Porous structure concentric shell

The increase in the monomer amount results in nanocapsules with different morphology and shell thickness. In Fig. 5, the TEM images of PBCA capsules obtained with 5 wt. % of Span 80 and different amounts of butyl-cyanoacrylate are presented. From the TEM images one can see that the polymeric shell formed with a lowest amount of butylcyanoacrylate (70 xl) is thin and has a porous structure. A more dense and regular PBCA shell can be observed for capsules obtained with higher amounts of monomer. The shell thickness depends on the monomer concentration and was in the range of 5-15 nm and 20-40 nm for 100 and 200 (xl of butylcyanoacrylate, respectively. 

Where 4 rr is the inner superficial area of the spherical shell, D, effis the effective overall diffusion coefficient of i component through the porous structure, dQ/dr is the concentration gradient of i component at the spherical surface, p is the particle density of catalyst, and R, is the rate of i component. 

Quite original is the attempt to obtain porous materials, for example, from crystalline calcium carbonate (aragonite) similar to the natural material chalk of a certain porosity [192]. Another attempt was made to synthesize macro-porous aragonite with a structure similar to the cocco-spheres of certain marine algae [295]. For this purpose, oil-water-surfactant microemulsions supersaturated with calcium bicarbonate were obtained. The pore size was determined by the water and oil concentration ratio. Microemulsions were applied on the substrate of micrometersized polystyrene beads. Hollow spherical shells of finished structure were produced as a result of a rapid mineralisation. The authors suggest that such materials could gain widespread use in materitils chemistry. 

It is possible to shape catalyst bodies, in which the catalytically active substances are not distributed over the complete bulk, but rather located in concentric areas. Many fluidized-bed catalysts, for instance, are spheres in which the active phase represents the core, and the shell is a porous, protective layer to prevent attrition. Bodies exhibiting the active phase in the core are denoted as egg-yolk catalysts. For fixed-bed applications, so-called egg-shell structures are more convenient, in which the catalytic material is located at the external surface, whereas the core is nonreactive. 

Interactions of ID polymers with porous solid particles depend on many factors types (chemistry) of a polymer and a solid, textural, and morphological characteristics of solid particles (5, V, PSD, particle size), dispersion medium (solvent can be a strong competitor especially in narrow pores), concentration, temperature, and time of interactions. In this case, the confined space effects can play a much stronger role than in the case of nanooxides composed of nonporous nanoparticles. A polymer shell on adsorbent particles can form a strong barrier (thick cross-linked 3D strictures) or a semipermeable membrane (thin 2D structures at a lower degree of cross-linking). Core-shell... 

However, while the above was a rather crude approach to fabricate more porous electrode layers with oxidic support materials, a more elegant way was chosen for home-made ATO by 3D morphology engineering. ATO powder with unique hollow-sphere morphology was synthesized by ultrasonic spray p)irolysis (USP). Depending on precursor concentration and temperature, this process yields a powder composed of individual nano-crystallites forming the shells of hollow spheres with a controlled nano- and microporosity [98]. This offers efficient mass transport and is assumed to prevent the collapse of the electrode structure with time during operation. 

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