The adsorption of the unsaturated fatty acids oleic, linoleic, and linolenic acid on steel surfaces has been investigated by means of a quartz crystal microbalance (QCM). Two different solvents were used, n-hexadecane and its highly branched isomer, viz., 2,2,4,4,6,8,8-heptamethylnonane. The area occupied per molecule of oleic acid at 1 wt % corresponds to what is needed for adsorption parallel to the surface. At the same concentration, the adsorbed amount of linoleic acid and linolenic acid indicates that they adsorb in multilayers. The chemisorbed amount estimated from static secondary ion mass spectroscopy (SIMS) measurements was found to be similar for the three unsaturated fatty acids. In the case of linolenic acid, it was found that the presence of water significantly alters the adsorption, most likely because of the precipitation of fatty acid/water aggregates. Furthermore, static SIMS results indicate that the amount of water used here inhibits the chemisorption of linolenic acid.

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The nature, strength, and reactivity of the sorption sites of single crystals of the microporous gallophosphate cloverite were studied in siru by IR microscopy. Two kinds of structural hydroxyl groups of high (Ga-OH groups) and moderate (P-OH groups) Brgnsted acid strength were identified. Upon sorption of polar molecules, however, a partial opening of the Ga-0 bond next to the structural hydroxyl group occurs, leading to a concerted Brgnsted (Ga-OH) and Lewis (Ga ion) type interaction of the sorption site with the probe molecule. This change in coordination of the Ga ion upon sorption of polar molecules leads to an unusual reactivity. Methanol, for example, reacts with different surface species in cloverite, which lead to different reaction products. While the weakly hydrogen-bonded molecules interacting with the P-OH groups desorbed unreacted at 300 K, the molecules sorbed at the Ga-OH groups reacted to either dimethyl ether (characteristic for Bronsted acid sites) or formaldehyde (characteristic for Lewis acid sites). The stability of the cloverite structure was found to be strongly dependent on the coordination of the Ga ions. While the microporous structure is stable, when the structural rearrangement of the Ga ions is confined to a 5-fold (as it occurs in the as-synthesized form or after sorption of larger polar molecules) or a 4-fold (activated form, in inert atmosphere) coordination, it collapses upon sorption of small polar molecules which force the Ga ion in an octahedral (6-fold) coordination. This occurs, for example, with sufficient concentrations of water at 300 K and with ammonia at elevated temperatures.