Surface Force Apparatus
Surface Force Apparatus
(Manual)
The SFA measures the forces between two surfaces in vapors or liquids with a sensitivity of a few millidynes ( 10 nN) and a distance resolution of 1 Angstrom (0.1 nm). It can also be used to measure the refractive index of the medium between the surfaces, molecular orientations in thin films (under certain conditions), adsorption isotherms, capillary condensation, surface deformations arising from surface forces, dynamic interactions such as viscoelastic and frictional forces, and other time-dependent phenomena in real time. Though mica surfaces are the primary surfaces used for these measurements, it is possible to deposit or coat these surfaces with surfactants, lipids, polymers, proteins, metals, metal oxides, silica, etc., so as to alter the nature and chemistry of the interacting surfaces while keeping them smooth by virtue of the molecularly smooth mica substrate surface underneath.
The SFA has been modified with capabilities optimized towards measuring static interactions between soft materials, such as biological membranes, proteins, and thin polymeric layers. Time-resolved measurements of molecular forces between surfaces can be conducted with spatial accuracies to ±0.1 Å. Automation under computer-feedback control permits a wide range of high-resolution experiments to be performed, including programmed sequences of surface movement while distance and force information is analyzed and recorded in real time.
