Dynamics and yielding of binary self-suspended nanoparticle fluids

Abstract

Yielding and flow transitions in bi-disperse suspensions of particles are studied using a model system comprised of self-suspended spherical nanoparticles. An important feature of the materials is that the nanoparticles are uniformly dispersed in the absence of a solvent. Addition of larger particles to a suspension of smaller ones is found to soften the suspensions, and in the limit of large size disparities, completely fluidizes the material. We show that these behaviors coincide with a speeding-up of de-correlation dynamics of all particles in the suspensions and are accompanied by a reduction in the energy dissipated at the yielding transition. We discuss our findings in terms of ligand-mediated jamming and un-jamming of hairy particle suspensions.

Asymmetric soft-hard colloidal mixtures: Osmotic effects, glassy states and rheology

“…At larger strain amplitudes the onset of nonlinearity is marked by an increase of G", which eventually reaches a maximum before decreasing according to a power-law. At the same time, G' decreases with strain smoothly and eventually follows a power-law with exponent almost double compared to that of G'' as reported for different jammed systems [72], [75], [49], [71], [76]. This is not further discussed in this work.…”

“…For the mixtures characterized by a single yield process, γy does not exhibit any appreciable dependence on hard star concentration (γy ~ cHS 0 ) or frequency: we obtainγy≈10%,which falls in the typical range of values reported for colloidal suspensions [10], [77], [72], [73], [74]. Interestingly, the two yield strains appearing in the APS state at 10 rad/s are appreciably different from those characterizing the single yield point of the single (RG) and double (DG) glass states, suggesting that the very processes driving the yield of the suspensions in the APS state differ from those driving the yield of solid repulsive states [42], [49], [77]. Indeed, multiple yield processes are thought of as reflecting multiple constraining length scales (in our case dictated by bonds and cages) which occur in systems where interactions lead to additional length scale such as due to clustering in binary colloidal mixtures [77], [49], [42], attractive glasses [10], [71] or arrested phase separating systems alike.…”

“…Interestingly, the two yield strains appearing in the APS state at 10 rad/s are appreciably different from those characterizing the single yield point of the single (RG) and double (DG) glass states, suggesting that the very processes driving the yield of the suspensions in the APS state differ from those driving the yield of solid repulsive states [42], [49], [77]. Indeed, multiple yield processes are thought of as reflecting multiple constraining length scales (in our case dictated by bonds and cages) which occur in systems where interactions lead to additional length scale such as due to clustering in binary colloidal mixtures [77], [49], [42], attractive glasses [10], [71] or arrested phase separating systems alike. Given the yield strain behavior, the yield stress y(=Gpγy) expectedly follows the same qualitative trend observed for the plateau modulus Gp (Figure 9).…”

“…Once the mixtures enter in the basin of ergodic states, the characteristic time of the liquid (extracted from the terminal crossover of the moduli, i.e., r = 1/crossover) varies over three decades; it first decreases with cHS, then goes through a minimum and finally increases as the re-entrance is approached. This is a generic behavior for an ergodic phase between two glassy states [61], [62], [71], [49]. The re-entrant solid-like state has been discussed and identified as an arrested phase separation [61], [62] whose rheology (dynamics) is dominated by that of soft stars.…”

“…More recently, binary mixtures of self-suspended grafted nanoparticles (silica particles with covalently bonded small polyethylene glycol chains, in the absence of solvent) were investigated [49].These systems have been proposed as a paradigm of solvent-free colloids [50], [51]. It was found that adding larger particles to a glassy suspension of smaller particles led to its softening, and in the limit of large size disparities, to its complete fluidization.…”