MEASUREMENTS OF ELECTROSTATIC DOUBLE-LAYER FORCES DUE TO CHARGED FUNCTIONAL-GROUPS ON LANGMUIR-BLODGETT-FILMS WITH AN ATOMIC-FORCE MICROSCOPE

Using an atomic force microscope, we measured the forces between a Si3 N4 tip and monolayers with different polar functional groups (-NH2, -C OOH, -CONH2, and -OH) prepared by the Langmuir-Blodgett method while v arying the pH value of aqueous solutions. The obtained force vs distan ce curves were related to the surface charges of the tip and the disso ciation of the functional groups from the pH dependency, and the charg ed state of functional groups could thus be discerned. In addition, th e electrostatic origin of the force has been confirmed assuming consta nt potentials on both surfaces.