Chen Raylin, Wang Hanyu, Doucet Mathieu, Browning James F, Su Xiao
Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
JACS Au. 2023 Nov 21;3(12):3333-3344. doi: 10.1021/jacsau.3c00486. eCollection 2023 Dec 25.
Electro-responsive metallopolymers can possess highly specific and tunable ion interactions, and have been explored extensively as electrode materials for ion-selective separations. However, there remains a limited understanding of the role of solvation and polymer-solvent interactions in ion binding and selectivity. The elucidation of ion-solvent-polymer interactions, in combination with the rational design of tailored copolymers, can lead to new pathways for modulating ion selectivity and morphology. Here, we present thermo-electrochemical-responsive copolymer electrodes of -isopropylacrylamide (NIPAM) and ferrocenylpropyl methacrylamide (FPMAm) with tunable polymer-solvent interactions through copolymer ratio, temperature, and electrochemical potential. As compared to the homopolymer PFPMAm, the P(NIPAM--FPMAm) copolymer ingressed 2 orders of magnitude more water molecules per doping ion when electrochemically oxidized, as measured by electrochemical quartz crystal microbalance. P(NIPAM--FPMAm) exhibited a unique thermo-electrochemically reversible response and swelled up to 83% after electrochemical oxidation, then deswelled below its original size upon raising the temperature from 20 to 40 °C, as measured through spectroscopic ellipsometry. Reduced P(NIPAM--FPMAm) had an inhomogeneous depth profile, with layers of low solvation. In contrast, oxidized P(NIPAM--FPMAm) displayed a more uniform and highly solvated depth profile, as measured through neutron reflectometry. P(NIPAM--FPMAm) and PFPMAm showed almost a fivefold difference in selectivity for target ions, evidence that polymer hydrophilicity plays a key role in determining ion partitioning between solvent and the polymer interface. Our work points to new macromolecular engineering strategies for tuning ion selectivity in stimuli-responsive materials.
电响应性金属聚合物可具有高度特异性且可调节的离子相互作用，并且已被广泛研究作为用于离子选择性分离的电极材料。然而，对于溶剂化作用以及聚合物 - 溶剂相互作用在离子结合和选择性方面所起的作用，人们的了解仍然有限。阐明离子 - 溶剂 - 聚合物相互作用，并结合定制共聚物的合理设计，能够为调节离子选择性和形态开辟新途径。在此，我们展示了由N - 异丙基丙烯酰胺（NIPAM）和甲基丙烯酰基二茂铁丙胺（FPMAm）组成的热 - 电化学响应共聚物电极，其通过共聚物比例、温度和电化学势实现了可调节的聚合物 - 溶剂相互作用。与均聚物PFPMAm相比，通过电化学石英晶体微天平测量发现，P（NIPAM - FPMAm）共聚物在电化学氧化时每个掺杂离子吸收的水分子数量多了2个数量级。通过椭圆偏振光谱法测量发现，P（NIPAM - FPMAm）表现出独特的热 - 电化学可逆响应，在电化学氧化后溶胀高达83%，然后在温度从20℃升高到40℃时收缩至其原始尺寸以下。还原态的P（NIPAM - FPMAm）具有不均匀的深度分布，存在低溶剂化层。相比之下，通过中子反射法测量发现，氧化态的P（NIPAM - FPMAm）显示出更均匀且高度溶剂化的深度分布。P（NIPAM - FPMAm）和PFPMAm对目标离子的选择性几乎存在五倍差异，这证明聚合物亲水性在决定溶剂与聚合物界面之间的离子分配中起关键作用。我们的工作为在刺激响应材料中调节离子选择性指出了新的大分子工程策略。
