Biomedical Engineering Reference
In-Depth Information
Reducing agent
Organic phase
Biosurfactant
Aqueous phase
Metal salt
Mixture of
microemulsions
Microemulsion A
Metal reduction and
precipitation of nanoparticles
Dimer formation and
exchange of contents
Microemulsion B
FIGURE 9.1
(See color insert.)
Mechanism for microemulsion-based nanoparticles syn-
thesis. (Adapted from Capek, I.,
Adv
.
Colloid Interface Sci
., 110, 49, 2004.)
involves the mixing of two suspensions of reverse-micellar solutions, one containing
the salt of a metal and the other having a reducing agent as given in Figure 9.1.
Further, the presence of surfactants in the reverse micelles can act as capping
agents that prevent aggregation of products (Soma and Papadopoulos, 1996).
Xie et al. (2006) successfully generated a single-phase microemulsion system
involving pseudoternary mixtures of ionized-rhamnolipid/n-butanol/n-heptane/
water. Butanol as cosurfactant formed a stable single-phase microemulsion when
compared to other lower alcohols, as revealed by the phase diagrams. Here the rham-
nolipids inside the micelles prevented the aggregation of silver nanoparticles by
inducing both electrostatic repulsion as well as steric hindrance around the nanopar-
ticles. TEM studies revealed that the particles were of the size range of 2-8 nm and,
further, they were found to be consistent in size over a period of 60 days when sus-
pended in a solution. Using a similar approach, Kiran et al. (2010) investigated the
synthesis of silver nanoparticles using glycolipid biosurfactant of
Brevebacterium
Casei
MSA19. The particles were reported to be homogeneous in size and were
stable over a period of 2 months.
Maity et al. (2011) synthesized crystalline calcium pyrophosphate nanopar-
ticles of different morphologies by varying the water-to-surfactant (W/S) ratio in
water/hexane/Surfactin reverse-microemulsion system. Nanoparticles with size
distribution of 50-500 nm were obtained when the as-synthesized noncalcinated
calcium phosphate (synthesized at room temperature) particles were subjected to
calcination at a temperature of 800°C. The water-to-surfactant ratio influenced
the shape and size of the micelle to a greater extent, which in turn changed the
morphology of the calcinated nanoparticles. TEM image revealed transformation
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