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Arrays of silicon nanochannels were used to investigate the layer-by-layer (LbL) assembly of nanoparticle-containing multilayers in confined geometries. LbL assembly of poly(vinylsulfonic acid)/titania (PVS/TiO2) and poly(diallyldimethylammonium chloride)/silica (PDAC/SiO2) resulted in conformal, uniform thickness multilayers throughout the high-aspect-ratio nanochannels. These multilayers were also calcinated to form nanoporous coatings within the nanochannels. Confined and unconfined multilayers were compared using scanning electron microscopy (SEM), showing significantly lower bilayer thicknesses when layers were assembled in confined geometries. Deposition was found to essentially stop at a nanochannel gap size of 55 nm for the PVS/TiO2 system and at 210 nm for the PDAC/SiO2 system, even though the channels were not plugged. These results provide further evidence of surface charge-induced depletion of unadsorbed species during LbL assembly, which occurs because of the closely spaced walls with like su...

In situ synthesis of inorganic clusters in polyelectrolyte multilayers (PEMs) has typically relied on free carboxylic acid groups as the binding sites, limiting the scheme to the loading of cationic precursor reagents. The use of amine groups for similar purposes has not been demonstrated because of the challenge of incorporating free amine groups that are not paired with the oppositely charged groups residing on the polyanion of the PEM. In this paper, we use specific PEM assembly conditions to produce ultrathin conformal films of PAH/PAA (poly(allylamine hydrochloride)/poly(acrylic acid)) and PAH/PSS (poly(styrene sulfonate)) that upon suitable postassembly treatment undergo substantial molecular rearrangements that generate free amine groups in the films. These PEMs are capable of binding anionic precursors including complexes widely used for the synthesis of gold nanoparticles. On the basis of our understanding of the gold binding mechanisms, we demonstrate systematic control over the size and spatial...

We demonstrate that the structure and properties of layer-by-layer assembled multilayer thin films comprising positively charged TiO2 and negatively charged SiO2 nanoparticles can be varied by controlling assembly conditions. The average incremental thickness of the all-nanoparticle thin films after a pair of 7 nm TiO2 and 22 nm SiO2 nanoparticle adsorption steps was strongly dependent on the pH of each nanoparticle suspension, varying from a few nanometers to 30 nm. The surface charge density of the adsorbing nanoparticles and that of the previously adsorbed nanoparticle layers are the crucial factors in determining the average bilayer thickness of the films. Zeta-potential measurements of polystyrene microspheres coated with TiO2/SiO2 nanoparticle multilayers indicated that incomplete charge reversal after the deposition of nanoparticles leads to a very small thickness increase at each adsorption step, whereas complete charge reversal results in significantly larger thickness increments. Other film char...

We show that hydrogen-bonded multilayer thin film coatings assembled on colloidal particles can be used as templates for the in situ synthesis of nanoparticles. The concentration and size of nanoparticles grown within the coatings can be tuned by the number of loading cycles. The hydrogen-bonded multilayer thin films were coated on polystyrene micrometer-sized colloidal particles and subsequently cross-linked via water-soluble carbodiimide chemistry. We show that metal nanoparticles (e.g., Ag and Pd) can be synthesized via the nanoreactor scheme, where corresponding metal ions are loaded into the coating and then subsequently reduced to create nanoparticles dispersed within the coating. In addition, we demonstrate the multiple loading capability of the hydrogen-bonded multilayer coatings. UV−vis spectroscopy and direct observation by transmission electron microscopy confirm that the nanoparticles are well-dispersed within the thin film coating. Finally, the polystyrene particles can be extracted by treati...

We report a novel approach that uses block copolymer micelles as a means to create large area arrays of iron-containing nanoclusters capable of catalyzing the growth of carbon nanotubes (CNTs). The amphiphilic block copolymer poly(styrene-block-acrylic acid) (PS-b-PAA) forms micelles in solution which are capable of self-organizing into ordered structures on surfaces. By spin-coating these solutions onto a variety of substrates, we can create quasi-hexagonal arrays of PAA spheres within a PS matrix. The carboxylic acids groups in the PAA domains can be utilized in an ion-exchange protocol to selectively sequester iron ions, which results in iron-containing nanoclusters that are nearly monodisperse in size (diameter ∼8 nm) and patterned at a density of approximately 1011 particles per cm2. In principle, this route for synthesizing iron-containing nanoclusters offers the capability of controlling the cluster size and spacing by altering the molecular weight of the block copolymer. In this report, we demonst...

Palladium nanoparticles within polyelectrolyte multilayers of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were prepared as seeds for further growth by electroless nickel deposition. The seeds were generated by binding tetraaminepalladium from aqueous solution to PAA carboxylic acid functionalities in the polymer film and subsequent reduction. Nickel was electrolessly deposited on the small, 2-nm-diameter catalytic particles. By manipulation of the rate and duration of the electroless deposition, a nickel shell of arbitrary thickness could be grown; up to 14-nm-diameter particles were obtained. Elemental analyses showed that the composition of the electrolessly deposited material, nickel with several weight percent boron, was similar to that obtained from macroscopic surface electroless nickel plating. The electroless chemistry facilitated control over nanoparticle size independent of the process of nanoparticle nucleation and hence particle concentration.

We demonstrate a method for the directed formation of layered metallic copper structure within the subsurface morphology of a bulk lamellar block copolymer. Using an electroless deposition process, copper was selectively deposited inside the interconnected microdomain network of the water-permeable block containing preloaded palladium ions. The relatively simple process yields a novel nanoscale composite consisting of alternating layers of metallic copper with those of the hydrocarbon block matrix. The extent of the copper deposition can be controlled by adjusting the deposition rate and deposition time.

Free-standing block copolymer films containing magnetic iron oxide nanoclusters within the microdomains were produced by static casting. The thickness of the nanocomposite films was easily controlled to make optically transparent thin films. The size distribution of the nanoclusters was relatively narrow and the nanoclusters were uniformly distributed within the films. The spherical nanoclusters, ca. 5 nm in diameter, were identified as γ-Fe2O3 and had a well-defined crystalline structure. Magnetic measurements revealed that the nanocomposite films are superparamagnetic.

Small palladium and platinum clusters have been synthetized within a purely hydrocarbon polymer matrix. The procedure consists of ring-opening metathesis polymerisation of norbornene-derived organometallic complexes, Pd(Cp N )(PA) and Pt(Cp N )Me 3 (Cp N = endo-2-(cyclopentadienylmethyl)norbon-5-ene and PA = η 3 -1-phenylallyl), using W or Mo alkylidene initiators, followed by static casting of films and subsequent reduction of the organometallic complexes under mild conditions using molecular hydrogen