Bendersky Marina, Santore Maria M, Davis Jeffrey M
Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA 01003, United States.
Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, United States.
J Colloid Interface Sci. 2015 Jul 1;449:443-51. doi: 10.1016/j.jcis.2015.02.031. Epub 2015 Feb 21.
Electrostatic surface heterogeneity on the order of a few nanometers is common in colloidal and bacterial systems, dominating adhesion and aggregation and inducing deviations from classical DLVO theory based on a uniform distribution of surface charge. Topographical heterogeneity and roughness also strongly influence adhesion. In this work, a model is introduced to quantify the spatial fluctuations in the interaction of microparticles in a flowing suspension with a wall aligned parallel to the flow. The wall contains nanoscale chemical and topographical heterogeneities ("patches") that are randomly distributed and produce localized attraction and repulsion. These attractive and repulsive regions induce fluctuations in the trajectories of the flowing particles that are critical to particle capture by the wall. The statistical distribution of patches is combined with mean-field DLVO calculations between a particle and two homogeneous surfaces: one with the surface potential of the patches and one with the potential of the underlying wall. These surface potentials could be obtained in experiments from zeta potential measurements for the bare wall and for one saturated with patches. This simple model reproduces the mean DLVO interaction force or energy vs. particle-wall separation distance, its variance, and particle adhesion thresholds from direct simulations of particle trajectories over patchy surfaces. The predictions of the model are consistent with experimental findings of significant microparticle deposition onto patchy, net-repulsive surfaces whose apparent zeta potential has the same sign as that of the particles. Deposition is significantly enhanced if the patches protrude even slightly from the surface. The model predictions are also in agreement with the observed variation of the adhesion threshold with the shear rate in published studies of dynamic microparticle adhesion on patchy surfaces.
在胶体和细菌系统中，几纳米量级的静电表面异质性很常见，它主导着粘附和聚集，并导致与基于表面电荷均匀分布的经典DLVO理论产生偏差。形貌异质性和粗糙度也会强烈影响粘附。在这项工作中，引入了一个模型来量化流动悬浮液中微粒与平行于流动方向排列的壁之间相互作用的空间波动。壁上含有随机分布的纳米级化学和形貌异质性（“斑块”），会产生局部吸引和排斥。这些吸引和排斥区域会引起流动颗粒轨迹的波动，这对颗粒被壁捕获至关重要。斑块的统计分布与颗粒和两个均匀表面之间的平均场DLVO计算相结合：一个表面具有斑块的表面电势，另一个具有下层壁的电势。这些表面电势可以在实验中通过测量裸壁和被斑块饱和的壁的zeta电势来获得。这个简单的模型通过对颗粒在斑块表面上的轨迹进行直接模拟，再现了平均DLVO相互作用力或能量与颗粒 - 壁分离距离的关系、其方差以及颗粒粘附阈值。该模型的预测与实验结果一致，即在表观zeta电势与颗粒具有相同符号的斑块状、净排斥表面上有大量微粒沉积。如果斑块甚至稍微从表面突出，沉积会显著增强。该模型预测也与已发表的关于动态微粒在斑块表面上粘附的研究中观察到的粘附阈值随剪切速率的变化一致。
