聚合物
纳米颗粒
材料科学
分子动力学
小角X射线散射
化学工程
膜
化学物理
高分子化学
纳米技术
化学
复合材料
计算化学
散射
生物化学
物理
工程类
光学
作者
Sophia Y Chan,Mayank Jhalaria,Yucheng Huang,Ruipeng Li,Brian C. Benicewicz,Christopher J Durning,Thi Vo,Sanat K. Kumar
出处
期刊:ACS Nano
[American Chemical Society]
日期:2022-07-11
卷期号:16 (7): 10404-10411
标识
DOI:10.1021/acsnano.2c00643
摘要
Polymer-grafted nanoparticle (GNP) membranes show unexpected gas transport enhancements relative to the neat polymer, with a maximum as a function of graft molecular weight (MWg ≈ 100 kDa) for sufficiently high grafting densities. The structural origins of this behavior are unclear. Simulations suggest that polymer segments are stretched near the nanoparticle (NP) surface and form a dry layer, while more distal chain fragments are in their undeformed Gaussian states and interpenetrate with segments from neighboring NPs. This theoretical basis is derived by considering the behavior of two adjacent NPs; how this behavior is modified by multi-NP effects relevant to gas separation membranes is unexplored. Here, we measure and interpret SAXS data for poly(methyl acrylate)-grafted silica NPs and find that for very low MWgs, contact between GNPs obeys the two-NP theory─namely that the NPs act like hard spheres, with radii that are linear combinations of the NP core sizes and the dry zone dimensions; thus, the interpenetration zones relax into the interstitial spaces. For chains with MWg > 100 kDa, the interpenetration zones are in the contact regions between two NPs. These results suggest that for MWgs below the transition, gas primarily moves through a series of dry zones with favorable transport, with the interpenetration zone with less favorable transport properties in parallel. For higher MWgs, the dry and interpenetration zones are in series, resulting in a decrease in transport enhancement. The MWg at the transport maximum then corresponds to the chain length with the largest, unfavorable stretching free energy.
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