Nanoporous metals prepared by the corrosion of an alloy can take the form of monolithic, millimeter-sized bodies containing approximately 1015 nanoscale ligaments per cubic millimeter. Their structure size can reach down to the very limits of stability of nanoscale objects. The prospect of using alloy corrosion as a means of making nanomaterials for fundamental studies and functional applications has led to a revived interest in the process. One of the distinguishing features of the materials in question is their bicontinuous microstructure, with two contiguous and interpenetrating phases. When at least one of the phases—for instance, a gas in the void space—allows the fast transport of a signal, then the interfaces can be addressed and their properties manipulated. That predestines nanoporous solids as objects of study for a new class of functional materials, in which interfacial behaviour is controlled reversibly by external variables, and the entire material reacts. Nanoporous metal actuators or ‘metallic muscles’ exemplify that concept, as do photonic metamaterials with tuneable resonances and structural materials with tuneable strength and ductility. The quite distinct mechanical properties of nanoporous metals are of interest in themselves, since the relevant studies probe the collective deformation behaviour of macroscopic arrays of objects with dimensions at the lower end of the size scale.
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