Weiyi Lu

Temperature variation in liquid infiltration and defiltration in a MCM41

In a calometric measurement of infiltration and defiltration of pressurized liquid in a hydrophobic MCM41, it is observed that in nanopores the energy change between solid and liquid phases is dependent on the direction of liquid motion: liquid infiltration is exothermic and liquid defiltration is endothermic. The sorption curves and the temperature variation are insensitive to the loading rate. The magnitude of temperature decrease in defiltration is smaller than the temperature increase in infiltration, fitting well with the hysteresis of the sorption curve. These phenomena can be attributed to the confinement effect of nanopore walls and the thermally/mechanically aided surface diffusion of liquid molecules.

Effective viscosity of glycerin in a nanoporous silica gel

The infiltration of glycerin in a lyophobic nanoporous silica gel is investigated experimentally, and the effective interfacial tension and viscosity are discussed. While the simple superposition principle can be employed for the analysis of interfacial tension, in a nanopore the effective liquid viscosity is no longer a material constant. It is highly dependent on the pore size and the loading rate, much smaller than its bulk counterpart.

The dependence of infiltration pressure and volume in zeolite Y on potassium chloride concentration

In a previous work we developed a volume-memory liquid that can expand or shrink significantly as the temperature varies. The working mechanism is based on the thermally induced infiltration and defiltration of an electrolyte solution in the nanopores. In the current study, we investigate the influence of electrolyte concentration on the infiltration behavior, as well as its dependence on temperature. The testing data show that, as the electrolyte concentration varies, the effective interfacial tension changes rapidly. This phenomenon can be attributed to the amplification effect of nanopore surfaces on the solid–liquid interaction. It provides a scientific basis for developing smart liquids for various temperature and pressure ranges.

Effects of additional multiwall carbon nanotubes on impact behaviors of LiNi0.5Mn0.3Co0.2O2 battery electrodes

This work introduces a new mechanically triggered thermal runaway mitigation mechanism. The homogenizer of electrode failure (HEF), multiwall carbon nanotube (MWCNT), was added into LiNi0.5Mn0.3Co0.2O2 (NMC532) battery electrodes. We have studied the effect of the HEF additive on the internal electrical resistance and the mechanical impact resistance of the electrodes. The additional MWCNTs reduced the internal electrical resistance of electrodes before mechanical abuse. Upon mechanical abuse, they could mitigate internal shorting and thermal runaway at normal battery working temperature.

Deformation of a nanoporous silica under compressive loading

In a compression experiment on a nanoporous silica gel, it is observed that at a high pressure the collapse of nanoporous structure provides a mechanism for plastic deformation, leading to an energy absorption efficiency much higher than that of many conventional protection and damping materials. Even though the network material is brittle, the overall behavior of the silica gel is ductile. After the compression test, the nanopore volume is largely reduced while the variation in nanopore surface area is secondary. According to a first-order poromechanic analysis, the effective plastic deformation is dominated by the buckling of the nanopore walls parallel to the external loading.

Eletrowetting effect in a nanoporous silica.

In the past, electrowetting was usually analyzed on large solid surfaces. In the current study, the effective solid-liquid interfacial tension in a nanoporous silica, which is measured by the ion transport pressure, is investigated experimentally. The interfacial tension decreases as the applied potential difference increases, while the magnitude of variation is much smaller than its bulk counterpart. The effect of the external electric field is saturated at a relatively low voltage. These unique phenomena can be attributed to the confinement effect of nanopore walls.

Non-dissipative energy capture of confined liquid in nanopores

In the past, energy absorption of protection/damping materials is mainly based on energy dissipation, which causes a fundamental conflict between the requirements of safety/comfort and efficiency. In the current study, a nanofluidic “energy capture” system is reported, which is based on nanoporous materials and nonwetting liquid. Both molecular dynamics simulations and experiments show that as the liquid overcomes the capillary effect and infiltrates into the nanopores, the mechanical energy of a stress wave could be temporarily stored by the confined liquid phase and isolated from the wave energy transmission path. Such a system can work under a relatively low pressure for mitigating high-pressure stress waves, not necessarily involved in any energy dissipation processes.

Electrically controlled hydrophobicity in a surface modified nanoporous carbon

Conventional surface treatments lead to constant surface morphologies and properties. Here we show that as the inner surfaces of a nanoporous carbon are modified by 16-mercaptohexadecanoic acid through a two-step grafting process, due to the flexibility of the surface chains, the end groups can be repelled by negative surface charges and attracted by positive surface charges. Thus, the surface wettability is controlled electrically. The effective solid-liquid interfacial tension in the nanopores is analyzed in a pressure induced infiltration experiment.

Effects of ion concentration on thermally-chargeable double-layer supercapacitors

The concept of thermally-chargeable supercapacitor was discussed and validated experimentally. As two double-layer supercapacitor-type devices were placed at different temperatures and connected, due to the thermal dependence of surface charge structures, the electrode potentials became different, and thermal energy could be harvested and stored as electric energy. The important effect of ion concentration was investigated. The results were quite different from the prediction of conventional surface theory, which should be attributed to the unique behaviors of the ions confined in the nanoporous electrodes.

A defiltration control method of pressurized liquid in zeolite ZSM-5 by silanol introduction

The defiltration performance of the zeolite ZSM-5/liquid system can be effectively modified by sodium hydroxide (NaOH) additive with various concentrations. The infiltration of NaOH aqueous solutions increases the density of silanol (Si-OH) groups on inner surface of the porous ZSM-5, converting the originally hydrophobic surface to hydrophilic and ceasing the liquid outflow. More importantly, the defiltration performance of the system can be adjusted independently without affecting the working pressure of the system. This unique infiltration associated hydrophobic-hydrophilic transition of nanopore surface leads the ZSM-5 based liquid system to an efficient energy absorption system instead of a super-elastic molecular spring.