Molecular Dynamics Simulation of Sheared Polymer Brushes

Le principal objectif de cette thèse est d'enquêter sur la réponse des brosses polymères à une contrainte de cisaillement par le biais de simulations de dynamique moléculaire utilisant le modèle générique bille-ressort de Kremer et Grest. Ces simulations peuvent être vues comme un microscope à haute résolution qui va fournir des informations microscopiques au-delà du simple cas de la description statistique du système à l'équilibre. Le système modèle de brosses de polymères utilisé lors des simulations numériques est constitué de chaînes de polymères neutres et monodisperses attachées à deux substrats plans sous condition de bon solvant [...]The main subject of this thesis is to investigate the complex fluid response utilizing Molecular Dynamics simulation of the generic bead-spring model by Kremer and Grest as a "high-resolution microsope" to resolve molecular structure beyond static equilibrium. The model system contains charge-neutral polymer chains attached to two substrates under good solvent condition, creating two opposing polymer brushes. Furthermore, explicit solvent molecules (Lennard-Jones dimers) are added to the system simulating an incompressible fluid. The Dissipative Particle Dynamics Thermostat is implemented to keep the temperature constant fulfilling Newtons third law, thus assuring momentum conservation and simulating hydrodynamic correlations correctly. Those systems are compared to solvent-free counterparts while varying the wall distance between the grafted layers and their molecular parameters, such as chain length and grafting density. This work employs the planar Couette flow geometry, where both opposing brushes are strongly compressed and a simple shear flow is applied by moving the substrates laterally in opposite directions.[...