Venkata K. Punyamurtula

Nanoscale Fluid Transport: Size and Rate Effects

The transport behavior of water molecules inside a model carbon nanotube is investigated by using nonequilibrium molecular dynamcis (NMED) simulations. The shearing stress between the nanotube wall and the water molecules is identified as a key factor in determining the nanofluidic properties. Due to the effect of nanoscale confinement, the effective shearing stress is not only size sensitive but also strongly dependent on the fluid flow rate. Consequently, the nominal viscosity of the confined water decreases rapidly as the tube radius is reduced or when a faster flow rate is maintained. An infiltration experiment on a nanoporous carbon is performed to qualitatively validate these findings.

Energy absorption performance of steel tubes enhanced by a nanoporous material functionalized liquid

The compressive behaviors of steel cells enhanced by a nanoporous silica functionalized liquid are investigated. As the empty space in the ductile cell is filled by an aqueous suspension of hydrophobic nanoporous silica gel, the work done by the compressive load along the axial direction can be dissipated not only through the ordinary cell-wall buckling but also via the extended yielding and the pressure-induced infiltration. As a result, the energy absorption efficiency, either on mass or on volumetric basis, is considerably improved.

Temperature dependence of working pressure of a nanoporous liquid spring

The thermal effect on nanofluidic behaviors in a hydrophobic zeolite is investigated experimentally. At a constant temperature, water can be forced to infiltrate into the nanopores as an external pressure is applied and defiltrate as the pressure is lowered, leading to a springlike pressure-volume relationship. As temperature varies, due to the variation in solid-liquid interfacial tension, the infiltration pressure changes significantly. Consequently, the system exhibits a thermally controllable volume memory characteristic, with the energy density higher than that of ordinary shape-memory solids by more than one order of magnitude, providing a promising way for developing high-performance intelligent devices.

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.

Conversion of mechanical work to interfacial tension in a nanoporous silica gel

A calometric measurement is performed to analyze energy exchange in a nanoporous material functionalized (NMF) liquid. As an external pressure is applied, the hydrophobic nanopore surfaces can be exposed to the liquid phase. When the pressure is removed, the system does not return to its initial configuration. Unlike ordinary energy absorption systems, no significant temperature variation can be detected during the infiltration of pressurized liquid water, indicating that the sorption process is nonexothermic. This is attributed to the conversion of mechanical work to excess solid-liquid interfacial tension.

Electrification of a nanoporous electrode in a continuous flow

By forcing an electrolyte solution to flow across a nanoporous electrode, a significant output voltage was measured. In contradiction to the classic streaming-potential theory, the output voltage was independent of the flow rate and the electrode distance. The discharge time was longer by orders of magnitude than the retention time. If the external resistance was relatively small, the voltage would eventually vanish. These unique phenomena can be attributed to the amplification effect of the large nanopore surface area on the mechanical disturbance of surface capacity.

Effects of cation size on infiltration and defiltration pressures of a MCM-41

With the nanopore structure, ionic charge, solvent, and testing condition being kept the same, the cation size effects on liquid motion in a MCM-41 are investigated by using chloride salts. As the cation becomes larger, both infiltration and defiltration pressures decrease. The variation in infiltration pressure is more pronounced.

An experimental investigation on a nanoporous carbon functionalized liquid damper

The behaviour of a p-xylene-based lyophobic nanoporous carbon system under high hydrostatic pressures is investigated. As the pressure is increased to a critical value, the nanopore surfaces between graphene layers are exposed to the liquid phase, leading to a considerable increase in solid–liquid interfacial energy. During unloading, defiltration does not occur until the pressure is much lower. Thus, the system is energy absorbing. Owing to the large solid–liquid contact area, the energy absorption efficiency is much higher than that of conventional dampers.