Fluid Dynamics, Power Generation and Environment, EDF R&D, 6 quai Watier, Chatou 78401, France.
Langmuir. 2011 Apr 19;27(8):4603-12. doi: 10.1021/la104488a. Epub 2011 Mar 15.
In this paper, we investigate the deposition of nanosized and microsized particles on rough surfaces under electrostatic repulsive conditions in an aqueous suspension. This issue arises in the general context of modeling particle deposition which, in the present work, is addressed as a two-step process: first particles are transported by the motions of the flow toward surfaces and, second, in the immediate vicinity of the walls, the forces between the incoming particles and the walls are determined using the classical DLVO theory. The interest of this approach is to take into account both hydrodynamical and physicochemical effects within a single model. Satisfactory results have been obtained in attractive conditions but some discrepancies have been revealed in the case of repulsive conditions, in line with other studies which have noted differences between predictions based on the DLVO theory and experimental measurements for similar repulsive conditions. Consequently, the aim of the present work is to focus on this particular range and, more specifically, to assess the influence of surface roughness on the DLVO potential energy. For this purpose, we introduce a new simplified model of surface roughness where spherical protruding asperities are placed randomly on a smooth plate. On the basis of this geometrical description, approximate DLVO expressions are used and numerical calculations are performed. We first highlight the existence of a critical asperity size which brings about the highest reduction of the DLVO interaction energy. Then, the influence of the surface covered by the asperities is investigated as well as retardation effects which can play a role in the reduction of the interaction energy. Finally, by considering the random distribution of the energy barrier of the DLVO potential due to the random geometrical configurations, the overall effect of surface roughness is demonstrated with one application of the complete deposition model in an industrial test case. These new numerical results show that nonzero deposition rates are now obtained even in repulsive conditions, which confirms that surface roughness is a relevant aspect to introduce in general approaches to deposition.
在本文中，我们研究了在带静电排斥条件下纳米级和微米级颗粒在粗糙表面上的沉积。这个问题出现在颗粒沉积建模的一般背景下，在本工作中，它被视为一个两步过程：首先，颗粒通过流的运动被输送到表面，其次，在壁面附近，使用经典的 DLVO 理论确定入射颗粒与壁面之间的相互作用力。这种方法的优点是在单个模型中同时考虑水动力和物理化学效应。在吸引条件下已经得到了令人满意的结果，但在排斥条件下却出现了一些差异，这与其他研究一致，其他研究也注意到了基于 DLVO 理论的预测与类似排斥条件下的实验测量之间的差异。因此，本工作的目的是集中研究这一特殊范围，更具体地说，评估表面粗糙度对 DLVO 位能的影响。为此，我们引入了一种新的简化表面粗糙度模型，其中球形突出的粗糙峰随机放置在光滑板上。基于这种几何描述，使用近似的 DLVO 表达式并进行数值计算。我们首先强调存在一个临界粗糙峰尺寸，它会导致 DLVO 相互作用能的最大降低。然后，我们还研究了粗糙峰覆盖的表面以及可能在降低相互作用能方面起作用的迟滞效应。最后，通过考虑由于随机几何构型导致的 DLVO 位能能垒的随机分布，我们用一个工业测试案例中的完整沉积模型来展示表面粗糙度的整体影响。这些新的数值结果表明，即使在排斥条件下，也能得到非零的沉积速率，这证实了表面粗糙度是引入沉积一般方法的一个相关方面。
