Mapping nonlinear stress propagation in non-equilibrium complex fluids
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Excerpt of abstract: Topologically-novel entangled polymers and enzyme-driven active matter systems are examples of complex fluids that exhibit intriguing spatiotemporally varying responses to strain. Yet, how local nonlinear stresses propagate through these soft systems remains an open question. Here, we combine optical tweezers microrheology (OTM) with differential dynamic microscopy (DDM) to map the time-dependent deformation fields arising from local nonlinear straining in ‘topologically-active’ DNA fluids. Specifically, we measure the stresses imposed in the fluids by local nonlinear strains and simultaneously image labeled DNA molecules surrounding the strain site. Using DDM, we characterize the macromolecular dynamics and deformation as a function of strain rate and distance from the applied strain. We perform these measurements on blends of circular DNA undergoing enzymatically-driven topological conversion and fragmentation. Our coupled OTM-DDM platform directly links nonlinear stress propagation to macromolecular dynamics and network structure and is applicable to a wide range of active and heterogeneous complex fluids.