Abstract
Microrheology experiments show that viscoelastic media composed by wormlike micellar networks display complex relaxations lasting seconds even at the scale of micrometers. By mapping a model of patchy colloids with suitable mesoscopic elementary motifs to a system of worm-like micelles, we are able to simulate its relaxation dynamics, upon a thermal quench, spanning many decades, from microseconds up to tens of seconds. After mapping the model to real units and to experimental scission energies, we show that the relaxation process develops through a sequence of non-local and energetically challenging arrangements. These adjustments remove undesired structures formed as a temporary energetic solution for stabilizing the thermodynamically unstable free caps of the network. We claim that the observed scale-free nature of this stagnant process may complicate the correct quantification of experimentally relevant time scales as the Weissenberg number.
Highlights
Many soft materials with important industrial and medical applications are formed by thermodynamic self-assembly of elementary constituents dispersed in aqueous solution.[1]
A generic understanding of the transient behavior of living polymers can be sought by addressing the following questions: which are the dominant local structures that compete dynamically in the rearrangement of a relaxing living random network? How does the long-time relaxation depend on the mechanisms of local rewiring and scission of the fibers? Is the time dependence of relevant observables undergoing relaxation characterized by simple exponentials or is it more similar to a dynamical scaling with power laws? Simulations of coarse grained models at mesoscopic level are an ideal tool for answering these questions: they allow a direct investigation both at short/small and long/large scales and they may adopt a well controlled protocol for driving the system out of equilibrium
We have introduced a patchy particle model to study the relaxation dynamics of living polymer networks driven out equilibrium by a deep thermal quench
Summary
Many soft materials with important industrial and medical applications are formed by thermodynamic self-assembly of elementary constituents dispersed in aqueous solution.[1] This process gives rise to networks of linear or branched fibers or even more complex objects[2] that can continuously break, rejoin or get entangled These ‘‘living’’ materials[3] have remarkable viscoelastic properties that are typically studied either by imposing a shear stress with a rheometer[1,4] or by dragging a micro-sized probe through the medium as in active microrheology.[5,6] The response and relaxation dynamics of living polymers are the result of large-scale reorientation and mutual reptation of the fibers that, in turn, depend on small scales mechanisms such as scission and rewiring of branches. A generic understanding of the transient behavior of living polymers can be sought by addressing the following questions: which are the dominant local structures (or ‘‘microstates’’) that compete dynamically in the rearrangement of a relaxing living random network? How does the long-time relaxation depend on the mechanisms of local rewiring and scission of the fibers? Is the time dependence of relevant observables undergoing relaxation characterized by simple exponentials or is it more similar to a dynamical scaling with power laws? Simulations of coarse grained models at mesoscopic level are an ideal tool for answering these questions: they allow a direct investigation both at short/small and long/large scales and they may adopt a well controlled protocol for driving the system out of equilibrium
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