Out-of-equilibrium dynamics of a fractal model gel

• Published in: The Journal of chemical physics 2009-05, Vol.130 (19), p.194904-194904-15
• Main Authors: Suarez, M.-A., Kern, N., Pitard, E., Kob, W.
• Format: Article
• Language: English
• Subjects: Physics
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3129247

Using molecular dynamics computer simulations we investigate the dynamics of a gel. We start from a fractal structure generated by the diffusion limited cluster aggregation-deflection algorithm, onto which we then impose an interaction potential consisting of a short-range attraction as well as a long-range repulsion. After relaxing the system at zero temperature, we let it evolve at a fixed finite temperature. Depending on the temperature T we find different scenarios for the dynamics. For T ≳ 0.2 the fractal structure is unstable and breaks up into small clusters which relax to equilibrium. For T ≲ 0.2 the structure is stable and the dynamics slows down with increasing waiting time. At intermediate and low T the mean squared displacement scales as t 2 / 3 and we discuss several mechanisms for this anomalous time dependence. For intermediate T , the self-intermediate scattering function is given by a compressed exponential at small wave vectors and by a stretched exponential at large wave vectors. In contrast, for low T it is a stretched exponential for all wave vectors. This behavior can be traced back to a subtle interplay between elastic rearrangements, fluctuations of chainlike filaments, and heterogeneity.