Instituto de Química, Universidad Nacional Autonoma de México, Circuito Exterior, Ciudad Universitaria, 04510, México, DF.
J Chem Phys. 2011 Jun 7;134(21):214702. doi: 10.1063/1.3597773.
Density functional approach is applied to study the phase behavior of symmetric binary Lennard-Jones(12,6) mixtures in pillared slit-like pores. Our focus is in the evaluation of the first-order phase transitions in adsorbed phases and lines delimiting mixed and demixed adsorbed phases. The scenario of phase changes is sensitive to the pore width, to the energy of fluid-solid interaction, the amount, and the length of the pillars. Quantitative trends and qualitative changes of the phase diagrams topology are examined depending on the values of these parameters. The presence of pillars provides additional excluded volume effects, besides the confinement due to the pore walls. The effects of attraction between fluid species and pillars counteract this additional confinement. We have observed that both the increasing surface pillar density and the augmenting strength of fluid-solid interactions can qualitatively change the phase diagrams topology for the model with sufficiently strong trends for demixing. If the length of pillars is sufficiently large comparing to the pore width at low temperatures, we observe additional phase transitions of the first and second order due to the symmetry breaking of the distribution of chain segments and fluid species with respect to the slit-like pore center. Re-entrant symmetry changes and additional critical points then are observed.
密度泛函方法被应用于研究对称二元 Lennard-Jones（12,6）混合物在柱状狭缝状孔中的相行为。我们关注的是吸附相和混合相和分相吸附相之间的分界线的一阶相变的评估。相变化的情况对孔径、流体-固体相互作用的能量、柱的数量和长度敏感。取决于这些参数的值，检查了相图拓扑的定量趋势和定性变化。除了由于孔壁引起的限制之外，柱还提供了额外的排除体积效应。流体物质之间的吸引力和柱子之间的吸引力对这种额外的限制产生了抵消作用。我们观察到，随着表面柱密度的增加和流体-固体相互作用强度的增加，可以定性地改变具有足够强分相趋势的模型的相图拓扑。如果柱的长度相对于低温下的孔径足够大，则由于链段和流体物质相对于狭缝状孔中心的分布的对称性破坏，会观察到第一和第二阶的额外相变。然后会观察到再入对称性变化和附加临界点。
