Departamento de Física, Instituto de Física Aplicada, Universidad Nacional de San Luis-CONICET, San Luis, Argentina.
Langmuir. 2012 Oct 23;28(42):14917-24. doi: 10.1021/la302693n. Epub 2012 Oct 10.
Monte Carlo (MC) simulations have been carried out to study the adsorption on square and triangular lattices of particles with two bonding sites that, by decreasing temperature or increasing density, polymerize reversibly into chains with a discrete number of allowed directions and, at the same time, undergo a continuous isotropic-nematic (IN) transition. The process has been monitored by following the behavior of the adsorption isotherms (chemical potential μ as a function of the surface coverage θ) for different values of lateral interaction energy/temperature. The numerical data were compared with mean-field analytical predictions and exact functions for noninteracting and 1D systems. The obtained results revealed the existence of three adsorption regimes in temperature. (1) At high temperatures, above the critical one characterizing the IN transition at full coverage T(c)(θ = 1), the particles are distributed at random on the surface and the adlayer behaves as a noninteracting 2D system. (2) At very low temperatures, the asymmetric monomers adsorb, forming chains over almost the entire range of coverage, and the adsorption process behaves as a 1D problem. (3) In the intermediate regime, the system exhibits a mixed regime and the filling of the lattice proceeds according to two different processes. In the first stage, the monomers adsorb isotropically on the lattice until the IN transition occurs in the system and, from this point, particles adsorb, forming chains so that the adlayer behaves as a 1D fluid. The two adsorption processes are present in the adsorption isotherms, and a marked singularity can be observed that separates both regimes. Thus, the adsorption isotherms appear as sensitive quantities with respect to the IN phase transition, allowing us (i) to reproduce the phase diagram of the system for square lattices and (ii) to obtain an accurate determination of the phase diagram for triangular lattices.
已进行蒙特卡罗（MC）模拟，以研究在具有两个键合位点的正方形和三角形晶格上的吸附，通过降低温度或增加密度，这些颗粒可逆地聚合为具有离散允许方向数量的链，同时经历连续各向同性-向列（IN）转变。通过跟踪不同侧向相互作用能/温度下吸附等温线（化学势μ作为表面覆盖率θ的函数）的行为来监测该过程。数值数据与非相互作用和 1D 系统的平均场分析预测和精确函数进行了比较。获得的结果揭示了温度下存在三种吸附状态。（1）在高于完全覆盖时 IN 转变的临界温度 T（c）（θ=1）的高温下，颗粒随机分布在表面上，吸附层表现为非相互作用的 2D 系统。（2）在非常低的温度下，不对称单体吸附，在几乎整个覆盖范围内形成链，吸附过程表现为 1D 问题。（3）在中间状态下，系统表现出混合状态，晶格的填充根据两个不同的过程进行。在第一阶段，单体在晶格上各向同性吸附，直到系统中发生 IN 转变，从这一点开始，颗粒吸附形成链，使得吸附层表现为 1D 流体。两种吸附过程都存在于吸附等温线上，可以观察到一个明显的奇点，将两个状态分开。因此，吸附等温线是对 IN 相转变敏感的量，使我们能够（i）再现系统的正方形晶格相图，（ii）准确确定三角形晶格的相图。
