Mark-II
	Applications:
	Forces between surfaces in liquids or vapor Forces between surfactant and polymer-coated surfaces Interactions of model bio-surfaces such as lipid bilayers Surface chemistry of metals, metal oxides, semiconductors Adhesion between similar or dissimilar materials Contact deformation Wetting and capillary condensation Viscosity and other flow processes in thin films
	This Surface Forces Apparatus is capable of measuring the flow between two molecularly smooth surfaces in vapors or liquids with a sensitivity of a few millidynes (10nN) and a distance resolution of about 1A (0.1nm). It can also measure the refractive index of the medium between the surfaces, adsorption, isotherms, capillary condensation, dynamic and time-dependent phenomena, and surfaces deformations arising from surface forces. Though mica surfaces are the primary surfaces used for these measurements, it is possible to deposit or coat these surfaces with surfactant, lipids, polymers, metals, etc., so as to alter the nature and chemistry of the interacting surfaces while keeping them smooth by virtue of the moleculary smooth mica substrate surface underneath.
The SFA MK-II is an apparatus for measuring forces between two curved molecularly smooth surfaces in liquids or vapors. The above figure also shows some of the alternative force-measuring springs suitable for different types of experiments. The basic Apparatus has a simple single-cantilever spring (not shown here)
to which the lower silica disk is attached. This drawing shows the assembled apparatus with the 'variable stiffness spring' whose stiffness can be varied by a factor of 1000 during experiments by shifting the position of the dove-tailed 'clamp' using the 'adjusting rod'.
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Mark-III
The new surface forces apparatus (FSA Mk-III) is for measuring the forces between two molecularly smooth surfaces. Mk-III employs four distance controls instead of three as in the Mk-II. The four controls are: micrometer, differential micrometer, different spring and piezoelectric tube.
The mica surfaces are glued to cylindrical support disks of radius R and positioned in a crossed cylinder geometry. The lower surface is mounted on a variable-stiffness double-cantilever force-measuring spring within the lower chamber and is connected to the upper (control) chamber via a Teflon bellow.
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