introduction of benzene ring between hydrophobic tail and hydrophilic headgroup can significantly reduce the CMC 1/8 of the pre-introduced.（3）ErBTA,ErBCho,and ErBBTA in water can self-assemble into viscoelastic worm-like micelles at a certain concentration,without any additives,showing a good self-viscosity effect.Furthermore,the introduction of benzene ring between hydrophobic tail and hydrophilic headgroup leads to a lower critical overlap concentration,which is about 1/3 of that without benzene ring.Due to the sensitivity of the carboxylic acid group to the p H,ErBTA-viscoelastic fluid can be reversibly tuned with the addition of traditional acid and base.Meanwhile,the p H was also changed by bubbling CO₂.In addition,the introduction of photoacid-generater,diphenyliodonium nitrate（DPIN）,can endow ErBTA-worm with photoresponse characteristics.However,CO₂ or light induced gel-sol transition is irreversible.（4）Aggregation behaviors of ErCho in eutectic solvents（DES）,including glycerol/choline chloride（ChGly）,ethylene glycol/choline chloride（Ch EG）and phenol/choline chloride（Ch Ph）were investigated.The results showed that ErCho in the dilute DES solution possesses similar surface tension curve with aqueous solution.Although ErCho has higher CMC in DES solution,wormlike micelles can be formed by increasing the concentration of ErCho in ChGly,showing a certain thickening ability to DES.Whereas,the apparent viscosity of ErCho solution was only5.3 m Pa·s even at 300 mmol·L^-1.Further increasing the concentration of ErCho in ChGly,lamellar liquid crystals can be formed.