Controlling Structure and Water Miscibility of Polyion - Surfactant Ion Complex Salts

Sammanfattning: The interaction between poylions and oppositely charged surfactant ions has been investigated. This has been done by using the pure complex salt (polyion + surfactant ion) as a point of departure. Different parameters of the complex salt have been varied in a systematic way and the effect on structure and water miscibility has been investigated. Complex salts (CxTAPAy) consisting of alkyl trimethyl ammonium surfactants (CxTA+, with x being the alkyl chain length) and poly(acrylate) (PAy, with y being the degree of polymerization) have been used. Surfactants with the oligocarboxylate counterions oxalate, succinate, citrate, and butyl tetra-carboxylate (BTA) have also been used. By changing the surfactant alkyl tail length from 6 to 16 the size of the rodlike surfactant aggregates formed with a polymeric counterion at low water content could be controlled. Also the size of the surfactant aggregates in the cubic phase found varied with surfactant tail length. The C16TAPAy systems were virtually insoluble in water, but took up 40 - 50 wt% of water in equilibrium with excess water. When changing from shorter to longer polyions, the concentrated phase in equlilibrium with excess water switched from a cubic phase to a hexagonal phase. It was also shown that the solubility of the complex salts was higher with a shorter alkyl chain length and a longer polyion. By lowering the charge density of the polyion, the size of the surfactant aggregates decreased and the curvature of the aggregates increased. At very low charge densities, the systems lost long-range order. Additions of decanol to aqueous solutions of the complex salts decreased the curvature of the surfactant aggregates, causing a switch to a lamellar phase. By adding small oils (p-xylene, cyklohexane), the diameter of the surfactant rods in the hexagonal phase could be increased. Surfactants with dimeric counterions did not phase separate at high water content, but tri- and tetrameric counterions caused phase separation for spherical surfactant aggregates. Compared to the complex salts, there was very little difference between the surfactant with a tetrameric counterion and the complex salt with a short polyion, indicating a fast convergence of the effect of connecting the surfactant counterions. There was very little difference in the swelling of lamellar aggregates for di-, tri-, and tetrameric counterions.