Shape and Interfacial Viscoelastic Response of Emulsion Droplets in Shear Flow - Food Colloids: Self-Assembly and Material Science - page 350

Figure 3 Frequency-dependent dynamic moduli of emulsions with dominant shape relax-
ation stabilized by excess SDS. (a) Reduced storage and loss moduli, G 0 and G 00 ,
of the continuous phase. Data are from time/temperature superposition: factor a T
(20, 25 , 301C) ¼ 1, 0.365, 0.232; and factor b T (20, 25, 301C) ¼ 1, 1.070,
1.252. (b) G 0 and G 00 at 201C of an emulsion prepared with SDS (oil phase
fraction f ¼ 4.5 vol.%). The arrow indicates the characteristic relaxation
shoulder of the storage modulus, caused by shape relaxation of the deformed
droplets. (c) Comparison of experimental G 0 ( o ) data with calculated 40 values
(dashed line) based on measured interfacial tension, individual phase moduli and
mean droplet diameter d 43 from laser diffraction. (d) Normalized relaxation
time spectra calculated 41 from G*( o ) data at three different temperatures.
Maxima indicate characteristic droplet relaxation timescales: reducing the
temperature lowers the overall viscosity, thus slowing down droplet retraction

(bio)polymers 25 and immiscible polymer blends; 24 the value of the Capillary

number in our experiment was Ca 0.1, which is far below the critical value

needed for break up. Therefore, the scattering anisotropy can be assumed to be
due to deformation of the droplets in the flow direction. For the emulsion
stabilized with b-lactoglobulin, the scattering patterns are isotropic throughout
the frequency spectrum. This indicates the absence of any detectable droplet
deformation, a result in line with the missing relaxation shoulder in the G 0 ( o )
curve. We note that other authors 42 have found a markedly different behaviour
for immiscible polymer blends containing surface-active agents (the so-called
'compatibilizers'): in those cases, the relaxation shoulder did not disappear in
the presence of the compatibilizer, but a second 'slow' relaxation shoulder was

B