Delivered by Publishing Technology to: Nanyang Technological University IP: 180.218.219.74 On: Sat, 14 Nov 2015 07:12:26 Copyright: American Scientific Publishers Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Nanoscience and Nanotechnology Letters Vol. 3, 603–611, 2011 Multi-Technique Approach for the Study of Block Copolymer-Mediated Gold Nanoparticles Debes Ray and Vinod Kumar Aswal ∗ Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India A number of different techniques (UV-visible spectroscopy, small-angle neutron scattering, small- angle X-ray scattering, dynamic light scattering and transmission electron microscopy) have been used to characterize the synthesis of block copolymer-mediated gold nanoparticles in aqueous system. The measurements are carried out on high-yield gold nanoparticles as synthesized from HAuCl 4 · 3H 2 O precursor in the presence of block copolymer along with trisodium citrate. UV-visible spectroscopy confirms the formation of gold nanoparticles by the presence of surface plasmon resonance (SPR) peak. The high contrast of gold nanoparticles for electrons and X-rays enables transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) to determine the size distribution of gold nanoparticles. On the other hand, the high scattering contrast of neutrons for hydrogenous system in deuterated solvent allows small-angle neutron scattering (SANS) to examine the role of block copolymers in the synthesis. Dynamic light scattering (DLS) sees both the gold nanoparticles and block copolymer structures coexist during the synthesis. Keywords: Block Copolymer, Gold Nanoparticles, Scattering Techniques. The gold nanoparticles are of great interest in the field of nanotechnology for diverse applications due to their unique optical, electronic, thermal, catalytic, chemical and magnetic properties. 1–4 An ultimate application is decided by the control over the synthesis. 5–7 Recently an economi- cal and environmentally benign synthesis of gold nanopar- ticles using block copolymer has been reported. In this synthesis, block copolymer plays the dual role of reducing agent as well as stabilizing agent. 8–13 The role of block copolymer in the synthesis (formation rate, yield, stability, shape and size of nanoparticles) varies with their molec- ular weight, PEO/PPO block length, polymer concentra- tion and temperature. 14–17 Also the presence of additional reductant has been found to increase the nanoparticle yield by manyfold. 18–19 Therefore, it is important to under- stand the role of different components in controlling the synthesis. There are various techniques used to charac- terize such nanoparticle systems. Unfortunately, a single technique is not sufficient but requires a combination of techniques. The most commonly used characterization techniques for nanomaterials include microscopic, thermal analy- sis, spectroscopic, chemical analysis, scattering, etc. 20–21 Microscopic techniques (e.g., TEM, SEM, AFM and STM) ∗ Author to whom correspondence should be addressed. give the direct visualization of the morphology, particle size, phases, defects etc. 22–23 Thermal analysis methods such as thermo gravimetric analysis TGA, differential thermal analysis DTA and differential scanning calorime- try DSC monitor the presence and quantity of hydrated water, oxygen content, decomposition and product forma- tion in precursor routes, phase transition and the associ- ated enthalpy change etc. involved during the synthesis of the nanoparticles. 24 Spectroscopic techniques (Raman, IR, UV-visible, NMR, ESR/EPR, etc.) are employed for the confirmation of the presence of molecular species and electronic transitions, monitoring phase transitions and band gap calculations, studying luminescence, fluores- cence and chemical species, etc. 25 The goal of chemical analysis (iodometric titrations, electron probe microanal- ysis EPMA, energy-dispersive X-ray spectroscopy EDX) is to determine the stoichiometry or elemental composi- tion of the sample. 20 Scattering techniques (DLS, SANS, SAXS and XRD) are extremely reliable for finding the par- ticle size, shape, number density, interactions and crystal structure. Due to differences in the interaction of different radiations used in scattering (photon, neutron and X-ray) with matter, these techniques together give complemen- tary information on a multi-component system. 26–27 All the above different techniques probe structures at different length scale as well as resolution and hence combing them can provide detailed information. Nanosci. Nanotechnol. Lett. 2011, Vol. 3, No. 5 1941-4900/2011/3/603/009 doi:10.1166/nnl.2011.1230 603