The charge stability of electret materials can directly affect the performance of electret-based devices such as electrostatic energy harvesters. In this paper, a spray-coating method is developed to deposit an electret layer with enhanced charge stability. The long-term stability of a spray-coated electret is investigated for 500 days and shows more stable performance than a spin-coated layer. A second-order linear model that includes both the surface charge and space charge is proposed to analyze the charge decay process of electrets in harsh environments at a high temperature (120 °C) and high humidity (99% RH); this model provides better accuracy than the traditional deep-trap model. To further verify the stability of the spray-coated electret, an electrostatic energy harvester is designed and fabricated with MEMS (micro-electromechanical systems) technology. The electret material can work as both the bonding interface and electret layer during fabrication. A maximum output power of 11.72 μW is harvested from a vibrating source at an acceleration of 28.5 m/s2. When the energy harvester with the spray-coated electret is exposed to a harsh environment (100 °C and 98% RH), an adequate amount of power can still be harvested even after 34 h and 48 h, respectively.

A spray-coating method for cyclic olefin copolymer (COC) electret material with polystyrene (PS) nanoparticles is developed here. Compared with the traditional polymer electret materials, the COC electrets with PS nanoparticles achieved better surface charge stability when exposed to harsh environment at high humidity or high temperature. With the spray coating technique, they can easily control the thickness of the electret layer. The surface charge stability of the electret has been detailed studied with various concentrations of the nanoparticles. They have also applied the spray coated electret to electrostatic energy harvesting devices. The experiments confirmed that the energy harvesting devices can generate more stable power output using the spray coated electret with nanoparticles.

Shale oil has been receiving more and more attention, because of its promising contribution to energy development and utilization. Capillary imbibition in shale nanopores widely exists in the storage and recovery of shale oil. Despite the ubiquitous nature, shale oil imbibition in nanoconfined space and the effect of nanopore walls on flow are still unclear. Here, we report an experimental study of shale oil capillary imbibition in single nanochannels with heights ranging from 34 nm to 100 nm. Nanofluidic chips with silicon dioxide surface were designed and fabricated, and a shale oil sample from the Shengli Oil field was adopted and characterized. It was found that, during the imbibition process, the meniscus position exhibited a square root relation with time, which was consistent with the trend predicted by the Lucas–Washburn equation. However, the observed imbibition process was slower than the theoretical prediction, up to 60% slower for imbibition in 34 nm channels, and the deviation increased as the channel height decreased. The height dependence of the deviation was investigated and the interfacial layer model was proposed to quantitatively dissect the dominant mechanism. Our results showed that, because of the strong intermolecular force between surface and liquid, shale oil formed an interfacial layer of two to three layers of molecules on the channel walls, which significantly increased flow resistance in the nanochannels. The effects of dynamic contact angle, surface wettability, and trapped gas were also discussed. Our research investigates natural shale oil imbibition in single nanochannels and quantitatively analyzes the deviation of the nanoconfined flow from the theoretical flow process, which provides novel insights for shale oil exploration and recovery.

Gated protein channels act as rapid, reversible, and fully-closeable nanoscale valves to gate chemical transport across the cell membrane. Replicating or outperforming such a high-performance gating and valving function in artificial solid-state nanopores is considered an important yet unsolved challenge. Here we report a bioinspired rapid and reversible nanopore gating strategy based on controlled nanoparticle blockage. By using rigid or soft nanoparticles, we respectively achieve a trapping blockage gating mode with volatile memory where gating is realized by electrokinetically trapped nanoparticles near the pore and contact blockage gating modes with nonvolatile memory where gating is realized by a nanoparticle physically blocking the pore. This gating strategy can respond to an external voltage stimulus (∼200 mV) or pressure stimulus (∼1 atm) with response time down to milliseconds. In particular, when 1,2-diphytanoyl-sn-glycero-3-phosphocholine liposomes are used as the nanoparticles, the gating efficiency, defined as the extent of nanopore closing compared to the opening state, can reach 100%. We investigate the mechanisms for this nanoparticle-blockage-enabled nanopore gating and use it to demonstrate repeatable controlled chemical releasing via single nanopores. Because of the exceptional spatial and temporal control offered by this nanopore gating strategy, we expect it to find applications for drug delivery, biotic–abiotic interfacing, and neuromorphic computing.

Living organisms can sense extracellular forces via mechanosensitive ion channels, which change their channel conformations in response to external pressure and regulate ion transport through the cell membrane. Such pressure-regulated ion transport is critical for various biological processes, such as cellular turgor control and hearing in mammals, but has yet to be achieved in artificial systems using similar mechanisms. In this work, we construct a nanoconfinement by reversibly blocking a single nanopore with a nanoparticle and report anomalous and ultra-mechanosensitive ionic transport across the resulting nanoconfinement upon assorted mechanical and electrical stimuli. Our observation reveals a suppressed ion conduction through the system as the applied pressure increases, which imitates certain behaviors of stretch-inactivated ion channels in biological systems. Moreover, pressure-induced ionic current rectification is also observed despite the high ionic concentration of the solution. Using a combined experimental and simulation study, we correlate both phenomena to pressure-induced nanoparticle rotation and the resulting physical structure change in the blocked nanopore. This work presents a mechanosensitive nano-confinement requiring minimal fabrication techniques and provides new opportunities for bio-inspired nanofluidic applications.