title: phase instability and molecular kinetics provoked by repeated crossing of the demixing transition of PNIPAM solutions.
abstract: The demixing process of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions can occur either via a nucleation and growth process or via spinodal decomposition. The ensuing self-assembly, leading to heterogeneous morphologies within the PNIPAM solution, is codetermined by kinetic processes caused by molecular transport. By subjecting PNIPAM solutions to cyclic changes in temperature leading to repeated crossing of the demixing transition, we are able to assess the importance of kinetics as well as of overheating and supercooling of the phase transition within the metastable range delimited by the binodal and spinodal lines. First indications about the location of these stability limits for the low- and high-temperature phases, separated by about 1.6 K, could be gained by detailed kinetic studies of the refractive index. These investigations are made possible due to the novel technique of temperature-modulated optical refractometry.
authors.affiliation: Laboratoire de Physique des Matériaux, Université du Luxembourg , Campus Limpertsberg, 162A, avenue de la faïencerie, L-1511 Luxembourg, Luxembourg.
authors.forename: Ralitsa
authors.initials: R
authors.lastname: Aleksandrova
authors.forename: Martine
authors.initials: M
authors.lastname: Philipp
authors.forename: Ulrich
authors.initials: U
authors.lastname: Müller
authors.forename: Rafael Jiménez
authors.initials: RJ
authors.lastname: Riobóo
authors.forename: Martin
authors.initials: M
authors.lastname: Ostermeyer
authors.forename: Roland
authors.initials: R
authors.lastname: Sanctuary
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum
authors.forename: Jan K
authors.initials: JK
authors.lastname: Krüger