通过Keggin型多金属氧酸盐离子特异性调控微凝胶的本体行为与二维界面自组装
Tuning the bulk behavior and 2D interfacial self-assembly of microgels by Keggin-type polyoxometalate ionic specificity
AI总结：
本研究利用Keggin型多金属氧酸盐POM调控pNIPAM微凝胶的本体与二维界面行为，揭示了其电荷反转、多步溶胀/去溶胀及二维饱和效应等特性，改性后微凝胶抗刻蚀性能提升，可用于软胶体光刻。
摘要：
寻找调控热响应微凝胶在本体及二维液体界面受限状态下行为的新方法，是深化对这些智能材料的理解与实现精准调控的关键。我们研究了带正电的pNIPAM微凝胶与Keggin型多金属氧酸盐$Na_{3}PW_{12}O_{40}$（POM）的相互作用。在本体体系中，我们观察到在体积相转变温度（VPTT）上下，低至$5\cdot10^{-5}$ M的POM浓度下即可发生电荷反转。在POM存在时，微凝胶在VPTT以下表现出“去溶胀-溶胀-去溶胀”行为，在VPTT以上则呈现两步进一步去溶胀的特性。当微凝胶被限制在二维水/空气界面时，在VPTT以下添加$10^{-5}$ M的POM，其效果等同于将温度升高至VPTT以上，并将单分子层从$5$ mN m$^{-1}$压缩至$20\\,\text{mN m$^{-1}$}$。在VPTT以上时，界面处的直径未发生变化，但浸入亚相的部分进一步去溶胀，这与本体中的行为一致。继续添加POM既不会改变界面处的直径，也不会改变微凝胶的高度，表明二维体系中存在饱和效应。我们通过EDS能谱 mapping和X射线光电子能谱（XPS）表征了POM对pNIPAM聚合物网络的重构作用。负载POM的微凝胶单分子层提升了抗等离子体刻蚀能力，这一特性可应用于软胶体光刻领域。
英文摘要：
Finding new ways to tune the behavior of thermoresponsive microgels in bulk and confined at 2D liquid interfaces is key to achieve a deeper understanding and control of these smart materials. We studied the interaction of positively charged pNIPAM microgels with the Keggin-type polyoxometalate $Na_{3}PW_{12}O_{40}$ (POM). In bulk, we observed charge inversions below and above the volume phase transition temperature (VPTT) at significantly low POM concentrations as $5\cdot10^{-5}$ M. In the presence of POM, the microgels exhibited a deswelling-swelling-deswelling behaviour below the VPTT, and a two-step further deswelling above the VPTT. When microgels were confined at 2D water/air interfaces, adding $10^{-5}$ M of POM below the VPTT was equivalent to heat above the VPTT and compress the monolayer from $5$ to $20\,\text{mN m$^{-1}$}$. Above the VPTT, the diameter at the interface did not change while the portion immersed in the subphase further deswelled, in agreement with the behavior in bulk. Adding more POM did not change the diameter at the interface nor the height of the microgels, showing a saturation effect in 2D. The restructuring of the pNIPAM polymeric network by the POM was characterized by EDS mapping and XPS. The microgel monolayers with POM improved their resistance to plasma etching, which could be useful for soft colloidal lithography.
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