Shape and Interfacial Viscoelastic Response of Emulsion Droplets in Shear Flow - Food Colloids: Self-Assembly and Material Science - page 348

Interfacial shear rheology. (a) Sketch of the biconical disc rheometer. 37
(b) Combined time and frequency sweep data for an adsorbed layer of
b -lactoglobulin at the oil solution interface. Identical frequency sweep tests
were performed at 201C for different interface ages (c ¼ 100 mg L 1 ; ionic
strength 90 mM; strain g ¼ 0.75%). (c) Loss tangent G 00 /G 0 as a function
of the interface age for the same data. (d) Power-law exponent n in fits of G 0
p o n

Figure 2

for the same data

of the timescale of changes in film properties. Figure 2(b) shows the frequency-
dependent interfacial storage modulus G 0 ( o ) at different interface ages. Even at
the shortest interface ages studied, the adsorbed b-lactoglobulin films were
found to be predominantly solid like (G 0 4 G 00 ), indicating that in the concen-
tration range studied here the interface is already densely packed with the
globular protein molecules. Figure 2(c) shows the loss tangent tan d ¼ G 00 /G 0 at a
frequency of o ¼ 0.755 rad s 1 at different interface ages; a decrease in the
viscous modulus from 0.5 to 0.18 G 0 after 8 h of ageing was observed. The

frequency dependence of G 0 is summarized in Figure 2(d), indicating solidifica-
tion of the interface as G 0 ¼ f( o ) becomes flatter at longer experimental times.
For the 1 wt.% SDS system, no significant interfacial shear properties were
found in steady, oscillatory or transient shear. Dilatational experiments with

B