Interactions between an Associative Amphiphilic Block Polyelectrolyte and Surfactants in Water: Effect of Charge Type on Solution Properties and Aggregation

Abstract

The study of interactions between polyelectrolytes (PE) and surfactants is of great interest for both fundamental and applied research. These mixtures can represent, for example, models of self-assembly and molecular organization in biological systems, but they are also relevant in industrial applications. Amphiphilic block polyelectrolytes represent an interesting class of PE, but their interactions with surfactants have not been extensively explored so far, most studies being restricted to non-associating PE. In this work, interactions between an anionic amphiphilic triblock polyelectrolyte and different types of surfactants bearing respectively negative, positive and no charge, are investigated via surface tension and solution rheology measurements for the first time. It is evidenced that the surfactants have different effects on viscosity and surface tension, depending on their charge type. Micellization of the surfactant is affected by the presence of the polymer in all cases; shear viscosity of polymer solutions decreases in presence of the same charge or nonionic surfactants, while the opposite charge surfactant causes precipitation. This study highlights the importance of the charge type, and the role of the associating hydrophobic block in the PE structure, on the solution behavior of the mixtures. Moreover, a possible interaction model is proposed, based on the obtained data.

Keywords: amphiphilic block copolymers; polyelectrolyte-surfactant complexes; polyelectrolytes; rheology; surface activity; surfactants.

Figure 1

Conformation of various kind of PE in solution: (a) salt-free conditions; (b) in saline water; (c) pearl-necklace model for hydrophobic PE; (d) globule conformation for highly hydrophobic PE; (e) amphiphilic block polyelectrolytes (ABPE) in salt-free conditions; (f) APBE in saline water.

Figure 2

Graphical representation of PESCs of opposite sign charge (top) and same sign charge (bottom).

Figure 3

(a) surface tension curve of Enordet at different polymer concentrations; (b) master curve of surface tension as a function of the surfactant/polymer ratio. The dotted line is intended as a guide for the eye.

Figure 4

Shear viscosity of a 1 wt % polymer solution with (a) increasing amount of Enordet; (b) 0.1% of CTAB, Pluronic and PEGMe.

Figure 5

Proposed schematic model for APBE/surfactant interactions.