Mechanical properties of holographically-defined porous polymers and carbonized polymers

A new class of porous materials, so called a holographically-defined porous material (HDPM), has been available by the interference of multiple laser beams. Since the solid volume fraction ($f_{V})$ can be systematically adjusted without altering periodicity, we studied the mechanical behavior of polymer-HDPM as a function of $f_{V}$ using nanoindentation. The observed elastic modulus of the polymer-HDPM has a significantly lower value than what expected from theoretical models at a high $f_{V}$. We confirmed that polymer-HDPM has two different plastic deformation modes from the transition in modulus and in energy absorption associated with the deformation. We also studied carbon-HDPM and compared these materials with the polymer-HDPM in energy absorption. Although carbon is a highly elastic material in bulk, carbon-HDPM absorbs energy by inelastic deformation including highly localized cracks. The energy absorption per residual indentation volume is proportional to a cube of indentation depth for all carbon-HDPM. Interestingly, when a carbon-HDPM has a partially disconnected network, its behavior was clearly different with the connected and rather similar to polymer-HDPM.