Flow-Induced Aggregation and Breakup of Particle Clusters Controlled by Surface Nanoroughness

Abstract

Interactions between colloidal particles are strongly affected by the particle surface chemistry and composition of the liquid phase. Further complexity is introduced when particles are exposed to shear flow, often leading to broad variation of the final properties of formed clusters. Here we discover a new dynamical effect arising in shear-induced aggregation where repeated aggregation and breakup events cause the particle surface roughness to irreversibly increase with time, thus decreasing the bond adhesive energy and the resistance of the aggregates to breakup. This leads to a pronounced overshoot in the time evolution of the aggregate size, which can only be explained with the proposed mechanism. This is demonstrated by good agreement between time evolution of measured light-scattering data and those calculated with a population-balance model taking into account the increase in the primary particle nanoroughness caused by repeated breakup events resulting in the decrease of bond adhesive energy as a function of time. Thus, the proposed model is able to reproduce the overshoot phenomenon by taking into account the physicochemical parameters, such as pH, till now not considered in the literature. Overall, this new effect could be exploited in the future to achieve better control over the flow-induced assembly of nanoparticles.

Effect of particle size distribution on rheological properties of chocolate

“…In the case of smoother surfaces, the probability for direct surface-surface contact is larger and adhesion forces therefore may be more pronounced. [30][31][32] These results also indicate that a high yield stress does not necessarily lead to a high viscosity, as quartz beads systems give lower viscosity values than the other systems, as discussed in the previous section. Viscosity is not only determined by the interactions between the particles, but more by particle packing effects.…”

“…A possible reason for the stronger interactions in quartz beads systems is their smoother surface, which facilitates contact between particles, and also results in stronger adhesion forces. [30][31][32] For some of the quartz beads systems, even negative values were obtained. This indicates a more effective network formation between the dispersed particles over time, which leads to an increase in the viscosity.…”

Is Modeling the PSD in Emulsion Polymerization a Finished Problem? An Overview

“…Actually, considering these contributions as additive is equivalent to saying that particle stabilization (e.g., due to the presence of surfactant at their surface) is not efficient against orthokinetic coagulation. Thus, the additive‐flux assumption is supposed to work well in the limit of completely screened electrostatic repulsion . However, in relatively stable dispersions, there is a strong nonlinear coupling between convection and diffusion, which means that the overall coagulation rate coefficient is not equal to the sum of the two aggregation mechanisms.…”

“…Thus, the additive-flux assumption is supposed to work well in the limit of completely screened electrostatic repulsion. [196] However, in relatively stable dispersions, there is a strong nonlinear coupling between convection and diffusion, which means that the overall coagulation rate coefficient is not equal to the sum of the two aggregation mechanisms. Thus, orthokinetic coagulation is slowed down due to the surfactant.…”

Tracking of Fluorescently Labeled Polymer Particles Reveals Surface Effects during Shear-Controlled Aggregation

“…11,12 Shear aggregation experiments carried out in our group on certain polystyrene particles have led us to hypothesize that, upon aggregation, their surface roughness was changing as a function of time, leading to completely different time evolutions of clusters' morphology and to progressively decrease the average cluster sizes, instead of commonly encountered steady-state conditions. 9 Indeed, the increase in surface roughness leads to weaker bonds among particles within clusters, thus progressively increasing their breakage rate with time. Despite the importance of such effects, it is generally challenging to experimentally demonstrate not only the presence of surface roughness but even more a modification of this parameter upon prolonged exposure to shear forces.…”