The Solid Interior

A solid phase extended upon another solid support may not possess its normal lattice structure due to epitaxial effects it may be more stable as a sheet of leptons, as a patchwork of small two-dimensional platelets, or as disseminated, isolated leptons. 

---

Since liposomes have an aqueous interior, they are also termed as nanovesicles or nanocapsules. On the other hand, nanoparticulates with a solid matrix-type interior represent another type of drug carrier called nanospheres.27 Compared with liposomes, the solid interior of nanospheres generally offers a lower drug-loading capacity but at the same time provides some unique physical properties that can be advantageous in certain applications. 

For an interface such as silver iodide-electrolyte solution the electric potential difference between the solid interior and the bulk solution varies according to the Nernst equation ... 

Drying is defined as the process of eliminating the solvent from the solid precursor. Drying is accomplished by diffusion of the solvent from the solid interior to the surface and by evaporation of the solvent with heat and/or vacuum. The pore structure may start to form during this process. 

Commercial dryers differ fundamentally by the methods of heat transfer employed (see classification of diyers, Fig. 12-45). These industrial-diyer operations may utihze heat transfer by convection, conduction, radiation, or a combination of these. In each case, however, heat must flow to the outer surface and then into the interior of the solid. The single exception is dielectric and microwave diying, in which high-frequency electricity generates heat internally and produces a high temperature within the material and on its surface. 

When a solid is dried experimentally, data relating moisture content to time are usually obtained. These data are then plotted as moisture content (dry basis) W versus time 0, as shown in Fig. 12-41 7, This curve represents the general case when a wet sohd loses moisture first by evaporation from a saturated surface on the sohd, followed in turn by a period of evaporation from a saturated surface of gradually decreasing area, ancf finally, when the latter evaporates in the interior of the solid. 

Retention of a given solids particle in the system is on the average veiy short, usually no more than a few seconds. This means that any process conducted in a pneumatic system cannot be diffusion-controlled. The reaction must be mainly a surface phenomenon, or the solids particles must be veiy small so that heat transfer and mass transfer from the interiors are essentially instantaneous. 

There is a qualitative distinction between these two types of mass transfer. In the case of vapour phase transport, matter is subtracted from the exposed faces of the particles via dre gas phase at a rate determined by the vapour pressure of the solid, and deposited in the necks. In solid state sintering atoms are removed from the surface and the interior of the particles via the various diffusion vacancy-exchange mechanisms, and the centre-to-cenU e distance of two particles undergoing sintering decreases with time. 

Surface evaporation can be a limiting factor in the manufacture of many types of products. In the drying of paper, chrome leather, certain types of synthetic rubbers and similar materials, the sheets possess a finely fibrous structure which distributes the moisture through them by capillary action, thus securing very rapid diffusion of moisture from one point of the sheet to another. This means that it is almost impossible to remove moisture from the surface of the sheet without having it immediately replaced by capillary diffusion from the interior. The drying of sheetlike materials is essentially a process of surface evaporation. Note that with porous materials, evaporation may occur within the solid. In a porous material that is characterized by pores of diverse sizes, the movement of water may be controlled by capillarity, and not by concentration gradients. 

The term P is a fictitious pressure because the cross-sectional area. A, is not equal to either the surface area of the particles or the actual contact areas. In actual cakes, there is a small area of contact. A, and the solid pressure may be defined as F /A. Taking differentials with respect to x in the interior of the cake, we obtain ... 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

Equation (15) is derived under the assumption that the amount of adsorbed component transferred by flow or diffusion of the solid phase may be neglected. This assumption is clearly justified in cases of fixed-bed operation, and it is believed to be permissible in many cases of slurries or fluidized beds, since the absolute amount of adsorbed component will probably be quite low due to its low diffusivity in the interior of the catalyst pellet. The assumption can, however, be waived by including in Eq. (15) the appropriate diffusive and convective terms. 

Figure 124 shows some details of the cell interior. The skirt is a solid Monel alloy sleeve extending about 2 cm below the electrolyte. (Teflon and Kel-F fluoropolymers could not be used as skirts for extended periods because they react with fluorine at the temperatures used they could probably be used as screens, however.) The screen (not shown) is an extension of the skirt. It consists of a Monel alloy sleeve with numerous 1-mm holes. The skirt and screen float electrically. They are bipolar and... 

Chemists were greatly surprised when soccer-ball-shaped carbon molecules were first identified in 1985, particularly because they might be even more abundant than graphite and diamond The C60 molecule (10) is named buckminsterfullerene after the American architect R. Buckminster Fuller, whose geodesic domes it resembles. Within 2 years, scientists had succeeded in making crystals of buckminsterfullerene the solid samples are called fullerite (Fig. 14.32). The discovery of this molecule and others with similar structures, such as C70, opened up the prospect of a whole new field of chemistry. For instance, the interior of a C60 molecule is big enough to hold an atom of another element, and chemists are now busily preparing a whole new periodic table of these shrink-wrapped atoms. 

In terms of applications, TPE industries will remain closely linked with the motor vehicle industry. The solid gains forecast for TPEs in this market are due to the development of new products for exterior (e.g., body seal) and interior (e.g., instrument and door panel skins) applications at the expense of EPDM and thermoplastics such as PVC [278]. The new environmental... 

Consider the surface of a solid. In the interior, we see a certain s mmetry which depends upon the structure of the solid. As we approach the surface from the interior, the symmetry begins to change. At the very surface, the surface atoms see only half the symmetry that the interior atoms do (and half of the bonding as weU). Reactions between solids take place at the surface. Thus, the surface of a solid represents a defect in itself since it is not like the interior of the solid. 

The fact that the photon does traverse the lattice planes does not mean that the photon wUl be absorbed or even scattered by the solid. The reflectance of the photon is a function of the nature of the compositional surface, whereas absorption depends upon the interior composition of the solid. A "resonance" condition must exist before the photon can transfer energy to the solid (absorption of the photon), hi the following, we show this resonance condition in general terms of both R A. 

A thin slab of solid material dries first by evaporation from the top surface and then by diffusion from the interior of the solid. The water movement is approximated by the diffusion equation... 

In a study on the thermal and UV ageing of two commercial polyfoxymethy-lene) (POM) samples, one of which was a copolymer (see related study discussed later under Section 4.3, thermogravimetric analysis (TGA)), used in car interior applications, involving both DSC and TGA, isothermal OIT measurements were made at several different temperatures [8]. One conclusion from this study was that "extrapolation of the OIT data from high temperatures (molten state) to ambient temperatures in the solid state does not reflect effective antioxidant performance at room temperature", and thus measurements close to the melting point are not appropriate for reliable lifetime estimations. 

The wicking of liquid into a porous solid is also of importance. Excessive wicking may give rise to a coat of varying thickness. Furthermore, to produce a coat of the desired thickness, additional coating material may be required due to the loss of coating into the particle interior. 

---