Department of Chemical Engineering, National Chung Cheng University, Chia-Yi, 621 Taiwan, Republic of China.
J Chem Phys. 2010 Jun 14;132(22):224904. doi: 10.1063/1.3447890.
The van der Waals (vdW) potentials governing macroscopic objects have long been formulated in the context of classical theories, such as Hamaker's microscopic theory and Lifshitz's continuum theory. This work addresses the possibility of constructing the vdW interaction potentials of nanoparticle species using multiscale simulation schemes. Amorphous silica nanoparticles were considered as a benchmark example for which a series of (SiO(2))(n) (n being an integer) has been systematically surveyed as the potential candidates of the packing units that reproduce known bulk material properties in atomistic molecular dynamics simulations. This strategy led to the identification of spherical Si(6)O(12) molecules, later utilized as the elementary coarse-grained (CG) particles to compute the pair interaction potentials of silica nanoparticles ranging from 0.62 to 100 nm in diameter. The model nanoparticles so built may, in turn, serve as the children CG particles to construct nanoparticles assuming arbitrary sizes and shapes. Major observations are as follows. The pair interaction potentials for all the investigated spherical silica nanoparticles can be cast into a semiempirical, generalized Lennard-Jones 2alpha-alpha potential (alpha being a size-dependent, large integral number). In its reduced form, we discuss the implied universalities for the vdW potentials governing a certain range of amorphous nanoparticle species as well as how thermodynamic transferability can be fulfilled automatically. In view of future applications with colloidal suspensions, we briefly evaluated the vdW potential in the presence of a "screening" medium mimicking the effects of electrical double layers or grafting materials atop the nanoparticle core. The general observations shed new light on strategies to attain a microscopic control over interparticle attractions. In future perspectives, the proposed multiscale computation scheme shall help bridge the current gap between the modeling of polymer chains and macroscopic objects by introducing molecular models coarse-grained at a similar level so that the interactions between these two can be treated in a consistent and faithful way.
范德华（vdW）势长期以来一直被用于经典理论中，例如哈马克的微观理论和 Lifshitz 的连续体理论。本工作探讨了使用多尺度模拟方案构建纳米粒子种类的 vdW 相互作用势的可能性。无定形二氧化硅纳米粒子被认为是一个基准示例，对于该示例，已经系统地研究了一系列（SiO2）n（n 为整数）作为潜在的组装单元，这些组装单元在原子分子动力学模拟中再现了已知的体材料性质。该策略导致了球形 Si6O12 分子的识别，后来将其用作基本的粗粒（CG）粒子，以计算直径从 0.62 到 100nm 的二氧化硅纳米粒子的对相互作用势。如此构建的模型纳米粒子反过来可以作为儿童 CG 粒子，构建任意尺寸和形状的纳米粒子。主要观察结果如下。所有研究的球形二氧化硅纳米粒子的对相互作用势都可以采用半经验的广义 Lennard-Jones 2alpha-alpha 势（alpha 是一个依赖于尺寸的大整数）进行拟合。在其简化形式中，我们讨论了控制一定范围的无定形纳米粒子种类的 vdW 势所隐含的普遍性，以及如何自动实现热力学传递性。鉴于胶体悬浮液的未来应用，我们简要评估了存在“屏蔽”介质时的 vdW 势，该介质模拟了电双层或接枝材料在纳米粒子核心上的影响。这些普遍观察结果为实现对粒子间吸引力的微观控制提供了新的思路。在未来的展望中，所提出的多尺度计算方案将通过引入类似水平的粗粒化分子模型来帮助弥合聚合物链和宏观物体建模之间的当前差距，以便以一致和忠实的方式处理这两者之间的相互作用。
