Hydration and Mobility of Poly(ethylene oxide) Brushes

Poly­(ethylene oxide) (PEO) hydration is an important factor determining brush properties and application efficacy. Using atomistic molecular dynamics simulations, we investigate hydration, static, and dynamic properties of PEO brushes on gold surface as functions of grafting density, σ. We found that at lower grafting densities PEO is well-hydrated except for the surface vicinity where we observe PEO adsorption substituting for the water layering. In pure THF or mixed THF/water solvent, there is no PEO adsorption on gold surface with water preferentially residing inside the PEO layer and THF forming a thin layer near the gold surface. In aqueous solutions, an increase in the grafting density results in PEO stretching away from the surface, the loss of hydration, and a steplike density profile with the brush height satisfying the expected σ1/3 scaling. We show that PEO hydration in the brush is the same as in aqueous solutions of the corresponding water content. While the residence time of hydrogen-bonded water increases, the hydration shell and PEO tail mobility are found to decrease substantially with an increase in grafting density, indicating that these properties associated with protein inhibition capability may be compromised in a dense brush.