Effective potentials induced by nematic order

NICOLÁS A. GARCÍA; NICOLETTA GNAN; EMANUELA ZACCARELLI

Milan

Congreso; Italian Soft Days; 2016

Politécnico de Milan

Effective interactions play an important role in the physics of colloidal dispersions. The most established way to tune effective potentials is by means of depletion[1]. More recently, effective forces modified by the spontaneous self-assembly of the co-solute have been studied, with critical Casimir forces being a famous example[2]. In addition Casimir-like forces have been found close to the percolation transition[3].In this work, we examine the effective forces generated by a co-solute which self-organizes into linear chains[4]. Such situation may be relevant in crowded environments and for biological systems. We thus perform equilibrium 3D Monte Carlo simulations to calculate the effective potential between two large colloids immersed in a solution composed of depletant particles ten times smaller. These particles are modelled as patchy colloids in which a hard-core repulsion is complemented by two short-ranged attractive ´sticky´ spots at the particle poles[5]. At low depletant densities, we evaluate the potentials for a range of temperatures to assess the validity of a polydisperse Asakura-Oosawa model[3] which treats the patchy particle chains as an ideal depletant of size given by their radius of gyration. At higher cosolute densities, we find that the polymer chains tend to correlate their orientations, turning the solution into a quasi-nematic system (see figure). We will present results under these conditions and the features of the associated effective potentials.