Inner void

Template synthesized silica nanotubes (SNTs) provide unique features such as end functionalization to control drug release, inner voids for loading biomolecules, and distinctive inner and outer surfaces that can be differentially functionalized for targeting and biocompatibility.50 A general path to synthesize nanotubes utilizes anisotropic materials as template. They are coated with silica using Si(OR)4 precursors and nanotubes of Si02 are obtained after removal of the template (Figure 1.24). 

Surface pores and channels Present Inner voids... 

In analogy to the relation between SPE and SPME discussed below, a refinement of LEE is achieved by the LLLME method. Analytes in a stirred matrix solution (the donor) are extracted into a thin solvent film filling the pores in the walls of a hollow fiber and diffuse into a collecting solution (the acceptor) filling the inner void of the hollow fiber. The enrichment factor depends not only on the volume ratio between the donor and the acceptor, but also on the operational conditions. The main advantages of the method are simplicity of operation, low cost, the scarce use of organic solvents and avoidance of evaporation operations120. 

Emptiness creates the temptation to experiment with new experience to fill up the inner void. "I couldn t stand feeling nothing inside, so I dropped some acid and it gave me a sense of myself I d never had before."... 

Figure 3.93 Possible sites for the intercalation of small particles or atoms inlude the tube s inner void (a) as well as the interstitial space In multiwalled tubes (b) and the hollow space within bundles of nanotubes (c).

Functional micro- and nanocontainers represent unique class of materials, in which a spatially-confined inner nanovolume is combined with controllable permeability and protective properties of the shell [4,5]. However, a lot of research work still remains, especially in better understanding of the detailed mechanism of the shell permeability and structure of the inner void. Moreover, notwithstanding to the fact that perspectives of nanocontainer applications are already demonstrated, the necessary up-scaling technologies for fabrication of micro- and nanocontainers in large quantities are not yet comprehensively developed. 

A conventional polyhedron has as many loops as surfaces, no holes but one inner void which is the volume itself that give rise to only one outer shell. Equation (7.8) reduces then to Eq. (7.5). 

Figure 5.4 A schematic illustration of the shape selectivity concept, classically referring to a significant modification in the distribution of products in a catalytic reaction due to the localisation of the active sites within a confined space of the catalyst. Reactant shape selectivity (a) occurs when some but not all the components in a reaction mixture can reach the inner active sites and react. When the size and shape of the inner void modify the distribution of products by limiting the number of possible transition states, the effect is called transition state shape selectivity (b). And, finally, when a molecule can be formed but cannot be desorbed due to its size and shape, the product distribution is altered by product shape selectivity (c). In addition to these broad concepts, thermodynamic effects are also of importance. Reproduced by permission from Macmillan Publishers Ltd Nature, B. Smit and T.L.M. Maesen, 451, 671 (20). Copyright (2008) Macmillan Publishers Ltd.

Well-defined inorganic crystalline structures yielding a large variety of structural types differing in the channel diameters, geometry, and dimensionality. Precisely defined inner void volume providing high-surface areas up to 600 m"/g. 

The constrained geometry of the inner void volume of zeolites, and particularly of mesoporous materials, provides an important space of nanodimensions for accommodation of large molecules. It is expected that flexible polymers synthesized in the conditions of constrained geometry could exhibit different properties compared to nonconstrained systems. Considerable effort has been exerted to synthesize conducting polymers by polymerization of the respective monomers in the presence of zeolites ion-exchanged with some transition metals. 

Modification in this category consist in grafting more or less bulky molecules to external or internal hydroxyl groups in order to modify either pore mouth or inner void volume in a king of inner coating. Many examples may be found as P compounds (34), disilane (35), boric oxide (36) etc. 

Figure 13 Calix[4]arene-derived carcerand used by Warmuth et al. to stabilize reactive intermediates, such as o-benzyne and a singlet carbene. Note the butylene spacers that account for the larger size of the inner void space, compared to Cram s original structure.

Important parameters controlling productivity are the cure time, cleaning intraval of the molding die, yield (main failure modes being insufficient molding and pin holes), and flash on the lead. It is also important to keep good quality without wire sweqj, inner voids, or inner lead deformation. 

Insufficient molding, inner voids, wire sweep and lead tteformation are generally related to flow characteristics and gel time. A material with lower melt visctsity (D), and longer gel time (F) will have fewer failures. 

As reported, ferroelectrets are thin polymer films with open or closed cavities, such as a foamed material although they differ from those due to the trapped electrical charges on the inner void surfaces. These characteristics allow the material to exhibit high J33 piezoelectric coefficients. In this section we describe the most accepted model, which explains this electromechanical behavior. 

After reducing the complex voided stmcture to a simplified three-layer system, the electret microphone theory can be applied. To demonstrate the relation between this theory and the ferroelectret model, the electric charged layered system, as shown in Fig. 2b, was considered. The eharged model represents the charges trapped on the inner void surfaces and the charges induced on the proximity of the electrodes, after the stmcture has been submitted to an external high electric field and dielectric barrier discharges had occiured inside the air cavities. 

If all the inner voids are accessible via pores the density obtained at 20(X) bar should be equal to the apparent density measured by helium pycnometry. Results shown in Table 14.8 showed slightly higher densities for helium pycnometry measurements, indicating that not all pores, which are permeable for helium, are accessible by mercury intrusion [32]. 

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