EFFECT OF TEMPERATURE ON THE MOBILITY OF NITROXIDE PROBES IN CYCLOHEXANE AND AT THE ALUMINA-CYCLOHEXANE INTERFACE

dNitroxide spin probes have been widely used to study the behavior of surfactants in solution as well at solid-liquid interfaces. In this st udy the effect of temperature on the mobility of nitroxide spin probes in cyclohexane and at the alumina/cyclohexane interface is investigat ed in the presence of anionic aerosol-OT (AOT). The probe mobility in AOT micelles in solution is markedly dependent on the amount of solubi lized water. The variation with temperature of the mobilities of adsor bed doxyl stearic acid with the nitroxide probe at the 5th, 10th, and 16th positions from the - COOH group has shed some light on the mechan isms of interaction of the probe with the solid surface as well as the molecular structure of the adsorbed layer. The results indicate that the adsorption of the probe occurs mainly through interactions of the -COOH group with the surface while the -NO group interacts only weakly with the surface. The adsorption of AOT causes changes in probe mobil ity with the changes being most significant when the nitroxide group o n the stearic acid chain is farthest from the anchoring group. It is s uggested that the adsorption of the surfactant causes an orientational rearrangement of the probe molecules. The relatively low-temperature effect on the probe mobility observed in the presence of surfactant is attributed to the compactness of the adsorbed layer which is found to be stable even at elevated temperatures. (C) 1996 Academic Press, Inc .