Indian Journal of Engineering & Materials Sciences Vol. 15, October 2008, pp. 425-428 Effect of variation of PVP/PVA weight ratio on the behaviour of nanocrystalline silver Manab Mallik & R K Mandal* Centre of Advanced Study, Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India Received 11 September 2007; accepted 6 August 2008 The effect of poly-vinyl-pyrrolidone/poly-vinyl-alcohal (PVP/PVA) weight ratio on the resulting size and shape of nanocrystalline (NC) silver is presented. It is shown that all the NC silver samples investigated, in this study, have displayed face centered cubic structure. The average coherently scattering domain size is estimated with the help of Scherrer equation. Having computed this, an attempt has been made to understand the UV-Vis spectra of the NC sols in terms of localized surface plasmon resonance (LSPR) behaviour. The change in the nature of LSPR in visible range of spectrum of the sols has been attributed to the complex interplay of shape, size and distribution of NC silver. The chemical reduction synthesis route 1-3 has been employed for producing NC phase of noble metals. The NC particles of these metals have lot of potentials for bio-medical applications 4 . Apart from these, their sols offer very good opportunity to understand the (localized surface plasmon resonance) LSPR characteristics of metals. The variation in shape and size of particles with same crystal structures is required for comprehending their effects on LSPR in the presence of visible light 5 . There has been lot of efforts in literature to alter the shape and size of the particles in the nanometer range 6,7 . The strategy for accomplishing this task revolves around the change of polymeric stabilizers and reducing agents. By all these efforts, the space available for encapsulating the reduced silver is altered and thereby a change in the size of the nanocrystalline(NC) silver is achieved. It has been shownin references 3,6 that polyvinylpyrrolidone (PVP) acts as a very good capping agent irrespective of the method of synthesis of NC silver. The purpose of this investigation has been to understand the capping behaviour of PVP in presence of polyvinylalcohal (PVA). This will be inferred based on the average shape and size of NC Ag. Experimental Procedure Wang et al. 3 have used only PVP solution as polymer stabilizer. Silver nitrate, glucose and sodium hydroxide were utilized respectively as precursor, reducing agent and accelerator. Following this, Tiwari 8 had synthesized NC silver by replacing PVP with PVA. The protocol established ealier 3 was adopted. It is shown that PVA changes the role of PVP and as a consequence of this the geometrical characteristics of NC silver get modified. The weight ratio of PVP/PVA was changed systematically keeping other compositional variables utilized in reference 3 unchanged. This is done to study the effect of size on the crystal structure of silver. If the structure remains invariant then characteristics of LSPR can be correlated with the shape and size. Following chemicals were utilized: AgNO 3 (CDH), glucose (Qualikems), NaOH (Merck), PVP and PVA (S.D.Fine). The molecular weights of PVP and PVA were ~44,000 and ~14,000 respectively. For the synthesis, two solutions A and B were made. Solution A was prepared by adding 3.4 g of AgNO 3 into 20 mL of deionised water. The solution B was prepared by dissolving PVP (5.1 g), glucose (6.8 g) and sodium hydroxide (1.3 g) in 60 mL deionised water. Weight ratio of PVP and AgNO 3 was kept 1.5. Molar ratio of NaOH and AgNO 3 was 1.6. Solution B was heated to 60°C and stirred with magnetic stirrer. Solution A was added into B drop by drop. Rate of addition was maintained at one drop/s. After all the silver nitrate solution was added, it was stirred for10 min more. The mixed solution thus obtained was of shiny black colour and thick. Solution was left to cool for whole night. Next day, it was filtered and precipitate was used for further characterization. This is designated as sample 1. __________________________ *For correspondence (Email: rkmandal21@yahoo.com, rkmandal.met@itbhu.ac.in)