Synthesis And Solution Viscoelasticities Of Novel Trimeric Anionic Surfactants

Oligomeric surfactant has a complex molecular structure. Novel self-assembly behavior are often discovered in oligomeric surfactant systems because of the synergistic effect of a variety of structural elements at the molecular level. In recent years, Gemini surfactant has received wide attention with their excellent performances. However, the investigation on the oligomeric surfactants with higher polymerization degree is rarely involved. The structure-property relationship of surfactants is the important topic in surfactant field. By changing the molecular structure of the surfactant, it is expected to create novel aggregate morphologies. In this thesis, we have synthesized two series of trimeric anionic surfactants with different rigid spacer groups. Their self-assembly in aqueous solutions have been investigated. The main results are summarized as follow:1.Two series of novel trimeric anionic surfactants, sodium 2,2’,2’’-（benzene-1,3,5-triyltris（oxy）） tritetradecanoate（abbreviated as Ph-Tris Cn Na, n=12, 14, 16） and sodium 2,2’,2’’-（（ethane-1,1,1-triyltris（benzene-4,1-diyl））tris（oxy）） tritetradecanoate（abbreviated as C-Tris Ph Cn Na, n=12, 14, 16）, have been synthesized by bromination, esterification and saponification processes successively. The molecules of Ph-Tris Cn Na（n=12, 14, 16） has a short rigid spacer, and C-Tris Ph Cn Na（n=12, 14, 16） have a longer rigid spacer. The chemical structures of intermediates and final products were all identified by 1H NMR and elemental analysis. The aggregation behavior of two series of surfactants was studied by fluorescence probe method. The results showed that, due to the presence of the spacer group, trimeric surfactants have a strong aggregation ability, and the critical micelle concentration were at the magnitude of 0.01 mmol ?L-1.2. The rheological behavior of Ph-Tris Cn Na with a short rigid spacer（n=12, 14, 16） and Ph-Tris C₁4Na/cationic additive systems was investigated. Cationic additives are n-butyl bromide（C₄TAB）, n-hexyl bromide（C₆TAB） and n-octyl bromide（C₈TAB）. The results showed that wormlike micelles can be formed in these aqueous systems at a suitable concentration. The rheological behavior of these systems was obvious effected by The alkyl chain length. The addition of cationic additives can significantly promote the viscoelastic properties of the solutions. For example, by adding C₄ TAB, C₆ TAB and C₈ TAB into Ph-Tris C₁4 Na systems, a maximum value can be reached at a molar fraction of 2, 0.8 and 0.5, respectively. And the maximum in η0 of mixed systems was increased by 585-fold, 1.24×105-fold and 3.84×105-fold, respectively.3. The rheological behavior of C-Tris Ph Cn Na（n=12, 14, 16） with a long rigid spacer was investigated by steady state and dynamic rheological measurements. The effect of temperature on rheological behavior of these systems was also considered. The results showing that, due to the volume effect of long rigid spacer at the molecular level, C-Tris Ph Cn Na surfactants can form wormlike micelles more easily. The viscoelastic properties of their solutions could be enhanced with increasing the hydrophobic chain length. For C-Tris Ph C16 Na system, the zero shear viscosity at 65 mmol·L-1 can reach up to 1380 Pa·s. Flow activation energy of the three systems increases with the C-Tris Ph Cn Na hydrophobic chain length. The zero shear viscosity of surfactant solutions usually decreased with temperature increasing. However, for C-Tris Ph C16 Na system, the rising in temperature causes microstructure change of the wormlike micelles. As a result, at the region where the zero shear viscosity increased with the concentration, a maximum value was revealed at the variation of the zero shear viscosity with the temperature. This system reflects the complexity of the trimeric anionic surfactant in forming wormlike micelles. The conclusions will be helpful for further understanding the properties of anionic wormlike micelles.