Science and Prospects of Using Nanoporous Materials for Energy Absorption
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Science and Prospects of Using Nanoporous Materials for Energy Absorption Xi Chen1, and Yu Qiao2 1 Columbia University, New York, NY, 10027 2 University of California, San Diego, La Jolla, CA, 92093 ABSTRACT With its ultra-large specific surface area, a nanoporous material is an ideal, yet relatively unexplored, platform for accepting or actuating liquids, with potential performance gains for energy dissipation and output typical of disruptive technologies. Our experimental and theoretical results indicate either dramatically improved performance or unique combinations of properties and capabilities not attainable in conventional materials, which make the novel nanoporous structures studied herein very attractive as advanced protective intelligent systems. INTRODUCTION For more than a decade, intensive studies have been conducted on manufacturing nanostructured protective composites. The basic idea is quite straightforward: in a nanoparticle or nanolayer reinforced composite, if under external loadings most nanofillers could debond from the matrix, a large amount of energy would be dissipated at the nanofiller-matrix interface such a composite would be ideal for protection or damping applications, including car bumpers, body armors, mounting stages, etc. However, one intrinsic difficulty is the lack of control of the filler-matrix interaction. For example, very often the nanocomposite becomes less ductile with the addition of the nanofillers; thus, it tends to fail by catastrophic cracking and only a small fraction of nanofiller-matrix interface could be involved in the energy dissipation process, i.e. the large interface area cannot be utilized. In order to fully take advantage of the large surface/interface area of a nanostructured system, at least one of the components must be sufficiently "flexible". Inspired by this understanding, and noticing the fact that the most "flexible" materials are actually liquids, recently we have pioneered incorporating liquid phases in nanoporous materials. Nanoporous materials are solids containing large volume fractions of nano-sized pores (Fig. 1). The most dominant Nanopore characteristic of them is the ultrahigh specific area of pore surfaces. They have been widely used for absorption and catalysis, yet the potential applicability in mechanical systems has not received the necessary attention. The system under our investigation is manufactured by dispersing surface charged nanoporous particles in a nonwetting liquid. Beyond a critical pressure, the "flexible" liquid phase could be forced into the nanopores and almost all of the nanopore surfaces could be exposed to it. Thus, the solid-liquid interactions (i.e. the capillary effect) can be greatly amplified by the large specific area, A. That is, accompanied by the pressure-induced SEM, TEM, and pore infiltration, a large amount of external work would be transformed Fig.1 structure of synthetic nanointo the solid-liquid interfacial energy, which can be regarded as porous zeolites. being absorbed. Denoting ∆γ as the
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