Interface-Induced Disassembly of a Self-Assembled Two-Component Nanoparticle System

Abstract

We present a study of static and dynamic interfacial properties of self-assembled polyelectrolyte complex nanoparticles (size 110-120 nm) containing entrapped surfactant molecules at a fluid/fluid interface. Surface tension vs time measurements of an aqueous solution of these polyelectrolyte complex nanoparticles (PCNs) show a concentration-dependent biphasic adsorption to the air/water interface while interfacial microrheology data show a concentration-dependent initial increase in the surface viscosity (up to 10(-7) N·m/s), followed by a sharp decrease (10(-9) N·m/s). Direct visualization of the air/water interface shows disappearance of particles from the interface over time. On the basis of these observations, we propose that the PCNs at fluid/fluid interfaces exist in two states: initial accumulation of PCNs at the air/water interface as nanoparticles, followed by interface induced disassembly of the accumulated PCNs into their components. The lack of change in particle size, charge, and viscosity of the bulk aqueous solution of PCNs with time indicates that this disintegration of the self-assembled PCNs is an interfacial phenomenon. Changes in energy encountered by the PCNs at the interface lead to instability of the self-assembled system and dissociation into its components. Such systems can be used for applications requiring directed delivery and triggered release of entrapped surfactants or macromolecules at fluid/fluid interfaces.

Effects of monovalent and multivalent ions on the stability of a polyelectrolyte complex with entrapped surfactants

“…In this article, we report monovalent-and multivalent-salt-induced changes in the particle size and stability of refined PECs with entrapped surfactants. We showed previously that these PECs were stable over several months 14 when suspended in water and ascertained that the effects described in this study were a result of the addition of salts. In contrast with the observations for polyelectrolyte-surfactant mixtures, we found that overall for our nanoparticle system without any excess components, the addition of salts caused an increase in the particle size, a decrease in the f potential, and ultimately, a decrease in the precipitation.…”

“…The PEI/SDS PECs were formed as a result of strong electrostatic interactions between the branched cati-onic PEI of high molecular weight and SDS in a ratio of 3 : 1 w/w. 14 This stoichiometry implies that in our system of nanoparticles, there was originally an excess of PEI. Dautzenberg and Kriz 29 proposed that polyelectrolyte-surfactant complexes exist as highly compact, almost spherical particles with a chargeneutralized core, surrounded by chains of the polyelectrolyte that is in excess.…”

“…The PEI/SDS mixtures were prepared according to the same procedure described in a previous work. 14 The positively charged PEI/SDS nanoparticles were prepared by the mixture and constant stirring of 0.25% PEI and 26.6 mM SDS stock solutions at a weight ratio of 3 : 1. After 5 min of mixing, the free surfactants and PEI were eliminated from the freshly prepared PEC dispersions by repeated centrifugation at 15,000 rpm for 1.5 h; this caused the free polyelectrolytes and surfactants to separate into the supernatant, whereas the desired PECs were contained in the coarcevate phase.…”

“…13 In a recent publication, we reported the interfacial and bulk properties of such a polyelectrolyte-based system with entrapped surfactant and demonstrated that these PECs displayed a uniform size of 110-120 nm and remained extremely stable in bulk water solutions over several months. 14 In this article, we focus on the effects of the addition of monovalent and multivalent ions on the stability of our PEC system. The effect of salts on the stability of polyelectrolyte-surfactant mixtures and the formation of polyelectrolyte-surfactant Additional Supporting Information may be found in the online version of this article.…”

Polyelectrolyte/surfactant films spread from neutral aggregates

“…26 Approaches to control the interfacial properties of P/S mixtures by tuning the experimental pathway have been recently employed. For example, Dhar et al described the preparation of films from refined P/S nanoparticles, 27,28 while Tong et al reported the interfacial disassembly of positively charged P/S nanoparticles triggered by particle-particle interactions. 29 Also, Lee et al formed stable films of poly(sodium styrene sulfonate) and alkyltrimethylammonium bromides of different chain lengths by spreading a small aliquot of mixed solution in an organic solvent.…”