Materials in extreme conditions : experimental developments and studies of systems far from equilibrium

Abstract

Advances to shock wave generation and characterizations techniques are presented. Building upon previous work employing a novel quasi-2D focusing geometry, pressures of at least 100 GPa are achieved on the benchtop at the micron scale. Diagnostics for optical visualization of these generated waves were also refined; an existing single-shot multiframe imaging technique was extended into phase sensitive imaging. These techniques are applied to a range of material systems (energetic materials, brittle solids and biological membranes), pushing them far from equilibrium, and studying their response. While the explosive 1,3,5-triaza-1,3,5-trinitrocyclohexane (RDX), has been used for almost a century, questions remain about its initiation, reactivity, and interaction with shock waves. Very little work has directly addressed the coupling between mechanical deformation and chemistry in this system. Further, the literature to date mostly comprises studies with idealized 1-dimensional waves.

Herein, the reactivity of single crystals of RDX responding to multiple shockwaves is considered. A surprising transient sensitivity to low pressure reflected shockwaves following a high-pressure initial excitation is discovered. This effect confirms the link between morphological change, and sensitivity previously reported. Silica glass is a widely studied system under shock compression and high pressure. A relatively low pressure phase transition is known and several distinct amorphous states exist prior to the transition. Several studies have also reported a lagging wave following dynamic compression in glasses. This "failure wave" is thought to precede fracture and brittle failure. We demonstrate a method of generating shock waves in glass and show the ability to image the dynamics in real-time. Additionally, we directly image fracture following shock compression and an associated failure wave. Finally, we address the interaction of shock and acoustic waves with cell membranes.

This interaction is of great interest in biomedical technology for targeted cell lysing, as well as drug and vaccine delivery. Basic science questions also exist regarding the interactions between these waves and biological cells and membranes. Here we employ simultaneous interferometric and fluorescence imaging to elucidate the mechanism of transmembrane transport in cells and cell models. We show that under single cycle shock conditions the spatial structure of the wave is key to transfection; the wave must be spatially narrower than the cell itself. However, in a multicycle acoustic case spatially wider waves can still affect transfection suggesting that we have moved from a mechanism relying on a pressure gradient across the cell (in the shock case) to a pore formation mechanism.