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Figure 1 Arrangement for the Rheo-SALS experiments: (a) He-Ne laser; (b) aperture
and neutral density filter; (c) prisms; (d) rotating glass plate; (e) base plate
containing circulating heating/cooling water and glass window; (g) translucent
screen; (h) beam stop; (j) CCD camera
(Rheometric Scientific, USA). The light source is a monochromatic 5 mW He-
Ne laser (Melles-Griot, USA) with a wavelength of 632.8 nm, guided through
the transparent parallel-plate geometry by two prisms (see Figure 1). The plate
diameter is 40 mm and the gap between the two quartz glass plates is 1 mm.
Disperse phase fractions of
0.1 vol.% were required for the scattering
B
experiments.
Stress-step experiments were performed at nominal shear stresses from 20 to
1500 Pa. Video images of the translucent screen were recorded with a CCD
camera (Sony DFW-V 500, Japan) operated at 30 frames per second and
mounted vertically below the rheometer. To obtain the calculated Capillary
numbers for each experiment, stress values were multiplied by a factor of 0.8,
since the laser beam passes through the parallel plate at a radius of 80% of the
plate diameter. Scattering patterns were processed with Matlab. Unlike in flow
scattering experiments on immiscible polymer blends,
24,26,27
it was unnecessary
to pre-shear the samples prior to the scattering experiments, since the initial
morphology was produced in the preliminary dispersing step, during which
time the droplets were broken down to their final sizes in the homogenizer.
Coalescence during the flow was not observed in either the surfactant- or
protein-stabilized dilute systems, as was verified by independent droplet-size
distribution measurements before and after the experiments.
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