Abstract
Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (<1% by mass) has been observed in scattering experiments and molecular dynamics simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics.
Highlights
Of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (o1% by mass) has been observed in scattering experiments and molecular dynamics simulations
We demonstrate that at high-polymer concentration, both AB diblock and ABA triblock copolyelectrolytes assemblies have near identical scattering signatures; the evolution of scattering patterns with increasing polymer concentrations follow distinct pathways
The scattering intensity (I(q), q is the wave vector) profiles from both di- and triblock copolyelectrolyte assemblies, shown in Fig. 1a, indicate incipient ordering in the structures at high-polymer concentration f (10% by mass), with strong correlations among the polyelectrolyte complex (PEC) domains leading to prominent primary peaks in the I(q) profiles
Summary
Of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (o1% by mass) has been observed in scattering experiments and molecular dynamics simulations. We show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Our findings mark a significant departure from the established uncharged, amphiphilic block copolymer-like assembly mechanisms for complexation driven assemblages, and will have implications in guiding the design principles for PEC gels for many applications such as cell scaffolds for tissue engineering, charge based flocculating agents for water purification, thin nutrient films for agriculture and extremely sensitive theranostic probes
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