Transport in supported polyelectrolyte brushes.
Transport in supported polyelectrolyte brushes.
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DOI：
10.1021/ar3001537
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发表时间：
2012-11-20
影响因子：
18.3
通讯作者：
Landes CF
中科院分区：
文献类型：
--
作者：
Reznik C;Landes CF
功能聚合物具有广泛的应用，从能量存储到药物输送。对于能量存储应用，理想的材料特性包括低成本、高电荷存储和/或迁移率以及低降解率。各向同性薄膜已用于许多此类应用，但研究表明，聚合物刷等不同结构可以将电荷传输改善一个数量级。通过“接枝”聚合方法产生的支撑聚合物刷结构为在分子尺度上对这些材料进行受控研究提供了框架。使用这些材料，研究人员可以研究受阻扩散的基础，因为它们含有相对均匀的聚电解质膜。此外，研究人员可以使用具有不同电荷的荧光分子探针来检查聚合物刷附近和内部运输的空间和库仑贡献。在本报告中，我们讨论了使用荧光相关光谱、单分子偏振分辨光谱和新颖的 3 维定向技术来了解带电染料探针与强聚阴离子刷聚（苯乙烯磺酸盐）相互作用的传输的最新进展。我们的初步实验表明，阳离子染料罗丹明 6G 作为抗衡离子探测刷，因此扩散由库仑力主导，这导致扩散系数与自由扩散相比降低了一万倍。我们还通过分子动力学模拟支持我们的实验结果。进一步的实验表明，高达 50% 的时间，罗丹明 6G 在刷子内平移，而没有明显的旋转扩散，这表明与菲克输运机制存在很大偏差（其中平移和旋转扩散通过化学势、尺寸、溶液粘度和热性质等参数直接相关）。为了理解这种定向传输，我们讨论了一种实验技术的开发，该技术使我们能够在画笔内传输的时间尺度上量化 3 维方向。这种方法使我们能够确定罗丹明 6G 在聚（苯乙烯磺酸盐）刷内的独特定向传输方向，并报告定向染料“跳跃”的初步证据。
Functional polymers have a wide variety of applications ranging from energy storage to drug delivery. For energy storage applications, desirable material properties include low cost, high charge storage and/or mobility, and low rates of degradation. Isotropic thin films have been used for many of these types of applications, but research suggests that different structures such as polymer brushes can improve charge transport by an order of magnitude. Supported polymer brush structures produced by ‘grafting-from’ polymerization methods offer a framework for a controlled study of these materials on the molecular-scale. Using these materials, researchers can study the basis of hindered diffusion because they contain a relatively homogeneous polyelectrolyte membrane. In addition, researchers can use fluorescent molecular probes with different charges to examine steric and Coulombic contributions to transport near and within polymer brushes. In this Account, we discuss recent progress in using fluorescence correlation spectroscopy, single-molecule polarization-resolved spectroscopy, and a novel 3-dimensional orientational technique to understand the transport of charged dye probes interacting with the strong polyanionic brush, poly(styrene sulfonate). Our preliminary experiments demonstrate that a cationic dye, Rhodamine 6G, probes the brush as a counterion, and diffusion is therefore dominated by Coulombic forces, which results in a ten-thousand-fold decrease in the diffusion coefficient in comparison with free diffusion. We also support our experimental results with molecular dynamics simulations. Further experiments show that up to 50 percent of the time, Rhodamine 6G translates within the brush without significant rotational diffusion, which indicates a strong deviation from Fickian transport mechanisms (In which translational and rotational diffusion are related directly through parameters such as chemical potential, size, solution viscosity, and thermal properties). To understand this oriented transport, we discuss the development of an experimental technique that allows us to quantify the 3-dimensional orientation on the time scale of intra-brush transport. This method allowed us to identify a unique orientational transport direction for Rhodamine 6G within the poly(styrene sulfonate) brush and to report preliminary evidence for orientational dye ‘hopping.’