Is Osmotic Pressure Relevant in the Mechanical Confinement of a

Article pubs.acs.org/Macromolecules

Is Osmotic Pressure Relevant in the Mechanical Confinement of a Polymer Brush? Stephen B. Abbott,†,‡ Wiebe M. de Vos,*,‡,§ Laura L. E. Mears,† Beatrice Cattoz,† Maximilian W. A. Skoda,∥ Robert Barker,⊥ Robert M. Richardson,† and Stuart W. Prescott‡,# †

H H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, U.K. School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K. § Membrane Science and Technology, Mesa+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, Netherlands ∥ STFC ISIS Facility, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, U.K. ⊥ Institut Laue Langevin, 71 avenue des Martyrs, F-38042 Grenoble, France # School of Chemical Engineering, UNSW Australia, UNSW, Sydney, NSW 2052, Australia ‡

S Supporting Information *

ABSTRACT: The structures of polymer brushes under confinement were measured using a combination of neutron reflectivity and a surface force type apparatus. The samples were either poly(ethylene oxide), PEO, used to investigate the effect of the grafting density or poly(acrylic acid), PAA, used to determine the effect of charge on the structure of a polymer brushes under confinement. Without confinement both PEO and PAA brushes are found to be highly swollen with water, >50% v/v, with the expected parabolic brush structure. Compression of the PEO brushes with as little as 0.5 bar of confinement is found experimentally to reduce the brush to a polymer block of uniform density that is significantly dehydrated,