Polydispersity template

Rzysko, W., Sokolowski, S., and Pizio, O. (2002). Theory of adsorption in a polydisperse templated porous material hard sphere systems. J. Chem. Phys., 116, 4286-92. 

Templates made of surfactants are very effective in order to control the size, shape, and polydispersity of nanosized metal particles. Surfactant micelles may enclose metal ions to form amphiphilic microreactors (Figure 11a). Water-in-oil reverse micelles (Figure 11b) or larger vesicles may function in similar ways. On the addition of reducing agents such as hydrazine nanosized metal particles are formed. The size and the shape of the products are pre-imprinted by the constrained environment in which they are grown. 

Let us consider a template, i.e., the average representative particle or the average representative structural entity in a material with polydisperse structure. The template is described by its structure pr (r). The sample is full of dilated images... 

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. 

Biopolymers are either synthesized by template-dependent or template-independent enzymatic processes. For the synthesis of nucleic acids and proteins a template is required, whereas all other polymers are synthesized by template-independent processes. The templates for nucleic acids are desoxyribonucleic acids or ribonucleic acids depending on the type of nucleic acid synthesized. For proteins, the template is messenger ribonucleic acid (mRNA). This has different impacts on the structure and on the molecular weights (MWs) of the polymers. Although both nucleic acids and proteins are copolymers with each type consisting of 4 or 22 different constituents, respectively, the distribution of the constituents is absolutely defined by the matrix and is not random. Furthermore, each representative of the two polymers has a defined MW. Polymers synthesized in template-dependent processes are monodisperse. All this is different in polymers synthesized by template-independent processes first of all, these polymers are polydisperse secondly, if these polymers are copolymers, the distribution of the constituents is more or less fully random. 

As polymer spheres are easily accessible with low polydispersity, they are attractive templates. Coating in non-aqueous solvents is usual as most metal alkoxide precursors rapidly undergo hydrolysis and condensation in the presence of water. 

The structure of such metallopolymers can be regulated by varying the ratio of sizes of block-copolymer (general molecular weight, composition) and micelle parameters (size of nucleus/cover, form, polydispersion), and this enables us to use block-copolymers as nanoreactors or templates. The ratio between the molecular weights of the first (polar) and the second (hydrocarbon) components Mi and M2) is important to provide steric stabilization M = nM2 (where n is the number of the second component chains). As a rule, M is 10 -10 andM2 = 10 -10. ... 

A number of parameters determine whether or not the morphology of interest is adopted by a microphase separating copolymer melt. Of these, most important are the interaction parameter, the volume ratio of the blocks, the degree of polymerization, the individual block molecular weight distributions, the overall polydispersity, the interactions with the interfaces, and last but not least, the temperature. Only the latter two parameters are experimentally accessible and can be altered after the synthesis of the copolymer (disregarding polymer blends). Control over the self-assembly at the film interfaces becomes essential when the polymer films are intended to be used as templates. Meuler et al. recently published a comprehensive review on how these various parameters affect the formation of gyroid-like morphologies in polymeric materials [47]. 

We have been exploring the possibility of using block copolymers as templates to control pore formation in composites that are precursors to ultra low-k films (5). Block copolymers are of interest since they are commercially available for a wide variety of monomers with well-controlled molecular weights and polydispersities, and it is possible to control the film morphology with the proper choice of monomer, molecular weight or architecture. 

WulflF sees the polydispersity of the imprinted receptor sites, nonspecific binding problems and the poor mass transfer properties of typical imprinted materials as key problems. He has recently published work on imprinting using strong noncovalent interactions to achieve near-stoichiometric association of templates and functional monomers in an attempt to improve the homogeneity of receptor sites and minimize the fraction of functional monomers dispersed non-specifically in the polymer structure. Continuation of this work, along with related work from other groups, will no doubt lead to further advances in this area. 

Suspension in water Polydispersed spherical particles Medium Mature technology, very reproducible, scalable to large batches Water poorly compatible with noncovalent interactions between functional monomers and templates... 

Although the majority of the examples in the literature have used viral capsids to nudeate and template inorganic materials, it is also possible to template the formation of organic polymers on their surface. Niu et used the TMV capsid as a scaffold to bind and polymerize pyrrole and aniline into conductive polymer nanowires. Using the capsid as the scaffold allowed for the creation of well-defined constmcts with a low polydispersity, high processability, and a high aspect ratio. 

It may be pertinent to mention here, before discussing more of the influence of w on the particle size polydispersity, that polydispersity of droplet size in W/O microemulsions should also play a specific role. It has been indicated on the other hand that generally speaking, droplet polydispersity in reverse microemulsions is relatively low [125, 403]. This factor, thus, may not have a pivotal role to play. For engineering a synthesis of monodisperse particle batches, standardization of the water pool droplets seems to be necessary [242] (see below) at least theoretically, though it has been shown by examples in this Chapter that droplets as templates cannot often exert a very precise control on the particle size. 

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