ABSTRACT
One of the most effective ways to properly disperse and selectively place metallic nanoparticles into microdomains of self-assembled block copolymer, preventing their agglomeration, is to chemically modify their surface with polymeric chains compatible with one of the blocks of the copolymer. This so-called grafting process can be done by three different ways: grafting from, grafting to and grafting through. Each process presents its advantages and drawbacks, but all of them could make possible to place nanoparticles on the desired domains. Depending on the molecular weight and grafting density of brushes, self-assembled morphology of the copolymer and properties of nanocomposites
can be tuned in order to obtain periodic structures to form materials with enhanced mechanical strength as well as to achieve unique optical, electronic and magnetic properties at the nanometer scale, for applications in solar cells, catalysts or high density magnetic storage media. 2.1 Introduction
Engineering the self-assembly of inorganic nanoparticles within block copolymer nanodomains is useful for the design of periodic structures to form materials with enhanced mechanical strength as well as to achieve unique optical, electronic and magnetic properties at the nanometer scale, for applications in solar cells, catalysts or high density magnetic storage media. Block copolymers are a versatile platform material because they can self-assemble into various periodic structures for proper compositions and under adequate conditions, owing to the microphase separation between dissimilar blocks [1-3]. To overcome the problem of the tendency of nanoparticles to aggregate due to their high surface area and surface energy and to facilitate their dispersion in a selected block of a block copolymer different routes have been used [1, 3-5]. One of them has been the use of surfactants. In that way, Peponi et al. [1] used surfactants to disperse conductive silver nanoparticles in the desired domains of poly(styrene-bbutadiene-b-styrene) (SBS) copolymer. Emrick et al. [4] controlled the surface hydrophobicity by using different surfactants in order to disperse CdSe nanoparticles in poly(styrene-b-2-vinylpiridine) (PS-b-P2VP) copolymer, creating hierarchically ordered patterns with CdSe nanoparticles located in PS or P2VP domains depending on the surfactant. Electrophoretic deposition of nanoparticles [5] has been another method to disperse nanoparticles. Zhang et al. [5] used this method for placing CdSe nanoparticles in diblock copolymer templates. The so-called in situ approach has also been used by several authors [6-9] for incorporating inorganic nanoparticles into block copolymer nanostructures: Nanoparticles are directly synthesized within a block copolymer domain from metal precursors. Preformed micelles of block copolymers containing metal precursors are used as nanoreactors
to synthesize nanoparticles selectively in block copolymers. Due to its chemical affinity, the salt selectively infiltrates the hydrophilic copolymer domain. Nanoparticles then form selectively, upon reduction within the precursor-loaded domains. In that way Chan et al. [6] prepared nanocomposites with block copolymers and Pb or Pt nanoparticles. Saito et al. [7, 8] synthesized silver nanoparticles in the lamellar and spherical domains of PS-b-P2VP copolymer. Cohen et al. [9] prepared nanocomposites based on poly(styrene-b-acrylic acid) (PS-b-PAA) copolymer and metallic nanoparticles of Pd, Cu, Au and Ag.
