SAIF UR REHMAN et al., Chem.Soc.Pak.,Vol. 35, No.3, 2013 717 Synthesis and Optical Studies of Silver Nanoparticles (Ag NPs) and their Hybrids of Smart Polymer Microgel SAIF UR REHMAN, SYED MUJTABA SHAH, MOHAMMAD SIDDIQ* Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan. m_sidiq12@yahoo.com* (Received on 27 th July 2012, accepted in revised form 6 th February 2013) Summary: Ag NPs were synthesized by the chemical reduction method and were optically characterized. The change in size of the nanoparticles and position of surface Plasmon resonance was studied as a function of concentration of different reactants by using UV-Visible spectroscopy. Red shift was observed in the position of SPR by increasing the concentration of silver nitrate, sodium hydroxide and ascorbic acid whereas the SPR was blue shifted by increasing the concentration of silver seed and Cetyl trimethylammonium bromide (CTAB).The former shift shows increase whereas the latter indicates decrease in the size of the nanoparticles. The crystalline nature and morphology of the silver nanoparticles was studied by using X-ray powder diffraction (XRD) and Atomic Force microscopy (AFM). These Ag NPs were hybridized with multiresponsive micro gel system, poly(N- isopropylacrylamide-co-acrylic acid), synthesized by emulsion polymerization. The hybrid system was subjected to Dynamic Laser Light Scattering (DLS) to determine the hydrodynamic radius (Rh) of the hybrid micro gels at different pH and different temperatures. Under different conditions of pH, variation in VPTT value was observed. Fluorescence study was also carried out at different pH values to observe the swelling behavior of hybrid system. The photoluminescence (PL) emission intensity decreased with increase in pH which showed that the hybrid micro gels were more fluorescence active at low pH. Key words: Hybrid gels; Deswelling ratios; Dynamic laser light scattering; Volume phase transition temperature. Introduction Silver nanoparticles (Ag NPs) are becoming promising system for the last two decades on account of their applications in various fields such as electronics and optics [1]. They have unique chemical, physical and optical properties which differ significantly from the bulk materials. Additionally they have characteristics field enhancement which have direct linkage with surface plasmons [2]. Their optical properties depend strongly on particle size and shape. Thus, control of particle size, shape and structure is a powerful approach to adjust their electronic structure and optical properties [3, 4]. The variation in chemical compositions of reactants involved in the wet chemical synthesis of NPs has strong influence on their optical properties. The reactants mostly contain silver salt, reducing agent, solvent, precursor and a capping agent. Gulrajani et al: observed that the morphology and surface chemistry of the synthesized Ag NPs are mainly influenced by the stabilizers, their molar ratio to the silver salt, the stirring speed and the temperature of the synthesis reaction. Of all the mentioned parameters, the concentration of the stabilizer has the highest influence [5]. Kallol K. Ghosh et al: synthesized colloidal Ag NPs from AgNO 3 using PBHA and ascorbic acid as reducing agents. They reported that the rate of the formation of Ag NPs was greatly accelerated by increasing the pH value [6]. Addition of surfactants may control particle growth and stabilize the intermediates. Jian Xu et al: successfully prepared uniform Ag NPs in reverse micelles of gemini surfactant. Gemini surfactant displayed excellent properties in the preparation and stabilization of Ag NPs [7]. This technique could be extended to the preparation of a variety of metal nanoparticles under appropriate conditions. So, a lot of work has been done on the synthesis and characterization of NPs. However, the study of effect of the composition of reactants on their optical properties is of prime importance in the field of nanomaterials. Like surfactants, polymer microgel can also be used as a stabilizer or capping agent. Dong et al: observed that very useful optical, catalytic and conductive properties are achieved when Ag NPs are integrated into polymer matrices to form nanocomposites or when they are combined with other metal nanoparticles acting as a shell or a core to form bimetallic nanoparticles [8]. * To whom all correspondence should be addressed. J. Chem. Soc. Pak., Vol. 35, No.3, 2013