W. Richard Bowen and Nidal Hilal 4

9.6 MESOSCALE ExPERIMENTAL STUdIES 263
FIguRE 9.8 Photograph of unmodified (left) and modified (right) explorer AFMs.
The base-section of the modified AFM has been modified to provide access for peripheral
lenses.
the observation of microfilaments is plausible. For cavitation and tackrelated
phenomena, the rates of separation may be comparatively high,
and in order to verify the existence of microfilaments and determine
their form by direct visualisation, high-speed video microscopy studies
are necessary.
The combination of high-magnification microscopy and high-speed
video presents a considerable challenge due to the illumination requirements,
particularly when using high magnifications, optical filters (often
necessary due to diffuse reflection of the AFM laser source) and fast
shutter speeds. The design of most AFMs restricts direct observation of
confined fluid samples, as the physical dimensions do not readily permit
the inclusion of supplementary (high-speed) imaging systems. Several
different AFMs have been used to study microfluidic aspects including
a Thermomicroscopes Explorer, a Digital Instruments Dimension 3100,
a Veeco Multimode and more recently a PSIA XE-120 with optical head.
Studies using high-speed video systems, namely, a Kodak Ektapro 4540 mx
and a Photron APX Fastcam, were used to record microfluidic defomation
using ‘cold light’ sources to reduce the effect of evaporation when studying
microlitres of aqueous polymer solutions.
The enclosed nature of the Explorer prevents the use of peripheral
lenses; therefore a section of the base of the AFM was removed (shown
in Figure 9.8). For the Dimension 3100, the colloidal probe and cantilever
are unobtrusively located beneath the scanner such that an objective lens