Study On The Synthesis And Self-assembly Of Surfactants With Unusual Head Group Structure

The structure-property relationship of surfactants is the important topic in surfactant field.By incorporating functional groups into the molecular structure of surfactants, new interactionmanner between surfactants can be generated, which resulted in new aggregate morphologies.The head group chemistry of surfactants play important roles in the self-assembly process ofsurfactants. In this thesis, we have synthesized surfactants with unusual head groupstructures, including Gemini surfactants whose head groups contain hydroxyl groups, and anovel double tailed surfactant2-ODTAB。Their self-assembly in aqueous solutions have beeninvestigated. The main results are summarized as follows:(1) Four quaternary ammonium Gemini surfactants with head groups containinghydroxyl groups,12-3(OH)-12,12(2Et)-3(OH)-12(2Et),12(2OH)-3-12(2OH),12(2OH)-3(OH)-12(2OH), have been synthesized. Their solution properties such as Krafftpoint, electric conductivity, surface tension and solubilization capacity, have been explored.The results showed that the position and number of hydroxyl groups have different effects onthe self-assembly of surfactants. In the solubilization experiment, the position and number ofhydroxyl groups were revealed to have little effects on the capacity. However, the surfactantswith head groups modified by ethyl groups showed stronger capacity of solubilization.(2) The properties of three catanionic surfactant systems,12-3(OH)-12/Sodium dodecylsulfate (SDS),12-3(OH)-12/Sodium dodecyl benzene sulfonate (SDBS) and12-3(OH)-12/Sodium laurate (NaL) were investigated by steady state and dynamicrheological measurements. It is found that small addition of anionic surfactants has atremendous effect on the viscoelasticity of12-3(OH)-12solutions, showing high efficiency.Here by adding SDS, SDBS and NaL, a maximum value is reached at a molar fraction assmall as0.16,0.075and0.14, respectively, and the maximum in η0increases by160-fold,87-fold and157-fold, respectively. Adding a small amount of oppositely charged surfactantscan cause a huge increase in viscosity is an important characteristic of ionic Gemini surfactantdominated system.(3) The surfactant (2-ODTAB) with Single-head, two-tailed structure were synthesized.The properties of its aqueous solutions were studied, including surface tension, Zeta potential,dynamic light scattering and cryogenic-TEM. The results show that2-ODTAB can formvesicles with average particle diameter of200nm at low concentrations. In contrast with theother surfactants having similar structures, the particular head group structure played animportant role.