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

Abstract

Surface chemistry is believed to be the key parameter affecting the aggregation and breakage of colloidal suspensions when subjected to shear. To date, only a few works dealt with the understanding of the role of the physical and chemical properties of the particles' surface upon aggregation under shear. Previous studies suggested that surface modifications strongly affect polymer particles' adhesion, but it was very challenging to demonstrate this effect and monitor these alterations upon prolonged exposure to shear forces. More importantly, the mechanisms leading to these changes remain elusive. In this work, shear-induced aggregation experiments of polymer colloidal particles have been devised with the specific objective of highlighting material transfer and clarifying the role of the softness of the particle's surface. To achieve this goal, polymer particles with a core−shell structure comprising fluorescent groups have been prepared so that the surface's softness could be tuned by the addition of monomer acting as a plasticizer and the percentage of fluorescent particles could be recorded over time via confocal microscopy to detect eventual material transfer among different particles. For the first time, material exchange occurring on the soft surface of core−shell polymer microparticles upon aggregation under shear was observed and proved. More aptly, starting from a 50% labeled/nonlabeled mixture, an increase in the percentage of particles showing a fluorescent signature was recorded over time, reaching a fraction of 70% after 5 h.

PVdF-HFP and Ionic-Liquid-Based, Freestanding Thin Separator for Lithium-Ion Batteries

“…Therefore, the gel can be easily redispersed in the form of individual clusters. The average radius of gyration, ⟨ R g ⟩, and the mass fractal dimension, d f , of the PCs are measured using the SALS instrument, Mastersizer 2000. , Figure a shows the average structure factor, ⟨ S ( q )⟩, as a function of the magnitude of the scattering wave vector, q . From the ⟨ S ( q )⟩ curve, the Guinier region gives ⟨ R g ⟩ = 28 μm, and the power-law region covers a q range of almost 2 orders of magnitude, indicating that the clusters can be well-considered as fractal objects.…”

Mechanisms behind overshoots in mean cluster size profiles in aggregation-breakup processes

“…However, restructuring is not the only mechanism that leads to an overshoot and other mechanisms might apply too. One such mechanism was proposed by Moussa et al [11] and corroborated by Caimi et al [22]. These studies argue that the aggregates get weaker as the stirring proceeds, i.e.…”

“…Repeated breakup and re-aggregation can cause surface alterations of the primary particles contained in the aggregates, which lowers the bond strength between primary particles, making the aggregates weaker [11,22]. In our model, the decay of the aggregate strength translates into a decrease of the strength parameter C that enters the breakup rate through Eq.…”

Effect of SiO2 Nanoparticles on the Performance of PVdF-HFP/Ionic Liquid Separator for Lithium-Ion Batteries

“…Small-angle light scattering (SALS) measurements were taken using a Mastersizer 2000 (Malvern, UK) equipped with a laser having a wavelength = 633 nm to characterize the obtained clusters in terms of their average radius of gyration, 〈 R 〉, and their fractal dimension, d , following the procedure reported elsewhere [ 45 , 46 ]. Measures of dynamic light scattering and zeta potential were conducted using Zetasizer Nano ZS 3600 from Malvern Instruments (Malvern, UK).…”