Study On The Aggregation Behavior Of Imidazole Ionic Liquid Surfactant [C₁₆imC_n]Br And Its Complex System

The molecular self-assembly of surfactants based on noncovalent interactions provides a powerful tool for the creation of well-defined structures in certain dimensions,such as spherical,rod,fiber,disk,laminar structure,vesicle and 3D networks.The noncovalent interactions involve basic molecular interactions such as hydrophobic-hydrophilic effects,hydrogen bonding,coulombic interactions,or van der Waals forces.Over the past two decades,there have been a great deal of interests in the aqueous self-assembly of surfactants from a theoretical viewpoint and from the industrial and technological applications,such as biology,energy,information and nanomaterials,et.al.The study of different aggregates is a very important research topic in the field of colloid and interface chemistry.The transition between different aggregates under different conditions is currently one of the hot topics in the research of colloid and interface science.Alkyl chain length of surfactant is one of the parameters controlling the structural arrangement of micelle monomers,so that one can tailor the monomers for different applications.In recent years,ionic liquids composed of 1-alkyl-3-methylimidazolium salts have attracted much attention for their wide application in the field of catalysis,electrochemistry,organic synthesis and material preparation.Meanwhile,as a kind of cationic surfactant,aggregation properties of ionic liquids in water have been studied.The surfactants based ionic liquid can be used to develop new kinds of aggregates by changing the alkyl chain length or the counter anion.The present work is to generate a series of new ionic liquid-type amphiphiles and to investigate their aggregation behavior to establish the structure-property relationship.Then the impacts of nonionic surfactant Brij 30 and anionic surfactant SDS on the aggregation behavior of ionic liquid surfactants with various alkyl chain length are investigated.The main content in the present dissertation are divided into five parts:1.Concentration and thermo dual-responsive wormlike micelles to hydrogels transition in ionic liquid-type surfactant[C16imC9]Br aqueous solution without additivesHigh viscoelastic fluid formed by the ionic liquid-type surfactant 1-hexadecyl-3-nonyl imidazolium bromide([C16imC9]Br)in water in the absence of any additive was studied.The phase behaviour and morphology of the aggregates were studied by a combination of rheological techniques,small-angle X-ray scattering(SAXS),cryo-etch-scanning electron microscopy(cryo-etch-SEM)and freeze-fractured transmission electron microscopy(FF-TEM).[C16imC9]Br aqueous solutions showed interesting rheological behaviour as a function of both concentration and temperature,which experienced a transition between wormlike micelle and hydrogel.With the increase in[C16imC9]Br concentration,the aqueous solution can form viscoelastic wormlike micelle(50-80 mM),hydrogel(90-110 mM)and wormlike micelle(120-180 mM).As the temperature increased,the hydrogel(90-110 mM)could also transit to wormlike micelle.These unusual phase transitions between wormlike micelle and elastic hydrogel were postulated to be the change of the average micellar length.2.Impact of alkyl chain length on the transition of hexagonal liquid crystal-wormlike micelle-gel in ionic liquid-type surfactant aqueous solutions without any additive.The search for functional supra molecular aggregations with different structures has attracted interest of chemists because they have potential in industrial and technological application.Hydrophobic interaction has great influence on the formation of these aggregations,such as hexagonal liquid crystal,wormlike micelle and hydrogel.So a systematic investigation was performed on the influence of alkyl chain length of surfactants 1-hexadecyl-3-alkyl imidazolium bromide on their aggregation behavior in water.These ionic liquid surfactants are denoted as C16-Cn(n=2,3,4,6,8,10,12,14,16).The rheological behavior and microstructure were characterized via a combination of rheology,cryo-etch scanning electron microscopy(cryo-SEM),polarization optical microscopy(POM)and X-ray crystallography(XRD).The result shows that the alkyl chain has obvious influence on the formation of surfactant aggregates in water at the molecular level.With increasing alkyl chain length,different aggregates,such as hexagonal liquid crystal,wormlike micelle and hydrogel are obtained:C16-C2 aqueous solution only forms hexagonal liquid crystal;C16-C3 aqueous solution forms both wormlike micelle and hexagonal liquid crystal;C16-C4,C16-C6 and C16-Cg aqueous solutions only form wormlike micelle;C16-C10,C16-C12,C16-C14 and C16-C16 only form hydrogel.The mechanism of various microstructures of different aggregation with different alkyl chain length was also proposed.3 Brij 30-induced rodlike micelle-to-wormlike micelle and wormlike micelle-to-hydrogel transition in the system of ionic liquid-type surfactant C16-C8 and waterThe aggregation behavior of the ternary surfactant system composed by the cationic surfactive ionic liquid(IL),1-hexadecyl-3-octyl imidazolium bromide(C16-C8),the nonionic surfactant(Brij 30),and water has been investigated.The aggregation behaviour and morphology of the aggregates were studied by rheological techniques,nuclear magnetic resonance,freeze-fractured transmission electron microscopy,zeta potential measurements and polarization optical microscopy.The C16-C8 aqueous solution forms rodlike micelle and wormlike micelle at different concentration.With the addition of Brij 30,the rodlike micelle can transit to wormlike micelle and then transit to hydrogel.The C16-C8 wormlike micelle transits to hydrogel when Brij 30 is added.The obtained results are helpful for better understanding of the relationship between rodlike micelle-wormlike micelle and wormlike micelle-hydrogel.They are expected to have potential value for industrial and technological applications.4.The influence of added Brij 30 on the aggregation behavior of ionic liquid surfactants C16-Cn(n=2-16)in water.The aggregation behavior of the ternary surfactant system composed by a series of cationic surfactive ionic liquids(IL),1-hexadecyl-3-alkyl imidazolium bromide C16-Cn(n=2-16),a nonionic surfactant(Brij 30)and water has been investigated.The aggregation behaviour were characterized by rheological techniques.The addition of Brij 30 can induce the transition of rodlike micelles to viscoelastic wormlike micelles in C16-C2 solution.The appropriate addition of Brij 30 can improve the viscoelasticity of C16-C4,C16-G6 and C16-C8 rodlike micelles and wormlike micelles.Excess addition of Brij 30 can induce the transition from wormlike micelle to rodlike micelles.Furthermore,the addition of Brij 30 can decrease the minimum concentration of gelation for C16-C10,C16-C12,C16-C14 and C16-C16 aqueous system.At the same time,Brij 30 increases the viscoelastic properties of original gels.The impacts of Brij 30/C,6-Cn mole ratio and alkyl chain length on the micelle length,relaxation time and network density of wormlike micelles are discussed.The influence of Brij 30 concentration on the temperature of gel-sol transition is also investigated.The mechanism of the transition between sphere micelle-rodlike micelle,rodlike micelle-wormlike micelle,wormlike micelle-gel,rodlike micelle-gel and wormlike micelle-rodlike micelle is proposed.5.The influence of SDS on the aggregation behaviour of ionic liquid-type surfactants C16-Cn(n=2-16)in water.The addition of SDS have great impact on the phase behaviour of ionic liquid surfactants C16-Cn(n=2-16)in water.SDS can induce the transition of the C16-C2,C16-C4 and C16-C6 rodlike micelle to hydrogel.The gelation concentration,the mole ratio of anionic surfactant and ionic liquid surfactant for the gelation and the gel-sol transition temperature decrease monotonically with the increase of alkyl chain length.The SDS/C16-C8 mixed solution can not form hydrogel.New hydrogels with lower viscoelasticity could be formed by adding appropriate SDS to the C,6-C10,C16-C12,C16-C14 and C16-C16 hydrogels.However,excess addition of SDS can cause the destruction of the C16-C10,C16-C12,C16-C14 and C16-C16 hydrogels.So the addition of SDS can induce the transitions of rodlike micelle-hydrogel and hydrogel-rodlike micelle.