Abstract
The rheological properties of hydrogels prepared by physical interactions between oppositely charged polyelectrolyte and surfactant in micellar form were studied. Specifically, hyaluronan was employed as a negatively charged polyelectrolyte and Septonex (carbethopendecinium bromide) as a cationic surfactant. Amino-modified dextran was used as a positively charged polyelectrolyte interacting with sodium dodecylsulphate as an anionic surfactant. The effects of the preparation method, surfactant concentration, ionic strength (the concentration of NaCl background electrolyte), pH (buffers), multivalent cations, and elevated temperature on the properties were investigated. The formation of gels required an optimum ionic strength (set by the NaCl solution), ranging from 0.15–0.3 M regardless of the type of hydrogel system and surfactant concentration. The other compositional effects and the effect of temperature were dependent on the polyelectrolyte type or its molecular weight. General differences between the behaviour of hyaluronan-based and cationized dextran-based materials were attributed to differences in the chain conformations of the two biopolymers and in the accessibility of their charged groups.
Highlights
Interactions between polyelectrolytes and oppositely charged surfactants constitute an area of intensive research for theoretical reasons and because of the practical applications of these systems, e.g., in cosmetic, pharmaceutical, and food products [1]
We focused in more detail on the effects of various processing parameters on the properties of similar gels prepared using a slightly different cationic surfactant and investigated a reversely charged system—a positively charged polyelectrolyte and an anionic surfactant
The independency of viscoelastic properties on the preparation method was observed for all tested hyaluronan and dextran hydrogels
Summary
Interactions between polyelectrolytes and oppositely charged surfactants constitute an area of intensive research for theoretical reasons and because of the practical applications of these systems, e.g., in cosmetic, pharmaceutical, and food products [1]. Kizilay et al [1] overviewed the mechanistic and structural features of the complexation and coacervation of polyelectrolytes with oppositely charged colloids, including surfactant micelles. The first interaction step is the linking of the colloid and polyelectrolyte, which is described by two types of model—either the “condensation”. Polyelectrolyte–colloid interactions depend mainly on the charge per polyelectrolyte repeat unit, the ionic strength, pH and the colloid charge density. Association typically continues in several subsequent steps, controlled by the concentration of interacting species: non-interacting, individual polymers and colloids (e.g., due to the low concentration of interacting species or the subcritical colloid surface charge density); primary complexes of an intrapolymer type; soluble aggregates; and coacervates (the whole system is separated into two immiscible liquid phases, one of which—the coacervate—is relatively concentrated in macromolecules). Intrapolymer complexes are Polymers 2019, 11, 927; doi:10.3390/polym11050927 www.mdpi.com/journal/polymers
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