title: Dynamic evolving two-component supramolecular gels-hierarchical control over component selection in complex mixtures.
abstract: We report a two-component acid-amine gelation system which forms instant organogels on simple mixing. We investigate self-assembly using a wide range of different amines and identify the optimum amines for gelation to occur. Using NMR and other spectroscopic methods, we unambiguously determine the stoichiometry of the complex responsible for gelation (1:1) and characterize the noncovalent interactions responsible for gelation. Using Kamlet-Taft parameters we gain a detailed understanding of the role of solvent on gelation. Most importantly, we explore the ability of these multicomponent systems to assemble from complex mixtures, and using NMR can determine which components are preferentially taken up into the immobile "solid-like" fiber network and which components remain mobile in the "liquid-like" solvent phase. In this way, we determine that the component selection process is controlled by the two key steps in hierarchical assembly: (i) acid-base complex formation (as predicted by the pKa of the amine) and (ii) gel fiber assembly (as predicted by the Tgel value). These parameters therefore enable a predictive understanding of the way in which complex mixtures self-organize and assemble and also how the sorted assemblies disassemble on heating. In a key experiment, we demonstrate that these materials are highly responsive and that a preformed gel, exposed to a new component, evolves, adapts, and heals its composition in response to the thermodynamic preferences of the overall system.
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
authors.forename: William
authors.initials: W
authors.lastname: Edwards
authors.forename: David K
authors.initials: DK
authors.lastname: Smith