Scot F. Morse
David B. Thiessen
Philip L. Marston
Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814
A liquid bridge between two solid surfaces is known as a capillary bridge.
In the experiments to be described, the bridge liquid is a mixture of PDMS with
a dense organic liquid. The bridge has the same density as the surrounding
water bath such that its equilibrium shape between circular posts is a circular
cylinder of length L and radius R. Low-frequency modes of such a bridge are
known to exist where surface tension provides the restoring force. Even
neglecting viscosity, the modal characteristic equation is complicated by the
boundary conditions. It is demonstrated that low-frequency modulation of an
ultrasonic standing wave in the surrounding bath can be used to excite specific
axisymmetric or nonaxisymmetric capillary modes. Coupling to each mode depends
on the location of the bridge in the standing wave. The coupling is a
consequence of the space-time modulation of the radiation pressure as discussed
previously for drops and bubbles [P. L. Martson,