Fig. 1.

DLSμR Workflow Scenarios Summary. (1) Tracer particles are mixed with the material to be characterized. Larger particles may be subject to sedimentation over measurement time t. (2) The particle and fluid mixture is measured by a DLS instrument, where incident light is scattered by the particles. The collected scattering intensity depends on the particles’ ability to explore the material structure. A particle that is effectively trapped or caged explores only a limited region of the total material space. 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.^24-29 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. 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. Scattering intensity also depends on possible attractive forces between particles and the fluid (for example, charge interactions), which result in hindered particle movement. (3) The scattering intensity autocorrelation function in different samples indicates the mean-squared displacement of the tracer particles in each material. (4) A frequency-dependent complex modulus can then be determined using a custom analysis package, optimized for minimizing noise introduced during measurement.