Study On Agglomeration Behavior Of Surface Active Ionic Liquid Containing Aromatic Anions

As novel and green solvent, ionic liquids(ILs) have been received much attention of global researchers in recent years. Their chemical and physical properties can be effectively and easily tailored by designation of their chemical structures. ILs bearing long alkyl chain can be named as surface active ionic liquids(SAILs). The combination of ILs and surfactants brings unique properties of aggregation and exploits application of ILs. Based on above, in this dissertation, we synthesized a series of new SAILs containing aromatic counterions and investigated their aggregation behavior in aqueous solution or IL. There are four main parts in this dissertation as follows.Chapter 1 is a brief introduction of basic knowledge and recent achievements closely related to the ordered aggregates constructed by SAILs and the research ideas for this dissertation.In Chapter 2, we investigated the influence of diverse counterions on the aggregation behavior of SAILs with aromatic counterions. Two imidazolium-based SAILs, viz.1-dodecyl-3-methylimidazolium salicylate(C12mim Sal) and 1-dodecyl-3-methylimidazolium3-hydroxy-2-naphthoate(C12mim HNC) were synthesized and their aggregate behavior in aqueous solutions was systematically explored. Both C12 mim Sal and C12 mim HNC show superior surface activity than the common imidazolium-based SAIL with the same hydrocarbon chain length, namely 1-dodecyl-3-methylimidazolium bromide(C12mim Br). For one thing, the electrostatic repulsion between imidazolium head groups is reduced more effectively for the weaker hydration of the aromatic counterion than the inorganic anion. For another, aromatic counterions enhance the hydrophobic interaction of SAILs molecules and play a crucial role in facilitating the micellar formation. With the increasing content of SAILs in aqueous solution, C12 mim Sal can form hexagonal liquid crystalline phase(H1) and a broad region of cubic liquid crystalline phase(V2), while lamellar liquid crystalline(Lα) phase is observed for C12 mim HNC/H2 O system. The interaction energies(Eint) for C12 mim Sal/H2 O and C12 mim HNC/H2 O systems calculated by density functional theory(DFT) calculations method are-110.47 and-56.11 k J·mol-1, respectively. This means that stronger interaction of C12 mim Sal with solvent molecules results in a higher cmc value, compared to C12 mim HNC.This work will enrich the investigations of phase behaviors formed by SAILs, and has potential application in some fields, such as nano-structured material fabrication and drug delivery, etc.In Chapter 3, we examined the substituent and solvent effects on the aggregation behavior of SAILs with aromatic counterions. 1-dodecyl-3-methylimidazolium m- andp-hydroxybenzoates(m-C12 mim HB and p-C12 mim HB) were synthesized and their aggregate behavior in water and ethylammonium nitrate(EAN) was investigated. Surface tension measurements indicate that the cmc values of SAILs in EAN are much higher than those in water, resulting from the weaker solvophobic effect of EAN, and the stronger stability of SAILs/EAN complexes proven by DFT calculations. Compared to C12 mim Sal, the effect of substituent position leads to weaker interactions between aromatic counterions and head groups. H1 phase formed by C12 mim HB in water or EAN at a higher concentration was determined by POM, SAXS and rheology techniques. For C12 mim HB, the formation of H1 phase in H2 O is easier than that in EAN. Furthermore, compared to C12 mim Sal, C12 mim HB exists a broad region of H1 phase, which is due to the different position of the substituents on the aromatic ring of counterions. In addition, multi-walled CNTs(MWCNTs) could be uniformly dispersed in the H1 phase formed by the C12 mim HB/H2 O system, which does not destroy the structure of H1 phase but influences its structure effectively.In Chapter 4, to demonstrate the effect of head group on self-assembly behavior of SAILs with aromatic counterions, N-dodecyl-N’-methylpyrrolidinium salicylate(C12MPSal)and N-dodecyl-N-methylpiperidinium salicylate(C12PDSal) were synthesized and their aggregate behavior in aqueous solutions was systematically explored. C12 PDSal displays higher surface activity than C12 MPSal, resulting from the additional-CH2- group of saturated ring. And the larger steric-hindrance effect of piperidine ring results in a looser arrangement of C12 PDSal than C12 MPSal molecules at the air-liquid interface. In addition, the absence ofπ-π interaction between head group and aromatic counterion leads to a lower packing density than C12 mim Sal reported previously. For C12 MPSal, H1 and V2 phases appeared successionally with the increasing concentration of SAIL, while for C12 PDSal, only a broad region of H1 phase was observed. Structural parameters calculated from SAXS patterns suggest that a higher concentration of SAILs or a higher temperature leads to a closer alignment. The rheological results of H1 phase formed by the two SAILs show traits of general Maxwell model.