title: Phase separation in semidilute aqueous poly(N-isopropylacrylamide) solutions.
abstract: The phase separation mechanism in semidilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is investigated with small-angle neutron scattering (SANS). The nature of the phase transition is probed in static SANS measurements and with time-dependent SANS measurements after a temperature jump. The observed critical exponents of the phase transition describing the temperature dependence of the Ornstein-Zernike amplitude and correlation length are smaller than values from mean-field theory. Time-dependent SANS measurements show that the specific surface decreases with increasing time after a temperature jump above the phase transition. Thus, the formation of additional hydrogen bonds in the collapsed state is a kinetic effect: A certain fraction of water remains as bound water in the system. Moreover, H-D exchange reactions observed in PNIPAM have to be taken into account.
authors.affiliation: Physik-Department, Lehrstuhl für Funktionelle Materialien/Physik Weicher Materie, Technische Universität München, James-Franck-Str.1, 85748 Garching, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Meier-Koll
authors.forename: Vitaliy
authors.initials: V
authors.lastname: Pipich
authors.forename: Peter
authors.initials: P
authors.lastname: Busch
authors.forename: Christine M
authors.initials: CM
authors.lastname: Papadakis
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins; D001709:Biotechnology; D006860:Hydrogen Bonding; D007700:Kinetics; D033363:Neutron Diffraction; D044367:Phase Transition; D011108:Polymers / Q000737:chemistry*; D053838:Scattering, Small Angle; D012996:Solutions; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D011108:Polymers; D012996:Solutions; D014867:Water; C052970:poly-N-isopropylacrylamide