Dipartimento di Fisica, Sapienza Università di Roma, P.le Aldo Moro 5, 00185 Roma, Italy.
Soft Matter. 2017 Aug 2;13(30):5185-5193. doi: 10.1039/c7sm00739f.
Microgel suspensions of an interpenetrated Polymer Network (IPN) of PNIPAM and PAAc in DO have been investigated through dynamic light scattering as a function of temperature, pH and concentration across the Volume Phase Transition (VPT). The dynamics of the system is slowed down under H/D isotopic substitution due to different balance states between polymer/polymer and polymer/solvent interactions suggesting the crucial role played by H-bonding. The swelling behavior, reduced with respect to PNIPAM and water, has been described by the Flory-Rehner theory, tested for PNIPAM microgel and successfully expanded to higher order for IPN microgels. Moreover the concentration dependence of the relaxation time at neutral pH has highlighted two different routes to approach the glass transition: Arrhenius and super-Arrhenius (Vogel Fulcher Tammann) respectively below and above the VPT and a fragility plot has been derived. Fragility can be tuned by changing temperature: across the VPT particles undergo a transition from soft-strong to stiff-fragile.
聚 N-异丙基丙烯酰胺（PNIPAM）和聚（丙烯酸）（PAAc）互穿聚合物网络（IPN）的微凝胶悬浮液在 DO 中已通过动态光散射进行了研究，其功能是随温度、pH 值和浓度跨越体积相转变（VPT）。由于聚合物/聚合物和聚合物/溶剂相互作用之间的不同平衡状态，系统的动力学在 H/D 同位素取代下减慢，这表明氢键起着至关重要的作用。溶胀行为相对于 PNIPAM 和水减少，已通过 Flory-Rehner 理论进行了描述，该理论针对 PNIPAM 微凝胶进行了测试，并成功扩展到更高阶的 IPN 微凝胶。此外，在中性 pH 值下，弛豫时间的浓度依赖性突出了两种不同的方法来接近玻璃化转变：分别在 VPT 以下和以上的 Arrhenius 和超 Arrhenius（Vogel Fulcher Tammann），并且已经得出了易碎性图。通过改变温度可以调整易碎性：在 VPT 期间，颗粒从软-强转变为硬-脆。
