Wall slip and flow of concentrated hard-sphere colloidal suspensions
Wall slip and flow of concentrated hard-sphere colloidal suspensions
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DOI：
10.1122/1.4719775
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发表时间：
2012-09-01
影响因子：
3.3
通讯作者：
Besseling, R.
中科院分区：
文献类型：
--
作者：
Ballesta, P.;Petekidis, G.;Besseling, R.
我们提出了一个全面的研究的滑移和流动的浓缩胶体悬浮液使用锥板流变仪和同步共聚焦成像。在胶态玻璃体系中，对于光滑的不粘壁，悬浮液的固体性质导致流变学从大应力下的Herschel-Bulkley（HB）整体流动行为转变为低应力下的宾汉样滑移行为，这对于足够的胶体壁吸引力或胶体级壁粗糙度被抑制。可视化显示了滑移剪切过渡如何取决于间隙大小和两个壁的边界条件，以及部分滑移在屈服应力以上持续存在。一个唯象模型，结合宾汉滑移定律和HB散装流量，充分考虑的行为。微观上，宾汉定律与壁处的薄（亚胶体）润滑层有关，从而引起滑移参数对颗粒尺寸和浓度的特性依赖性。我们将其与悬浮液的渗透压和屈服应力联系起来，并分析了货车德瓦尔斯相互作用的影响。对于最大的浓度，我们观察到屈服应力周围的不均匀流动，与最近的工作集中膏体剪切带。我们还描述了残余滑移在浓缩的液体悬浮液中，消失的屈服应力导致共存的（弱）滑移和散装剪切流的所有测量速率。(C)2012流变学学会。[http：//dx.doi.org/10.1122/1.4719775]
We present a comprehensive study of the slip and flow of concentrated colloidal suspensions using cone-plate rheometry and simultaneous confocal imaging. In the colloidal glass regime, for smooth, nonstick walls, the solid nature of the suspension causes a transition in the rheology from Herschel-Bulkley (HB) bulk flow behavior at large stress to a Bingham-like slip behavior at low stress, which is suppressed for sufficient colloid-wall attraction or colloid-scale wall roughness. Visualization shows how the slip-shear transition depends on gap size and the boundary conditions at both walls and that partial slip persist well above the yield stress. A phenomenological model, incorporating the Bingham slip law and HB bulk flow, fully accounts for the behavior. Microscopically, the Bingham law is related to a thin (subcolloidal) lubrication layer at the wall, giving rise to a characteristic dependence of slip parameters on particle size and concentration. We relate this to the suspension's osmotic pressure and yield stress and also analyze the influence of van der Waals interaction. For the largest concentrations, we observe nonuniform flow around the yield stress, in line with recent work on bulk shear banding of concentrated pastes. We also describe residual slip in concentrated liquid suspensions, where the vanishing yield stress causes coexistence of (weak) slip and bulk shear flow for all measured rates. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4719775]