Chemistry Reference
In-Depth Information
Table 1 Theoretical maximum percentage surface coverage of 5.5-nm colloidal
silica particles by DDAB molecules, for a 0.5 wt % silica particle
concentration at different DDAB concentrations
[DDAB] (mol dm
3
)
Surface coverage (%)
4
10
4
4
6
10
4
5
8
10
4
7
1
10
3
9
4
10
3
35
Table 2 Theoretical maximum percentage surface coverage of 5.5-nm colloidal
silica particles by DDAB molecules, for different particle concentra-
tions at 10
3
mol dm
3
DDAB
Silica content (wt%)
Surface coverage (%)
0.5
9
1
4
1.5
3
2
2
optimum surface coverage appears to be 3%. Similar considerations show that,
at fixed [DDAB]
ΒΌ
4
10
3
mol dm
3
, the optimum coverage is 11%. Given
the possible errors in this calculation due to slightly different states of disper-
sion of the particles, the range of inferred coverage values, from 3% to 11%,
may be considered as reasonably consistent. It is noteworthy that this calcu-
lated optimum coverage is quite low. But this is consistent with the contact
angle measurements in Figure 3, which suggest that only a relatively small
increase in
y
(and by implication a small increase in surfactant coverage) is
required to impart the necessary degree of hydrophobicity to the particles.
24.3.5 Colloidal Silica Particles + Protein
Measurement of the shrinkage kinetics of bubbles stabilized by silica particles
+ b-LG was carried out for particle and protein concentrations ranges of 0.5-3
wt% and 0.005-0.5 wt%, respectively. Figure 9 shows the variation of the radii
of several individual bubbles in such systems. As with the fumed silica (Figures
4 and 5), it is clear that the shrinkage of bubbles stabilized by the protein +
colloidal silica is considerably slower than with the protein alone. On the other
hand, Figure 10 shows that the DDAB + silica system is still more effective in
stabilization than b-LG + silica. The compositions of the systems in Figure 10
are at the optimum concentrations of particles and amphiphilic molecules
giving maximum stability as evidenced by the F versus time plots.
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