Dynamics of Mesoscale Order Formation by Colloidal Nanoparticles Adsorbing onto a Solid Surface

纳米颗粒有序阵列通常表现出独特的特性，近年来在作为高功能材料方面受到了极大的关注。为了开发这样的材料和器件，人们必须知道粒子-粒子和粒子-衬底相互作用的影响，例如，对已建立的结构的影响。因此，迫切需要一种模拟方法来预测订单形成过程的动力学。本研究致力于发展介于分子动力学和离散元方法之间的胶体吸附体系的介观模拟方法。研究结论如下：1.研究结果。理论研究：基于朗之万方程，我们成功地开发了布朗动力学模拟程序。对静电稳定的胶体纳米粒子在带反电荷的衬底上进行了广泛的模拟。通过对模拟结果的分析，得出以下三项结论。1)…此外，有序形成的决定因素不是吸附粒子之间的平均相互作用势能，这是过去提出的，到目前为止被认为是有效的。相反，这个因素被发现是我们所说的“单向平均力”。2)基于上述发现的决定因素，可以通过控制吸附粒子之间的间距来构建有序结构。3)证明了订单形成过程本质上是一个随机过程，并成功地建立了订单形成概率随时间变化的模型。实验研究：衬底必须带有反电荷才能使粒子吸附在其上。然后对二氧化硅粒子使用蓝宝石板，对带正电荷的聚苯乙烯粒子使用云母板。通过非原位扫描电子显微镜观察和原子力显微镜原位观察观察了吸附过程。因此，我们阐明了吸附的速率过程，以及颗粒在表面的流动性对有序形成的重要影响。综上所述，成功地建立了胶体吸附体系的介观模拟方法，可以给出大量详细的吸附和有序形成过程的信息。在此基础上，从理论和实验两个方面成功地模拟了胶体吸附体系中的许多重要过程和现象。较少

Ordered arrays of nanoparticles often exhibit unique characteristics, which are attracting much attention recently to be utilized as high-functional materials. For the development of such materials and devices, one has to know effects of particle-particle and particle-substrate interactions, e.g., onto the established structure. Thus a simulation method for predicting the dynamics of the order-formation process must be pressing need. This study has been aiming at developing a mesoscale simulation method for colloidal adsorption system, which would stand between the molecular dynamics and the discrete element method. The conclusions are as follows.1. Theoretical study: Based on the Langevin equation, we successfully developed a Brownian dynamics simulation code. Extensive simulations were conducted for a electrostatically stabilized colloidal nanoparticles onto a substrate with counter charge. The findings through the analysis of the simulation results are the following three items. 1) … More The determinant factor for order formation was NOT the average interaction potential energies between adsorbed particles, which was proposed in the past and has been believed to be valid so far. Instead, the factor was found to be what we call "one-directional average force". 2) Based on the above found determinant factor, the ordered structure can be made up with a controlled spacing between adsorbed particles. 3) The order formation process was proven to be essentially a stochastic process, and a model to estimate the probability of order formation against time was successfully developed.2. Experimental study: The substrate must possess a counter charge to have particles adsorbed on it. Then a sapphire plate was used for silica particles, while mica plate was used with polystylene particle with positive charge. Adsorption processes were observed by ex-situ SEM observation, and by in-situ AFM observation. As a result, we clarified the rate process of adsorption, and the importance of the mobility of particles on the surface that severely affects the onset of the order formation.Summarizing, a mesoscale simulation method for colloidal adsorption system was successfully developed, which can give a large amount of detailed information on the adsorption and order formation process. Further, both in theoretical and experimental aspects, many important process and phenomena in colloidal adsorption system were modeled successfully. Less