Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods
Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods
复制标题
通过先进的小角中子散射方法检测聚（正异丙基丙烯酰胺）浅淬火水溶液中的项链状微观结构
DOI：
10.1039/c8sm02416b
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发表时间：
2019
期刊：
影响因子：
3.4
通讯作者：
Masahiko Annaka and Dietmar Schwahn
中科院分区：
文献类型：
--
作者：
Satoshi Koizumi; Masahiko Annaka and Dietmar Schwahn
用小角中子散射（SANS）研究了聚N-异丙基丙烯酰胺（PNIPA）水溶液和凝胶在TV（= 34 °C）下的体积相变附近的微观结构。SANS技术通过折射中子透镜和完美单晶得到加强，以获得μm的长度尺度。在31 °C时，SANS显示了溶胀凝胶中的Ornstein-Zernike（OZ）型散射，而在32 °C时开始偏离OZ-形式，表现出过度散射，并且在波数qc = 10 − 5 × 10−3 −1处与Porod的渐近q−4幂律交叉。对于ΔT < 1.0 K的浅猝灭，超过TV的过量散射强度进一步增加，而qc向低值移动。基于这种观察和分析的SANS的q-配置文件，我们提出了一个项链状的微观结构组成的PNIPA丰富的小球的R 100大小的连接膨胀PNIPA链和稳定超过一天的钉扎链连接。在TV附近PNIPA球的形成被讨论在部分合作脱水方面，这是至关重要的解释PNIPA水溶液的“可溶解性方形相行为”。球状结构也被发现在PNIPA水溶液中的大小略大于凝胶。在高于TV（ΔT > 1.0 K）的凝胶深度猝灭下，微球聚集成R = 0.24 μm的较大物体，这是由USANS小q区的强强度上升确定的。
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.