Micelle-soft-templates

Since the formation of the micelle-soft-template is strongly affected by the nature of polymeric chain and dopant as well as polymerization conditions, the structure of micelle-soft templates formed in a reaction solution can vary [5cj. Moreover, the micelle-soft template and the molecular interactions as the driving forces coexist in the reaction solution, resulting in cooperation between them that might be employed to complex micro/nanostructures of PANI via the self-assembly process. This prediction has been confirmed by the formation of hollow rambutan-like spheres [64], hollow dandelion-like microstructure [65] and hollow cube box-like 3D microstructures of PANI [66] as shown in Figure 17.4. These complex 3D micro/nanostructures are self-assembled from ID nanofibers and show electrical and supper-hydrophobic properties. The trick is to use perfluorooctane sulfuric acid (PFOSA) or perfluorosebadc acid (PFSEA) as the dopant, which has doping. 

Electro-optic composite nanostructures or chiral nanostructures of conducting polymers have received great attention in the application of electro-optic nanodevices [100]. Coordination of micelle soft-template with functional dopant induced method is a simple and an efficient approach to prepare electro-optical... 

Sodium bis(2-ethylhejQ l) sulfosuccinate (AOT), which can solubilize a relatively large amount of water [116], was selected as the sulfactant for the reverse microemulsion system. An aqueous FeCIa solution was added into an AOT/ apolar solvent mixture at room temperature. Subsequently, cylindrical reverse micelles, soft templates for the fabrication of nanotubular structures, were generated [117]. AOT micelles are generally a few nanometers in size in the absence of water. However, the addition of water dramatically increases the average aggregation number of the reverse micelles and thus the hydrod mamic radius of the aqueous micellar core increases [118]. 

Compared to inorganic materials, organic materials such as polymers, surfactant molecules and micelles also act as a capping material or soft template. Figure 5.15 shows TEM images of gold nanorods and nanoparticles synthesized by sonochemical reduction of Au(I) in the presence of cetyltrimethylammonium bromide,... 

The kinds of structures adopted by these microorganisms as well as other mineral morphologies, are the subject of increasing study as chemists look at soft templated routes to nanoscale objects. Early work in the 1990s by a team at Mobile used supramolecular micelles, lamellae and bicontinuous phases4 formed by amphiphiles, to assemble inorganic materials, particularly silica and alumina. A range of new... 

Mesophase structures self-assembled from surfactants (Figure 8.35) provide another class of useful and versatile templates for generating ID nanostructures in relatively large quantities. It is well known that at critical micellar concentration (CMC) surfactant molecules spontaneously organize into rod-shaped micelles [315c]. These anisotropic structures can be used immediately as soft templates to promote the formation of nanorods when coupled with appropriate chemical or electrochemical reaction. The surfactant needs to be selectively removed to collect the nanorods/nanowires as a relatively pure sample. Based on this principle, nanowires of CuS, CuSe, CdS, CdSe, ZnS and ZnSe have been grown selectively by using surfactants such as Na-AOT or Triton X of known concentrations [238, 246]. 

The templates used in the synthesis of mesostructured and mesoporous materials can be classified into two categories The first class of templates includes soft templates, which are ordered arrays of self-assembled surfactant micelles, similar to the ones used by the researchers at Mobil. Alternately, mesoporous materials can themselves be used as templates to synthesize new mesostructured materials, and such templates can be termed as rigid templates. In the following sections, we focus on the use of supramolecular assemblies of surfactants as well as on the use of rigid templates as the templates for the synthesis of mesostructured materials. 

Successful nanocrystals synthesis has also been carried out employing soft templates such as the water pool in a reverse micelle, the interface of two... 

The soft-template methods are based on the use of structure-directing molecules, such as various soluble oligomers and polymers, as well as surfactants and amphiphilic acids which are able to form, alone or with aniline, aggregates such as cylindrical micelles, and other supramolecular 1-D aggregates. 

To obtain nanocontainers, Wei et al. employed micelles as soft templates to assist the polymerization [83]. Hollow conical nanostructures are produced by a slow polymerization process (Figure 11.8). Microcontainers could be produced in the open or closed state by changing the polymerization time. However, as far as we are aware, most of the reported actuators were based on bulk materials or synergistic properties of nanostmcture bundles instead of single nanostmcture. Wei et al. realized the manipulation of separated nanocontainers by an electrochemical approach to control of the state of the nanocontainer in situ . Studying the switching of single nanostmctured CPs will open potential... 

Figure 11.11 A schematic representation of the soft-template method used to prepare CPCs (a) micelles, (b) oil droplets, (c) gaseous bubbles...

Using functional molecules as structural directors in the chemical polymerization bath can also produce polyaniline nanostructures. Such structural directors include surfactants [16-18], liquid crystals [19], polyelectrolytes (including DNA) [20,21], or complex bulky dopants [22-24]. It is believed that functional molecules can promote the formation of nanostructured soft condensed phase materials (e.g., micelles and emulsions) that can serve as soft templates for aniline polymerization (Figure 7.3). Polyelectrolytes such as polyacrylic acid, polystyrenesulfonic acid, and DNA can bind aniline monomer molecules, which can be polymerized in situ forming polyaniline nanowires along the polyelectrolyte molecules. Compared to templated syntheses, self-assembly routes are more scalable but they rely on the structural director molecules. It is also difficult to make nanostructures with small diameters (e.g., <50 nm). For example, in the dopant induced self-assembly route, very complex dopants with bulky side groups are needed to obtain nanotubes with diameters smaller than 100 nm, such as sulfonated naphthalene derivatives [23-25], fidlerenes [26], or dendrimers [27,28]. 

Recently, a facile soft template synthesis was developed for fabricating PPy nanotubes against the hard template synthesis [153,249]. PPy nanotubes could be readily produced through a cylindrical micelle templating in re-... 

The array of PPy dots (diameter 80-180 nm) was patterned in a parallel fashion using block copolymer micelle as a soft template [256]. The Langmuir-Blodgett (LB) film composed of PS-fi-poly(2-vinylpyridine) was deposited onto the solid substrate, and the ahgned PPy dots could be formed through the chemical oxidation polymerization of pyrrole in the presence of the block copolymer micelle template. The chemical differentiation (hydrophilic vs. hydrophobic) between the core and the corona in block copolymer micelle led to spatially-limited PPy growth. 

Figure17.4 Three-dimensional multifunctional microstructures of PANI self-assembled from ID nanofibers by a cooperative effect of micelles as soft-templates and molecular interactions as driving forces [64-67].

Both of the above templated methods are often referred to as hard template methods, as template dimensions are well-defined, pre-formed, and hence robust. In contrast to the former are the so-called soft templates. There, self-assembly processes are responsible for the formation of spatially defined geometric structures (the soft template) around which the polymer tube is then formed. Reverse rod-shaped micelles are a typical example around which polymeric tubes can be formed. Removal of the soft template releases the nanotubular structure. 

---