Capacitance
Dilatometry Attachment -
ANU MkIV Surface Force Apparatus
Department of
Applied Mathematics
Research School of Physical Sciences and Engineering
The Australian National University, Canberra, Australia
A capacitance dilatometry attachment
has been constructed for the Surface Forces Apparatus. The distance
between the active surfaces is obtained from the capacitance of a
cylindrical parallel plate capacitor measured with a variable ratio
transformer bridge, the surface separation is made to vary with a
magnetic force transducer. Displacements of 0.1 nm can be
detected.
The method permits measurements of forces
between opaque surfaces over periods of time ranging in suitable
circumstances from tens of milliseconds to days. The attachment is
able to measure adhesion of single crystal mica surfaces with high
accuracy and reproducibility and has been used to measure forces
between mica surfaces in electrolyte using the droplet method.
Measurements have been made of the dispersion
force between mica and silica surfaces in air and it is found that
above 20 nm separation Casimir-Polder theory, that takes account of
retardation, fits the results much better than non-retarded van der
Waals theory. This is the first time that direct measurements of
dispersion forces have been made in the retarded regime. The
method may be applied to metallic surfaces to measure the Casimir
effect. The device is described in:
Capacitance dilatometry in a surface force
apparatus, A.M.Stewart. Measurement Science and
Technology 11, 298 - 304 (2000).
E-mail contact:
Surface.Forces@rsphysse.anu.edu.au
Back
to
Instrumentation
page or
Back
to
SFA
Mark 4 home
Updated 1/2003
Page by Anthony Hyde