Journal Article

FZJ-2020-00690

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Necklace-like microstructure in shallow-quenched aqueous solutions of poly( n -isopropylacrylamide), detected by advanced small-angle neutron scattering methods

Koizumi, S. (Corresponding author) ; Annaka, M. ; Schwahn, D.TUM*

2019
Royal Soc. of Chemistry London

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Please use a persistent id in citations: doi:10.1039/C8SM02416B

Abstract: The microstructure of aqueous poly(N-isopropyl acrylamide) (PNIPA) gel and solution was investigated by small-angle neutron scattering (SANS) in the vicinity of the gel volume phase transition at TV (= 34 °C). The SANS technique was reinforced by refractive neutron lenses and perfect single crystals in order to get access to μm length scales. At 31 °C SANS shows Ornstein–Zernike (OZ) type scattering in the swollen gel which at 32 °C starts to deviate from the OZ-formalism, exhibiting excess scattering and at the wave number qc ≅ 5 × 10−3 Å−1 a crossover to Porod's asymptotic q−4 power law. For shallow quenches of ΔT < 1.0 K above TV the excess scattering intensity is further increasing whereas qc is shifting toward lower values. Based on this observation and analysis of the SANS q-profiles, we propose a necklace-like microstructure consisting of PNIPA-rich globules of R ≅ 100 Å size which are connected by swollen PNIPA chains and stabilized for more than a day by pinning of chain connectivity. The formation of PNIPA globules near TV is discussed in terms of partially cooperative dehydration which is crucial to explain the “miscibility square phase behavior” of aqueous PNIPA solutions. Globule-like structure was also found in aqueous PNIPA solution of size slightly larger than in gels. At deeper quenches of gels above TV (ΔT > 1.0 K) the globules are aggregating to larger objects of R ≅ 0.24 μm size as determined from a strong intensity upturn in the small q-region of USANS

Keyword(s): Chemical Reactions and Advanced Materials (1st) ; Chemistry (2nd)

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Contributing Institute(s):

1. JCNS-FRM-II (JCNS-FRM-II)
2. Neutronenstreuung (JCNS-1)
3. Heinz Maier-Leibnitz Zentrum (MLZ)

Research Program(s):

1. 6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623) (POF3-623)
2. 6G15 - FRM II / MLZ (POF3-6G15) (POF3-6G15)

Experiment(s):

1. KWS-1: Small angle scattering diffractometer (NL3b)

Appears in the scientific report 2020

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Database coverage:
; Allianz-Lizenz / DFG ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; IF < 5 ; JCR ; National-Konsortium ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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