Microscopic Stmcture

This approximation, known as Vegard s laM>, accurately describes the average lattice constant (but not the microscopic stmcture ) of most ternary compounds. However, the expression for the gap must be modified by the inclusion of a quadratic tenn... 

Foams that ate relatively stable on experimentally accessible time scales can be considered a form of matter but defy classification as either soHd, Hquid, or vapor. They are sol id-1 ike in being able to support shear elastically they are Hquid-like in being able to flow and deform into arbitrary shapes and they are vapor-like in being highly compressible. The theology of foams is thus both complex and unique, and makes possible a variety of important appHcations. Many features of foam theology can be understood in terms of its microscopic stmcture and its response to macroscopically imposed forces. 

Fig. 5. Microscopic stmcture of amphibole fibers (10). Reprinted with permission.

The capacity to use visualisation as the basis for the construction ofpredictions of behaviour in respect of a given model. For example, being able to visualize the sub-microscopic stmcture of an ionic crystal so as to predict how it will cleave when subjected to an external force ... 

The large phylum Cnidaria (coelenterates), numbering about 5000 species, includes fire coral, Portuguese man-o-war, box jellyfish, sea nettle, and anemones. Despite considerable morphologic variation, all of these organisms have venom contained in microscopic stmctures like water balloons, called nematocysts. 

When explosive compounds bind to these V-shaped cantilevers, the microscopic stmctures, vvhich are about the width of a hair, bend and produce a signal. 

Thereafter, it begins to decrease again slowly and eventually becomes nearly zero beyond 0.8. The variation in the size of the DMSO clusters is opposite to that of the water clusters. This result is evidence that the microscopic stmcture in DMSO-water mixtures can vary nonlinearly with the solvent composition, exhibiting the existence of a critical value of the mixing ratios, atx 0.91-0.93, where... 

The microscopic stmcture of SMPU treated cotton was studied by SEM. The aim of this investigation was to ensure the presence of SMPU on the fabric. The macroscopic properties of the treated fabrics, such as flat appearance, crease retention and breaking strength, were then measured. The flat appearance of the fabric was measured after five cycles of washing in hot water and tumble-drying at 66 5°C. Hot air drying can activate the shape memory effects of SMPUs and therefore improve the appeararKe of the fabric (Li et al., 2005). Finally, the internal structure of the fabrics treated was studied by X-ray diffraction and Raman spectroscopy. Based on the results, a model of the reaction mechanism of these treatments on cotton fabric was proposed. 

Neutron diffraction - in particular SANS - yields information on the microscopic stmcture of the sample, proper use of H/D... 

Considering existing microscopical techniques, one can find that non-destmctive information from the internal stmcture of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstmction allows getting three-dimensional information about the internal microstmcture [1-3]. In this case any internal area can be reconstmcted as a set of flat cross sections which can be used to analyze the two- and three-dimensional morphological parameters [4]. For X-ray methods the contrast in the images is a mixed combination of density and compositional information. In some cases the compositional information can be separated from the density information [5]. Recently there has been a... 

Light microscopy allows, in comparison to other microscopic methods, quick, contact-free and non-destmctive access to the stmctures of materials, their surfaces and to dimensions and details of objects in the lateral size range down to about 0.2 pm. A variety of microscopes with different imaging and illumination systems has been constmcted and is conunercially available in order to satisfy special requirements. These include stereo, darkfield, polarization, phase contrast and fluorescence microscopes. 

The microscopic understanding of tire chemical reactivity of surfaces is of fundamental interest in chemical physics and important for heterogeneous catalysis. Cluster science provides a new approach for tire study of tire microscopic mechanisms of surface chemical reactivity [48]. Surfaces of small clusters possess a very rich variation of chemisoriDtion sites and are ideal models for bulk surfaces. Chemical reactivity of many transition-metal clusters has been investigated [49]. Transition-metal clusters are produced using laser vaporization, and tire chemical reactivity studies are carried out typically in a flow tube reactor in which tire clusters interact witli a reactant gas at a given temperature and pressure for a fixed period of time. Reaction products are measured at various pressures or temperatures and reaction rates are derived. It has been found tliat tire reactivity of small transition-metal clusters witli simple molecules such as H2 and NH can vary dramatically witli cluster size and stmcture [48, 49, M and 52]. 

In the last section we considered tire mechanical behaviour of polymers in tire linear regime where tire response is proportional to tire applied stress or strain. This section deals witli tire nonlinear behaviour of polymers under large defonnation. Microscopically, tire transition into tire nonlinear regime is associated with a change of tire polymer stmcture under mechanical loading. 

Liquid crystal phases possess characteristic textures when viewed in polarized light under a microscope. These textures, which can often be used to identify phases, result from defects in tire stmcture. Compendia of micrographs showing typical textures exist to facilitate phase identifications [37, 38]. These monographs also discuss tire origins of defect stmctures in some detail. 

Electron microscopy (see section B1.18) is very valuable in characterizing particles (see, for instance, figure C2.6.1). The suspension stmcture is, of course, not represented well because of tire vacuum conditions in tire microscope. This can be overcome using environmental SEM [241. 

The atomic force microscope (ATM) provides one approach to the measurement of friction in well defined systems. The ATM allows measurement of friction between a surface and a tip with a radius of the order of 5-10 nm figure C2.9.3 a)). It is the tme realization of a single asperity contact with a flat surface which, in its ultimate fonn, would measure friction between a single atom and a surface. The ATM allows friction measurements on surfaces that are well defined in tenns of both composition and stmcture. It is limited by the fact that the characteristics of the tip itself are often poorly understood. It is very difficult to detennine the radius, stmcture and composition of the tip however, these limitations are being resolved. The AFM has already allowed the spatial resolution of friction forces that exlribit atomic periodicity and chemical specificity [3, K), 13]. 

The most recent approach to reductive nanofabrication that can indeed constmct nanoscale stmctures and devices uses microscopic tools (local probes) that can build the stmctures atom by atom, or molecule by molecule. Optical methods using laser cooling (optical molasses) are also being developed to manipulate nanoscale stmctures. 

Optical Techniques. The most important tool in a museum laboratory is the low power stereomicroscope. This instmment, usually used at magnifications of 3—50 x, has enough depth of field to be useful for the study of surface phenomena on many types of objects without the need for removal and preparation of a sample. The information thus obtained can relate to toohnarks and manufacturing techniques, wear patterns, the stmcture of corrosion, artificial patination techniques, the stmcture of paint layers, or previous restorations. Any art object coming into a museum laboratory is examined by this microscope (see Microscopy Surface and interface analysis). 

One technique that does probe the foam stmcture directly is cryomicroscopy. The foam is rapidly frozen, and the soHd stmcture is cut open and imaged with an optical or electron microscope (14). Such methods are widely appHcable and provide a direct image of the foam stmcture however, they destroy the sample and may also perturb the foam stmcture in an uncontroUed manner during the freezing. 

Gelatin stmctures have been studied with the aid of an electron microscope (23). The stmcture of the gel is a combination of fine and coarse interchain networks the ratio depends on the temperature during the polymer-polymer and polymer-solvent interaction lea ding to bond formation. The rigidity of the gel is approximately proportional to the square of the gelatin concentration. Crystallites, indicated by x-ray diffraction pattern, are beUeved to be at the junctions of the polypeptide chains (24). 

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