Quasi-crystalline structure

Two types of swelling may occur. Surface hydration is one type of swelling in which water molecules are adsorbed on crystal surfaces. Hydrogen bonding holds a layer of water molecules to the oxygen atoms exposed on the crystal surfaces. Subsequent layers of water molecules align to form a quasi-crystalline structure between unit layers which results in an increased c-spacing. All types of clays swell in this manner. 

It may be mentioned that in 2D and 3D the possible rotations (the symmetry axes) that superimpose an infinitely periodic structure on itself are limited to angles 360°/n with n = 1, 2, 3, 4 or 6. Notice that for non-periodic, noncrystalline, quasi-crystalline structures, other symmetry axes are possible. See 3.11.3 and Fig. 3.45 on quasi-periodic crystals. 

According to X-ray investigation the lower alcohols also have partially a quasi-crystalline structure similar to that of water. 

Alkali metal halide melts are characterized by a quasi-crystalline structure originating by dilatation of the crystal structure and by the occurrence of different kinds of positional disordering. Cations and anions are preferably surrounded by ions of the opposite charge... 

Andrade,5 on the basis of the quasi-crystalline structure of liquids, deduced ... 

The quasi-crystalline structure of natural starch granules causes them to be insoluble in water at normal room temperature and gives them relative resistance to carbohydrases other than a-amylase and glucoamylase unless the granules become swollen. Three-dimensional arrangements of crystalline and amorphous zones in starch granules have been suggested (2). 

Fullerene is a promising material to be applied in membrane blocks for filtration systems because fullerene films possess a quasi-crystalline structure with pores whose dimensions are suitable for a gas separation. Our complex study is devoted to the development of a production technology of polymeric fullerene films and composite fullerene membranes and examination of their efficiency as a part of ventilation-filtration-disinfection systems. 

Skin barrier functions can be mainly attributed to the outermost layer of mammalian epidermis, the stratum corneum (SC). This region consists of dead, cornified cells embedded in a matrix of extracellular lipids, containing mainly ceramides, cholesterol, cholesterol sulphate and free fatty acids. The SC lipids are organized in a specific lamellar, quasi-crystalline structure, which is critical for optimal skin barrier homeostasis. However, formation of the lamellar structure requires presence of the lipid subclasses in a defined ratio, and ceramides by weight comprise roughly 50% of total SC lipids. The structure and formation of the epidermal lipid barrier is explained in Figure 12.15. 

It was therefore suggested that there is a possible aggregation of the domains into superdomains , similarly with the growth of spherulites in crystalline polymers, inducing formation of lamellar and fibrillar crystals (a model proposed by Kabanov [694]). Such a quasi-crystalline structure may have a characteristic period of ordering of 1 pm. 

Hydrophobic interaction. When hydrocarbons are dispersed in water, hydrophobic hydration takes place Solvent molecules in their vicinity get organized into a quasi-crystalline structure which favors hydrogen-bonding but strongly reduces their entropy [51-55]. That is why hydrocarbon chains tend to associate into a separate phase or into a complex structure, releasing water molecules in the bulk solution. 

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