Robert L. Leheny’s primary research interests are in experimental soft condensed matter physics with particular focus on disordered and out-of-equilibrium systems such as glass-forming liquids, liquid crystal-colloid composites, and gels.
I am an experimental physicist at Johns Hopkins University working in the field of condensed matter. Condensed matter physics is the discipline within physics that seeks to explain the material world around us. Our understanding of materials' properties relies crucially on the tools of statistical mechanics that allow us to predict the average behavior of a system with many particles, and the fluctuations about that average, without knowing the detailed behavior of every single particle. Disorder and out-of-equilibrium conditions in a condensed matter system can profoundly affect its behavior, creating novel material properties that pose unique challenges for statistical mechanics. Much of my research at Johns Hopkins has been directed at understanding the physics of disordered and out-of-equilibrium materials.
Most of the materials on which I focus my research can be described as complex fluids. Complex fluids, such as colloidal suspensions and liquid crystals, are soft materials that possess liquid-like properties but that differ from simple liquids due to internal structure on the nanometer or micrometer scale. Often the properties of complex fluids derive from a delicate balance of interactions at the microscale including entropic, electrostatic, and interfacial forces. The fragile nature of the states that complex fluids assume, as well as their experimental accessibility, make these systems particularly well suited for exploring the consequences of disorder and out-of-equilibrium behavior. Among the disordered systems I have been studying recently include liquid-crystal/colloid composites, gels, and emulsions.
Much of my research involves x-ray and neutron scattering techniques. I am a frequent user of Sector 8-ID of the Advanced Photon Source and also perform experiments at the National Synchrotron Light Source and at the NIST Center for Neutron Research. I am also a member of the Materials Research Science and Engineering Center (MRSEC) at Johns Hopkins. In collaboration with the group of Dan Reich, I have been pursuing a research program that employs state-of-the-art magnetic nanostructure fabrication to create custom-synthesized particles for microrheology. Our strategy is to optimize the probes' geometry as well as their magnetic and surface properties to match specific complex fluid environments and measurements objectives. We have applied this approach to explore the novel elastic forces experienced by anisotropic particles in nematic liquid crystals and to investigate the shear rheology of thin fluid films.