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E
E
E=0
moving direction
moving direction
electrophoresis
coalescence
oleate head group
(negatively charged)
Ag nanoparticle
surfactant molecule
(a)
(b)
(c)
Figure 7.14
Schematic description of electrophoretic deposition (EPD) process in
lamellar LLC. (a) Ag nanoparticles capped by oleates in water layer without electric
fi eld; (b) rearrangement of capping layer under higher electric fi eld; and (c) larger
particle formation by coalescence (Zhang et al., 2006).
nanoparticle aggregation (Zhang et al., 2006). The dissociation of capped
oleate molecules allows the nanoparticle surface to be fully negatively
charged and therefore movable to the anode under electric fi eld (i.e., elec-
trophoresis). Unlike the particles moving randomly in hydrosol, particles in
LLC hybrid are confi ned in the water layer and move parallel along the
surfactant bilayers, directing the particles to be arranged densely and ordered.
Additionally, the limited space also enhanced contact and coalescence of
nanoparticles, hence greater size of particles and denser arrays were obtained
from hybrid compared to those from hydrosol, as shown in Figures 7.13a
and 7.13 b.
Applying higher fi eld strength, the electrostatic attractions caused the
oleates to move toward the anode. The Ag particle surface is then partially
exposed due to the rearrangement or deformation of the oleate capping layer
(Fig. 7.14b). As a result, particle coalescence and larger particle formation took
place to reduce the high surface tension or energy in the nanoscale dimension
(Fig. 7.14 c).
Higher electric fi eld in a given time period affected the size of the nanopar-
ticles as was shown in Figures 7.13a, 7.13c, and 7.13d (Zhang et al., 2006). The
higher the electric fi eld, the more particles contacted and, hence, the larger
particles were formed as was seen in Figures 7.13c, 7.13a, and 7.13d. Yet, in the
LLC viscous medium, electrophoretic time also exhibited an important effect
on the fi nal product. As time increased, more particles reached the anode
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