title: Swelling of polyelectrolyte and polyzwitterion brushes by humid vapors.
abstract: Swelling behavior of polyelectrolyte and polyzwitterion brushes derived from poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in water vapor is investigated using a combination of neutron and X-ray reflectivity and spectroscopic ellipsometry over a wide range of relative humidity (RH) levels. The extent of swelling depends strongly on the nature of the side-chain chemistry. For parent PDMAEMA, there is an apparent enrichment of water vapor at the polymer/air interface. Despite extensive swelling at high humidity level, no evidence of charge repulsion is found in weak or strong polyelectrolyte brushes. Polyzwitterionic brushes swell to a greater extent than the quaternized brushes studied. However, for RH levels beyond 70%, the polyzwitterionic brushes take up less water molecules, leading to a decline in water volume fraction from the maximum of ~0.30 down to ~0.10. Using a gradient in polymer chain grafting density (σ), we provide evidence that this behavior stems from the formation of inter- and intramolecular zwitterionic complexes.
authors.affiliation: Department of Chemical and Biomolecular Engineering, North Carolina State University , Raleigh, North Carolina 27695-7905, United States.
authors.forename: Casey J
authors.initials: CJ
authors.lastname: Galvin
authors.forename: Michael D
authors.initials: MD
authors.lastname: Dimitriou
authors.forename: Sushil K
authors.initials: SK
authors.lastname: Satija
authors.forename: Jan
authors.initials: J
authors.lastname: Genzer