Location of Imbibed Solvent in Polymer-Grafted Nanoparticle Membranes.
Location of Imbibed Solvent in Polymer-Grafted Nanoparticle Membranes.
复制标题
聚合物接枝纳米颗粒膜中吸收溶剂的位置。
作者：
E. Buenning;J. Jestin;Yucheng Huang;B. Benicewicz;C. Durning;Sanat K. Kumar
纯由接枝有聚合物链的纳米颗粒（NPs）制成的膜相对于类似的纯聚合物膜显示出增加的气体渗透性，这种效果显然可随着聚合物接枝密度和分子量的系统变化而调节。为了探索这些不寻常的运输结果的结构起源，我们使用小角散射（中子，X-射线）的干纳米复合材料薄膜，并严格检查原位吸收溶剂的结构效应。典型溶剂的相对较低的扩散系数（约10-12 m2/s）限制了我们的薄膜（约1 μm厚），如果溶质浓度分布在1 s的时间尺度上平衡。然而，这种薄膜的使用使它们成为弱散射体。受我们近二十年前工作的启发，我们通过使用定制设计的流动池来解决这些相互冲突的要求，其中使用10个单独的10 μm厚的支撑膜堆叠，同时确保每个膜单独暴露于溶剂蒸气。通过使用同位素标记的溶剂，我们研究了膜内的溶剂分布，并令人惊讶地表明，在我们检查的所有条件下，溶剂均匀地溶胀聚合物。当前理论没有预料到这些结果，但它们表明，至少在某些条件下，由于链与纳米颗粒的接枝，自由体积增加，显然在这些材料中各向同性分布。
Membranes made purely from nanoparticles (NPs) grafted with polymer chains show increased gas permeability relative to the analogous neat polymer films, with this effect apparently being tunable with systematic variations in polymer graft density and molecular weight. To explore the structural origins of these unusual transport results, we use small angle scattering (neutron, X-ray) on the dry nanocomposite film and to critically examine in situ the structural effects of absorbed solvent. The relatively low diffusion coefficients of typical solvents (∼10-12 m2/s) restricts us to thin films (≈1 μm in thickness) if solute concentration profiles are to equilibrate on the 1 s time scale. The use of such thin films, however, renders them as weak scatterers. Inspired by our nearly two decades old previous work, we address these conflicting requirements through the use of a custom designed flow cell, where stacks of 10 individual ≈1 μm thick supported films are used, while ensuring that each film is individually exposed to solvent vapor. By using isotopically labeled solvents, we study the solvent distribution within the film and show surprisingly that the solvent homogeneously swells the polymer under all conditions that we examined. These results are not anticipated by current theories, but they suggest that, at least under some conditions, the free volume increases due to the grafting of chains to nanoparticles is apparently distributed isotropically in these materials.