Materials Science and Technology of Polymers, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
ACS Appl Mater Interfaces. 2013 Feb;5(4):1400-7. doi: 10.1021/am302820y. Epub 2013 Feb 11.
Several nanoporous platforms were functionalized with pH-responsive poly(methacrylic acid) (PMAA) brushes using surface-initiated atom transfer radical polymerization (SI-ATRP). The growth of the PMAA brush and its pH-responsive behavior from the nanoporous platforms were confirmed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The swelling behavior of the pH-responsive PMAA brushes grafted only from the nanopore walls was investigated by AFM in aqueous liquid environment with pH values of 4 and 8. AFM images displayed open nanopores at pH 4 and closed ones at pH 8, which rationalizes their use as gating platforms. Ion conductivity across the nanopores was investigated with current-voltage measurements at various pH values. Enhanced higher resistance across the nanopores was observed in a neutral polymer brush state (lower pH values) and lower resistance when the brush was charged (higher pH values). By adding a fluorescent dye in an environment of pH 4 or pH 8 at one side of the PMAA-brush functionalized nanopore array chips, diffusion across the nanopores was followed. These experiments displayed faster diffusion rates of the fluorescent molecules at pH 4 (PMAA neutral state, open pores) and slower diffusion at pH 8 (PMAA charged state, closed pores) showing the potential of this technology toward nanoscale valve applications.
几种纳米多孔平台通过表面引发原子转移自由基聚合（SI-ATRP）用 pH 响应性聚（甲基丙烯酸）（PMAA）刷进行功能化。通过扫描电子显微镜（SEM）、傅里叶变换红外（FTIR）光谱和原子力显微镜（AFM）证实了 PMAA 刷的生长及其从纳米多孔平台的 pH 响应行为。通过原子力显微镜在 pH 值为 4 和 8 的水相环境中研究了仅从纳米孔壁接枝的 pH 响应 PMAA 刷的溶胀行为。AFM 图像显示在 pH 4 时打开的纳米孔和在 pH 8 时关闭的纳米孔，这证明了它们可用作门控平台。通过在各种 pH 值下进行电流-电压测量研究了纳米孔的离子电导率。在中性聚合物刷状态（较低 pH 值）下观察到纳米孔的电阻增强较高，而在刷带电荷时（较高 pH 值）电阻较低。通过在 PMAA 刷功能化纳米孔阵列芯片一侧的 pH 4 或 pH 8 环境中添加荧光染料，跟踪了荧光分子在纳米孔中的扩散情况。这些实验显示，在 pH 4 时（PMAA 中性状态，打开的孔）荧光分子的扩散速度更快，而在 pH 8 时（PMAA 带电荷状态，关闭的孔）扩散速度更慢，表明该技术在纳米级阀门应用方面具有潜力。
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