Orientational glasses

Below 90 K, [60]fullerene freezes into an orientational glass in which it adopts a simple cubic stmcture [19]. This low temperature stmcture can be traced to the anisotropic electronic stmcture. Alignment of the electron rich regions of... 

Poly(phenylene ether). The only commercially available thermoplastic poly(phenylene oxide) PPO is the polyether poly(2,6-dimethylphenol-l,4-phenylene ether) [24938-67-8]. PPO is prepared by the oxidative coupling of 2,6-dimethylphenol with a copper amine catalyst (25). Usually PPO is blended with other polymers such as polystyrene (see PoLYETPiERS, Aromatic). However, thermoplastic composites containing randomly oriented glass fibers are available. 

If the matrix in 3.7 was reinforced with the same volume fraction of glass but in the form of randomly oriented glass fibres rather than continuous filaments, what would be the tensile strength of the composite. The fibres are 15 mm long, have an aspect ratio of 1000 and produce a reinforcement efficiency of 0.25. The fibre strength is 2 GN/m and the shear strength of the interface is 4 MN/m". 

This technique is most useful in studying triplet carbenes since it responds to triplet states only. The carbenes are mostly generated at low temperatures (4 or 77 °K) by photolysis of diazoalkanes in a) solid solutions in single crystals or b) in randomly oriented glasses. 

Many different types of materials were later shown to exhibit aging and nonequilibrium dynamics, including polymers [91], orientational glasses [92], gels [93], and ceramic superconductors [94]. 

The information from the oriented glasses is not redundant since it suggests in broad terms the different origins of the diffuse peaks in the scattering curve. Those which are weighted... 

The orientational transition temperature goes down by about 12 K. The lattice parameter jump is less pronounced. The anomaly near the orientational glass transition (around 90 K) is smoothed out. 

Fig. 10. Pentagonal pinch mode of a C60 crystal at different pressures suggesting the formation of an orientational glass (from Chandrabhas et al. [14]).

This technique is the best one to prove the triplet multiplicity of a nitrene. The nitrenes investigated so far were always generated by photolysis of the corresponding azides at low temperatures (4 or 77 K) in randomly oriented glasses. The resulting ESR-spectra show transitions between spin states (S = 1, 0, —1) of a reactive species with two unpaired spins. The spectrum can then be described by the following equation ... 

Sulfur-fiber composites have been prepared and studied by a number of workers. Rods have been prepared (8) by passing parallel orientated glass strands through molten sulfur under vacuum to form rein-foroed bars 150 mm long and 6 mm in diameter. Glass-fiber mats have been impregnated with sulfur also, the mat being covered with powdered elemental sulfur and then placed in an oven at 185 °C for 1.5 hr so that polymeric sulfur is formed. 

Like other composite properties, the wear resistance is influenced by the orientation of reinforcing fibres. Sung and Suh found that with biaxially-oriented glass fibre and molybdenum disulphide in a PTFE matrix (Duroid 5813), the wear resistance was greatest when the highest proportion of fibre was normal to the sliding surface. The same effect was found with a graphite fibre/epoxy composite and a Kevlar fibre/epoxy composite. 

This substance also shows a transition from a liquid to a bcc plastic phase at 309 K but, unlike Freon 112, transits into a more stable ordered phase at 158 K and then a glass transition at 90 K, the same temperature as the transition of Freon 112. But, like most orientational glasses, it is rather strong. " ... 

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