Peculiar Feature in Pressure of Fluids Confined in Nanospace and their Phase Behavior

许多多孔介质如沸石、二氧化硅和活性炭具有纳米级的孔，而诸如被限制在纳米空间中的流体的相图这样的基本信息是不可预测的。本研究利用分子模拟技术和原子力显微镜（AFM）直接获得受限流体的相行为特征，并基于分子在纳米空间中感受到的压力，建立了对受限流体相行为的系统认识和预测模型。所获得的结果总结如下。分子模拟应用最初由首席研究员开发的分子动力学技术（Miyahara等人，J.Chem. Phys.，1997），在不同的围壁相互作用强度和体相平衡压力条件下，详细观察了纳米空间中流体的相变.实验测量我们开发了独特的实验系统 ...更多信息 用于直接观察受限液体的液-固相变。AFM配备有温度控制单元。选择石墨化程度高的碳颗粒，成功地附着在AFM悬臂梁的针尖上，构成胶体探针。在不同温度下，测量了探针与浸没在环境温度为凝固点的有机液体中的解理石墨表面之间的力曲线。结果表明，在“有利的”壁面中，液体的冻结温度比在本体中高。成功地得到了凝固点漂移与表面分离之间的关系.模型的建立和验证我们建立了一个新的模型，用于预测相行为的限制液体，定量的基础上的概念，“压力感受到的限制流体，“这不同于散装，因为影响的吸引相互作用的限制壁。该模型成功地预测了模拟系统和实验系统中观察到的相变点，无需任何可调参数，证明了该模型在定性概念和定量方面的有效性，以及它的实用性。少

Many porous media such as zeolites, silica and activated carbons posses nanoscale pores, while such a basic information as the phase diagram of fluids confined in nanospace is left unpredictable. This research project pursued phase behavior of the confined fluids using the molecular simulation technique and an atomic force microscopy (AFM) to obtain their characteristics directly, which were utilized to establish a systematic understanding and a predictable model for the phase behavior, based on the 'pressure felt by the molecules in nanospace.' The obtained results are summalized in the followings.1. Molecular SimulationsApplying a molecular dynamics technique developed originally by the head investigator (Miyahara et al., J.Chem. Phys., 1997), phase transitions of fluids confined in nanospace were observed in detail under various conditions of interaction strength of the confining wall and bulk equilibrium pressure.2. Experimental MeasurementsWe developed a unique experimental system … More for observing directly the liquid-solid phase transition of confined liquids as follows. The AFM was equipped with a temperature control unit. A carbon particle with high degree of graphitization was selected and successfully attached to the tip of AFM cantilever to make up a so-called colloidal probe. Force curves between the probe and a cleaved graphite surface immersed in an organic liquid with ambient temperature of the freezing point were measured under various temperatures. The results clarified that the liquid, which was confined in "favorable" walls, exhibits higher freezing temperature than that in bulk. The relation between the freezing point shift and the surface separation was successfully obtained.3. Model Development and VerificationWe developed a new model for predicting phase behavior of confined liquids, quantitatively, based on the concept of the "pressure felt by the confined fluid, " which differs from bulk because of the influence by the attractive interaction from confining walls. The proposed model successfully predicted the phase transition points observed both in simulation systems and experimental ones, without any adjustable parameter, and proved its validity both in the qualitative concept and quantitative aspect, and its usefulness. Less