In contrast, a particle that is not caged can explore the full material space (indicated by the homogeneously purple material in the Ergodic case), resulting in equivalent ensemble-averaged and time-averaged behaviors that is the hallmark of ergodicity. If different particles are confined within micro-environments that have varying physical properties, their ensemble-averaged displacement will be different from the time-averaged motion of a single particle, resulting in non-ergodic behavior. Such cages (indicated in pink in the Non-ergodic case) could arise from heterogeneity in the material and can be one source of ergodicity breaking. A particle that is effectively trapped or caged explores only a limited region of the total material space. The collected scattering intensity depends on the particles’ ability to explore the material structure. (2) The particle and fluid mixture is measured by a DLS instrument, where incident light is scattered by the particles. Larger particles may be subject to sedimentation over measurement time t. (1) Tracer particles are mixed with the material to be characterized. DLSμR is an easy, efficient, and economical rheological technique that can guide the design of new polymeric materials and facilitate the understanding of the underlying physics governing behavior of naturally derived materials.ĭLS μR Workflow Scenarios Summary. We focus on the advantages of applying DLSμR to biologically relevant materials: breast cancer cells encapsulated in a collagen gel and cystic fibrosis sputum. In this work, we detail the procedure for applying the technique to new materials and discuss the critical considerations for implementing the technique, including a custom analysis script for analyzing data output. We demonstrate the use of dynamic light scattering microrheology (DLSμR) on a variety of soft materials, including dilute polymer solutions, covalently-crosslinked polymer gels, and active, biological fluids. This microrheology technique only requires a small sample volume of 12 μL to measure up to six decades in time of rheological behavior. present a method for using dynamic light scattering in the single-scattering limit to measure the viscoelastic moduli of soft materials. 7 Department of Materials Science, Stanford University, Stanford, CA 94305, USA.and Department of Applied Physics, Stanford University, Stanford, CA 94305, USA and Biophysics Program, Stanford University, Stanford, CA 94305, USA. and Department of Materials Science, Stanford University, Stanford, CA 94305, USA. 6 Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.5 Stanford Immunology, Stanford University, Stanford, CA 94305, USA.4 Center for Excellence in Pulmonary Biology, Department of Pediatrics, Stanford University, Stanford, CA 94305, USA.3 Department of Chemical & Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA.and Stanford Immunology, Stanford University, Stanford, CA 94305, USA. 2 Department of Materials Science, Stanford University, Stanford, CA 94305, USA. 1 Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
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