Effect of Grafting Density on the Adsorption of End-Grafted Polymer Chains

The critical adsorption temperature (T-CAP) and adsorption process of end-grafted polymer chains with grafting density f on a homogeneous, attractive surface are studied using Langevin dynamics simulations. Results show that T-CAP is roughly a constant at low f far below the critical grafting density f(c) which separates the polymer brush from the mushroom region, then it decreases with increasing f due to the inter-polymer repulsive interactions, and finally becomes a constant roughly independent of polymer length at f > f(c) because only the chain sections closest to the surface are involved in the adsorption process. However, T-CAP is only estimated for f less than f(limit) = 1.5/N where more than 50% of polymer monomers (N) per chain can be adsorbed at low temperature. The dynamic adsorption process for the polymer chains below f(limit) and T-CAP shows that the adsorption time tau(ads) (for polymer chains from desorbed state to adsorbed state) changes non-monotonically with f and exhibits a maximum at f(tau,max) = 0.5f(limit). The increase of tau(ads) below f(tau,max) is due to the inter-polymer repulsive interactions which hinder the adsorption. Whereas the decrease of tau(ads) at high f is attributed to the decrease of the number of adsorbed monomers per chain. Our study reveals that the critical adsorption temperature and adsorption process of the end-grafted polymer chains are dependent on the grafting density.