@article{ortiz_riehn_daniels_2016, title={Nonaffine deformation under compression and decompression of a flow-stabilized solid}, volume={2016}, ISSN={["1742-5468"]}, DOI={10.1088/1742-5468/2016/08/084003}, abstractNote={Understanding the particle-scale transition from elastic deformation to plastic flow is central to making predictions about the bulk material properties and response of disordered materials. To address this issue, we perform experiments on flow-stabilized solids composed of micron-scale spheres within a microfluidic channel, in a regime where particle inertia is negligible. Each solid heap exists within a stress field imposed by the flow, and we track the positions of particles in response to single impulses of fluid-driven compression or decompression. We find that the resulting deformation field is well-decomposed into an affine field, with a constant strain profile throughout the solid, and a non-affine field. The magnitude of this non-affine response decays with the distance from the free surface in the long-time limit, suggesting that the distance from jamming plays a significant role in controlling the length scale of plastic flow. Finally, we observe that compressive pulses create more rearrangements than decompressive pulses, an effect that we quantify using the Dmin2 statistic for non-affine motion. Unexpectedly, the time scale for the compression response is shorter than for decompression at the same strain (but unequal pressure), providing insight into the coupling between deformation and cage-breaking.}, number={8}, journal={JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT}, publisher={IOP Publishing}, author={Ortiz, Carlos P. and Riehn, Robert and Daniels, Karen E.}, year={2016}, month={Aug} }
 @article{ortiz_daniels_riehn_2014, title={Nonlinear elasticity of microsphere heaps}, volume={90}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000341301600006&KeyUID=WOS:000341301600006}, DOI={10.1103/physreve.90.022304}, abstractNote={Thermal fluctuations, geometric exclusion, and external driving all govern the mechanical response of dense particulate suspensions. Here, we measure the stress-strain response of quasi-two-dimensional flow-stabilized microsphere heaps in a regime in which all three effects are present using a microfluidic device. We observe that the elastic modulus and the mean interparticle separation of the heaps are tunable via the confining stress provided by the fluid flow. Furthermore, the measured stress-strain curves exhibit a universal nonlinear shape, which can be predicted from a thermal van der Waals equation of state with excluded volume. This analysis indicates that many-body interactions contribute a significant fraction of the stress supported by the heap.}, number={2}, journal={Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics}, publisher={American Physical Society (APS)}, author={Ortiz, C. P. and Daniels, K. E. and Riehn, R.}, year={2014}, pages={9} }
 @article{roushan_kaur_karpusenko_countryman_ortiz_lim_wang_riehn_2014, title={Probing transient protein-mediated DNA linkages using nanoconfinement}, volume={8}, number={3}, journal={Biomicrofluidics}, author={Roushan, M. and Kaur, P. and Karpusenko, A. and Countryman, P. J. and Ortiz, C. P. and Lim, S. F. and Wang, H. and Riehn, R.}, year={2014} }
 @article{ortiz_riehn_daniels_2013, title={Flow-driven formation of solid-like microsphere heaps}, volume={9}, ISSN={["1744-683X"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000311964800025&KeyUID=WOS:000311964800025}, DOI={10.1039/c2sm26762d}, abstractNote={We observe the formation of heaps of repulsive microspheres, created by flowing a colloidal microsphere suspension towards a flat-topped ridge placed within a quasi two-dimensional microfluidic channel. This configuration allows for both shear and normal forces on the microspheres in contact with the ridge. The heaps, which are formed against the ridge, are characterized by two distinct phases: a solid-like bulk phase in the interior and a highly fluctuating, liquid-like state which exists along its leading edge. We observe that heaps only form above a critical flow velocity, vc, and that they are destroyed by thermal rearrangements when the flow ceases. We monitor the dynamics of heap formation using fluorescence video microscopy, measuring the heap volume and the angle of repose in response to microsphere deposition and erosion processes. We find that the steady state angle of repose, θf, increases as a function of inflow velocity, v∞, with a functional form .}, number={2}, journal={SOFT MATTER}, publisher={Royal Society of Chemistry (RSC)}, author={Ortiz, Carlos P. and Riehn, Robert and Daniels, Karen E.}, year={2013}, pages={543–549} }