Abstract
Anomalous aging in soft glassy materials has generated a great deal of interest because of some intriguing features of the underlying relaxation process, including the emergence of “ultra-long-range” dynamical correlations. An intriguing possibility is that such a huge correlation length is reflected in detectable ensemble fluctuations of the macroscopic material properties. We tackle this issue by performing replicated mechanical and dynamic light scattering (DLS) experiments on alginate gels, which recently emerged as a good model-system of anomalous aging. Here we show that some of the monitored quantities display wide variability, including large fluctuations in the stress relaxation and the occasional presence of two-step decay in the DLS decorrelation functions. By quantifying elastic fluctuation through the standard deviation of the elastic modulus and dynamic heterogeneities through the dynamic susceptibility, we find that both quantities do increase with the gel age over a comparable range. Our results suggest that large elastic fluctuations are closely related to ultra-long-range dynamical correlation, and therefore may be a general feature of anomalous aging in gels.
Highlights
Physical macromolecular gels are characterized by a network of long polymers bonded by reversible cross-links
By quantifying elastic fluctuation through the standard deviation of the elastic modulus and dynamic heterogeneities through the dynamic susceptibility, we find that both quantities do increase with the gel age over a comparable range
We recently showed that strontium alginate gel is a good model system of anomalous aging [5]
Summary
Physical macromolecular gels are characterized by a network of long polymers bonded by reversible cross-links. The rearrangements generated by internal stresses propagate over very large distances, driven by the elasticity of the network and poorly disturbed by thermal fluctuations Such a picture draws on the observation of dynamic heterogeneities (DHs) characterized by an “ultra-long” correlation length, eventually comparable with the system size. Such ultra-long-range correlations were first detected through spatially resolved scattering experiments on colloidal gels [7,29] and were recently reproduced by numerical simulations [28], emerging as another striking benchmark of anomalous aging. Our results suggest that ultra-long-range heterogeneities have implications on the macroscopic properties of anomalous aging gels
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