High Frequency Viscoelasticity of Soft Particle Glasses

The storage and loss moduli for jammed soft particles are studied computationally for a variety of interparticle potentials and volume fractions. The qualitative behavior of the storage modulus is independent of the nature of the interparticle potential. The frequency dependence of the storage modulus computed in the simulations is described by a universal logistic formula exhibiting two plateaus at low and high frequencies. While the high-frequency modulus G∞ follows the prediction of the Zwanzig–Mountain expression, which depends on the pair distribution function and pairwise interparticle potential, no such formula exists for the low-frequency modulus G0. Here, we show that for jammed soft particles at a given volume fraction G0∼G∞/gmax, where gmax is the maximum in the pair distribution function. The qualitative nature of the loss modulus depends on the form of the near-field drag forces between the soft particles. At moderate to high frequency, the loss modulus increases with the frequency according to a power law whose exponent is related to the drag force expression between two sliding particles. Computational predictions of the storage and loss moduli match most experimental observations but some discrepancies are observed indicating behavior beyond pairwise particle interactions at high frequencies.