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@ARTICLE{Koizumi:873378,
      author       = {Koizumi, Satoshi and Annaka, Masahiko and Schwahn, Dietmar},
      title        = {{N}ecklace-like microstructure in shallow-quenched aqueous
                      solutions of poly( n -isopropylacrylamide), detected by
                      advanced small-angle neutron scattering methods},
      journal      = {Soft matter},
      volume       = {15},
      number       = {4},
      issn         = {1744-6848},
      address      = {London},
      publisher    = {Royal Soc. of Chemistry},
      reportid     = {FZJ-2020-00690},
      pages        = {671 - 682},
      year         = {2019},
      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},
      cin          = {JCNS-FRM-II / JCNS-1 / MLZ},
      ddc          = {530},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-1-20110106 / I:(DE-588b)4597118-3},
      pnm          = {6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)
                      / 6G15 - FRM II / MLZ (POF3-6G15)},
      pid          = {G:(DE-HGF)POF3-6G4 / G:(DE-HGF)POF3-6G15},
      experiment   = {EXP:(DE-MLZ)KWS1-20140101},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:30623191},
      UT           = {WOS:000457329700009},
      doi          = {10.1039/C8SM02416B},
      url          = {https://juser.fz-juelich.de/record/873378},
}