Effect of grafting density on the adsorption of end-grafted polymer chains

Abstract

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 τ ads (for polymer chains from desorbed state to adsorbed state) changes non-monotonically with f and exhibits a maximum at f τ,max = 0.5 f limit . The increase of τ ads below f τ,max is due to the inter-polymer repulsive interactions which hinder the adsorption. Whereas the decrease of τ 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. • Critical adsorption temperature of polymer is dependent on the grafting density. • Inter-polymer repulsive interactions decrease the critical adsorption temperature. • Critical adsorption temperature decreases fast near the critical grafting density. • Inter-polymer repulsive interactions increase the adsorption time of polymer. • Adsorption time decreases when the number of adsorbed monomers per chain decreases.