a solid, in particular water’s energetic interaction with a drug
or excipient. Specifically, the BET or GAB models do not incorporate
interactions between adsorbed vapor molecules, in
particular water–water interactions, which presumably are an
important factor in the sorption process as theRHincreases, especially
for the water molecule that exhibits strong H-bonding
with itself. Indeed, IR spectroscopic experiments of moisture
sorption on NaCl have shown H-bonding of water with itself
at submonolayer coverage