Etude de la formation de complexes entre nanoparticules et polyelectrolytes de charges opposées par simulations du type Monte Carlo.’’

Due to their fascinating, complex and important modifications of solutions properties, mixtures of polyelectrolyte chains (such as synthetic polymers, polysaccharides, DNA…) and oppositely charged colloids (such as organic and inorganic particles, proteins, micelles …) stimulate a great interest in soft condensed matter, biology, environmental chemistry and industrial applications. Applications in the field of water treatment as flocculating water insoluble mixtures, food technology, powder processing are numerous and extension to gene therapy and bioengineering is today under consideration. In environmental chemistry, interactions between inorganic colloids and biopolymers and complexation processes are expected to control the coagulation of colloidal material in suspension and the fate and transport of trace pollutants associated to them. However, the long range attractive and/or repulsive character of electrostatic interactions between polyelectrolytes and colloids, solution chemistry, geometry and concentration of both polyelectrolytes and colloids, etc, give these solutions specific properties which are partially understood. Thus, so far, little is known in the rational use of polyelectrolytes with oppositely charged colloidal particles for e.g in water treatment processes. Owing to the important potential of computer simulations to provide qualitative and quantitative means of understanding the factors that could influence polyelectrolyte chains and particle interactions, we describe here a Monte Carlo approach to get insight into the behaviour of a flexible, semi-flexible and rigid polyelectrolyte with the presence of an oppositely charged colloid. As the ionic concentration is expected, via screening effects, to play a key role in controlling both chain conformation (via the electrostatic persistence length) and polyelectrolyte/particle interaction energy we also focused on it. The adsorption/desorption limit which is a key parameter for technical applications of polyelectrolyte/particle mixtures is also investigated. The polyelectrolyte conformations are analysed prior to and after adsorption, the polymer interfacial structure is investigated as well as the particle surface coverage and polyelectrolyte adsorbed amount.