PHYS01200704032 Debes Ray - Homi Bhabha National Institute

interactions between the templating ion and the electron lone pairs of the ethylene oxide
linkages. PPO facilitates growth of gold clusters to nanoparticles by block copolymer
adsorption on gold clusters and reduction of gold ions on the surface of these clusters. The
formation of gold nanoparticles from gold salt comprises three main steps: (i) reduction of
gold ions by the block copolymers in the solution and formation of gold clusters, (ii)
adsorption of block copolymers on gold clusters and reduction of gold ions on the surfaces of
these gold clusters and (iii) growth of gold particles in steps and finally its stabilization by
block copolymers. This thesis aims to look into the improvement of the overall synthesis
process by tuning these steps of the reaction mechanism in different ways [10-20].
A multi-technique approach combining spectroscopy, microscopy and scattering
techniques has been used in this thesis for the characterization of gold nanoparticles [10, 11].
The use of different techniques is required for obtaining complementary results for
understanding and tuning of the synthesis. The different techniques used are UV-visible
spectroscopy, small-angle neutron scattering (SANS), small-angle x-ray scattering (SAXS),
dynamic light scattering (DLS) and transmission electron microscopy (TEM). The details of
these techniques are described in Chapter 3. The technique of UV-visible spectroscopy
measures the absorbance or transmittance of the sample solution to characterize nanoparticles
through the characteristic SPR peak. This peak arises due to the resonance between the
incident radiation and collective oscillation of conducting electrons of nanoparticles. The
gold nanoparticles show SPR peak at ~ 530 nm. The broadening of peak relates the shape and
size of the nanoparticles. The absorbance is proportional to the number density and hence can
be used to measure the formation rate and the stability of gold nanoparticle during the
synthesis. The high contrast of gold nanoparticles for electrons enables TEM to determine
directly the shape and size of gold nanoparticles. However, this technique is statistically less
accurate (probes small sample volumes) as well as insensitive to low-Z elements such as
block copolymers. The different scattering techniques (SAXS, SANS, DLS) probe systems
under native conditions and over large sample volumes. In all these scattering techniques the
radiation (X-ray, neutron or light) is scattered by the sample and the resulting scattering
pattern is analyzed to provide information about the structure (shape and size), interaction
and the order of the components of the samples. X-rays are scattered by the electron density
fluctuation, which is proportional to the atomic number and enables SAXS to determine the
size distribution of the nanoparticles. The fact that scattering is very different for neutrons
from hydrogen and deuterium (isotope effect), contrast variation SANS by mixing
hydrogenous and deuterated constituents can be used to study different components (gold
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