Sorption and retention of ethylene glycol monoethyl ether (EGME) on silicas

Sorption of ethylene glycol monoethyl ether (EGME) was studied gravimetrically and correlated with the results of retention experiments where samples wetted with EGME were evacuated. If a sorption measurement is done conventionally by increasing the vapor pressure slowly by small steps, molecules are packed smoothly along the surface, and a fairly flat isotherm is obtained. If the sample is directly exposed to a high vapor pressure or the normal sorption mode is disturbed by directly reducing the pressure, more EGME is sorbed. Then some of the molecules may be fixed only at their hydroxy ends. The evacuation curves are best interpreted in a semilogarithmic form, by which the value of the monolayer capacity can be estimated. EGME can be used for surface area measurements of silicas, but with porous samples areas that are too large are probably obtained. When EGME is packed smoothly on standard silica TK 800, one molecule occupies an area of 0.44 nm², computed by the BET equation with three parameters, or 1 mg of EGME covers 3.0 m².