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(a)
(b)
(c)
25 nm
25 nm
25 nm
(d)
(e)
(f)
25 nm
50 nm
50 nm
Figure 7.13
TEM images of deposits at different conditions. Electric fi eld strength (V/
mm) and deposition time (s) were: (a) 2.0, 4000; (b) 2.0, 4000; (c) 1.0, 4000; (d) 3.3, 4000;
(e) 2.0, 1800; and (f) 2.0, 7000. (b) Image of deposit in Ag-SO hydrosol for reference
while others are those in hybrids (Zhang et al., 2006).
The electric fi eld strength and the length of electrophoretic time were
shown to affect the deposit morphology as depicted in Figure 7.13. Comparing
the nanoparticles obtained using lamellar LLC (AOT/Ag-sodium oleate
hybrid, Fig. 7.13a) to a common technique as previously reported (Wang
et al., 1999), forming sodium oleate-stabilized silver colloids (Ag-SO hydro-
sol), both under fi xed electric fi eld strength and time (2.0 V/mm for 4000 s)
demonstrated the advantages of the LLC system. Utilizing the lamellar LLC
reservoir causes the fabrication of larger silver nanoparticles with a much
denser distribution and ordered arrays (Fig. 7.13a), while those in Figure 7.13b
appeared as individual ones and no signifi cant ordering was found. Deposition
under different electric fi eld strengths at 1.0, 2.0, and 3.3 V/mm for 4000 s
led to the formation of larger nanoparticles of 10 nm (Fig. 7.13c), 15-20 nm
(Fig. 7.13 a), and 30 - 50 nm (Fig. 7.13 d), respectively, proportional to the fi eld
strength. A long electrophoretic time had a strong impact on the morphology
of deposits. A short time (less than 1800 s) was not enough to bring the par-
ticles together and resulted in the formation of only dispersed particles of
about 10 nm (Fig. 7.13e). Longer deposition time (4000 s) enabled assembling
ordered arrays with more uniform size of 15-20 nm (Fig. 7.13a). After 7000 s
the particle sizes increased and the particles were accompanied by coales-
cence (Fig. 7.13 f).
To elaborate on these results the authors proposed a schematic description
of the electrophoretic deposition process in lamellar LLC (Fig. 7.14) (Zhang
et al., 2006). As illustrated in Figure 7.14a, with no electric fi eld or low electric
fi eld strength, the oleates form a capping layer along the LLC water layer to
protect the nanoparticles from contacting by steric repulsion, thus preventing
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