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  1. Reduced Water Density in a Poly(ethylene oxide) BrushJames P. Viccaro, University of Chicago, CHE 0822838 ChemMatCARS laterally uniform flat PEO brush layer prepared at the air-water interface Air Objective: To investigate the electron density distribution inside a poly(ethylene oxide) (PEO) brush layer Poly(ethylene oxide)-poly(n-butyl acrylate) (PEO-PnBA) Water • condition for spreading: S (≡ γair-water– γpolymer-air – γpolymer-water)> 0 • S(air-PnBA-water) = +21 mJ/m2 > 0 XR measurements performed at various grafting density conditions XR measurements Conclusion: Inside of the PEO brush, the water density is significantly lower than that of bulk water, in particular, in the region close to the PnBA–water interface. This observation supports that PEO chains are hydrophobic when they are arranged in the polymer brush configuration. box model analysis Lee et al. J. Phys. Chem. Lett. (2012)