Gemini Surfactant-Water Mixtures:Some Physical-Chemical Properties

The phase diagram of the water-Gemini 16-4-16 system has been investigated and the phase boundaries were detd. DSC and optical microscopy were used to define the region of existence of the different phases. No liq. cryst. phases have been obsd., however, a two-phase region and a wide gel phase follow the soln. region. The soln. region can be highly viscous, depending on compn. and temp. Surface tension and elec. conductance expts. have been performed, to define micelle formation and counter-ion binding to micelles. Interactions and motions over short distances were studied by 1H-NMR relaxation expts. The drastic decrease of spin-spin relaxation time, T2, with Gemini compn. (≈2 wt.%) was explained in terms of particle growth. Pulsed field gradient spin-echo (PGSE) NMR expts. were used to det. water and surfactant self-diffusion. Some modifications in the micellar structure were inferred on increasing the Gemini content in the mixt. Dynamic rheol. expts. were performed for probing the soln. microstructure. The obsd. high soln. viscosity and the shear relaxation processes were rationalized in terms of the presence of entangled threadlike aggregates at a moderate concn. (≈4 wt.%). According to the Bohlin theory of flow as a cooperative phenomenon, the no. of the micellar aggregates correlated to each other, and the interaction strength between the micellar units was obtained as a function of Gemini concn.