Effect of Temperature on the Reentrant Condensation in Polyelectrolyte−Liposome Complexation

Abstract

Interactions of oppositely charged macroions in aqueous solution give rise to intriguing aggregation phenomena, resulting in finite-size, longlived clusters, characterized by a quite narrow size distribution. Particularly, the adsorption of highly charged linear polyelectrolytes on oppositely charged colloidal particles is strongly correlated and some short-range order arises from competing electrostatic interactions between like-charged polymer chains (repulsion) and between polymer chains and particle surface (attraction). The charge inversion observed for the polyelectrolytedecorated primary particles has been recently explained in terms of correlated adsorption. In these systems, long-lived clusters of polyelectrolytedecorated particles form in an interval of concentrations around the inversion point. However, the mechanisms that drive the aggregation and stabilize, at the different polymer/particle ratios, a well defined size of the aggregates are not completely understood. Nor is clear the role that the correlated adsorption plays in the aggregation, although the importance of 'patchy interactions' has been stressed as the possible source of attractive interactions between colloidal particles. Different models have been introduced to explain the formation of the observed finite-size cluster phase. However a central question still remains unanswered, i.e., whether the clusters are true equilibrium or metastable aggregates. To elucidate this point, in this work, we have investigated the effect of the temperature on the formation of the clusters. We employed liposomes built up by DOTAP lipid interacting with a simple anionic polyion, sodium polyacrylate, over an extended concentration range below and over the isoelectric condition. Our results show that the aggregation process can be described by a thermally-activated mechanism.

Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: A Monte Carlo simulation study in the Debye–Hückel approximation

“…Aggregates stop growing after reaching a characteristic size, determined by the net charge and the degree of non-uniformity. Such behavior is consistent with the observed 'reentrant condensation' and with the thermally activated character of the aggregation [30,31].…”

Salt-induced reentrant stability of polyion-decorated particles with tunable surface charge density

“…Within this framework, the aggregation of the pd-particles can hence be described as a thermally activated process [26] where, since the potential barrier height increases with their own size, a finite size of the clusters turns out to be eventually stable [33,58].…”

“…In fact in the presence of an oppositely charged polyelectrolyte many colloids, characterized by different structures and chemical compositions, like bare [28] and lipid-coated latex particles [29], ferric oxide particles [30], dendrimers [31] and micelles [32], show the "reentrant condensation" phenomenon. Within this scenario the clusters formed by pd-particles in absence of added salt are electrostatically stabilized (out-of-equilibrium) and an increase of temperature has a destabilizing effect on the system [26,33,19]. …”

Composition and properties of complexes between anionic liposomes and diblock copolymers with cationic and poly(ethylene oxide) blocks

“…Binding of a macroion to a charged liposome surface usually causes the liposomes to aggregate or fuse . Additional stability can be imparted to liposomes via their decoration with a hydrophilic non‐ionic polymer, e.g.…”