Solid-state ordering

Even when complete miscibility is possible in the solid state, ordered structures will be favored at suitable compositions if the atoms have different sizes. For example copper atoms are smaller than gold atoms (radii 127.8 and 144.2 pm) copper and gold form mixed crystals of any composition, but ordered alloys are formed with the compositions AuCu and AuCu3 (Fig. 15.1). The degree of order is temperature dependent with increasing temperatures the order decreases continuously. Therefore, there is no phase transition with a well-defined transition temperature. This can be seen in the temperature dependence of the specific heat (Fig. 15.2). Because of the form of the curve, this kind of order-disorder transformation is also called a A type transformation it is observed in many solid-state transformations. 

A difference between microcrystallite-based ultrastructure and covalently-crosslinked systems is that microcrystallites melt at specific temperatures, allowing the polymer to be fabricated by heating at modest temperatures. Subsequent cooling of the system below the crystallization temperature allows the physical property advantages of the solid state to become manifest. Liquid crystallinity is also possible if some order is retained in the molten state. Crystalline order not only adds mechanical strength, it also provides opportunities for the appearance of other properties that depend on solid state order—such as electronic conductivity. 

D. Ofer, T.M. Swager, and M.S. Wrighton, Solid-state ordering and potential dependence of conductivity in poly(2,5-dialkoxy-/j-phenylene ethylene), Chem. Mater., 7 418-425, 1995. 

By solid-state ordering, the formation of s PdAu3 (68-88A11) and of PdCu3 (78-92Cu) with the AuCu3-type structure is observed. 

Fig. 14.2 Anthracene and its native solid-state order, showing edge-to-face interactions.

Bis(tert-butylethynyl)tetracene (44) and its solid-state order. 

Fig. 14.34 (a) rubrene structure and solid-state order, showing... 

Fig. 14.35 Representative 5,6,11,12-tetrachalcogenotetracenes (top), showing the solid-state ordering and intermolecular overlap for the sulfur derivative 46 (center) and the tellurium derivative 47 (bottom).

Fig. 3.6. Solid-state order of pentacenes 29 (left), 31 (center), and 27 (right), shown with their corresponding crystallographic axes.

Scheme 3.9. Synthesis and solid-state order of perfluoropentacene 41.

Other polymers with oligo ethylene oxide) spacers have been observed. The polymers of limura and coworkers, with mesogenic structures 10 and 12 of Table 1 and spacers of di-, tri- and tetraethylene oxide, had X-ray patterns in the melt that were virtually identical to those of the solid This result was also observed for Polymer 37 with a tetraethylene oxide spacer prepared by us Such patterns are consistent with a smectic E mesophase which maintains much of the solid state order in the liquid crystalline melt. 

It was shown that VT Si CP/MAS NMR chemical shifts (S), Si-relax-ation times (Ti) and calculated Si-shielding constants (cr) are very useful in studying the solid-state order-disorder transitions in the polysilanes. 

Anthony, J.E., Brooks, J.S., Eaton, D.L., and Parkin, S.R., Functionalized pentacene Improved electronic properties from control of solid-state order, J. Am. Chem. Soc., 123, 9482, 2001. 

Figure 1.63. Possible structures for the solid-state ordering of substituted poly(para-plienylene ethynylene)s (a) for side chains of uniform length (b) for alternating short and long side chains. Left viewed down the conjugated main-chain axis right viewed down the tr-stacking axis, (Reproduced from ref 369 with kind permission. Copyright (1995) American Chemical Society. Adapted from ref 370, Copyright (1989) American Chemical Society.)...

The position of the emission maximum (575 nm) is indistinguishable in HHTT and HT polymers, while Yamamoto s regiorandom polymer of the same constitution (16a) shows emission maxima at 529 and 558 nm in the solid state. Again, solid-state ordering must be the explanation for these differences in emissive behavior. 

Solid-state ordering of rigid-rod polymers generally obeys Neher s rule," which states that hairy rigid... 

P. Anilkumar and M. Jayakannan, Single-molecular-system-based selective micellar templates for polyaniline nanomaterials control of shape, size, solid state ordering, and expanded chain to coillike conformation. Macromolecules, 40, 7311-7319 (2007). 

Another area where structural energy calculations can be of great utility concerns the solid-state order-disorder transformation. Such transformations can be induced by pressure. At high pressures, a-quartz subsists as a metastable phase which gradually transforms to an amorphous form and, subsequently to a rutile-like crystalline structure[34]. Evidence for the onset of the amorphization has been reported at about 15 GPa from single crystal analysis[35].In powder measurements[36], the transition is observed to be complete by 35 GPa. Experiments performed on powered samples at pressures above 60 GPa indicate a crystalline structure which is thought to resemble the stishovite structure[37]. 

Dialkoxy-PPEs are very similar to the dialkyl-PPEs, but considerably less stable. While dialkyl-PPEs can be melted without decomposition, dialkoxy-PPEs tend to degrade above 120°C and no thermotropic phases have been reported, however, nematic lyotropic preparations [58] were observed. The solid state ordering of dialkoxy-PPEs is similar to that of the dialkyl-PPEs [59]. Dialkoxy-PPEs are more electron rich and show a smaller bandgap than dialkyl-PPEs, i.e., their absorption and emission are redshifted with respect to that of the dialkyl-PPEs. Mixed systems have been reported by West, but seem to show properties that are more like those of dialkoxy-PPEs than those of the dialkyl-PPEs [10]. 

It is very important to compare the solid-state order parameters based on DCs from LGCP measurements with solution-NMR order parameters from R-i relaxation and RDCs from a weakly oriented system for ubiquitin [138], because the solid-state order parameter is sensitive to motions that are on the submicrosecond scale, while the solution-NMR order parameter is sensitive to motions on the ps to ns time scale. Indeed, the solid-state NMR order parameter turns out to be generally smaller than the solution-NMR order parameter, and this inequality is easily rationalized by the difference in time scale. By contrast, many of the RDC-based order parameters are found to be very close to each other. 

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