Physical columnar phases

Figure 7. The intercolumn separation d in the columnar phases of HHTT plotted versus temperature, showing the negative coefficient of thermal expansion. ( ) Heating mode (O) cooling mode. (From Fontes et al. [18], reproduced by permission of the American Physical Society).

Transmission photomicrograph of freely suspended strands of triphenylene hexa-n-dodeconate in the tilted columnar phase, whose structure is illustrated below the photomicrograph. (Kcture and illustrations are reproduced from Reference 75 with the permission of American Physical Society Publishing.)... 

Separation of the components, or solutes, of a sample results from differences in their rates of adsorption, solution, or reaction with the mobile and stationary phases. In the light of these observations distinguishing the numerous chromatographic techniques only on the basis of specification of the physical states of the stationary and mobile phases is inadequate, and a more adequate classification of these techniques must additionally also take into account (i) the nature of the separation e.g. adsorption, and (ii) the configuration of the system e.g. columnar. Table 4.4 gives a system of classification which incorporates these considerations. 

Fig. 12 Configurations of a hexabenzocoronene dodecyl derivative in the columnar herringbone phase at 300 K (a) and the hexagonal one at 400 K (b). Reprinted with permission from [151], Copyright 2008, American Institute of Physics...

Figure 24. Proposed structure of the iodine-doped columnar (D d) phase of HHTT. The molecular cores are assembled in columns with short-range intracolumnar order and long-range hexagonal intercolumnar order. The black spheres in sets of three represent Ij ions, which are assumed to occupy the space between the columns in a disordered fashion. For the sake of clarity, the liquid-like tails filling the space between the columns ate not shown in the diagram. (From Vaughan etal. [85], reproduced by permission of the American Physical Society).

Substances by disk or bow-shaped molecules are formed of a flaf or cone-shape aromatic core surrounded by several peripheral aliphatic chains as shown in Figure 1.8. It is clear that the column is built with the same constraints as the lamellae in a smectic the cores are parallel, a segregation between chains and cores takes place, and the paraffins are in a melted state, which insures the decoupling between adjacent columns. In comparison between the columnar and smectic phases, we note that the weight of fhe chains is much larger fhan in smectics, and fhe physical properties are more governed by the behavior of fhe chains fhan by fhe ordering of fhe cores inside the columns. 

The experimental-theoretical study of mesophase formation in amphiphilic systems emphasizes the basic chemical, physical, and materials science aspects of the systems. The most commonly discussed mesophases, beyond the simple micelles discussed in Chapter 4, are lamellar aggregated micellar (packed in various cubic and hexagonal close-packed arrays), columnar or ribbon phases (rod-shaped micelles stacked in a two-dimensional hexagonal or rectangular array) microemulsions, and the cubic bicontinuous mesophases. The experimental techniques normally used to identify these mesophases are NMR Uneshape analysis, diffusion measurements, smaU-angle neutron and X-ray scattering, and optical texture analyses. In addition, reconstraction of electron density profiles and very low temperature transmission electron microscopy (TEM) have been used to elucidate the details of these mesostractures. 

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