Detailed Study on the Characterization of Silver Nanocluster in Poly(Methyl Methacrylate)
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ABSTRACT Solid sol of silver in poly(methyl methacrylate), Ag/PMMA, was prepared by bulk polymerization of methyl methacrylate solution of silver (I) triflluoroacetate (AgTfa) and followed by postheating. The formation of the metallic Ag nanocluster was characterized by visible spectroscopy, and effects of the concentrations of AIBN and AgTfa and the heat-treatment duration on the formation of Ag cluster were investigated. Furthermore, based on the kinetic study of MMA in the presence of AgTfa, possible mechanism for the reduction and agglomeration of silver is proposed.
INTRODUCTION Because of the drastic size effects that display specific properties being different from the metal particles, i.e., metal nanoclusters are of great importance in bulk metals, nanoscopic 1 the past decade. Among a variety of preparative methods to obtain metallic nanoclusters, it has been shown that the radiolytic method 2-5 and the chemical method are powerful means of producing metal aggregates, not only as subcolloidal solutions or supported clusters, but also as aggregates embedded in polymers. The reasons why these preparative methods are superior to the others are due to: (1) ease of preparation, (2) stability, (3) ease of size control, and (4) narrow size distribution of the clusters. In the chemical methods the principle is to reduce simple metal ions by using reducing reagent in the presence of stabilizing agents. Typical reducing reagents are; sodium borohydride (NaBH 4 ),6 ethylenediaminetetraacetic acid (EDTA) in alkali solution, 7 sodium citrate at boiling condition, 8 amines, 9 and ethanol. 10 On the other hand, Nakao has recently proposed a new method to prepare solid sols of Rh, Pd, Pt, Ag, and Au in polymer. 11,12 This method might be one of the most promising methods to prepare solid composite materials which are expected to be useful as a photosensitive and nonlinear optical material. According to his procedure, solid sols of polymers containing well dispersed various noble metal particles can be easily obtained, upon simply polymerizing the mixture of monomer and corresponding metal compound, followed by the post heat-treatment. However, peculiar in this new preparative procedure is that metal ions are reduced to form zero valent metal particles, in spite of the absence of specific reducing agents. For this reason, we decided to reinvestigate the procedure for the preparation of Ag nanocluster in PMMA, and tried to elucidate the chemical species that can act as a reducing agent.
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Mat. Res. Soc. Symp. Proc. Vol. 501 © 1998 Materials Research Society
EXPERIMENT All compounds were of commercial reagent grade and used without purification unless otherwise noted. 2,2'-azobisisobutylonitrile (AIBN) was recrystallized from methanol. Methyl methacrylate monomer (MMA) was washed with 10% aqueous NaOH and water, dried by anhydrous sodium sulfate. It was then vacuum distilled, and stored in vacuo until required. Silver trifluoroacetate (AgCF 3 CO 2 , AgTfa) was prepared based on literature 13 and recrystallized from ho
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