Recently, there has been a renewed interest in the study of the mechanisms governing the complexation of polyelectrolytes and oppositely charged colloidal particles, due to the still not completely understood aggregation phenomenology and to the increased awareness of their potential for innovative applications in nano-medicine and nano-biotechnology [1]. Despite the initial disparity of the early results that appeared in the literature, due to the variety of the experimental conditions and to the intrinsic complexity of these systems, the interesting phenomenology can now be described within a unified picture [2] where electrostatic interactions are the main driving force of the cluster formation, and the non-uniformity of charge distribution, resulting from the correlated adsorption of the polyelectrolyte on the colloid surface, plays a pivotal role. However, there is still a lack of a complete theory able to describe satisfactorily all the different features of the observed complexity. To clarify this point, we begin to explore systematically the phase diagram of a typical polyelectrolyte/colloid system, considering in addition to the effects of the polyelectrolyte/colloid charge ratio and temperature, also those of the ionic strength of the aqueous suspending medium. We show that a simple interparticle potential built up as the sum of two terms is able to account for the observed phase diagram very satisfactorily [3]. Now we consider the effect on the phase diagram of the surface charge density on the colloidal particles and show how the salt addition modifies the phase diagram promoting the cluster dissolution due to a polyion desorption, as predicted by theoretical models [4].
[1] Editorial, Nat. Biotechnol., 2003, 21, 1113 [2] F. Bordi et al, J. Phys.: Condens. Matter, 2009, 21, 203102 [3] S. Sennato, et al. Soft Matter, 2012, 8, 9384-9395 [4] R. G. Winkler et al. Phys. Rev. Lett., 2006, 96, 066103
simona.sennato@roma1.infn.it
