Prospects of Observing Ionic Coulomb Blockade in Artificial Ion Confinements

Nanofluidics encompasses a wide range of advanced approaches to study charge and mass transport at the nanoscale. Modern technologies allow us to develop and improve artificial nanofluidic platforms that confine ions in a way similar to single-ion channels in living cells. Therefore, nanofluidic platforms show great potential to act as a test field for theoretical models. This review aims to highlight ionic Coulomb blockade (ICB)—an effect that is proposed to be the key player of ion channel selectivity, which is based upon electrostatic exclusion limiting ion transport. Thus, in this perspective, we focus on the most promising approaches that have been reported on the subject. We consider ion confinements of various dimensionalities and highlight the most recent advancements in the field. Furthermore, we concentrate on the most critical obstacles associated with these studies and suggest possible solutions to advance the field further.     

Oppositely Charged Ti3C2Tx MXene Membranes with 2D Nanofluidic Channels for Osmotic Energy Harvesting

Membrane‐based reverse electrodialysis (RED) is considered as the most promising technique to harvest osmotic energy. However, the traditional membranes are limited by high internal resistance and low efficiency, resulting in undesirable power densities. Herein, we report the combination of oppositely charged Ti₃C₂T_x MXene membranes (MXMs) with confined 2D nanofluidic channels as high‐performance osmotic power generators. The negatively or positively charged 2D MXene nanochannels exhibit typical surface‐charge‐governed ion transport and show excellent cation or anion selectivity. By mixing the artificial sea water (0.5 m NaCl) and river water (0.01 m NaCl), we obtain a maximum power density of ca. 4.6 Wm^?2, higher than most of the state‐of‐the‐art membrane‐based osmotic power generators, and very close to the commercialization benchmark (5 Wm^?2). Through connecting ten tandem MXM‐RED stacks, the output voltage can reach up 1.66 V, which can directly power the electronic devices.     

超疏水性材料表面的制备、应用和相关理论研究的新进展

文章总结了Wenzel方程、Cassie方程及一种具有极高精确度的,可方便测出固体表面上液滴前进角和后退角的测试方法等超疏水表面的最新理论研究成果;回顾了溶胶凝胶法、化学修饰法、喷涂法、液相法、化学蚀刻法、水热法、微相分离法、原位聚合法、静电纺丝法、阳极氧化法等近几年出现的超疏水表面的制备方法;介绍了在微物质能量、生物医学、光学、燃料以及电池应用等领域超疏水表面的最新功能性的应用。最后,客观地展望了超疏水表面制备及理论研究的发展方向。     

Study on 172‐nm vacuum ultraviolet light surface modifications of polydimethylsiloxane for micro/nanofluidic applications

In this study, we developed a technique for modifying the surface of the silicone elastomer Poly(dimethylsiloxane) (PDMS) by 172‐nm wavelength vacuum ultraviolet (VUV) light exposure. Such materials have high potential for application to micro/nanofluidic devices if their surface properties can be adequately controlled. The hydrophilicity, zeta potential and bonding strength of the VUV‐exposed surfaces were investigated and compared to surfaces exposed to conventional vacuum oxygen plasma. It was found that the proposed technique was effective at modifying the surface conditions from hydrophobic to hydrophilic, increasing the zeta potential, and allowing good bonding to glass. The time required to produce the maximum bonding strength was found to be similar to that for vacuum oxygen plasma exposure. However, since VUV exposure does not require the creation of a vacuum, it offers a faster turnaround, making it suitable for mass production. Copyright © 2010 John Wiley & Sons, Ltd.     

耗散粒子动力学和纳维边界条件在微米纳米流体力学模拟中的应用

耗散粒子动力学是一种粗粒化的计算模拟方法,在微米和纳米流体力学中有着广泛的应用.由于界面在微小体积流体中的重要性,边界条件的选取在微米和纳米流体的研究中起到了关键性的作用.我们简单地介绍了耗散粒子动力学的模拟方法,并以此为基础,介绍了能够实现纳维边界条件的可调滑移长度的边界条件模拟方法.通过条纹状图案修饰的超疏水表面的流体力学行为研究,和高分子链在微米纳米流体器件中的运动研究2个例子,耗散粒子动力学结合纳维边界条件的模拟方法的实用性和可靠性得到了证实.     

基于水滴模板法的微纳复合超疏水结构制备的研究

利用粒子辅助水滴模板法的实施获得规则蜂窝状图案化多孔结构模板,并进一步利用聚二甲基硅氧烷(PDMS)复制转移技术获得表面具有微米尺寸蜂窝状突起阵列的反向图案化结构.以这种图案化突起结构作为微米尺寸所提供的微米级粗糙度为基础,设计了2种的简单的二次纳米结构的引入过程,最终实现了微米级阵列和纳米级粗糙度的复合.第一种方法借助银镜反应来实现纳米银结构的化学沉积,最终在PDMS阵列表面获得了致密的纳米银颗粒沉积层,并成功获得了表面接触角达166度的超疏水性质.第二种方法利用了聚电解质/二氧化硅粒子层层静电自组装的方法引入纳米结构,结果在仅仅进行了2个组装循环的条件下即可获得超疏水性质的表面复合结构.通过简单的实验设计试图提供一种基于水滴模板法的微纳复合超疏水结构的普适性制备方法.     

Fast Ion Transport and Phase Separation in a Mechanically Driven Flow of Electrolytes through Tortuous Sub‐Nanometer Nanochannels

Both nanostructured materials and nanotubes hold tremendous promises for separation and purification applications, such as water desalination. By using molecular dynamics, herein, we compare the transport of aqueous electrolyte solutions through a Y‐zeolite, which features interconnected, tortuous sub‐nanometer nanopores, and a model silica nanotube, which has the same composition but is straight and has much lower surface complexity. In the Y‐zeolite, ion transport is faster than the transport of water molecules, thus leading to a phenomenon of phase separation in which a gradient of salt concentration is generated along the flow direction. However, similar transport characteristics and phase separation are not found in the model silica nanotube. Detailed analysis suggests that, in nanochannels with complicated geometries, such as those of the Y‐zeolite, the structural and flow characteristics of confined nanofluids are highly coupled, thus influencing the transport of ions and solvents and causing the phenomenon of phase separation.     

From Extended Nanofluidics to an Autonomous Solar-Light-Driven Micro Fuel-Cell Device

Autonomous micro/nano mechanical, chemical, and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro-power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage, and delivery to the sensor. Herein, we realized a solar-light-driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen fuel is then consumed by the μFC to generate electricity. Importantly, the by-product water returns back to the photocatalytic μFG via recirculation loop without losses. Both devices rely on novel phenomena in extended-nano-fluidic channels that ensure ultra-fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ca. 17.2 mWh cm⁻² at room temperature.     

Ionic Diode Characteristics at a Polymer of Intrinsic Microporosity (PIM) | Nafion “Heterojunction” Deposit on a Microhole Poly(ethylene‐terephthalate) Substrate

Ionic diode phenomena occur at asymmetric ionomer | aqueous electrolyte microhole interfaces. Depending on the applied potential, either an “open” or a “closed” diode state is observed switching between a high ion flow rate and a low ion flow rate. Physically, the “open” state is associated mainly with conductivity towards the microhole within the ionomer layer and the “closed” state is dominated by restricted diffusion‐migration access to the microhole interface opposite to the ionomer. In this report we explore a “heterojunction” based on an asymmetric polymer of intrinsic microporosity (PIM) | Nafion ionomer microhole interface. Improved diode characteristics and current rectification are observed in aqueous NaCl. The effects of creating the PIM | Nafion micro‐interface are investigated and suggested to lead to novel sensor architectures.