| The present proposal deals with colloidal objects that arise in mixtures of polycations and polyanions. The common feature in all these systems is that they contain a small volume of insoluble polyelectrolyte complex or complex coacervate which is a peculiar kind of material combining characteristics of both common polymers and ionic liquids. A general thermodynamic theory that is capable of describing these complexes is still lacking. There are many unanswered questions as to the level of participation of small ions (protons, small cations and anions) into the complexes, their mechanical behaviour, diffusion of their components, kinetics of exchange and dissolution, and surface activity. Using polyelectrolyte complexation it is possible to construct a large variety of controlled 'microphases' or molecular assemblies in the nanoscopic size range. These molecular assemblies involving macro-ions form the focus of our project. It is part of a larger effort to (i) develop a 'construction kit' based on self-assembly principles (which allows to prepare alarge variety of (functional) colloidal structures by simple mixing operations), and (ii) understand the rules which govern various classes of molecular assemblies. Complex coacervate core micelles are colloidal particles formed when two polyelectrolytes (polyanion and polycation) are mixed, one of which carries a neutral, water-soluble block. Given the pH and ionic strength of the aqueous medium, micelles form in a particular composition window, which is easily monitored by means of light scattering. The very general self-assembling tendency of macro-ion mixtures is expected to give rise to a plethora of assemblies and structures, in particular when the macro-ionic interaction is judiciously combined with other kinds of attractive (e.g. solvophobic, hydrogen bonding) or repulsive (solvophilic or segregative) interactions. Our proposal is constructed around three themes, namely exploring (I) the morphological 'landscape' (surface curvature variations, mixed coronas, core variations), studying (II) the behaviour at interfaces (solid substrates and L/L interfaces, wetting phenomena, surface patterning effects), and (III) developing the theory for macro-ion assembly. The morphology (I) is expected to be particularly rich for the class of systems proposed here, mainly because the electrostatic attraction dictates the composition of the colloidal particles to a large extent. The interaction between surfaces (II) and complex coacervates has some unusual features, probably stemming from the hybrid character of these materials. This is rather unexplored territory. In addition, the morphological richness in solution is likely to have its impacton properties of interfacial films. Theoretical models (III) of macro-ion assembly (at the mesoscopic level) do hardly exist; constructing an improved theory is a major challenge. The use of self-consistent field (SCF) modeling of inhomogeneous polymer systems (a powerful tool for modelling molecularly complex, inhomogeneous systems) must be considered with care because the correlated plus/min interactions inside macro-ionic assemblies are so far not appropriately captured. We intend to develop a way to incorporate charge complexation into SCF. As a complement, we intend to use, e.g. dissipative particle dynamics, Monte Carlo procedures or integral theories for liquids to get complex coacervation phase diagrams. Finally, we want to derive coarse-grained scaling expressions for observed properties like aggregation number, size, and shape. Innovative aspects: Strategies based on ionic interactions aiming at assembling molecules into supramolecular objects of well-controlled, nanoscopic dimensions have never been very systematically explored nor have the possibilities for manipulating molecules using combinations of ionic and non-ionic interactions been exploited. Ionic interactions driving the assembly are not understood. This is a vast new territory that we want to explore. |
