Imaging Channel Connectivity in Nafion Using Electrostatic Force Microscopy
Imaging Channel Connectivity in Nafion Using Electrostatic Force Microscopy
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DOI：
10.1021/acs.jpcb.7b08230
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发表时间：
2018-01-25
影响因子：
3.3
通讯作者：
Buratto, Steven K.
中科院分区：
文献类型：
--
作者：
Barnes, Austin M.;Buratto, Steven K.
通道连通性是制造高性能质子交换膜时需要考虑的重要材料特性。我们的团队之前已经证明，Nafion 薄膜中近 50% 的水表面区域没有通往膜另一侧的连接路径。这些所谓的“死端”通道导致膜的电导效率损失。了解这些死端通道的结构是提高膜电导的重要一步。尽管传导原子力显微镜能够深入了解连接的通道，但它确实直接报告死端通道。为了解决这个问题，我们使用静电力显微镜 (EFM) 来探测环境条件下 Nafion 薄膜 (100-300 nm) 中的通道连接性。 EFM 提供了电容相移的图像，该图像受表面电荷、介电常数和尖端样品几何形状的影响。我们研究了几个单独的通道，并测量了 EFM 信号与偏置电压的二次相关性。应用简单的平行板模型使我们能够将 EFM 信号的差异分配给特定的通道形状：连接的圆柱形通道、死端圆柱形通道和瓶颈通道。
Channel connectivity is an important material property that is considered in making higher-performance proton-exchange membranes. Our group has previously demonstrated that nearly 50% of the aqueous surface domains in Nafion films do not have a connected path to the opposite side of the membrane. These so-called "dead-end" channels lead to a loss in the conductance efficiency of the membrane. Understanding the structure of these dead-end channels is an important step in improving the conductance of the membrane. Although conductive atomic force microscopy is able to provide insight into the connected channels, it does directly report on the dead-end channels. To address this, we use electrostatic force microscopy (EFM) to probe channel connectivity in a Nafion thin film (100-300 nm) under ambient conditions. EFM provided an image of the capacitive phase shift, which is influenced by surface charge, dielectric permittivity, and tip-sample geometry. We studied several individual channels and measured the quadratic dependence of the EFM signal with the bias voltage. Applying a simple parallel plate model allowed us to assign differences in the EFM signal to particular channel shapes: connected cylindrical channels, dead-end cylinder channels, and bottleneck channels.