Sepulveda-Medina Pablo I, Tyagi Madhusudan, Wang Chao, Vogt Bryan D
School of Polymer Science and Polymer Engineering, University of Akron, Akron, Ohio 44325, USA.
Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Chem Phys. 2021 Apr 21;154(15):154903. doi: 10.1063/5.0045341.
Understanding the properties of water under either soft or hard confinement has been an area of great interest, but nanostructured amphiphilic polymers that provide a secondary confinement have garnered significantly less attention. Here, a series of statistical copolymers of 2-hydroxyethyl acrylate (HEA) and 2-(N-ethylperfluorooctane sulfonamido)ethyl methacrylate (FOSM) are swollen to equilibrium in water to form nanostructured physically cross-linked hydrogels to probe the effect of soft confinement on the dynamics of water. Changing the composition of the copolymer from 10 to 21 mol. % FOSM decreases the average size of the assembled FOSM cross-link, but also the spacing between the cross-links in the hydrogels with the mean distance between the FOSM aggregates decreasing from 3.9 to 2.7 nm. The dynamics of water within the hydrogels were assessed with quasielastic neutron scattering. These hydrogels exhibit superior performance for inhibition of water crystallization on supercooling in comparison to analogous hydrogels with different hydrophilic copolymer chemistries. Despite the lower water crystallinity, the self-diffusion coefficient for these hydrogels from the copolymers of HEA and FOSM decreases precipitously below 260 K, which is a counter to the nearly temperature invariant water dynamics reported previously with an analogous hydrogel [Wiener et al., J. Phys. Chem. B 120, 5543 (2016)] that exhibits nearly temperature invariant dynamics to 220 K. These results point to chemistry dependent dynamics of water that is confined within amphiphilic hydrogels, where the interactions of water with the hydrophilic segments can qualitatively alter the temperature dependent dynamics of water in the supercooled state.
了解软约束或硬约束条件下水的性质一直是一个备受关注的领域，但提供二级约束的纳米结构两亲聚合物却很少受到关注。在这里，一系列丙烯酸2-羟乙酯（HEA）和甲基丙烯酸2-（N-乙基全氟辛烷磺酰胺基）乙酯（FOSM）的统计共聚物在水中溶胀至平衡，形成纳米结构的物理交联水凝胶，以探究软约束对水动力学的影响。将共聚物的组成从10摩尔% FOSM改变到21摩尔%，不仅会减小组装的FOSM交联的平均尺寸，还会减小水凝胶中交联之间的间距，FOSM聚集体之间的平均距离从3.9纳米减小到2.7纳米。用准弹性中子散射评估水凝胶内水的动力学。与具有不同亲水共聚物化学组成的类似水凝胶相比，这些水凝胶在抑制过冷时水结晶方面表现出优异的性能。尽管水的结晶度较低，但这些由HEA和FOSM共聚物形成的水凝胶的自扩散系数在260 K以下急剧下降，这与之前报道的一种类似水凝胶[维纳等人，《物理化学杂志B》120, 5543 (2016)]的水动力学几乎与温度无关相反，该类似水凝胶在220 K以下表现出几乎与温度无关的动力学。这些结果表明，受限在两亲水凝胶中的水的动力学取决于化学组成，其中水与亲水性链段的相互作用可以定性地改变过冷状态下水的温度依赖性动力学。
