Finner Shari P, Pihlajamaa Ilian, van der Schoot Paul
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 3500 MB Eindhoven, The Netherlands.
J Chem Phys. 2020 Feb 14;152(6):064902. doi: 10.1063/1.5141481.
We present a numerical study on geometric percolation in liquid dispersions of hard slender colloidal particles subject to an external orienting field. In the formulation and liquid-state processing of nanocomposite materials, particle alignment by external fields such as electric, magnetic, or flow fields is practically inevitable and often works against the emergence of large nanoparticle networks. Using continuum percolation theory in conjunction with Onsager theory, we investigate how the interplay between externally induced alignment and the spontaneous symmetry breaking of the uniaxial nematic phase affects cluster formation in nanoparticle dispersions. It is known that particle alignment by means of a density increase or by an external field may result in a breakdown of an already percolating network. As a result, percolation can be limited to a small region of the phase diagram only. Here, we demonstrate that the existence and shape of such a "percolation island" in the phase diagram crucially depends on the connectivity length-a critical distance defining direct connections between neighboring particles. For some values of the connectivity range, we observe unusual re-entrance effects, in which a system-spanning network forms and breaks down multiple times with increasing particle density.
我们对硬细长胶体颗粒的液体分散体在外部定向场作用下的几何渗流进行了数值研究。在纳米复合材料的配方和液态加工过程中，通过电场、磁场或流场等外部场使颗粒排列实际上是不可避免的，而且常常不利于大型纳米颗粒网络的出现。结合连续渗流理论和昂萨格理论，我们研究了外部诱导排列与单轴向列相的自发对称性破缺之间的相互作用如何影响纳米颗粒分散体中的团簇形成。众所周知，通过密度增加或外部场使颗粒排列可能导致已经渗流的网络崩溃。因此，渗流可能仅局限于相图的一个小区域。在此，我们证明相图中这种“渗流岛”的存在和形状关键取决于连通长度——定义相邻颗粒之间直接连接的临界距离。对于连通范围的某些值，我们观察到不寻常的再入效应，即随着颗粒密度增加，一个跨越整个系统的网络会多次形成和崩溃。
