Atomic force microscopy of polymeric liquid films

Abstract

We demonstrate the use of the atomic force microscope (AFM) for studying perfluoropolyether polymer liquid films as thin as ∼20 Å. With the AFM we are able to measure three distinct properties of the liquid film: (1) its thickness when the thickness of liquid on the AFM tip is taken into account, (2) the meniscus force acting on the AFM tip as a function of depth into the liquid film, and (3) the topography of the liquid/air interface. All three of these measurements can be done with a very high lateral resolution, ∼1000 Å, demonstrating the unique capability of AFM for studying liquid films. With AFM we have observed several interesting properties of these polymeric liquid films. First films thinner than ∼300 Å are fairly uniformly distributed, while films thicker than ∼300 Å slowly dewet the surface. Second, by measuring the meniscus radius of liquid in a micron sized hole on the surface, we can determine the disjoining pressure in a thin liquid film.