Article (Scientific journals)
Molecular versus macroscopic perspective on the demixing transition of aqueous PNIPAM solutions by studying the dual character of the refractive index
Philipp, Martine; Aleksandrova, Ralitsa; Müller, Ulrich et al.
2014In Soft Matter, 10 (37), p. 7297-7305
Peer reviewed
 

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Keywords :
volume phase-transition; main-chain gels; lorentz-lorenz; swelling behavior; critical solution temperature; coil-globule transition; n-isopropylacrylamide; poly(n-isopropylacrylamide) solutions; cooperative hydration
Abstract :
[en] The phase separation of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions is known to strongly affect their volume expansion behaviour and the elastic moduli, as the latter are strongly coupled to the macroscopic order parameter. On the molecular scale, considerable changes in H-bonding and hydrophobic interactions, as well as in the structure govern the demixing process. However, the relationship between the molecular and macroscopic order parameters is unclear for such complex phase-separating solutions. We contribute to the clarification of this problem by relating optical to volumetric properties across the demixing transition of dilute to concentrated aqueous PNIPAM solutions. Far from the demixing temperature, the temperature dependence of the refractive index is predominantly determined by thermal expansion. In the course of phase separation, the refractive index is dominated by the anomalous behaviour of the specific refractivity, which reflects the spatio-temporally averaged changes in molecular interactions and the structural reorganization of the demixing solutions. Moreover, the presence of relaxation processes is studied by the complex expansion coefficient using the novel technique of temperature modulated optical refractometry.
Disciplines :
Physics
Author, co-author :
Philipp, Martine ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Aleksandrova, Ralitsa ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Müller, Ulrich ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Ostermeyer, M.
Sanctuary, Roland ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Muller-Buschbaum, P.
Krüger, Jan-Kristian ;  University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Language :
English
Title :
Molecular versus macroscopic perspective on the demixing transition of aqueous PNIPAM solutions by studying the dual character of the refractive index
Publication date :
2014
Journal title :
Soft Matter
ISSN :
1744-683X
Volume :
10
Issue :
37
Pages :
7297-7305
Peer reviewed :
Peer reviewed
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since 27 February 2015

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