(572b) Adsorption Isotherms of Argon, Nitrogen, Carbon Dioxide, n-Butane, and Water for Pore Characterization of Chromatographic Particles

Gibbs ensemble Monte Carlo simulations are carried out to assist the pore characterization of chromatographic particles via adsorption and intrusion experiments. The simulations use planar slit pore models to represent the surface chemistries of three prototypical chromatographic materials that range from hydrophilic to hydrophobic: (a) a pristine silica phase (a hydrophilic material), (b) a dense dimethyl octyldecylsilane phase with some residual silanols (C18, with a grafting density of 3.65 mol/m²), and (c) a very hydrophobic, dimethyl octyldecylsilane phase with additional trimethylsilane endcaps (C18E, with C18 and C1 grafting densities of 3.65 and 0.54 mol/m², respectively). The temperatures studied are 87 K for argon, 77 K for N₂, 273 K for CO₂ and n-butane, and 298 K for H₂O, and the simulations cover adsorption/desorption from the gas phase and, if needed to close the hysteresis loop, also from the liquid phase. The sorption isotherms from molecular simulation are in qualitative agreement with experimental measurements that investigate superficially porous particles with more complex pore morphology. Analysis of the simulation trajectories provides information on adsorbate siting and orientational distribution along the adsorption/desorption paths and changes in the structure of the C18 ligands triggered by the wide range of temperatures and affinities for the different adsorbate molecules.