Olarte-Plata Juan D, Brekke-Svaland Gøran, Bresme Fernando
Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, White City Campus, 80 Wood Lane, London W12 0BZ, UK.
Nanoscale. 2020 May 28;12(20):11165-11173. doi: 10.1039/d0nr00834f.
We investigate the impact of nanoparticle roughness on the phase behaviour of suspensions in models of calcium carbonate nanoparticles. We use a Derjaguin approach that incorporates roughness effects and interactions between the nanoparticles modelled with a combination of DLVO forces and hydration forces, derived using experimental data and atomistic molecular dynamics simulations, respectively. Roughness effects, such as atomic steps or terraces appearing in mineral surfaces result in very different effective inter-nanoparticle potentials. Using stochastic Langevin Dynamics computer simulations and the effective interparticle interactions we demonstrate that relatively small changes in the roughness of the particles modify significantly the stability of the suspensions. We propose that the sensitivity of the phase behavior to the roughness is connected to the short length scale of the adhesive attraction arising from the ordering of water layers confined between calcite surfaces. Particles with smooth surfaces feature strong adhesive forces, and form gel fractal structures, while small surface roughness, of the order of atomic steps in mineral faces, stabilize the suspension. We believe that our work helps to rationalize the contrasting experimental results that have been obtained recently using nanoparticles or extended surfaces, which provide support for the existence of adhesive or repulsive interactions, respectively. We further use our model to analyze the synergistic effects of roughness, pH and ion concentration on the phase behavior of suspensions, connecting with recent experiments using calcium carbonate nanoparticles.
我们在碳酸钙纳米颗粒模型中研究了纳米颗粒粗糙度对悬浮液相行为的影响。我们采用了一种Derjaguin方法，该方法结合了粗糙度效应以及分别使用实验数据和原子分子动力学模拟得出的DLVO力和水化力对纳米颗粒之间的相互作用进行建模。粗糙度效应，例如矿物表面出现的原子台阶或平台，会导致非常不同的有效纳米颗粒间势能。利用随机朗之万动力学计算机模拟和有效的颗粒间相互作用，我们证明颗粒粗糙度相对较小的变化会显著改变悬浮液的稳定性。我们提出，相行为对粗糙度的敏感性与方解石表面之间受限水层有序排列产生的粘附吸引力的短长度尺度有关。表面光滑的颗粒具有很强的粘附力，并形成凝胶分形结构，而矿物表面原子台阶量级的小表面粗糙度会使悬浮液稳定。我们相信，我们的工作有助于解释最近分别使用纳米颗粒或扩展表面获得的对比实验结果，这些结果分别为粘附或排斥相互作用的存在提供了支持。我们进一步使用我们的模型来分析粗糙度、pH值和离子浓度对悬浮液相行为的协同效应，并与最近使用碳酸钙纳米颗粒的实验相关联。
