Meso-Structure Control of Colloidal Nanoparticles Adsorbed on a Substrate by Applying External Electric Potential

如果能够根据需要控制吸附在基底上的纳米颗粒阵列的宏观结构，将开发出各种高功能材料。本研究的目的是开发一种方法来控制动力学和结构的颗粒阵列，通过施加外部电势的导电基板上的胶体纳米粒子吸附。主要结论如下：1.实验研究：建立了一个由外加电位控制表面电位的导电基底实验系统，通过非原位扫描电镜观察和原位原子力显微镜观察，观察了荷正电聚苯乙烯胶乳胶体粒子的吸附过程。我们发现有一个极限表面电位为-28mV，低于此电位时，胶体颗粒以相当高的密度吸附，且颗粒间的距离几乎均匀;高于此电位时，即使电位为负，也几乎不发生吸附。重新 ...更多信息 在具有轻微负电荷的基底上没有吸附的原因可能是防止了表面上结构化水层的强吸附。这种弱吸附的粒子由于表面摩擦力的极大降低，有望形成有序的阵列。2.理论研究：对静电稳定的胶体纳米粒子在带反电荷的基底上的布朗动力学进行了广泛的模拟，以发现“单向平均力”的性质和估计方法，该力已被发现是有序/无序边界的决定性因素。通过与硬盘上的桤木转变的比较，我们成功地统一了硬盘和胶体系统中有序/无序转变的判据，引入了胶体粒子的有效直径，由于双层排斥力的存在，该有效直径应大于真实的直径。通过这一成功，有序结构和有序形成过程的动力学的先验预测现在是可能的。总之，介观尺度有序形成的胶体吸附在一个给定的电位表面上成功地理解和解析建模，这将代表的理论基础，通过施加外部电势控制的动力学和结构的颗粒阵列在衬底上。少

Various high-functional materials would be developed if masoscale structure of nanoparticle arrays adsorbed on a substrate can be controlled as desired. This study has been aiming at developing a methodology for controlling kinetics and structure of particle arrays by applying external electric potential to a conductive substrate onto which colloidal nanoparticles adsorb. The conclusions are as follows.1.Experimental study :Having developed an experimental system equipped with a conductive substrate with desired surface potential controlled by external electrical potential, adsorption processes of positively charged polystylene latex collodal particles were observed by ex-situ SEM observation, and by in-situ AFM observation. We found that there is a limiting surface potential of -28mV, below which colloidal particles adsorb with rather high density with almost uniform interparticle distances, and above which almost no adsorption occurs even though the potential remains negative. The re … More ason for no adsorption on the substrate with slightly negative charge may presumably be a prevention of strong adsorption by structured water layer on the surface. This kind of weakly adsorbed particles would be expected to form an ordered arrays because of extremely reduced friction on the surface.2.Theoretical study :Extensive simulations of Brownian dynamics were conducted for a electrostatically stabilized colloidal nanoparticles onto a substrate with counter charge in order to find out the nature and estimation method for "one-directional average force", which has been found to be the determinant factor for order/disorder boundary. Through comparison with the Alder transition by hard disks, we have successfully unified the criteria for order/disorder transition in both the hard-disk and colloidal systems by introducing an effective diameter for colloidal particles, which should be larger than the real diameter because of the repulsive double-layer forces. With this success a priori prediction of ordered structure and kinetics of the order-formation process can now be possible.Summarizing, a mesoscale order formation by colloidal adsorption on a surface with given potential was successfully understood and modeled analytically, which would stand for theoretical basis for the control of kinetics and structure of particle arrays on a substrate by applying external electric potential. Less