Dendrimer-Based Polyion Complex Vesicles: Loops Make Loose.

Abstract

Associations of amphiphiles assume their various morphologies (sphere, cylinder, lamella) according to the so-called packing parameter under thermodynamic control, which is the case for both small molecules like surfactants and polymeric amphiphiles. However, one may raise the question whether polymers can always relax fast enough to obey thermodynamic control, and how this may be checked. We discuss here a case of polyion complex (PIC) assemblies where the morphology appears to be subject to kinetic control. We combine poly (ethylene oxide)-co-polystyrene sulfonate block copolymers with cationic PAMAM dendrimers of various sizes (generations 2-7). The PEOm -PSSn diblocks, and the corresponding triblocks of twice the length (PSSn -PEO2m -PSSn ) should have nearly identical packing parameters, but we surprisingly find pronounced differences between their assemblies: the diblock produces core-shell micelles while the triblocks yield lamellar vesicles (PICsomes). Moreover, the micelles are very stable against added salt, whereas the vesicles are not only much more sensitive to added salt, but also appear to exchange matter on relevant time scales. We argue that small and largely quenched early-stage precursor complexes are responsible for the morphological and dynamic differences, implying that kinetic control may also be a way to obtain particles with well-defined and useful properties. The exciting new finding that triblocks produce more active vesicles will hopefully trigger the exploration of more pathways, and so learn how to tune PICsomes towards specific applications. This article is protected by copyright. All rights reserved.