A New Approach to the Phase Behavior of Oppositely Charged Polymers and Surfactants

Abstract

The complex salt (ionic surfactant + polymeric counterion) cetyltrimethylammonium polyacrylate (CTAPA) has been synthesized, and its aqueous mixtures with cetyltrimethylammonium bromide (CTABr) have been studied. These mixtures differ from conventional oppositely charged polymer/surfactant mixtures in that the conventional counterion of the polyion (usually sodium, for the polyacrylate) is absent, which simplifies the studies and their interpretation considerably. The phase diagram of the CTAPA/CTABr/water system at >20 wt % water and at 40 °C has been established, representing the first truly ternary phase diagram of an oppositely charged polymer/surfactant pair in water. The two dimensions of the phase diagram may be chosen as the water content (in weight percent) and the fraction of bromide counterions, x Br (in units of charge equivalents). The phase diagram is characterized by a large hexagonal phase (at low water contents and for all values of x Br ), a small cubic phase (at 55 wt % water content and for x Br < 0.1), a narrow isotropic (micellar) phase (at high water contents and for x Br > 0.9), and a large multiphase region (at water contents >50 wt %) containing two or three of the cubic, hexagonal, or isotropic phases in coexistence. The cubic and hexagonal phases are connected to the corresponding phases that separate out from aqueous NaPA/CTABr mixtures. The maximum water uptake of the hexagonal phase is remarkably constant at ca. 50 wt % over a large CTAPA/CTABr composition range (x Br < 0.9). The study confirms previous conclusions that the polyacrylate counterions favor a higher aggregate curvature (leading to smaller aggregates) than do the bromide counterions.

DNA-lipid systems: A physical chemistry study

“…The factors determining the type of aggregate formed can be assumed to be the same as for simple surfactant systems, a statement supported by some recent reports (8).…”

“…The surfactant molecules are in an aggregated form in the concentrated phase, but different types of aggregates are formed in different systems; micelles of different shape, cubic liquid crystalline phase, (normal or inverse) hexagonal phase and lamellar phase are the cases described so far (2)(3)(4)(5)(6)(7)(8)(9). The factors determining the type of aggregate formed can be assumed to be the same as for simple surfactant systems, a statement supported by some recent reports (8).…”

“…Later work has demonstrated the rich morphology possible. The best studied systems are mixtures of sodium poly(acrylate) with cationic surfactants (8).…”

Marked differences in volume phase transitions between gel and single molecule in DNA

“…[1][2][3][4][5][6][7][8][9][10][11][12] In fact, the physicochemical properties of gels have often been explained in terms of the conformation of a subchain in network. However, an essential difference exists between a gel and a single polymer chain; subchains are fixed by a network structure, whereas a single polymer chain is not fixed.…”

Interaction between Covalent DNA Gels and a Cationic Surfactant

“…[30][31][32][33][34] The transition to the collapsed state is promoted by the favorable electrostatic interaction between the polyion and surfactant micelles. The gels studied so far have been made up from highly flexible polyions, that is, systems where the polyion chain has a possibility to adapt to the curvature of surfactant aggregates.…”