Long-range-interaction induced ordered structures in deposition processes

TL;DR: In this article, the authors present a new model of sequential adsorption in which the adsorbing particles experience dipolar interactions and show that in the presence of these long-range interactions, highly ordered structures in the adorbed layer may be induced at low temperatures.

Abstract: We present a new model of sequential adsorption in which the adsorbing particles experience dipolar interactions. We show that in the presence of these long-range interactions, highly ordered structures in the adsorbed layer may be induced at low temperatures. The new phenomenology is manifest through significant variations of the pair correlation function and the jamming limit, with respect to the case of noninteracting particles. Our study could be relevant in understanding the adsorption of magnetic colloidal particles in the presence of a magnetic field. [S0031-9007(98)06352-2] The study of the irreversible adsorption of colloidal particles onto a surface has long since been the subject of a great deal of interest, due to its potential applications to physical, physicochemical, and biological problems [1]. Our global understanding of the process has been possible through the formulation of different models, analyzed either numerically or analytically. These models share a sequential and irreversible nature, and differ in the rules by which the particles accommodate when arriving at the surface. The various rules are responsible for the different values of the relevant quantities describing the adsorbed phase, such as the jamming limit, the pair correlation function, and the local variance of the number of deposited particles. In the random sequential adsorption model [2 ‐ 6] particles are placed at random positions on the substrate. If an incoming particle overlaps with a previously adsorbed one, it is rejected and a new one probed; otherwise it becomes irreversibly adsorbed. In the ballistic model (BM) [7 ‐ 10] the particles descend to the surface following straight vertical trajectories. An incoming particle that does not reach the substrate is allowed to roll over the previously adsorbed ones, following the steepest descent path, until it reaches a stable position. Only particles that fail to gain the surface are finally rejected. All these models, and their subsequent extensions, have been mainly implemented by considering short range —hard core—interactions among particles. With the exception of the analysis of the role played by electrostatic interactions [11], the case of long-range interactions remains essentially unexplored. Our purpose in this Letter is to analyze comprehensively the influence that these interactions have in the kinetics of deposition in a simple numerical model. We will show that when they are taken into account, a new aspect of the problem emerges. The structure of the adsorbed layer changes considerably, giving rise in some cases to the appearance of a higher degree of order in the substrate. To illustrate this point, we will focus on the case of anisotropic dipolar interactions, and present numerical simulations of the adsorption process on a line s1 1 1dd and on a plane s1 1 2dd. In our simulations we consider the adsorption of spherical magnetic particles of diameter a and magnetic moment $ m › m $ u, with m