PHYS01200704032 Debes Ray - Homi Bhabha National Institute

Chapter 4: Optimization of the Block Copolymer-mediated Synthesis of Gold Nanoparticles
4.3. Results and Discussion
The optimization of block copolymer-mediated synthesis of gold nanoparticles for its
dependence on gold salt and block copolymer concentrations has been examined in the
following sections [191-196].
4.3.1. Role of Gold Salt Concentration
Figure 4.1. Photograph of gold nanoparticles in aqueous solutions of 1 wt% P85 with varying
HAuCl 4 .3H 2 O concentration. The labels show the concentration of gold salt in wt%.
Gold nanoparticles have been synthesized from freshly prepared samples of 1 wt% P85 block
copolymer with varying HAuCl 4 .3H 2 O concentration in aqueous solution. It is observed that
a transparent P85 solution becomes coloured on addition of gold salt. The purple colour seen
in these samples is different from that of the pure salt solutions (yellow) and indicates the
formation of gold nanoparticles since the surface plasmon resonance (SPR) of gold
nanoparticles is known to show such colour [19]. Photograph of gold nanoparticles in
aqueous solutions of 1 wt% P85 with varying HAuCl 4 .3H 2 O concentration is shown in
Figure 4.1. There is an interesting variation in the colour intensity with the increase in the
salt concentration. It is observed that the colour intensity simply does not increase with the
increase in the gold salt concentration. The maximum in the colour intensity is found at 0.008
wt% HAuCl 4 .3H 2 O for 1 wt% of P85. The colour intensity decreases beyond this maximum
and finally the colour of the samples becomes yellow to that of gold salt at higher
87