LbL approach

Sonochemical methods have been used by the Cordoba de Torresi group to prepare Ni(OH)2, Co(OH)2 and mixed Ni/Co hydroxide NPs [33, 34]. For the sonochemical synthesis, the appropriate metal nitrate was mixed with ammonium hydroxide solutions and then sonochemically irradiated for various times. This produced about 5-nm diameter metal-hydroxide NPs that were then immobilized at ITO surfaces using a LbL approach with poly(allylamine) hydrochloride (PAH). In one study, the electrochromic behavior of the LbL deposits was compared with that of bulk deposits... 

Figure 6.59. Schematic and cross-section SEM image of a layer-by-layer (LbL) approach to deposit iron nanoclusters onto a surface to yield vertically aligned SWNTs. Reproduced with permission from Liu, J. Li, X. Schrand, A. Ohashi, T Dai, L. Chem. Mater. 2005, J 7,6599. Copyright 2005 American Chemical Society.

Figure 10. Schematic representation of the multilayered Pt-DENs/GOx network construction on the electrode using LbL approach (Adapted from Ref. [132]).

Capsules can then be formed by either a calcination or a dissolution step to create hollow structures. Calcination (typically carried out at a temperature of --450° C) removes all the organic constituents (like the colloidal template core and the organic shell-forming moieties), leaving the constituent inorganic NPs slightly sintered to form robust shell walls. Solvent dissolution of the core material yields hollow spheres, which retain all the shell constituents. The LBL approach is thus a versatile route for creation of NP-shelled hollow spheres. Extensive reviews on forming... 

This chapter describes the non-LBL approaches of tandem assembly and interfacial stabilization for the formation of closed shell structures, with an emphasis on ensembles in which NPs constitute the shell. Tandem assembly is a versatile and environmentally friendly route to the formation of useful NP-shelled capsules. In contrast to sacrificial core templating and LBL assembly methods, tandem assembly has the important differentiating feature that it avoids the incineration or solvent dissolution step to generate the hollow interior of the capsule. Enhancements in optical, mechanical, catalytic, and release properties of such materials hold great promise for their application in photoresponsive delivery systems, catalysis, and encapsulation. Interfacial stabilization routes are found to yield NP-shelled structures in the form of emulsions and foams that have enhanced stability over those from conventional, surfactant-based approaches. Unusual interactions of the NP with fluid interfaces have made possible new structures, such as water-in-air foams, colloidosomes, and anisotropic particles. 

Mechanical Properties of Composites Prepared Using LBL Approach... 

FIGURE 14.19 Photovoltaic performance for devices fabricated by the LbL approach using the materials described in the text, (a) The configuration of the heterostructured active layer the variable is the number of (PPV/Cgo ) layers, (b) The short circuit photocurrent ( ) and the open-circuit potential ( ) as a function of the number of (PPV/Cgo ) layers. (Reprinted from Baur, J.W., M.F. Durstock, B.E. Taylor, R.J. Spry, S. Reulbach, and LY. Chiang. 

In an opposite sense to the nanochannels, LbL assembly has been performed on microscopic protmsions to afford uniformly coated microneedle arrays, which are under development for transcutaneous therapeutic delivery.The precise control over coating thickness and composition that is offered by the LbL approach is a key advantage for this type of technology. The laboratories of Hammond and Irvine have demonstrated the systematic growth of alternating layers of poly(P-amino ester)s (PBAEs) and plasmid DNA, PBAE, and... 

Fig. 4.1. Schematic representation of preparation of capsules loaded with polymers. The templates with precipitated polymers (a) are covered with stable shell by LbL approach (b). Then the templating cores are decomposed (c) and polymers dissolve into interior (d). The polymers might be precipitated either by complexation with multivalent ions or by adding of non-solvent.

LbL) approach for ID pol)maeric supports to ensure a controlled fabrication of horizontally structured electrodes. Similar strategies reported for oxidic materials are, for instance, the use of pore-forming components. The application of ammonium carbonate as an additional agent has been reported by Fischer et al. already in 1998 [100]. 

Horizontal Electrode Structuring by a Layer-by-Layer (LbL) Approach... 

Good fits between experimental and theoretical amperometric responses at the tip were obtained for the composite films incorporating Pd nanoparticles to demonstrate that the generation of hydrogen peroxide (Equation 18.10) was accelerated from fe,=0.0014 cm/s to A ,=0.00534 cm/s as more Pd nanoparticles were loaded. By contrast, data for Pt composite films did not fit well with theory, which was ascribed to the formation of an oxide layer on Pt nanoparticles. In another study, LBL approach was employed to prepare the composite of gold nanoparticles, DNA, and polyethyleni-mine (PEI). Specifically, the SAM of 3-mercapto-l-propanesulfonic acid was formed on the gold electrode to deposit a cationic PEI film, which was followed by the deposition of double-stranded DNA or citrate-stabilized Au nanoparticles and PEL Approach curves were measured to demonstrate that 1 values for both FcMeOH and ferrocenecarboxyUc acid were highly dependent on the type of the outmost layer. 

The basic LbL approach as was described by Decher [24, 25] consists on the alternate deposition of opposite charged polyelectrolytes onto a solid substrate that is the template of the assembling. The alternate adsorption of the polyelectrolytes occurs mainly by direct electrostatic interaction between the successive adsorbed polyelectrolytes with opposite charge. The entropy change during the adsorption process may play an important role. 

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