From Molecular Dehydration to Excess Volumes of Phase-Separating PNIPAM Solutions

Philipp, Martine; Kyriakos, Konstantinos; Silvi, Luca; Petry, Winfried; Krüger, Jan-Kristian; Papadakis, Christine; Mueller-Buschbaum, Peter

doi:10.1021/jp501539z

Reference : From Molecular Dehydration to Excess Volumes of Phase-Separating PNIPAM Solutions


	Document type :	Scientific journals : Article
	Discipline(s) :	Physical, chemical, mathematical & earth Sciences : Physics
	To cite this reference:	http://hdl.handle.net/10993/16953

Title :	From Molecular Dehydration to Excess Volumes of Phase-Separating PNIPAM Solutions
Language :	English
Author, co-author :	Philipp, Martine [Technische Universität München - TUM > Physik Department]
	Kyriakos, Konstantinos [Technische Universität München - TUM > Physik Department]
	Silvi, Luca [Technische Universität München - TUM > Physik Department, Heinz Maier-Leibnitz Zentrum]
	Petry, Winfried [Technische Universität München - TUM > Physik Department, Heinz Maier-Leibnitz Zentrum]
	Krüger, Jan-Kristian [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
	Papadakis, Christine [Technische Universität München - TUM > Physik Department]
	Mueller-Buschbaum, Peter [Technische Universität München - TUM > Physik Department]
Publication date :	2014
Journal title :	Journal of Physical Chemistry B
Publisher :	American Chemical Society
Volume :	118
Pages :	4253-4260
Peer reviewed :	Yes (verified by ORBi^lu)
Audience :	International
ISSN :	1520-6106
e-ISSN :	1520-5207
City :	Washington
Country :	DC
Abstract :	[en] For aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions, a structural instability leads to the collapse and aggregation of the macromolecules at the temperature-induced demixing transition. The accompanying cooperative dehydration of the PNIPAM chains is known to play a crucial role in this phase separation. We elucidate the impact of partial dehydration of PNIPAM on the volume changes related to the phase separation of dilute to concentrated PNIPAM solutions. Quasi-elastic neutron scattering enables us to directly follow the isotropic jump diffusion behavior of the hydration water and the almost freely diffusing water. As the hydration number decreases from 8 to 2 for the demixing 25 mass % PNIPAM solution, only a partial dehydration of the PNIPAM chains occurs. Dilatation studies reveal that the transition-induced volume changes depend in a remarkable manner on the PNIPAM concentration of the solutions. The excess volume per mole of H2O molecules expelled from the solvation layers of PNIPAM during phase separation probably strongly increases from dilute to concentrated PNIPAM solutions. This finding is qualitatively related to the immense strain-softening previously observed for demixing PNIPAM solutions.
Permalink :	http://hdl.handle.net/10993/16953
DOI :	10.1021/jp501539z

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