Surface and aggregation properties of N-(4-nitrophenyl)-perfluorononanamide

ALEJANDRO M. GRANADOS; GERARDO FIDELIO; RITA H. DE ROSSI

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 1997 vol. 13 p. 4079 - 4084

0743-7463

It was determined thatN-(4-nitrophenyl)perfluorononanamide (1) forms a stable monolayer which suffers a liquid expanded (LE)fliquid condensed (LC) phase transition upon compression. The surface pressure of the transition was linearly dependent on the temperature indicating a diffuse first-order transition process. The transition was ascribed to rotation of the C-N bond of the amide. In the LE state, 1 has an ?L? conformation and in the LC state the phenyl group is aligned with the perfluoroalkyl chain. The pK of 1 is about 2 units higher than the value expected in the water solution. The surface potential of 1 at the air-water interface is negative at all measured pH values, indicating that the molecule on the surface can be considered as a vector having its air end negative. In solution, 1 is in an aggregated form even at 2 10-6 M concentration and these aggregates are destroyed in solutions containing 0.01 M of sodium dodecyl sulfate (SDS) or 7 10-3 M of perfluorononanoic acid 2. The kinetics of deaggregation occurs with two characteristic times with values of ô1 74.6 and 21.7 s and ô2 294 and 83 s for SDS and 2, respectively, at 25 °C.