Spheres multilayered

Multilayors and Structured Spheres. Multilayer structures are used extensively in photographic applications, such as optical and x-ray photography and xerographic processes, as well as in packaging materials. Several such materials were so far investigated with nexafs microscopy. 

The LB technique was chosen for covering the spheres because it was shown to provide enhanced thermal stability of many types of proteins in deposited layers (Nicolini et al. 1993, Erokhin et al. 1995, Antolini et al. 1995), which no other technique is able to achieve. Since only the upper protein layer is involved in the catalytic activity, no special attention was paid to check whether the deposited layer is a monolayer or multilayer. However, the samples were thoroughly washed to remove protein molecnles not bound covalently to the sphere surface, since during the functional test these molecules could contribute to the measured apparent catalytic activity. 

The described procedure allows one to deposit protein, in particular, enzyme, LB films onto the surface of small spheres. Deposited multilayer film was washed in order to leave at the surface only a layer covalently attached to the activated surface. The enzyme... 

The multilayer shells can also provide a protective barrier for the loaded enzyme in environments where enzyme-degrading substrates such as proteases may be present [67]. Dissolved catalase was inactivated immediately by protease, losing its entire activity within 60 min in solution. For catalase loaded in BMS spheres, inactivation is slower, with an activity loss of about 20 % in 60 min. Notably, a negligible decrease in... 

Caruso, R.A., Susha, A. and Caruso, F. (2001) Multilayered titania, silica, and laponite nanopartides coating on polystyrene colloidal templates and resulting inorganic hollow spheres. Chemistry of Materials, 13, 400—409. 

Encapsulation via the layer-by-layer assembly of multilayered polyelectrolyte (PE) or PE/nanoparticle nanocomposite thin shells of catalase in bimodal mesoporous silica spheres is also described by Wang and Caruso [198]. The use of a bimodal mesoporous structure allows faster immobilization rates and greater enzyme immobilization capacity (20-40 wt%) in comparison with a monomodal structure. The activity of the encapsulated catalase was retained (70 % after 25 successive batch reactions) and its stability enhanced. 

Chemists have synthesized a spectacular array of submicron- and nano-particles with well-defined size and atomic structure and very special properties. Examples include CdSe quantum dots and novel spheres and rods. Transport enters the picture via fundamental studies of the physical processes that affect the synthesis, which must be understood for even modest scale-up from the milligram level. Likewise, processes for assembling fascinating face-centered-cubic crystals or ordered multilayers must concentrate on organizing the particles via flow, diffusion, or action of external fields. Near-perfection is possible but requires careful understanding and control of the forces and the rates. 

Gauging catalysis by reference to an electrode where electrons are delivered (or eaten up) in an outer-sphere manner, redox catalysis is not expected to operate at a monolayer coated electrode (Figure 4.10), since, as discussed in Section 4.2.1, redox catalysis results from the three-dimensional dispersion of the catalyst. In contrast, there is no reason that chemical catalysis could not be operative at a monolayer coated electrode. For the same reasons, both redox catalysis and chemical catalysis are expected to function at multilayer electrode coatings (Figure 4.10). 

I he field scattered by any spherically symmetrical particle composed of materials described by the constitutive relations (2.7)-(2.9) has the same form as that scattered by the homogeneous sphere considered in Chapter 4. However, the functional form of the coefficients an and bn depends on the radial variation of e and ju. In this section we consider the problem of scattering by a homogeneous sphere coated with a homogeneous layer of uniform thickness, the solution to which was first obtained by Aden and Kerker (1951). This is one of the simplest examples of a particle with a spatially variable refractive index, and it can readily be generalized to a multilayered sphere. 

Based on the above general principles, quite a number of models have been developed to estimate pore size distributions.29,30,31-32,33 They are based on different pore models (cylindrical, ink bottle, packed sphere,. ..). Even the so-called modelless calculation methods do need a pore model in the end to convert the results into an actual pore size distribution. Very often, the exact pore shape is not known, or the pores are very irregular, which makes the choice of the model rather arbitrary. The model of Barett, Joyner and Halenda34 (BJH model) is based on calculation methods for cylindrical pores. The method uses the desorption branch of the isotherm. The desorbed amount of gas is due either to the evaporation of the liquid core, or to the desorption of a multilayer. Both phenomena are related to the relative pressure, by means of the Kelvin and the Halsey equation. The exact computer algorithms35 are not discussed here. The calculations are rather tedious, but straightforward. 

Watanabe and Regen 81 reported the construction of ordered, dendritic multilayers (10) via a bridged, outer sphere —outer sphere mode of assembly (Figure 9.5) whereby the transition metal Pt was used as a connector moiety. Although amine-terminated PAMAM-type dendrimers 76 were employed for this particular example, this process could easily be extended to other types of macromolecules. 

Abstract In this paper we report on AFM force spectroscopy measurements on hollow polymeric spheres of colloidal dimensions made from polyelectrolyte multilayers of polyal-lylamine and polystyrenesulfonate in water. We find that the shells show a linear force-deformation characteristic for deformations of the order of the shell wall thickness. This experimental outcome is discussed in terms of analytical results of continuum mechanics, in particular the scaling behaviour of the shell spring constant with wall thickness, shell radius and speed of the deformation is analysed. The experimental results agree well with the predictions of Reissner for thin shells and allow... 

In Model 2 the ratio 3a/2y may be considered approximately to represent the ratio of the dispersion interaction potential between an adsorbate molecule and a solid surface for a polarized as against a rigid, unpolarized adsorbate molecule, assuming in both cases that the potential may be represented by the 3-9 Lennard-Jones (surface) function. This approximation is based additionally on the assumption that the adsorbate is effectively hard sphere in the multilayer region. This ratio turns out to be 3.3 and 3.5 for 02 and N2 on anatase, respectively. Furthermore, the adsorbate-adsorbent interactions in the adsorbate-polarization case must evidently amount to 1.8 EL and 2.5 EL for 02 and N2 on anatase, re-... 

Caruso, R. A. Susha, A. Caruso, F. Multilayered Titania, Silica, and Laponite Nanoparticle Coatings on Polystyrene Colloidal Templates and Resulting Inorganic Hollow Spheres. Chem. Mater. 2001,13,400-409. 

Chemisorption or specific adsorption involves greater forces of attraction than physical adsorption. As hydrogen bonding or n rbital interactions are utilised, the adsorbed species lose their hydrated spheres and can approach the surface as close as the ionic radius. Whereas multilayer adsorption is possible in physical adsorption, chemisorption is necessarily limited to monolayer coverage. 

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