Template surfactant, morphologically controlled

Brinker CJ Dunphy DR, Morphological control of surfactant-templated metal oxide films, Curr. Opin. Colloid Interface Set, 2006, 11, 126-132. 

A. D. W. Carswell, E. A. O Rear, and B. P. Grady, Adsorbed surfactants as templates for the synthesis of morphologically controlled polyaniUne and polypyrrole nanostructures on flat surfaces from spheres to wires to flat films, J. Aon. Chem. Soc., 125, 14793-14800 (2003). 

Fig. 1.11 Illustration of the process to fabricate morphologically controlled nanostructures of electrically conducting polymers on surfaces by using surfactant templates. This particular schematic draw represents the proposed scheme of wire formation on (a) chemically treated HOPG and (b) HOPG (Reprinted with permission from Carswell et al. [139]. Copyright 2009 American Chemical...

The difficulty in direct synthesis of mesoporous transition metal oxides by soft templating (surfactant micelles) arises from their air- and moisture-sensitive sol-gel chemistry [4,10,11]. On the other hand, mesoporous silica materials can be synthesized in nimierous different solvent systems (i.e., water or water-alcohol mixtures), various synthetic conditions (Le., acidic or basic, various concentration and temperature ranges), and in the presence of organic (Le., TMB) and inorganic additives (e.g., CT, SO, and NOs ) [12-15]. The flexibility in synthesis conditions allows one to synthesize mesoporous silica materials with tunable pore sizes (2-50 nm), mesostructures (Le., 2D Hexagonal, FCC, and BCC), bimodal porosity, and morphologies (Le., spheres, rods, ropes, and cubes) [12,14,16-19]. Such a control on the physicochemical parameters of mesoporous TM oxides is desired for enhanced catalytic, electronic, magnetic, and optical properties. Therefore, use... 

Synthesis of solid state materials using surfactant molecules as template has been extensively used in this decade. Among the advantages of the use of amphiphilic molecules, the self-assembling property of the surfactants can provide an effective method for synthesising ceramic and composite materials with interesting characteristics, such as nanoscale control of morphology, and nano or mesopore structure with narrow and controllable size distribution [1-5]. 

The rhodium containing hybrid materials prepared with the BINOL bicarbamate moieties are less active and enantioselective than the previous hybrid catalyst. The observed enantioselectivity was attributed to supramolecular effect of the chiral tridimensional network owing to the weakness of the interaction of the transition metal and the chiral ligand. The control of the texture and morphology of these solids by templating methods firstly reported by Macquarrie39 and Mann40 with suitable surfactants would improve the catalytic performance of this new class of chiral materials. 

The formation of nanoparticles from microemulsions need not essentially follow the template shape. Pileni [32] (as quoted by Ganguli and Ganguli) has shown that with water/isooctane/Cu( AOT)2 shapes like sphere to cylinder to mixed spherulites and cylinders to other polydisperse shapes were possible with increasing to. According to Pileni [33], the presence of salt anions can control the shape while chloride ions favour formation of nanorods, nitrate ions hinder it. The surfactant content also can have a say on the shape of nanoparticles. The infrequently observed morphologies of nanoparticles, viz. wires, trigons, hexagons, cubes etc. have so far no specific and reliable reasons for formation in micro emulsion templates. 

Crystal morphologies of glycine can be controlled by using surfactant monolayers at the air/water interface as templates. Catalyzed nucleation may, for example, yield 010 pyramids of glycine in supersaturated aqueous phases below surface monolayers or at foam lamellae (Chen et aL, 1998). 

Moreover, Shi and his group reported electrochemical deposition of PPy microcontainers onto soap bubbles associated with O2 gas released from the electrolysis of H2O in an aqueous solution of /3-naphthalenesulfonic acid (/3-NSA), camphorsulfonic acid (CSA), or poly(styrene sulfonic acid) (PSSA), which act both the surfactant and dopant [79-81]. Morphologies such as bowls, cups, and bottles could be controlled by electrochemical conditions (Figure 11.6). However, the microcontainers were randomly located on the electrode surface, which limited further applications, Shi and coworkers reported a linear arrangement of PPy microcontainers by self-assembly with gas bubbles acting as templates on a silicon electrode surface patterned by photolithography [82]. They found that capillary interactions between the gas bubbles and the polymer photoresist walls led the microcontainers to be arranged linearly. 

Bell et al. [67] were one of the pioneers in proposing the fabrication of mesoporous carbon by using surfactants as template. This novel route produces mesoporous carbon monolithic using directly cationic micelles as nanomolds in the polymerization media. More recently, Fujikawa et al. showed a possible route to control the morphology of the polymer and carbon nanostructures [68, 69]. 

Miniemulsion systems are somewhere in between macro- and microsystems. They contain both micelles and monomer droplets, but the monomer droplets are smaller than in macrosystems [134-137]. For both micro- and minireaction systems in which the initiator is soluble in the continuous phase, the mechanism for polymerization is determined by the relative surface areas of micelles versus monomer droplets. Compared with the miniemulsion (5-10wt% of surfactant used), high concentration (15-30 wt%) of smfactant forms robust and compact micelle, and the inner space of micelle can be used as a nanoreactor. Besides sphere and layer morphologies, a wide range of morphological spectra could be obtained by carefully controlling the synthetic conditions. The surfactant templates for sphere, rod, and layer nanomaterials are schematically represented in Scheme 5. 

Ordered mesoporous materials synthesized using surfactant templates [60,61,99] have been widely used as hard templates to prepare various mesoporous carbons. Two Korean research groups were the first to independently demonstrate the use of ordered mesostructured silicas as hard templates [62,63]. Because they have larger pore sizes than zeolites, ordered mesoporous silicas with a 3-D pore system (e.g., MCM-48, SBA-15, and SBA-16) offer more flexibilities for control over the structural, morphological, and surface properties of templated mesoporous carbon. 

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