Physical Insight for Grafting Polymer Chains onto the Substrate via Computer Simulations: Kinetics and Property

Molecules adsorbed or attached on a surface is a quite basic phenomenon in numerous chemical or biological systems. Grafting-onto is considered as a feasible way to achieve it. The grafting reaction is essentially controlled by the diffusion of the molecules, thus it is more likely a physical issue, instead of a chemical issue. Because of the experimental difficulty in measuring the properties of surface-attached molecules ( e.g. , the polymeric molecules), the surface-bound molecules are often assumed as with the same properties as that of the start feeding ones in solution. This assumption was even used to guide further characterization, while it is proved to be invalid by different quantifying methods. Consequently, an effective prediction for the properties of surface-bound molecules is still lacking. Based on a microscopic level and a dynamic perspective, the grafting process onto a flat substrate with polydisperse feeding polymeric molecules is investigated in-depth by coarse-grained Brownian dynamics simulation as well as model analysis. We find from simulations that for the final grafting density σ g and the mean chain length of start feeding molecules < N 0 >, the dependence of σ g -< N 0 > γ with the constant exponential factor γ may be a determined rule for one-end functionalized flexible linear polymer chains grafting on the flat substrate. Since grafting-onto is a multiple interplayed process, our simulation study indicates that there is an optimized initial concentration of start feeding molecules for achieving high grafting density of surface-bound polymers. We also propose a correctional equation to quantitatively predict the molecular weight distribution (MWD) of surface-bound polymeric molecules, which may be effective for predicting the MWD of the surface-bound ones in specific conditions. This simulation study helps to better understand the kinetics of grafting-onto process, and serves as a theoretical guide to achieve the precise design of surface modification materials via grafting-onto strategy.