The KSV NIMA Surface Potential Sensor is an instrument that
offers complementary data on the packing and orientations of
surfactant molecules within the sampling region of the Langmuir
film. Whereas the surface pressure is measured as a change in
the surface tension of the air-water interface, the Surface
Potential Sensor measures the potential difference above and
below the film and is sensitive to the sum of all the individual
dipole moments. KSV NIMA SPOT measures surface potential by the
vibrating plate capacitor method: Changes in surface pressure
are only detected once a closely packed monolayer begins to
form. Changes in the surface potential, however, can be measured
as soon as molecules with dipoles appear at the surface. As the
orientation of the molecules change during compression, the
alignments of the dipoles cause a large change in the surface
potential. This is clearly demonstrated in the plot shown below.
The figure displays surface pressure-area (violet) and surface
potential- area (light blu