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Co-nonsolvency in concentrated aqueous solutions of PNIPAM: effect of methanol on the collective and the chain dynamics.
Soft Matter ( IF 2.9 ) Pub Date : 2020-08-20 , DOI: 10.1039/d0sm01007c Konstantinos N Raftopoulos 1 , Konstantinos Kyriakos 1 , Matthias Nuber 1 , Bart-Jan Niebuur 1 , Olaf Holderer 2 , Michael Ohl 3 , Oxana Ivanova 2 , Stefano Pasini 2 , Christine M Papadakis 1
Soft Matter ( IF 2.9 ) Pub Date : 2020-08-20 , DOI: 10.1039/d0sm01007c Konstantinos N Raftopoulos 1 , Konstantinos Kyriakos 1 , Matthias Nuber 1 , Bart-Jan Niebuur 1 , Olaf Holderer 2 , Michael Ohl 3 , Oxana Ivanova 2 , Stefano Pasini 2 , Christine M Papadakis 1
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The polymer dynamics in concentrated solutions of poly(N-isopropyl acrylamide) (PNIPAM) in D2O/CD3OD mixtures is investigated in the one-phase region. Two polymer concentrations (9 and 25 wt%) and CD3OD contents in the solvent mixture of 0, 10 and 15 vol% are chosen. Temperature-resolved dynamic light scattering (DLS) reveals the collective dynamics. Two modes are observed, namely the fast relaxation of polymer segments within the blobs and the slow collective relaxation of the blobs. As the cloud point is approached, the correlation length related to the fast mode increases with CD3OD content. It features critical scaling behavior, which is consistent with mean-field behavior for the 9 wt% PNIPAM solution in pure D2O and with 3D Ising behavior for all other solutions. While the slow mode is not very strong in the 9 wt% PNIPAM solution in pure D2O, it is significantly more prominent as CD3OD is added and at all CD3OD contents in the 25 wt% solution, which may be attributed to enhanced interaction between the polymers. Neutron spin-echo spectroscopy (NSE) reveals a decay in the intermediate structure factor which indicates a diffusive process. For the polymer concentration of 9 wt%, the diffusion coefficients from NSE are similar to the ones from the fast relaxation observed in DLS. In contrast, they are significantly lower for the solutions having a polymer concentration of 25 wt%, which is attributed to the influence of the dominant large-scale dynamic heterogeneities. To summarize, addition of cosolvent leads to enhanced large-scale heterogeneities, which are reflected in the dynamic behavior at small length scales.
中文翻译：
PNIPAM浓水溶液中的共非溶解性：甲醇对集体和链动力学的影响。
在单相区中研究了聚N-异丙基丙烯酰胺（PNIPAM）在D 2 O / CD 3 OD混合物中的浓溶液中的聚合物动力学。选择在溶剂混合物中的两种聚合物浓度（9和25 wt％）和CD 3 OD含量分别为0、10和15 vol％。温度分辨动态光散射（DLS）揭示了集体动力学。观察到两种模式，即团块内聚合物链段的快速弛豫和团块的缓慢集体弛豫。随着接近浊点，与快速模式相关的相关长度随CD 3的增加而增加OD含量。它具有关键的缩放行为，这与纯D 2 O中9 wt％PNIPAM解决方案的平均场行为和所有其他解决方案的3D Ising行为一致。而慢模式不处于纯d的9％（重量）溶液PNIPAM非常强的2 O，它是显著更突出为CD 3 OD，并将在所有CD 325重量％溶液中的OD含量可以归因于聚合物之间增强的相互作用。中子自旋回波光谱法（NSE）揭示了中间结构因子的衰减，这表明扩散过程。对于9 wt％的聚合物浓度，NSE的扩散系数与DLS中观察到的快速弛豫的扩散系数相似。相反，对于聚合物浓度为25 wt％的溶液，它们明显较低，这归因于主要的大规模动态异质性的影响。总而言之，助溶剂的添加会导致大规模的异质性增强，这反映在小规模的动态行为中。
更新日期：2020-09-23
中文翻译：
PNIPAM浓水溶液中的共非溶解性：甲醇对集体和链动力学的影响。
在单相区中研究了聚N-异丙基丙烯酰胺（PNIPAM）在D 2 O / CD 3 OD混合物中的浓溶液中的聚合物动力学。选择在溶剂混合物中的两种聚合物浓度（9和25 wt％）和CD 3 OD含量分别为0、10和15 vol％。温度分辨动态光散射（DLS）揭示了集体动力学。观察到两种模式，即团块内聚合物链段的快速弛豫和团块的缓慢集体弛豫。随着接近浊点，与快速模式相关的相关长度随CD 3的增加而增加OD含量。它具有关键的缩放行为，这与纯D 2 O中9 wt％PNIPAM解决方案的平均场行为和所有其他解决方案的3D Ising行为一致。而慢模式不处于纯d的9％（重量）溶液PNIPAM非常强的2 O，它是显著更突出为CD 3 OD，并将在所有CD 325重量％溶液中的OD含量可以归因于聚合物之间增强的相互作用。中子自旋回波光谱法（NSE）揭示了中间结构因子的衰减，这表明扩散过程。对于9 wt％的聚合物浓度，NSE的扩散系数与DLS中观察到的快速弛豫的扩散系数相似。相反，对于聚合物浓度为25 wt％的溶液，它们明显较低，这归因于主要的大规模动态异质性的影响。总而言之，助溶剂的添加会导致大规模的异质性增强，这反映在小规模的动态行为中。
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