Layered crystals, electron microscopy

Small needle-shaped single crystals were examined by transmission electron microscopy (TEM) and electron diffraction (ED) (see Fig. 16-17). The results show that the crystals are elongated along the b-axis, which is the direction of weak intermolecular n-n interactions, and have a well-developed (ab) top surface. It corresponds to the surface of aliphatic tails (direction of weak intermolecular interactions). There are indications of displacement of successive ( / )-laycrs along the fl-axis, in line with the other signs of disorder in the aliphatic layer. 

On the basis of crystallochemistry consideration and taking into account electron microscopy observations of the surface of crystals upon which some polymer was formed,99 Arlman and Cossee13 concluded that the active sites are located on crystal surfaces different from the basal (001) ones. In particular, these authors considered in detail active sites located on crystal surfaces parallel in the direction a — b of the unit cell defined as in Ref. 98. Figure 1.13 illustrates that, if we cut a TiCl3 layer parallel to the direction defined above, which corresponds to the line connecting two bridged Ti atoms, electroneutrality conditions impose that each Ti atom at the surface of the cut be bonded... 

Although when examined using optical or even electron microscopy, crystal surfaces appear smooth, this is rarely the case. Techniques such as AFM and STM and optical interference methods (see Chap. 7) show that both growth and cleavage surfaces consist of terraces separated by steps which can be as little as one atomic layer... 

Epitaxial growth of overlayer on the plane is envisaged in the field of material physics. Epitaxy of a relatively thick layer measurable In microns Is explained primarily by the matching of crystal planes. We assume a similar epitaxy for the deposition of silica on the external surface of zeolites, although direct observation by electron microscopy is extremely difficult. 

Monoglycerides and mono-diglycerides have low HLB values and cannot form micelles. They build up a multi-layer at the surface, resulting in a constantly decreasing surface tension as their concentration increases. However, in systems with proteins such as fat-free ice cream mixes, these emulsifiers behave as if they have a CMC. A possible explanation for this observation is that the unbound emulsifier in the fat-free mix is in equilibrium with the protein-bound emulsifier. Above a certain concentration of emulsifier in the mix, any surplus of emulsifier will adhere to the protein in the water phase after the surface has been saturated. The unadsorbed emulsifier is seen as very small crystals less than 200 nm by electron microscopy analysis4. ... 

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