Ten Brinke Annemieke J W, Bailey Louise, Lekkerkerker Henk N W, Maitland Geoffrey C
Van't Hoff Laboratory for Physical and Colloid Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, the Netherlands.
Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge, UKCB3 OEL.
Soft Matter. 2008 Jan 22;4(2):337-348. doi: 10.1039/b713144e.
We report the results of a comprehensive study of the rheological properties of a series of mixed colloid systems where the shape of one of the components has been varied systematically. Specifically we have measured the oscillatory, transient (creep) and continuous steady shear flow behaviour of a 2.5 wt% dispersion in water of a well-characterised hectorite clay modified by the addition of a series of aluminasol colloidal particles whose shape varies systematically from rod (boehmite) to platelet (gibbsite) to sphere (alumina-coated silica), all having essentially the same smallest dimension, which is similar to that of the hectorite. The particle characterisation and rheological properties of the pure components have recently been reported in Part I of this series (Soft Matter, 2007, 3, 1145). The mixtures show the same general behaviour as the pure systems, displaying a complex 'yield space' transition from an elastoviscous gel at low applied stresses to a viscous, weakly elastic, shear-thinning liquid at high stresses. The unifying theme of this work is that the addition of 0.25 wt% of the minor component in all cases results in dramatic enhancements to the dispersion rheological properties. At the same time the magnitude of this effect depends on the shape of the particles. Shear moduli, low stress viscosities and effective yield stresses all increase in the additive order rods < platelets < spheres, with enhancements for the latter being up to a factor of 500 and typically 20. At the same time the critical failure strains for the gels decreased in the same order - the strongest gels are also the most fragile in this sense. The physicochemical factors underlying this behaviour are discussed and a simple qualitative model described. While no complete explanation or model can be proposed at this stage, the study provides a quantitative model-system baseline for mixed colloidal dispersions already used for industrial applications (e.g. oilwell-drilling fluids) and suggests ways in which such fluids may be optimised and controlled.
我们报告了一系列混合胶体体系流变学性质的综合研究结果，其中一种组分的形状已被系统地改变。具体而言，我们测量了一种2.5 wt%的分散体在水中的振荡、瞬态（蠕变）和连续稳态剪切流动行为，该分散体由一种经过充分表征的锂蒙脱石粘土组成，通过添加一系列氧化铝溶胶胶体颗粒进行改性，这些颗粒的形状从棒状（勃姆石）到片状（三水铝石）再到球状（氧化铝包覆的二氧化硅）系统地变化，所有颗粒的最小尺寸基本相同，且与锂蒙脱石的最小尺寸相似。该系列的第一部分（《软物质》，2007年，3卷，1145页）最近已报道了纯组分的颗粒表征和流变学性质。混合物表现出与纯体系相同的一般行为，在低外加应力下呈现从弹性粘性凝胶到高应力下粘性、弱弹性、剪切变稀液体的复杂“屈服空间”转变。这项工作的统一主题是，在所有情况下添加0.25 wt%的次要组分都会显著增强分散体的流变学性质。同时，这种效应的大小取决于颗粒的形状。剪切模量、低应力粘度和有效屈服应力均按棒状＜片状＜球状的顺序增加，后者的增强高达500倍，通常为20倍。同时，凝胶的临界破坏应变按相同顺序降低——从这个意义上说，最强的凝胶也是最脆弱的。讨论了这种行为背后的物理化学因素，并描述了一个简单的定性模型。虽然现阶段无法提出完整的解释或模型，但该研究为已用于工业应用（如油井钻井液）的混合胶体分散体提供了一个定量模型系统基线，并提出了优化和控制此类流体的方法。
