Oligomeric Surfactants Based On Noncovalent Interactions And Their Aggregation Behavior

Due to the extensively industrialapplications, surfactants have been called "industrial monosodium glutamate". Development and application of various kinds of newsurfactant and self-assembled aggregates have been one of the most significant issuesin the colloids and interfacesciences recently. Due to the special performances and superior physicochemical properties, such as stronger ability to reduce the surface tension of aqueous solutions, lower critical micelle concentration, higher surface activity, and abundant aggregate structures, oligomeric surfactant has been one of the most popular topics in the field of colloid and interface sciences. However, their applications were limited due to the complicated synthesis and purification procedures. Intermolecular interaction or intermolecular weak interaction, is a kind of non-covalent force among the molecules. The superamphiphiles refer to amphiphiles that are formed on the basis of noncovalentinteractions. Superamphiphiles are the new progress of traditional amphiphilic molecules and the important enrichment and development of colloid and interface chemistry, which will provide new train of thoughts on the construction of pseudo-oligomeric surfactant by noncovalent interactions.In this dissertation, the cationicbuilding blocks which may introduce intermolecular weak interactionwere designed and synthesized. The pseudo-oligomeric surfactants by noncovalentinteractions were constructed and the self-assembled aggregates based on these pseudo-oligomeric surfactant were studied systematically. Our aim is to explore a new way to constructoligomeric surfactant systems, needless of much tedious chemical synthesis and to establish the dependence of aggregation behavior of surfactant systems on noncovalent weak interactions.Our research is helpful to achieve the controllability and functionalization of pseudo-oligomeric surfactants-based ordered molecular aggregates. The whole paper contains three sections, which are summarized as following:Section I:Briefly introduced the research background and applications of surfactant, ordered molecular aggregates and the progress of oligomeric surfactants. Briefly introduced the superamphiphiles based on intermolecular interaction and the construction of pseudo-oligomeric surfactant systems based on intermolecular interactions and its progress.Section Ⅱ, The construction of pseudogemini surfactants based on SDBS and cationic spacer through intermolecular interaction were investigated. The phase behavior of a kind of pseudogemini surfactants in aqueous solutions, formed by the mixture of sodium dodecyl benzene sulfonate (SDBS) and butane-1,4-bis (methylimidazolium bromide) ([mim-C4-mim]Br2) or butane-1,4-bis(methylpyrrolidinium bromide) ([mpy-C4-mpy]Br2) in a mole ratio of 2:1, is reported in the present work. When [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 is mixed with SDBS in aqueous solutions, one cationic [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 molecule "bridges" two SDBS molecules by noncovalent interactions (e.g. electrostatic, π-π stacking, and σ-π interactions), behaving like a pseudogemini surfactant. Vesicles can be formed by this kind of pseudogemini surfactant determined by freeze-fracture transmission electron microscopy (FF-TEM) or cryogenic-transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). The mixed system of sodium dodecyl sulfate (SDS) with [mim-C4-mim]Br2 or [mpy-C4-mpy]Br2 was also constructed, and only micelles were observed. We infer thatpseudogemini surfactant is formed under the synergic effect of electrostatic, π-π stacking, and σ-π interactions in the SDBS/[mim-C4-mim]Br2/H2O system, while electrostatic attraction and hydrophobic interaction may provide the directional force for vesicle formation in the SDBS/[mpy-C4-mpy]Br2/H2O system.Section Ⅲ, A novel linearpseudo-oligomeric surfactant, which was formed by mixing dodecyl benzene sulfonate (SDBS) and a linear tricationic imidazolium bromide salt (LTIB) in a molar ratio of 3:1, was investigated. The aggregation behavior, aggregate structures and interactions between SDBS and LTIB were investigated by surface tension measurement, dynamic light scattering, turbidity, cryogenic transmission electron microscopy and 1H NMR techniques. When SDBSwas mixed with LTIB in aqueous solutions, three SDBS molecules may be "bridged" to one cationic LTIB molecule by intermolecular interactions, behaving like a linearoligomeric surfactant. Vesicles could be formed by this kind of linear pseudo-oligomeric surfactant.The aggregation behavior of the LTIB/SDBS mixed aqueous solutions behaves ratio- and concentration- dependence. Our work paves a convenient way for constructing surfactant systems with the characteristics of linear pseudo-oligomeric surfactant through intermolecular interactions between commercially available single-chain surfactants and linear tricationic imidazolium counter-ions.