Brownian dynamics simulation on orthogonal superposition rheology: Time–shear rate superposition of colloidal gel

Abstract

The dynamics of model colloidal gels under a steady shear flow is studied by means of a Brownian dynamics (BD) simulation while applying orthogonal superposition rheometry, which superimposes a small amplitude oscillatory flow orthogonal to the main flow direction. Orthogonal dynamic frequency sweep (ODFS) curves are obtained at various magnitudes of the main flow, which shows shear thinning behavior of the colloidal gel. The viscoelastic spectra of the ODFS can be superimposed onto a master curve by the horizontal shift factor, which is equivalent to particle viscosity. That is, the shear rate controls a single master clock for all viscoelastic spectra of the ODFS in the form of a time–shear rate superposition, which bears an analogy with the time–temperature superposition of polymeric systems. In the low-frequency region of the master curve, both orthogonal moduli are well superimposed onto a single master curve, whereas the loss modulus deviates slightly from the master curve in the high-frequency region, which coincides with the experimental findings. We observe spatial and time-varying structural properties in both low- and high-frequency regions on the ODFS curves by decomposing the pair distribution function. It is verified that each flow condition shifted onto the same stress level on the master curve shows identical spatial orthogonal moduli at all radial distances despite the differences in the aggregate size and average particle connectivity.

Tracking colloidal silica particles to evaluate their dispersion and interactions in concentrated suspensions under shear force applications

“…In other words, using k, comparing the experimentally determined H/D and theoretical H/D, we can identify the nature (i.e., repulsive and attractive) and strength of the interaction present among the particles. Conventional radial distribution functions and structure factors are useful to capture ordered structural information [48][49][50][51][52], whereas our developed method can be applicable to investigate both ordered and nonordered structures. The latter is the case for this study that focused on investigating the nature and the degree of particle-particle interactions (Figure 4).…”

OrthoChirp: A fast spectro-mechanical probe for monitoring transient microstructural evolution of complex fluids during shear

“…Many complex materials which are of great importance to industrial applications including colloidal gels, polymer solutions and melts as well as fracking fluids undergo flow-induced micro-structural changes [1][2][3][4]. To probe these changes, researchers have developed superposition rheometrical techniques, which involves combining a small amplitude oscillatory probe signal with a unidirectional shear rate [3][4][5][6][7][8][9][10][11][12]. This family of techniques enables the determination of the relaxation spectrum of materials under flow or large deformations [13,14].…”