Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods

Satoshi Koizumi, Annaka Masahiko, Dietmar Schwahn

Research output: Contribution to journalArticle

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 T V (= 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 q c ≅ 5 × 10 −3 Å −1 a crossover to Porod's asymptotic q −4 power law. For shallow quenches of ΔT < 1.0 K above T V the excess scattering intensity is further increasing whereas q c 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 T V 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 T V (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.

Original languageEnglish
Pages (from-to)671-682
Number of pages12
JournalSoft Matter
Volume15
Issue number4
DOIs
Publication statusPublished - Jan 1 2019

Fingerprint

Neutron scattering
globules
neutron scattering
gels
aqueous solutions
Gels
microstructure
Microstructure
Scattering
scattering
dehydration
Phase behavior
Dehydration
crossovers
solubility
lenses
poly-N-isopropylacrylamide
Lenses
Neutrons
formalism

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Condensed Matter Physics

Cite this

Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods. / Koizumi, Satoshi; Masahiko, Annaka; Schwahn, Dietmar.

In: Soft Matter, Vol. 15, No. 4, 01.01.2019, p. 671-682.

Research output: Contribution to journalArticle

@article{e8ccc67546f84e95848a20926120b200,
title = "Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods",
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 T V (= 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 q c ≅ 5 × 10 −3 {\AA} −1 a crossover to Porod's asymptotic q −4 power law. For shallow quenches of ΔT < 1.0 K above T V the excess scattering intensity is further increasing whereas q c 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 {\AA} 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 T V 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 T V (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.",
author = "Satoshi Koizumi and Annaka Masahiko and Dietmar Schwahn",
year = "2019",
month = "1",
day = "1",
doi = "10.1039/C8SM02416B",
language = "English",
volume = "15",
pages = "671--682",
journal = "Soft Matter",
issn = "1744-683X",
publisher = "Royal Society of Chemistry",
number = "4",

}

TY - JOUR

T1 - Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods

AU - Koizumi, Satoshi

AU - Masahiko, Annaka

AU - Schwahn, Dietmar

PY - 2019/1/1

Y1 - 2019/1/1

N2 - 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 T V (= 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 q c ≅ 5 × 10 −3 Å −1 a crossover to Porod's asymptotic q −4 power law. For shallow quenches of ΔT < 1.0 K above T V the excess scattering intensity is further increasing whereas q c 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 T V 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 T V (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.

AB - 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 T V (= 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 q c ≅ 5 × 10 −3 Å −1 a crossover to Porod's asymptotic q −4 power law. For shallow quenches of ΔT < 1.0 K above T V the excess scattering intensity is further increasing whereas q c 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 T V 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 T V (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.

UR - http://www.scopus.com/inward/record.url?scp=85060396461&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85060396461&partnerID=8YFLogxK

U2 - 10.1039/C8SM02416B

DO - 10.1039/C8SM02416B

M3 - Article

VL - 15

SP - 671

EP - 682

JO - Soft Matter

JF - Soft Matter

SN - 1744-683X

IS - 4

ER -