Sachar Harnoor Singh, Sivasankar Vishal Sankar, Das Siddhartha
Department of Mechanical Engineering, University of Maryland, College Park, MD-20742, USA.
Soft Matter. 2019 Jul 24;15(29):5973-5986. doi: 10.1039/c9sm00765b.
In this paper, we develop a theory to quantify the electrokinetic energy conversion in electrolyte-filled nanochannels grafted with pH-responsive polyelectrolyte (PE) brushes. A pressure-driven flow drives the mobile electrolyte ions of the electric double layer (EDL) supported by the charged PE brushes leading to the generation of a streaming current, a streaming electric field and eventually an electrical energy. The salient feature of this study is that the brushes are described using our recently developed augmented Strong Stretching Theory (SST) model. In all the previous theoretical studies on liquid transport in PE-brush-grafted nanochannels, the brushes have either been assumed to be of constant height (independent of salt concentration or pH) or modelled using the Alexander-de-Gennes model that considers uniform monomer distribution along the brush height. Such simplifications have meant that the salt and the pH dependence of the brush height, the monomer distribution, and the resulting electrostatics have not been appropriately accounted for in the transport calculations. This paper addresses these limitations and provides a much more detailed description of the brushes while capturing the corresponding electrokinetic energy conversion. The results establish that the presence of the PE brushes ensures a localization of the average EDL charge density away from the grafting surface, thereby enabling the migration of the EDL ions with a larger background flow velocity; as a consequence, there is an enhancement of the streaming current, streaming electric field, and the resulting electrical energy generation under certain grafting densities of the PE brushes.
在本文中，我们提出了一种理论，用于量化接枝有pH响应性聚电解质（PE）刷的充满电解质的纳米通道中的动电能量转换。压力驱动的流动驱使由带电PE刷支撑的双电层（EDL）中的可移动电解质离子，从而产生流动电流、流动电场并最终产生电能。本研究的显著特点是使用我们最近开发的增强强拉伸理论（SST）模型来描述这些刷子。在之前所有关于PE刷接枝纳米通道中液体传输的理论研究中，要么假设刷子高度恒定（与盐浓度或pH无关），要么使用考虑沿刷子高度单体分布均匀的亚历山大 - 德热纳模型进行建模。这些简化意味着在传输计算中，刷子高度、单体分布以及由此产生的静电学对盐和pH的依赖性没有得到适当考虑。本文解决了这些局限性，并在捕捉相应的动电能量转换的同时，对刷子进行了更详细的描述。结果表明，PE刷的存在确保了平均EDL电荷密度远离接枝表面的局部化，从而使EDL离子能够以更大的背景流速迁移；因此，在PE刷的某些接枝密度下，流动电流、流动电场以及由此产生的电能生成都会增强。
