Computing the linear viscoelastic properties of soft gels using an optimally windowed chirp protocol

Abstract

We use molecular dynamics simulations of a model three-dimensional particulate gel, to investigate the linear viscoelastic response. The numerical simulations are combined with a novel test protocol (the optimallywindowed chirp or OWCh), in which a continuous exponentially-varying frequency sweep windowed by a tapered cosine function is applied. The mechanical response of the gel is then analyzed in the Fourier domain. We show that i) OWCh leads to an accurate computation of the full frequency spectrum at a rate significantly faster than with the traditional discrete frequency sweeps, and with a reasonably high signal-tonoise ratio, and ii) the bulk viscoelastic response of the microscopic model can be described in terms of a simple mesoscopic constitutive model. The simulated gel response is in fact well described by a mechanical model corresponding to a fractional Kelvin-Voigt model with a single Scott-Blair (or springpot) element and a spring in parallel. By varying the viscous damping and the particle mass used in the microscopic simulations over a wide range of values, we demonstrate the existence of a single master curve for the frequency dependence of the viscoelastic response of the gel that is fully predicted by the constitutive model. By developing a fast and robust protocol for evaluating the linear viscoelastic spectrum of these soft solids, we open the path towards novel multiscale insight into the rheological response for such complex materials. arXiv:1805.07987v1 [cond-mat.soft]

Rheology of protein-stabilised emulsion gels envisioned as composite networks 1– Comparison of pure droplet gels and protein gels

“…Both the protein gel and the droplet gel exhibit an increase of their viscoelasticity with the angular frequency ω, in agreement with previous studies on colloidal gels [7,26,12,53]. The storage modulus G increases moderately for the two types of gels, while the loss modulus G also rises with ω, but with a slightly different behaviour for protein gels and droplet gels.…”

“…The storage modulus G increases moderately for the two types of gels, while the loss modulus G also rises with ω, but with a slightly different behaviour for protein gels and droplet gels. The increase of G is at odds with the frequency dependence of dilute colloidal gels, for which a decrease of G was observed [50], but is in good correspondence with the computed linear viscoelasticity of a similar system [53]. This behaviour may indicate the presence of a relaxation process that is visible in the frequency range covered at low concentration, but which moves to much lower frequencies at higher concentrations, and so becomes invisible.…”

Rheoacoustic Gels: Tuning Mechanical and Flow Properties of Colloidal Gels with Ultrasonic Vibrations

“…Our fluidization results also strongly suggest that some of the mechanical effects observed here can be rationalized through an effective temperature. We believe that recent simulation methods developed for colloidal gels [61][62][63][64], once adapted to account for ultrasonic excitation, will certainly bring valuable insights into the local impact of ultrasound on the gel microstructure and its relationship with the global mechanical response.…”

Power law viscoelasticity of a fractal colloidal gel

“…RHEOS is currently limited to the broad family of linear viscoelastic models. A particular strength of the library is its ability to handle rheological models containing fractional derivatives, which have demonstrable utility for the modelling of biological materials [1,2,3,4], but have hitherto remained in relative obscurity -possibly due to their mathematical and computational complexity. RHEOS is written in Julia [5], which provides excellent computational efficiency and approachable syntax.…”