| Recently, long and flexible wormlike micelles which are self-assembled by small surfactants hold promise as a unique class of novel materials because they combine many of the attractive features of conventional polymers with properties that result from the reversibility of the non-covalent interactions between monomeric surfactant molecules. Architectural and dynamic parameters that determine wormlike micelle properties, such as packing number, lifetime of the chain, and its conformation, are a function of the strength of the non-covalent interaction, which can reversibly be adjusted. This results in materials that are able to respond to external stimuli in a way that is not possible for traditional macromolecules. In this paper, a series of gemini surfactants, 22:1-s-22:1 (s=2, 4, 6), with unsaturated erucyl chains and the corresponding monomeric surfactant EHAB were synthesized, their surface properties, abilities to form wormlike micelles and rheological properties of wormlike micellar solutions based on some surfactants were systematically invertigated. Our main findings are as follows.Highly pure erucyl bromide was prepared by selecting mild reaction conditions and low temperature recrystallization purification process from commercial ecrucic acid. The N,N,N',N'-tetramethylalkylenediamine, N,N,N-bis(2-hydroxyethyl) methylamine and erucyl bromide were used to synthesize the cationic gemini surfactants 22:1-s-22:1 and the corresponding monomeric surfactant EHAB, which are characterized by 1H-NMR and elemental analysis etc. The active matter contents of each sample were determined by manual direct two-phase titration procedure and were found to be more than 98.5%.The surface properties and aggregation behaviors of 22:1-s-22:1 and EHAB in the extremely dilute solution were studied by surface tension and electrical conductivity method. It was shown that the CMC values of 22:1-s-22:1 are only a little lower than that of EHAB surfactant, which indicated that 22:1-s-22:1 form some sub-micelle aggregates below the CMC owning to the enhanced hydrophobic interactions in the gemini surfactants. The CMC values and the micelle Gibbs energies are observed to decrease as the spacer length increases in the gemini series, while the areas per molecule at air-water interface and the premicelle Gibbs energies increase with the carbon numbers of the space groups. So we come to the conclusion that the micelle process is more favored as the length of the spacer group increases, but the pre-micelle aggregates are less stabilized.According to the results of viscosity measurement based on Ubbelohde viscometer, 22:1-6-22:1 and EHAB self-assemble into spherical micelles at first and then grow into rodlike micelles as their concentration increases in the dilute solution regime. The critical concentrations of 22:1-6-22:1 and EHAB at which spherical to rodlike micelle transition starts was 8.1×10-4mol/L and 9.0×10-4mol/L respectively. 22:1-2-22:1 forms vesicular aggregates, 22:1-4-22:1 seems to form mixed aggregates which contain vesicles and rodlike micelles. The critical concentrations (C*) that separate the dilute and semidilute regimes of 22:1-6-22:1 and EHAB wormlike micellar solutions are 3.5 mM and 9mM respectively.Linear viscoelastic properties of wormlike micellar solutions based on 22:1-6-22:1 and EHAB can be described by Cates' "living polymer" model, so the large hydrophobic groups of 22:1-2-22:1 doesn't change the breaking-recombining time of its wormlike micelles much. For the EHAB/NaSal system at CS/CD=0.5 (25℃), scaling exponents of Gp～CD2.66,η0～CD3.37 were found, these values are much higher than the experimental values of commercial EHAC system which contains about 15wt% impure surfactants with short tails, so this phenomenon indicates that elongation of surfactant's tail can improve its packing parameter and cause its molecules to form much larger wormlike micelles. For the 22:1-6-22:1/NaSal system at Cs/CD=0.5 (25℃), the plateau modulus Gp exhibits a power law, Gp～CD2.91, which is higher than EHAB system, this implies that covalent spacer in the hydrophilic part of 22:1-6-22:1 have changed this surfactant's packing parameter to a higher level and induced the growth of its aggregations. However,η0 describes pronounced maximum at intermediate surfactant concentration or Cs/CD, the most possible reason for the quick drop ofη0 at higher CD or Cs/CD includes a transition from linear to branched micelles. The nonlinear rheology of EHAB and 22:1-6-22:1 wormlike micellar system is closely related to the shear rate, at least four regimes have been observed in steady shear experiments as a function of applied shear rate in the semi-dilute regime, At extremely low shear rates, the solution behaves like a Newtonian fluid, and the viscosity of a dilute solution is independent of the shear rate. This is because the solution is random and isotropic in its microstructure. As the shear rate is increased, long wormlike micelles begin to disentangle and align to the flow direction, this structural transition leads to shear thinning as in linear polymer solutions. However, ata critical shear rate (γ|·)C1 and up to a second critical shear rate (γ|·)C2, a stress plateau or shear banding flow is observed, this phenomenon has been attributed to the breaking and reforming process of wormlike micelles which greatly influence theshear flow and stress relaxation process. Above (γ|·)C2, the flow becomes homogeneous again and a Newtonian behavior is observed with a smaller shear viscosity.
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