Li Zhidong, Cao Dapeng, Wu Jianzhong
Department of Chemical and Environmental Engineering, University of California, Riverside, California 92521-0425, USA.
J Chem Phys. 2005 Jun 8;122(22):224701. doi: 10.1063/1.1924603.
The phase behavior of short-chain fluids in slit pores is investigated by using a nonlocal-density-functional theory that takes into account the effects of segment size, chain connectivity, and van der Waals attractions explicitly. The layering and capillary condensation/evaporation transitions are examined at different chain length, temperature, pore width, and surface energy. It is found that longer chains are more likely to show hysteresis loops and multilayer adsorptions along with the capillary condensation and evaporation. Decreasing temperature favors the inclusion of layering transitions into the condensation/evaporation hysteresis loops. For large pores, the surface energy has relatively small effect on the pressures of the capillary condensation and evaporation but affects significantly on the layering pressures. It is also observed that all phase transitions within the pore take place at pressures lower than the corresponding bulk saturation pressure. The critical temperature of condensation/evaporation is always smaller than that of the bulk fluid. All coexistence curves for confined phase transitions are contained within the corresponding bulk vapor-liquid coexistence curve. As in the bulk phase, the longer the chain length, the higher are the critical temperatures of phase transitions in the pore.
通过使用一种非局部密度泛函理论，研究了狭缝孔中短链流体的相行为，该理论明确考虑了链段尺寸、链连接性和范德华引力的影响。在不同的链长、温度、孔宽和表面能条件下，研究了分层以及毛细凝聚/蒸发转变。结果发现，较长的链更有可能出现滞后环和多层吸附现象，同时伴随着毛细凝聚和蒸发。降低温度有利于将分层转变纳入凝聚/蒸发滞后环中。对于大孔，表面能对毛细凝聚和蒸发压力的影响相对较小，但对分层压力有显著影响。还观察到，孔内的所有相变都发生在低于相应体相饱和压力的压力下。凝聚/蒸发的临界温度总是低于体相流体的临界温度。受限相变的所有共存曲线都包含在相应的体相气-液共存曲线内。与体相一样，链长越长，孔中相变的临界温度越高。
