000873378 001__ 873378 000873378 005__ 20210130004423.0 000873378 0247_ $$2doi$$a10.1039/C8SM02416B 000873378 0247_ $$2ISSN$$a1744-683X 000873378 0247_ $$2ISSN$$a1744-6848 000873378 0247_ $$2altmetric$$aaltmetric:53011254 000873378 0247_ $$2pmid$$apmid:30623191 000873378 0247_ $$2WOS$$aWOS:000457329700009 000873378 037__ $$aFZJ-2020-00690 000873378 082__ $$a530 000873378 1001_ $$0P:(DE-HGF)0$$aKoizumi, Satoshi$$b0$$eCorresponding author 000873378 245__ $$aNecklace-like microstructure in shallow-quenched aqueous solutions of poly( n -isopropylacrylamide), detected by advanced small-angle neutron scattering methods 000873378 260__ $$aLondon$$bRoyal Soc. of Chemistry$$c2019 000873378 3367_ $$2DRIVER$$aarticle 000873378 3367_ $$2DataCite$$aOutput Types/Journal article 000873378 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1585912607_29481 000873378 3367_ $$2BibTeX$$aARTICLE 000873378 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000873378 3367_ $$00$$2EndNote$$aJournal Article 000873378 520__ $$aThe 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. 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