Electrostatic assembly

Carmichael D, Mathey F (2002) New Trends in Phosphametallocene Chemistry. 220 27-51 Caruso F (2003) Hollow Inorganic Capsules via Colloid-Templated Layer-by-Layer Electrostatic Assembly. 227 145-168... 

Carmichael D, Mathey F (2002) New Trends in Phosphametallocene Chemistry. 220 27-51 Caruso F (2003) Hollow Inorganic Capsules via Colloid-Templated Layer-by-Layer Electrostatic Assembly. 227 145-168 Caruso RA (2003) Nanocasting and Nanocoating. 226 91-118 Ceroni P, see Balzani V (2003) 228 159-191 Chamberlin AR, see Gilmore MA (1999) 202 77-99 Chasseau D, see Guionneau P (2004) 234 97-128... 

Recently, a new procedure was reported for the preparation of nanoporous polymeric spheres (NPSs) with well-controlled structure via the LbL infiltration and coating of MS spheres with preformed polymers (Figure 7.7) [69]. A main advantage of this approach is that it offers a general and versatile route to the preparation of NPSs of different and tailored compositions, as it is based on electrostatic assembly [69,109]. 

J.H. Rouse and P.T. Lillehei, Electrostatic assembly of polymer/single walled carbon nanotube multilayer films. Nano Lett. 3, 59-62 (2003). 

Scheme 2 Electrostatic assembly of positively charged dendrimers to form a well-defined photofunctional aggregate...

Fluorescence lifetime measurements on the aggregate have shown that the rate constant of the intermolecular energy transfer from the zinc porphyrin unit to the free-base porphyrin unit has been evaluated to be 3.0 x 109 s-1. This value is reasonable from a model in which dendritic donor 6b and acceptor 5a contact each other directly at their exterior surfaces (Scheme 2). Therefore, electrostatic assembly of positively and negatively charged dendrimers provides a promising supramolecular approach to construct photofunctional materials with nanometric precision. 

Scheme 3 Schematic representations of electrostatic assemblies of dendrimer porphyrins 6a, 7a with MV2+...

Wang X, Kim Y-G, Drew C, Ku B-C, Kumar J, Samuelson LA (2004) Electrostatic assembly of conjugated polymer thin layers on electrospun nanofibrous membranes for biosensors. 

Fig. 5.11 Schematic of the stepwise preparation of Fe304-PDA-RG0-Au NP hybrid via ex situ electrostatic assembly and in situ Au NP reduction.

The assembly of functionalized nanostructured silica with uniform pore channels using neutral alkylamine surfactants (S°I° -> HMS) and non-ionic alkylpolyethyleneoxide surfactants (N°I° —> MSU-X) provides many advantages over conventional electrostatic assembly pathways (S+f, etc.). In contrast with electrostatically assembled MCM-41-type materials, mesostructured adsorbents produced by non-electrostatic assembly methods typically possess pore channel structures and particle morphologies which improve their ability to interact with targeted adsorbate species. Moreover, non-electrostatic assembly pathways are well-suited for the direct synthesis of functionalized mesostructured silica by one-step preparation processes under ambient temperature, neutral pH conditions. The environmental application of such materials for the treatment of mercury-contaminated water is also demonstrated. 

Mesostructure synthesis modes electrostatic and non-electrostatic assembly... 

Typical characteristics of electrostatically and non-electrostatically assembled mesostructures... 

The ease by which the framework-forming surfactants can be removed from non-electrostatically-assembled mesostructures by low temperature solvent extraction without compromising the structural integrity of the materials is also of major benefit for the preparation of highly functionalized mesostructure derivatives. 

Non-electrostatic assembly is particularly well suited for the direct synthesis of derivatized mesostructures because the framework-forming surfactants can be removed by ambient-temperature solvent extraction and does not necessitate the potentially destructive acid leaching necessary in electrostatic direct assembly.17 Also, HMS and MSU-X materials typically have ultrafine (<1 pm) particle sizes, while electrostatically assembled MCM-type compounds usually have blocky and monolithic morphologies with comparatively large particle sizes (>10 pm). On this basis, non-electrostatically assembled mesostructures are expected to have improved diffusion properties compared to their electrostatic MCM analogs, as will be demonstrated in section 3.3 below. 

Physical chemical studies of dilute alkali metal-ammonia solutions indicate the principal solution species as the ammoniated metal cation M+, the ammoniated electron e , the "monomer M, the "dimer" M2 and the "metal anion" M. Most data suggest that M, M2, and M are simple electrostatic assemblies of ammoniated cations and ammoniated electrons The reaction, e + NH3 - lf 2 H2 + NH2 is reversible, and the directly measured equilibrium constant agrees fairly well with that estimated from other thermodynamic data. Kinetic data for the reaction of ethanol with sodium and for various metal-ammonia-alcohol reductions of aromatic compounds suggest that steady-state concentrations of ammonium ion are established. Ethanol-sodium reaction data allow estimation of an upper limit for the rate constant of e + NH4+ 7, H2 + NH3. 

Cho J, Caruso F (2003) Polymeric multilayer films comprising deconstructible hydrogen-bonded stacks confined between electrostatically assembled layers. Macromolecules 36 2845-2851... 

NIR-absorbing metal nanostructures are appealing for biomedical imaging applications for reasons discussed previously, and this includes biological applications of SERS. For example, NIR-active core-shell superparticles have been prepared by the electrostatic assembly of densely packed Au nanoparticles on submicron silica spheres.34 Such superparticle probes can be implanted into mammalian cells by cationic transfection,186 and have produced SERS signals from absorbed DNA.187 Biocompatible SERS nanoparticle tags can also be used as contrast agents for in vivo detection, as previously discussed.169... 

Electrostatic assembly, which involves attractive forces between two oppositely charged entities (polymers, nanoparticles, and substrates), has been proposed in the pioneering work of Her for the assembly of two- and three-dimensional structures.22 The LbL assembly of charged polyelectrolytes was later reported by Decher et al. for the fabrication of multilayer films of polyelectrolytes.10 23 Their technique is based on the consecutive adsorption of polyanions and polycations from dilute aqueous solutions onto a charged substrate (Fig. 13.2). 

The direct LbL assembly of oppositely charged nanoparticles, which did not involve polyelectrolytes, was also examined. Sastry et al. demonstrated the formation of alternating layers of gold and silver nanoparticles via sequential electrostatic assembly.36 In the absence of polyelectrolytes, the effective charging of gold and silver nanoparticles was accomplished by the adsorption of 4-aminothiophenol and 4-carboxythiophenol molecules on the nanoparticle surfaces, respectively. The multilayer films were stable up to 100°C. 

Hollow Inorganic Capsules via Colloid-Templated Layer-by-Layer Electrostatic Assembly... 

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