title: Neutron reflectivity study of the swollen structure of polyzwitterion and polyeletrolyte brushes in aqueous solution.
abstract: The swollen brush structures of polycation and zwitterionic polymer brushes, such as poly(2-methacryloyloxyethyltrimethylammonium chloride) (PMTAC), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS), in aqueous solutions of various ionic strengths were characterized by neutron reflectivity (NR) measurements. A series of the polyelectrolyte brushes were prepared by surface-initiated controlled radical polymerization on silicon substrates. A high-graft-density PMTAC brush in salt-free water (D2O) adopted a two-region step-like structure consisting of a shrunk region near the Si substrate surface and a diffuse brush region with a relatively stretched chain structure at the solution interface. The diffuse region of PMTAC was reduced with increase in salt (NaCl) concentration. The PMAPS brush in D2O formed a collapsed structure due to the strong molecular interaction between betaine groups, while significant increase in the swollen thickness was observed in salt aqueous solution. In contrast, no change was observed in the depth profile of the swollen PMPC brush in D2O with various salt concentrations. The unique solution behaviors of zwitterionic polymer brushes were described.
authors.affiliation: a Japan Science and Technology Agency, ERATO Takahara Soft Interfaces Project, CE80 Kyushu University , 744 Motooka, Nishi-ku, Fukuoka 819-0395 , Japan.
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ishihara
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takahara
mesh_terms: D004573:Electrolytes / Q000737:chemistry*; D033363:Neutron Diffraction / Q000379:methods*; D009994:Osmolar Concentration; D011108:Polymers / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D011108:Polymers; D012996:Solutions; D014867:Water
keywords: ionic strength; neutron reflectivity; phosphobetaine; polymer brushes; polyzwitterions; sulfobetaine