Micciulla, SamanthaMichalowsky, JulianSchroer, Martin A.Holm, ChristianKlitzing, Regine vonSmiatek, Jens2017-10-242017-10-2420161463-9076https://depositonce.tu-berlin.de/handle/11303/6883http://dx.doi.org/10.14279/depositonce-6222The binding effects of osmolytes on the conformational behavior of grafted polymers are studied in this work. In particular, we focus on the interactions between urea and poly(N-isopropylacrylamide) (PNIPAM) brushes by monitoring the ellipsometric brush thickness for varying urea concentrations over a broad temperature range. The interpretation of the obtained data is supported by atomistic molecular dynamics simulations, which provide detailed insights into the experimentally observed concentration-dependent effects on PNIPAM-urea interaction. In particular, in the low concentration regime (c(u) <= 0.5 mol L-1) a preferential exclusion of urea from PNIPAM chains is observed, while in the high concentration regime (2 <= c(u) <= 7 mol L-1) a preferential binding of the osmolyte to the polymer surface is found. In both regimes, the volume phase transition temperature (T-tr) decreases with increasing urea concentration. This phenomenon derives from two different effects depending on urea concentration: (i) for c(u) <= 0.5 mol L-1, the decrease of T-tr is explained by a decrease of the chemical potential of bulk water in the surrounding aqueous phase; (ii) for c(u) >= 2 mol L-1, the lower T-tr is explained by the favorable replacement of water molecules by urea, which can be regarded as a cross-linker between adjacent PNIPAM chains. Significant effects of the concentration-dependent urea binding on the brush conformation are noticed: at c(u) <= 0.5 mol L-1, although urea is loosely embedded between the hydrated polymer chains, it enhances the brush swelling by excluded volume effects. Beyond 0.5 mol L-1, the stronger interaction between PNIPAM and urea reduces the chain hydration, which in combination with cross-linking of monomer units induces the shrinkage of the polymer brush.en540 Chemie und zugeordnete WissenschaftenArticle1463-908426817960