Effect of geometrical confinement on the flow of soft microgel particle pastes

Abstract

In this paper we determine the effect of confinement on the shear flow of concentrated soft microgel particle suspensions. Utilizing a Flexure-based Microgap Rheometer (FMR), aqueous suspensions of swollen P(NIPAM-co-AA) microgel particles of 4 µm diameter at different volume fractions larger than 64 vol% are subjected to shearing deformations between plates separated by gaps of 5 −120 µm while monitoring the stress response at different rates. Describing the stress evolution from a balance of elastohydrodynamic lubrication and elastic forces following the approach of Cloitre and Bonnecaze, it could be shown that already below a critical confinement level on the order of 10 particle diameters an increase of the interparticle pressure leads to a rising shear stress at a given rate in the yielded regime. This effect is strongest for particle volume fractions close to the critical closest packing, with two orders of magnitude increase in flow resistance when approaching the single particle confinement level, whereas this confinement effect on the flow decreases when raising the concentration. Furthermore, it could be shown that, at the onset of the yielding of the suspensions, the confinement is increasing the effective modulus, but not the yield strain. 2 Giovanni Vleminckx et al. Rheologica Acta manuscript No.

Powdered Cross-Linked Gelatin Methacryloyl as an Injectable Hydrogel for Adipose Tissue Engineering

“…To rule out effects of confinement and particle compression, each hydrogel sample was measured at a gap height of at least three times the maximum size of a dry powder particle of that size fraction. This gap height was well above the critical confinement gap of microgel particles, which is defined by Vleminckx et al [ 80 ] to be 2D, with D the diameter of the particle. The hydrogel samples were prepared at a concentration of 10 w / v % in water and in the three salt solutions (see Table 3 ), and left to rest 2 h prior to the measurement, such that the particles could reach their equilibrium swelling.…”

Rheology of graphene oxide stabilized Pickering emulsions

“…[15][16][17] Start-up flow shows apparent shearthinning, steady yield stress, and especially a normal force that depends on particles' collisions and structural yield. 18,19 Dynamic amplitude tests are precise tools to characterize interfacial elasticity caused by nanoparticles' jamming networks in an undeformed state. [20][21][22] Strain and frequency sweep, as the standard dynamic oscillatory test, measure dynamic yield stress and maximum elastic limit concerning the transformation of linear to nonlinear behavior.…”

“…This approach has been applied to thixotropic fluids by studying particle interaction strengths, explicitly concerning the gradual breakdown and rebuilding of solid dispersed structures. 19,27,28 In our previous research, we introduced multiple interval thixotropy tests (miTT) to check how different shear rates influence the rheological properties. 29 The miTT profile set a series of shear rate ramps to destroy the sample and after each specific shear, identical time sweep intervals were used to monitor structural recovery.…”

Modeling amorphous materials: from hydrogel packings to mesoscale models

“…Previous modeling work has proceeded along many fronts. Many groups assume pair-wise additive interactions between particles even in a very high density regime far from jamming [8,226,196,45,20], sometimes modified to attempt to account for ϕ dependent effective interactions [222,122,72,101,132,76,75], which are, however, still pair-wise contact interactions.…”