Photogenerating Silver Nanoparticles and Polymer Nanocomposites by Direct Activation in the Near Infrared

Hindawi Publishing Corporation Journal of Nanomaterials Volume 2012, Article ID 512579, 6 pages doi:10.1155/2012/512579 Research Article Photogenerating Silver Nanoparticles and Polymer Nanocomposites by Direct Activation in the Near Infrared Lavinia Balan,1 Raphael Schneider,2 Colette Turck,1 Daniel Lougnot,1 and Fabrice Morlet-Savary3 1 Institut de Science des Matériaux de Mulhouse, CNRS LRC 7228, 15 rue Jean Starcky, 68057 Mulhouse, France 2 Laboratoire Réactions et Génie des Procédés, CNRS UPR 3349, Nancy-University, 1 rue Grandville, 54001 Nancy, France 3 Department of Photochemistry, CNRS FRE 3252, Haute Alsace University, 3 rue A. Werner, 68100 Mulhouse, France Correspondence should be addressed to Lavinia Balan, Received 8 August 2011; Accepted 6 September 2011 Academic Editor: Sevan P. Davtyan Copyright © 2012 Lavinia Balan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This work reports on an improvement of the photochemically assisted synthesis of silver nanoparticles by direct photoreduction of AgNO3 with a laser source emitting in the near infrared range (NIR). For this, polymethine dyes were used as the photoactive agents. Both the effects of central chain structure and activation intensity were investigated. The reduction kinetics was followed up by UV-Vis spectroscopy, and the particles size was evaluated by transmission electron microscopy. The results showed that light intensity affects both the average size and size distribution of Ag nanoparticles generated through this process. The particles can also be generated in situ in a photopolymerizable formulation so that metal/polymer nanocomposites become available through a one-step photoassisted process on the basis of NIR activation. The process described herein is very fast (seconds to a few minutes), and it readily lends itself to automatization for mass production of micro-optical elements implemented directly onto integrated NIR sources. 1. Introduction Recent developments in optics and photonics require novel, simple, and fast methods to fabricate metal nanoparticles (MNPs). In recent years, a whole bunch of synthetic methods for the preparation of MNPs have been developed: chemical, photochemical, and thermal. Amongst them, the photochemical synthesis of MNPs including direct photoreduction and photosensitization has attracted intense research interest, since it is a versatile and convenient process with distinguishing advantages such as space selectivity [1]. Embedding nanosized MNPs into polymer matrixes is also of great interest, because these materials combine properties from both inorganic and organic systems. Thus, MNPs homogeneously dispersed in polymer matrixes are already used as sensors [2–4], materials with solvent switchable electronic properties [5], optical limiters or filters [6, 7], optical data storage materials [8, 9], surface Plasmonenhanced random lasing media [10], catalytic additives [11], or antimicrobial coatings [12, 13]. Metal-polymer nanocomposites are usually obtained via multistep methods. Dry silver NPs produced beforehand can be dispersed into a polymerizable formulation to obtain self-assembly functionalized structures. However, besides the specific hazards related to handling dry NPs, their size dispersity over a large scale is difficult to control, thus limiting the interest of this “ex situ” method [14, 15]. The “in situ” approach that involves the generation of MNPs directly in a polymerizable medium through reduction of a cationic precursors offers the advantages of better dispersion ability and facile chemical or photochemical reduction [16, 17]. Several examples of in situ synthetic routes to MNPs and polymer/metal nanocomposite were reported as yet and the formulations used contain a variety of monomers and a collection of photoinitiators/photosensitizers [18–22]. They highlighted the flexibility in terms of temperature, dispersion, and rapidity of the process used to trigger the (photo)chemically assisted reduction of metal precursors. 2 Journal of Nanomaterials S1 N S + ClO4 − S N CH3 Cl N OH HO N Cl S2 + N N C4 H9 C4 H9 BF4 − Figure 1: Structures of the sensitizers S1: (5,5 -dichloro-11-diphenylamino-3,3 -diethyl-10,12-ethylenethiatricarbocyanine perchlorate) and S2: (1-Butyl-2-[5-(1-butyl-1H-benzo[cd]indol-2-ylidene)-penta-1,3-dienyl]-benzo[cd]indolium tetrafluoroborate) and of the coinitiator (N-methyldiethanolamine). In our recent studies, we have reported a novel approach for the preparation of metal-polymer nanocomposites in which MNPs were obtained by direct UV or visible photoreduction [20–22]. This powerful in situ approach, involving irradiation of an appropriated formulation, induces a homogeneous distribution of MNPs in a crosslinked polymer network. However, some recent developments in the field of applied micro-optics or nanofabrication turn round to producing highly integrated devices, and whenever the corresponding fabrication processes include photochemical steps, smallscale and low-cost light sources with low power consumption are preferred. In another respect, scientists involved in fundamental plasmonics are demanding systems capable of generating MNPs in situ through photochemical processes that could be triggered by NIR light sources. And lastly, the possibility of generating MNPs—with bactericidal or antimicrobial activity—directly in a living medium or as a thin film polymer top coating does not fail to stimulate interest in the field of microbiology. However, the spectral window in which the photogeneration can be carried out is often restricted to the far red or NIR, because the absorption of the sample itself obstructs the other regions of the spectrum. In this context, the present paper deals with the photochemically assisted fabrication of silver nanoparticles in situ in a polymerizable medium using a near infrared (NIR) source. Thus, the challenge consisted of tailoring a currently used process so that it could be activated with laser diodes (and even VCSELs) emitting in the 750 to 900 nm range instead of sources emitting in the visible or near UV. So far, this report is the first to deal with the synthesis of silver nanoparticles and polymer-metal nanocomposites through an NIR-assisted photoprocess. Even though some examples of NIR resins were reported during the past decade [23–25], pushing the sensitivity limits of the process, generating silver nanoparticles in situ up to ca 900 nm, turns out to be an important breakthrough. 2. Experimental The formulations used in this work contained a sensitizer absorbing in the NIR (5,5 -dichloro-11-diphenylamino3,3 -diethyl-10,12-ethylenethiatricarbocyanine perchlorate, (S1) and 1-Butyl-2-[5-(1-butyl-1H-benzo[cd]indol-2-ylid ene)-penta-1,3-dienyl]-benzo[cd]indolium tetrafluorobor (...truncated)