Klomkliang Nikom, Do D D, Nicholson D
School of Chemical Engineering, University of Queensland , St. Lucia, Queensland 4072, Australia.
Langmuir. 2014 Nov 4;30(43):12879-87. doi: 10.1021/la5035992. Epub 2014 Oct 24.
The hysteresis loop and scanning curves for argon adsorbed in a wedge pore with one end closed are studied with grand canonical Monte Carlo simulation. We have found multiple hysteresis loops for pores with either the narrow end or the wider end closed. In pores with the narrow end closed, adsorption and desorption exhibits a two-stage sequence of rapid change, followed by a gradual change in adsorbate density. The pore can be divided into zones of commensurate packing and junctions of incommensurate packing. A striking feature is that the sequence of these two stages is opposite for the adsorption and desorption processes. This can be explained by cohesion in the adsorbate, in which a steep condensation process is associated with the zones and a steep evaporation process is associated with the junctions between them. For pores with the wider end closed, the processes of adsorption and desorption from various zones are correlated with each other. In pores with the narrow end closed, the scanning curves trace reversibly along the segment of the isotherm, where the isotherm shows gradual change, and when the scanning curve reaches a point between the gradual change segment and the sharp change segment, the scanning curve crosses from one boundary of the hysteresis loop to the corresponding point on the other boundary. This indicates that the condensation and evaporation states are not affected by scanning but that, in scanning across the hysteresis loop, the adsorbate passes through a sequence of metastable states as the distribution of density is rearranged, without any significant change in the overall density. In contrast, for pores with the wider end closed, both the descending curve from a partially filled pore and the ascending curve are identical to the desorption branch of the corresponding pore with its narrow end closed.
采用巨正则蒙特卡罗模拟研究了一端封闭的楔形孔中氩气的滞后回线和扫描曲线。我们发现，对于窄端或宽端封闭的孔，存在多个滞后回线。在窄端封闭的孔中，吸附和解吸呈现出快速变化的两阶段序列，随后吸附质密度逐渐变化。孔可分为密排区和非密排区的交界处。一个显著特征是，这两个阶段的顺序在吸附和解吸过程中是相反的。这可以用吸附质中的内聚力来解释，其中陡峭的凝聚过程与区域相关，陡峭的蒸发过程与它们之间的交界处相关。对于宽端封闭的孔，来自各个区域的吸附和解吸过程相互关联。在窄端封闭的孔中，扫描曲线沿着等温线的渐变段可逆地追踪，当扫描曲线到达渐变段和突变段之间的一点时，扫描曲线从滞后回线的一个边界交叉到另一个边界上的对应点。这表明凝聚和蒸发状态不受扫描影响，但在扫描穿过滞后回线时，随着密度分布重新排列，吸附质会经历一系列亚稳态，而总体密度没有任何显著变化。相比之下，对于宽端封闭的孔，从部分填充孔的下降曲线和上升曲线都与窄端封闭的相应孔的解吸分支相同。
