Effect of pore configuration on cascade energy absorption characteristics of glycerol -based nanofluidic systems

• Infiltration and transport behaviors of glycerol into multistage pores are examined. • Formula of critical pore difference of Multistage systems are obtained. • Pore configurations that exhibit cascade energy storage characteristics are obtained. • Relation between critical pressure and system energy absorption was studied. The energy absorption efficiency of nanofluidic energy absorption system (NEAS), composed of nanoporous medium and functional liquid, is significantly higher than that of traditional energy-absorbing materials, benefiting by the large specific surface area of nanoporous medium. To further promote the application of NEAS in energy absorption and achieve cascade energy absorption, in this study, the carbon nanotubes (CNTs) were applied as a basic structural unit to construct two types of NEASs with multistage pore structures. Afterwards, the cascade energy absorption characteristics were investigated under two conditions: multiple pores with varying diameters (DDNEAS), and a single pore with variable diameters (SDNEAS). Glycerol was employed as the functional liquid of the NEAS, and the infiltration processes of glycerol molecules into various configurations of nanoporous channels were simulated. Results show that not all NEASs composed of porous medium with different diameters will demonstrate cascade characteristic. Subsequently, the critical pore diameter difference was defined, and all conditions were distinguished based on the presence or absence of the cascade characteristic and mapped, leading to the correlation formulas for this critical difference under the two models. In the DDNEAS, the infiltration processes and P in of large and small tubes are independent of each other, which are equivalent to those in single-stage systems. In the SDNEAS, the P in of the bottom tube (inlet side) remains unaffected by changes in the diameter of the top tube (next-stage tube), whereas the P in of the top tube is slightly reduced compared to that of the corresponding single tube NEAS with the same diameter. In the pore diameters range of 1.627 to 3.254 nm, the secondary infiltration pressure can be up to 31 times higher than the first infiltration pressure under different pore diameter combinations, where the corresponding energy absorption can be modulated by changing the critical infiltration pressure and pore volume. When the diameter of the bottom or the large tube is not more than 2.712 nm, the critical pore diameter difference required for cascade energy absorption characteristics is determined as 0.271 nm. These findings hold significant implications for the design and application of multistage nanofluidic systems.