PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 2: Block Copolymer-mediated Synthesis of Gold Nanoparticles
the ethylene oxide linkages [152,155]. The interaction between metal ions and PEO becomes
important for longer PEO chains [152,155]. Several oxygen atoms in the PEO chain interact
with one ion and therefore the strength of the attraction depends on the length of the PEO
chain [152,155,156]. This method is believed to be primarily responsible for metal ion
reduction in PEO-PPO-PEO block copolymer systems.
(ii) Amphiphilicity of PEO-PPO-PEO Block Copolymers for Nucleation and Growth of
Gold Nanoparticles
Although the reduction capability of PEO homopolymers is expected to be much more
effective than that of the PEO-PPO-PEO block copolymers (the metal ion complexation of
PPO is found to be much smaller than PEO), PEO homopolymers have not been found to be
effective in the synthesis of gold nanoparticles [94-98]. The differences in synthesis of gold
nanoparticles using PEO homopolymer and PEO-PPO-PEO block copolymer suggest that the
nucleation and growth of the nanoparticles is enhanced in the case of block copolymer, which
is attributed to the amphiphilic character of the block copolymers. The comparison of gold
nanoparticle synthesis with various PEO-PPO-PEO block copolymers reveals that the overall
block copolymer (i.e. both PEO and PPO blocks) contributes to AuCl - 4 ions reduction and
particle formation. PEO is more dominate than PPO in the initial stages of reduction. PPO
facilitates block copolymer adsorption on gold clusters and reduction of AuCl - 4 ions on the
surface of these gold clusters and/or particles [94-98].
(iii) Stabilization of Gold Nanoparticles by PEO-PPO-PEO Block Copolymers
Block copolymers also provide stability to the gold nanoparticles in solution. It is achieved
by the adsorbed layer of block copolymers around the surface of the nanoparticles. The
adsorption takes place because of the amphiphilic character of the block copolymers [94-98].
The PPO blocks are expected to be in contact with the nanoparticle surface. On the other
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