Preparation and Characterization of Nickel–Polystyrene Nanocomposite by Ultrasound Irradiation R. Vijaya Kumar, Yu. Koltypin, O. Palchik, A. Gedanken Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel Received 13 April 2001; accepted 14 January 2002 Published online 23 July 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.10930 ABSTRACT: Well-dispersed nickel nanoparticles in poly- styrene were obtained by a sonochemical method. The prop- erties of the as-prepared nanocomposite materials were characterized by XRD, TEM, EDAX, TGA, DSC, and a vi- brating sample magnetometer (VSM). The nickel particles were 5 nm in diameter and were very well dispersed in the polystyrene. The magnetization measurements established that the as-prepared nanocomposite materials are super- paramagnetic due to their small size. The saturation magne- tization (30.1 emu/g) and coercivity (5 Oe) of the materials were significantly smaller than were those of the bulk nickel, reflecting the nanoparticle nature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 160 –165, 2002 Key words: sonochemistry; nickel–polymer composite; magnetic materials; nanocomposites INTRODUCTION Due to their extremely small size and large specific sur- face area, nanoparticles usually exhibit unusual physical and chemical properties compared to that of bulk mate- rials. 1,2 The use of a polymer matrix as an environment for in situ nanopaticle growth combines, synergistically, the properties of both the host polymer matrix and the discrete nanoparticles formed within it. The nanopar- ticles of metals and metal oxides embedded in polymer matrices have attracted increasing interest because of the unique properties displayed by materials containing such nanoparticles. Such composite materials are ex- pected to have novel magnetic, optical, electrical, cata- lytical, and mechanical properties. 3–7 Many techniques have been exploited to prepare metal– or metal oxide– polymer composites. 8 –14 Copper–polymer composite materials were prepared by Huang et al. 15 and Lyons et al. 16 by two different methods: by in situ reduction within a Cu +2 –poly(itaconic acid-co-acrylic acid) com- plex and by thermal decomposition of a copper formate– poly(2-vinylpyridine) complex, respectively. Recently, Sidorov et al. 17 prepared cobalt nanoparticles embedded in hypercrosslinked polystyrene by a thermolysis tech- nique. Recently, Zach and Penner 18 and Chen and Wu 19 prepared pristine nickel nanoparticles by two different methods: electrochemical and by microemulsions, re- spectively. Chaudret and coworkers 20 synthesized nickel nanoparticles in polyvinylpyrrolidone by reduction of Ni(COD) 2 by H 2 in polyvinylpyrrolidone. Recently, Wang and Pan 21 prepared a poly(sty-co-MMA)–Ni com- posite by a chemical metal deposition method. Sonochemical processing has proven to be a useful technique for generating novel materials with unusual properties. Sonochemistry arises from the acoustic cavitation phenomenon, that is, the formation, growth, and implosive collapse of bubbles in a liquid medium. 22 The extremely high temperatures (5000 K), pressures (20 MPa), and very high cooling rates (10 7 Ks -1 ) 23 attained during cavity collapse lead to many unique properties of the irradiated solution. Using these extreme conditions, Suslick et al. prepared amorphous iron 23 by sonochemical decomposition of metal carbonyls dissolved in an alkane. We success- fully prepared amorphous nickel, 24 coating of nano- sized nickel on alumina 25 and silica 26 microspheres, and encapsulation of nickel nanoparticles in carbon 27 and various magnetic polymer composite materials. 28 However, all these methods used, as a starting mate- rial, Ni(CO) 4 , which is a hazardous material no longer commercially available. In the present investigation, we report on the prep- aration of a nickel–polystyrene nanocomposite using a sonochemical method. The precursor for the current study was nickel formate. EXPERIMENTAL Preparation of nickel formate precursor [Ni(HCO 2 ) 2  2H 2 O] Nickel formate was prepared according to a previ- ously described method. 29 A typical procedure for the Correspondence to: A. Gedanken (gedanken@mail.biu.ac.il). Contract grant sponsors: Israeli Ministry of Science, Cul- ture and Sports; German Ministry of Science; INTAS. Journal of Applied Polymer Science, Vol. 86, 160 –165 (2002) © 2002 Wiley Periodicals, Inc.