Determination of monolayer density by potentiometric titration

Potentiometric titration of acidic groups originating from the functionaliz ation of nanosized maghemite particles by a diacidic bolaamphiphile (DBSC-1 0) is described. The titrations are achieved in the solvent dimethyl-formam ide (DMF), using 0.01 N potassium hydroxide (KOH) in water as titrant. A re producible packing density of 3.4 mu mol of DBSC-10/m(2) of maghemite is fo und. This value falls between the approximated values estimated from molecu lar dimensions for vertically and horizontally oriented surfactant molecule s, indicating that DBSC-10 adopts a tilted-vertical orientation with the ma ghemite surface. Titration does not affect the. stability of the monolayer at higher pHs, as confirmed by infrared measurements on titrated particles. New strong peaks do appear at 1603 cm(-1) (v(COO- asymmetrical stretch)) a nd 1348 cm(-1) (v(COO- symmetrical stretch)), indicating the formation of i onic complexes between the free carboxylic moieties of the monolayer and K ions from titrant.