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 μ m diameter at different volume fractions larger than 64 vol% are subjected to shearing deformations between plates separated by gaps of 5–120 μ m 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.

中文翻译：

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几何限制对软微凝胶颗粒糊剂流动的影响

在本文中，我们确定了限制对浓缩软微凝胶颗粒悬浮液的剪切流的影响。利用基于弯曲的微间隙流变仪 (FMR)，直径为 4 μm、体积分数大于 64 vol% 的溶胀 P(NIPAM-co-AA) 微凝胶颗粒的水悬浮液在被间隙隔开的板之间发生剪切变形。 5–120 μ m，同时监测不同速率下的应力响应。描述遵循 Cloitre 和 Bonnecaze 方法的弹性流体动力润滑和弹性力平衡的应力演变，可以表明，已经低于 10 个粒子直径数量级的临界限制水平，粒子间压力的增加导致剪切力上升在屈服状态下以给定速率施加应力。对于接近临界最密堆积的颗粒体积分数，这种效应最强，当接近单颗粒限制水平时，流动阻力增加两个数量级，而当提高浓度时，这种对流动的限制效应会降低。此外，可以证明，在悬浮液开始屈服时，约束增加了有效模量，但没有增加屈服应变。