Synthesis soft-template process

Two kinds of template, viz. hard template and soft template, are usually available for nanocasting processes. The true liquid crystal templating synthesis can be considered a soft-template process. In general, the hard template means an inorganic solid. For example, mesoporous silica as a template to replicate other materials, such as carbon or metal oxides, by which the pore structure of the parent can be transferred to the generated porous materials. A 3-D pore network in the template is necessary to create a stable replica. Mesoporous silica and carbon are commonly used templates for nanocasting synthesis. 

In the case of soft-template self-assembly synthesis, mesostructure assembly and morphology growth can be controlled concurrently. Due to the versatility of the solvent-based soft-template self-assembly process, highly ordered mesoporous carbons can be produced relatively easily with different morphologies such as thin film and membrane, " monolith,fibre,sphere, rod, single-crystal, " and discus-like crystal. Initially, mesoporous carbons synthesised with soft templates were exclusively in the form of films. " ... 

One of the few reports on the preparation of mesoporous sihca nanofibers with a soft template other than triblock copolymers of the Pluronic type deals with the synthesis of sihca nanofibers with high aspect ratios containing linear arrays of mesopores by a solution-induced self-assembly process (Fig. 23), as previously reported for thin-film configurations [184]. To this end, PS-fo-PEO diblock copolymers were employed as structure-directing agents in sol solutions containing toluene/ethanol mixtures. For a Dp-value of 35 nm, a single line of mesopores formed, for a Dp-value of 60 nm two parallel rows of mesopores were obtained [185]. 

Till date, liquid-crystalline phases [51], colloidal particles [52], and structure-directing molecules [53[ as the soft-template have been employed to synthesize PANI nanostructures. Based on the traditional synthesis method of PANI, in particular, some simple approaches such as interfacial polymerization [54], mixed reactions [55], dilute polymerization [56] and ultrasonic irradiation [57] have also been employed to synthesize PANI. The interfacial polymerization method only allows the oxidative polymerization of aniline to take place at the interface of the organic/water phases and the product directly enters into the water phase, which could facilitate environmentally friendly processing. 

Figure 32.7 Schematic representation of the soft templating method via the cooperative self-assembly process for the synthesis of ordered mesoporous materials [70].

A wide variety of template synthesis methods have been developed for preparing nanomaterials by ECD. At a minimum, the ECD template process requires a conductive substrate that acts as a current collector and electrolyte wet pores. The growth of the material then proceeds from the conductive substrate through the template either along the surface of the template pores or filling them completely. In some cases, the material continues as overgrowth after the template has been filled. The variety of templates currently utilized can be found in the following text. They have been divided between hard and soft templates with a new, innovative example for each one. 

The template-directed synthesis of nano- and micromaterials has considerably evolved in recent years. Efforts were driven by the demand to produce in a controlled and reproducible way nano- and microstructures with applications in materials science, catalysis, and pharmacy. The idea to use templates is an old idea of mankind to produce reliably and reproducibly household goods and artworks needed in everyday life. The requirements for the template can easily be seen in the production of pottery. A template is filled or covered with a soft precursor material to bring the material into the desired form. Through a chemical reaction or a physical process the precursor material hardens and the template can be removed to obtain the desired product. The template has the advantage that its size and shape can be reproducibly controlled, in contrast to the desired material, where such control is more difficult. 

The methods of soft chemistry include sol-gel, electrochemical, hydrothermal, intercalation and ion-exchange processes. Many of these methods are employed routinely for the synthesis of ceramic materials. - There have been recent reviews of the electrochemical methods, intercalation reactions, and the sol-gel technique. The sol-gel method has been particularly effective with wide-ranging applications in ceramics, catalysts, porous solids and composites and has given rise to fine precursor chemistry. Hydrothennal synthesis has been employed for the synthesis of oxidic materials under mild conditions and most of the porous solids and open-framework structures using organic templates are prepared hydro-thermally. The advent of supramolecular chemistry has started to make an impact on synthesis, mesoporous solids being well known examples. ... 

One particular asset of structured self-assemblies is their ability to create nano- to microsized domains, snch as cavities, that could be exploited for chemical synthesis and catalysis. Many kinds of organized self-assemblies have been proved to act as efficient nanoreactors, and several chapters of this book discnss some of them such as small discrete supramolecular vessels (Chapter Reactivity In Nanoscale Vessels, Supramolecular Reactivity), dendrimers (Chapter Supramolecular Dendrlmer Chemistry, Soft Matter), or protein cages and virus capsids (Chapter Viruses as Self-Assembled Templates, Self-Processes). In this chapter, we focus on larger and softer self-assembled structures such as micelles, vesicles, liquid crystals (LCs), or gels, which are made of surfactants, block copolymers, or amphiphilic peptides. In addition, only the systems that present a high kinetic lability (i.e., dynamic) of their aggregated building blocks are considered more static objects such as most of polymersomes and molecularly imprinted polymers are discussed elsewhere (Chapters Assembly of Block Copolymers and Molecularly Imprinted Polymers, Soft Matter, respectively). Finally, for each of these dynamic systems, we describe their functional properties with respect to their potential for the promotion and catalysis of molecular and biomolecu-lar transformations, polymerization, self-replication, metal colloid formation, and mineralization processes. 

For all forms of DNA, hydrogen bonding between the two spiral chains stabilizes the double helix. Replication of DNA occurs when the hydrogen bonds are broken, and the two strands are separated. These form the templates that are used to make identical copies, via enzymes called DNA polymerases. In fact, the second strand of the double helix is complementary to the first, it contains no extra information but is involved in replication. Ribonucleic acid (RNA) is also found in cells. It has a similar structure to DNA, but the sugar is instead D-ribose and uracil bases replace thymine bases. RNA is important in the synthesis of proteins. It is produced from DNA templates via the process of transcription. Further details of protein biochemistry can be found elsewhere (e.g. Voet and Voet, 1995). Here we simply emphasize that life itself is created from that special class of soft material called polymers. 

Depending on the desired materials properties and structure, these approaches have been explored for sol-gel processing of alkoxide-based precursors and further developed in combination with many experimental parameters that can also be adjusted to control the sol composition and particle size, including alkoxide/ water ratio, concentration of the precursors, reaction temperature, reaction time, drying methods, choice and concentration of the catalyst, and the solvent used [42]. Besides the well-known hydrolytic sol-gel processes, even nonhydro-lytic approaches have been reported as a powerful method in the synthesis of mixed oxide materials and will be discussed in more detail subsequently [43]. Another processing option to tailor the material properties is the application of soft or hard templates [44]. In addition to the chemical parameters, drying and thermal treatments or firing processes determine the final architecture, chemical... 

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