Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208.
Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208.
Proc Natl Acad Sci U S A. 2020 Aug 18;117(33):19677-19684. doi: 10.1073/pnas.2007545117. Epub 2020 Aug 3.
Understanding nanoscale interactions at the interface between two media with different dielectric constants is crucial for controlling many environmental and biological processes, and for improving the efficiency of energy storage devices. In this contributed paper, we show that polarization effects due to such dielectric mismatch remarkably influence the double-layer structure of a polyelectrolyte solution confined between two charged surfaces. Surprisingly, the electrostatic potential across the adsorbed polyelectrolyte double layer at the confining surface is found to decrease with increasing surface charge density, indicative of a negative differential capacitance. Furthermore, in the presence of polarization effects, the electrostatic energy stored in the double-layer structure is enhanced with an increase in the charge amplification, which is the absorption of ions on a like-charged surface. We also find that all of the important double-layer properties, such as charge amplification, energy storage, and differential capacitance, strongly depend on the polyelectrolyte backbone flexibility and the solvent quality. These interesting behaviors are attributed to the interplay between the conformational entropy of the confined polyelectrolytes, the Coulombic interaction between the charged species, and the repulsion from the surfaces with lower dielectric constant.
理解具有不同介电常数的两种介质界面处的纳米尺度相互作用对于控制许多环境和生物过程以及提高储能设备的效率至关重要。在这篇投稿论文中，我们表明，由于这种介电失配引起的极化效应显著影响了受限在两个带电表面之间的聚电解质溶液的双层结构。令人惊讶的是，发现吸附在限制表面的聚电解质双层中的静电势随着表面电荷密度的增加而减小，表明存在负微分电容。此外，在存在极化效应的情况下，随着电荷放大（即同电荷表面上离子的吸收）的增加，双层结构中存储的静电能增强。我们还发现，所有重要的双层性质，如电荷放大、能量存储和微分电容，都强烈依赖于聚电解质主链的柔韧性和溶剂质量。这些有趣的行为归因于受限聚电解质的构象熵、带电物质之间的库仑相互作用以及来自介电常数较低的表面的排斥之间的相互作用。
