No abstract

Studies of adsorption and desorption of argon at 87 K in model ink-bottle pores have been carried out using Monte Carlo simulation. We show that the isotherms can be constructed as a composite of isotherms for a set of unit cells with constant pore size. The mechanisms of adsorption and desorption in an ink-bottle pore can be easily understood from the characteristics of these unit cells, providing insight into how the hysteresis loop would evolve in shape and area when the neck size is varied. The key factor controlling the characteristics of the loop is the relative position of the condensation and evaporation pressures of these unit cells. Two features of particular interest are noted: (i) a pore blocking mechanism might be mistaken as a cavitation if cavitation is interpreted as a sudden change in the amount adsorbed along the desorption branch and (ii) the shape of the hysteresis loop switches from type H1 for small neck sizes to type H2 for larger necks but reverts back to type H1 when the neck size approaches the cavity size.

We present GCMC simulations of argon adsorption in slit pores of different channel geometry. We show that the isotherm for an ink-bottle pore can be reconstructed as a linear combination of the local isotherms of appropriately chosen independent unit cells. Second, depending on the system parameters and operating conditions, the phenomena of cavitation and pore blocking can occur for a given configuration of the ink-bottle pore by varying the geometrical aspect ratio. Although it has been argued in the literature that the geometrical aspects of the system govern the evaporation mechanism (either cavitation or pore blocking), we here put forward an argument that the local compressibility in different parts of the ink-bottle pore is the deciding factor for evaporation. When the fluid in the small neck is strongly bound, cavitation is the governing process, and molecules in the cavity evaporate to the surrounding bulk gas via a mass transfer mechanism through the pore neck. When the pore neck is sufficiently large, the system of neck and cavity evaporates at the same pressure, which is a consequence of the comparable compressibility between the fluid in the neck and that in the cavity. This suggests that local compressibility is the measure of cohesiveness of the fluid prior to evaporation. One consequence that we derive from the analysis of isotherms of a number of connected pores is that by analyzing the adsorption branch or the desorption branch of an experimental isotherm may not lead to the correct pore sizes and the correct pore volume distribution.

A new theory of condensation in an open end slit pore, based on the concept of temperature dependent undulation, at the interface separating the adsorbed phase and the gas-like region, is presented. The theory, describes, for the first time, the microscopic origin of the critical hysteresis temperature and the critical hysteresis pore size, properties which are not accessible to any classical theories.

DEA increases DFT by a greater amount than its parent drug amiodarone. There is an effect of intravenous amiodarone on DFT that is dose dependent.