In both experiment and molecular simulation, it is found that a higher pressure is required to sustain the infiltration of smaller ions in a molecular-sized nanochannel. Simulations indicate that the effective ion solubility of the infiltrated liquid is reduced to nearly zero. Because of the strong interactions between the ion couples and the solid or liquid phases, an external force is required to continuously advance the confined liquid segment. The competition between the probability of ion entry and ion-couple formation causes the observed ion-size-dependent characteristics.

In a previous study [X. Kong and Y. Qiao, Appl. Phys. Lett. 86, 151919 (2005)], we analyzed the energy absorption behaviors of a nanoporous system subjected to quasi-static loadings. In this work, the performance of similar systems under dynamic loadings is investigated through a Hopkinson bar experiment. The energy absorption efficiency increases significantly with the loading rate, which is attributed to the effect of internal friction.

In this paper, the behaviors of nanoporous energy absorption systems subjected to cyclic loadings are investigated. The systems consist of hydrophobic mesoporous silica particles immersed in aqueous solutions of sodium chloride (NaCl). In the first loading-unloading loop, increasing NaCl concentration, $c$ , causes only slight increases in infiltration pressure and energy absorption efficiency. In the following loops, however, the system behaviors are strongly dependent on $c$ . As $c$ increases from $0\%\text{to}25.9\mathrm{wt.}\%$ , the recoverability is improved by a factor of 3, indicating clearly that the addition of NaCl has a beneficial effect to promoting the outflow in the nanoenvironment.

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.

In this article, we report the results of an infiltration∕defiltration experiment of a hydrophobic nanoporous silica gel. As the pressure is increased to the critical value, water can be forced into the nanopores. When the pressure is reduced, however, the “outflow” is difficult, leading to a significant hysteresis of sorption isotherm. A first-order thermodynamics analysis is performed to capture the confinement effect of nanopore walls and the mass and energy exchanges between liquid and gas phases in nanopores.