Reduced Water Density in a Poly(ethylene oxide) Brush.
A model poly(ethylene oxide) (PEO) brush system, prepared by spreading a poly(ethylene oxide)-poly(n-butyl acrylate) (PEO-PnBA) amphiphilic diblock copolymer onto an air-water interface, was investigated under various grafting density conditions by using the X-ray reflectivity (XR) technique. The overall electron density profiles of the PEO-PnBA monolayer in the direction normal to the air-water interface were determined from the XR data. From this analysis, it was found that 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. Separate XR measurements with a PnBA homopolymer monolayer confirm that the reduced water density within the PEO-PnBA monolayer is not due to unfavorable contacts between the PnBA surface and water. The above result, therefore, lends support to the notion that PEO chains provide a hydrophobic environment for the surrounding water molecules when they exist as polymer brush chains.
†School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Hoyoung
H
Lee
†School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Dae Hwan
DH
Kim
†School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Hae-Woong
HW
Park
†School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
Nathan A
NA
Mahynski
‡Advanced Photon Source, University of Chicago, Argonne, Illinois 60439, United States.
Kyungil
K
Kim
‡Advanced Photon Source, University of Chicago, Argonne, Illinois 60439, United States.
Mati
M
Meron
‡Advanced Photon Source, University of Chicago, Argonne, Illinois 60439, United States.
Binhua
B
Lin
†School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
You-Yeon
YY
Won
X-ray reflectivity; air−water interface; block copolymer; poly(ethylene oxide); poly(n-butyl acrylate)