Effect of solvent quality on the polymer adsorption from bulk solution onto planar surfaces

Abstract

Adsorption of uncharged homopolymers in good and theta solvents onto planar surfaces at various chain flexibility and polymer–surface attraction strengths was investigated by using a coarse-grained bead–spring polymer model and simulation techniques. Equilibrium properties of the interfacial systems were obtained from Monte Carlo simulations by monitoring the bead and polymer density profiles, the number of adsorbed beads and polymers, the components of the radius of gyration perpendicular and parallel to the surface as well as tail, loop, and train characteristics. The adsorption process starting with a polymer-free zone adjacent to the surface was examined by Brownian dynamic simulations. At equilibrium, the adsorbed amount increased upon increasing chain stiffness and in poorer solvent conditions, and the structural characteristics depended also on the chain stiffness and solvent condition. The initial adsorption was diffusion controlled, but soon it became governed by the probability of a polymer to be captured by the surface attraction. Flexible polymers became flattened after attaching, but their final relaxation mechanism involved an increase in perpendicular extension. There were fewer adsorbed beads and longer tails, which was driven by the surface pressure originating from the surrounding adsorbed polymers. This structural rearrangement became more prominent in poorer solvent conditions. Finally, the integration time, which denotes the adsorption time for adsorbed polymers to become fully integrated into the adsorbed layer, and the residence times of integrated polymers were analyzed. In particular, the latter became longer with increasing chain stiffness and shorter in poorer solvent conditions.