Order-disorder transitions transition temperature

Pyruvic acid has been identified in approximately half of seventy-seVen Klebsiella species investigated. On the basis of o.r.d. measurements and their interpretation from Moffitt-Yang plots, a helical superstructure is proposed for Klebsiella capsular polysaccharides of serotypes Kl, K5, K6, K8, Kll, K56, and K57. Measurements of the temperature dependence of the specific optical rotation reveal, in all cases, co-operative order-disorder transitions at temperatures between 25 and 40 C. 

Simultaneous measurements together with small-angle X-ray or neutron scattering were performed for more than ten years, as exemplified by the studies of Okamoto et al. [146,147] and those of Bates et al. [148]. The latter examined the influence of mechanical deformation on the melt-phase behaviour of a block copolymer poly(ethylene-propylene)-6/ocA -poly(ethylethylene) (PEP-PEE), which contains 77 vol. % PEP with an overall molecular weight of 1.0 x 10 and a molecular-weight distribution with Mw/Mn = 1.07. The order-disorder transition (ODT) temperature was increased by shear deformation in the weak segregation regime, i.e. the microphase separation was induced by the... 

Thermal stahility. Yor applications of LB films, temperature stability is an important parameter. Different teclmiques have been employed to study tliis property for mono- and multilayers of arachidate LB films. In general, an increase in temperature is connected witli a confonnational disorder in tire films and above 390 K tire order present in tire films seems to vanish completely [45, 46 and 45] However, a comprehensive picture for order-disorder transitions in mono- and multilayer systems cannot be given. Nevertlieless, some general properties are found in all systems [47]. Gauche confonnations mostly reside at tire ends of tire chains at room temperature, but are also present inside tire... 

The ability of XPD and AED to measure the short-range order of materials on a very short time scale opens the door for surface order—disorder transition studies, such as the surface solid-to- liquid transition temperature, as has already been done for Pb and Ge. In the caseofbulkGe, a melting temperature of 1210 K was found. While monitoring core-level XPD photoelectron azimuthal scans as a function of increasing temperature, the surface was found to show an order—disorder temperature 160° below that of the bulk. 

Figure 6.10. Dilatotneuic record of a sample of a Ni-AI-Fe alloy in the neighbourhood of an order-disorder transition temperature (Cahn ei al. 1987).

The ternary Ge halides, MGeX3 (M = Rb, Cs X = Cl, Br, I) are polymorphic with various distorted perovskite-like (p. 963) structures which reflect the influence of the nonbonding pair of electrons on the Ge" centre. Thus, at room temperature, rhombohedral CsGel3 has three Ge-I at 275 pm and three at 327 pm whereas in the high-temperature cubic form (above 277°C) there are six Ge-I distances at 320 pm as a result of position changes of the Ge atoms (reversible order-disorder transition). Again, RbGel3 has a lemon-yellow, orthorhombic form below —92° an intermediate, bordeaux-red orthorhombic perovskite form (—92° to —52°) a black rhombohedral form (—52° to —29°) and... 

Those Warren-Cowley parameters have been determined in situ above the order-disorder transition temperature by diffuse neutron scattering. From these experimentally determined static correlations, the first nine effective pair interactions have been deduced using inverse Monte Carlo simulations. 

For example, 0 describes the temperature dependence of composition near the upper critical solution temperature for binary (liquid + liquid) equilibrium, of the susceptibility in some magnetic phase transitions, and of the order parameter in (order + disorder) phase transitions. 

Fig. 19 Raman spectra of the torsional and external vibrations of pSg at two different temperatures showing the dramatic change due to the order-disorder transition, after [146]. Spectral resolution was 0.75 cm ...

There are few reports on block-copolymeric TPE (namely, polyurethane, EVA, SBS, poly (styrene-fo-butyl acrylate) (PSBA))-clay nanocomposites also [196-199]. Choi et al. [196] studied the effect of the silicate layers in the nanocomposites on the order-disorder transition temperature of... 

FIGURE 5.17 Temperature versus G —the shear storage modulus at a frequency of 1.6 Hz for diblock copolymer poly(ethylene propylene)-poly(ethylethylene) (PEP-PEE). The order-disorder transition (ODT) calculated to be 291°C 1°C. (From Rosedale, J.H. and Bates, F.S., Macromolecules, 23, 2329, 1990. With permission of American Chemical Society.)... 

The order-disorder transition temperature is a crucial parameter for biopolymers like Shellflo-S and xanthan, as it controls both rheology and breaking sensitivity. 

A reversible succession of order-order and order-disorder transition was observed for a poly(ethylene-a/f-propylene)- -poly(ethylene-co-butylene)-b-polystyrene terpolymer, which shows at room temperature non-hexagonally packed PS cylinders. Upon heating, this system reorganizes to a hexagonally packed one, and at higher temperatures dynamic-mechanical analysis indicates the transition to the disordered state [73],... 

The order-disorder transition of a binary alloy (e.g. CuZn) provides another instructive example. The body-centred lattice of this material may be described as two interpenetrating lattices, A and B. In the disordered high-temperature phase each of the sub-lattices is equally populated by Zn and Cu atoms, in that each lattice point is equally likely to be occupied by either a Zn or a Cu atom. At zero temperature each of the sub-lattices is entirely occupied by either Zn or Cu atoms. In terms of fractional occupation numbers for A sites, an appropriate order parameter may be defined as... 

The Inden model [20] is frequently used to describe second-order magnetic order-disorder transitions. Inden assumed that the heat capacity varied as a logarithmic function of temperature and used separate expressions above and below the magnetic order-disorder transition temperature (TtIS) in order to treat the effects of both long- and short-range order. Thus for z = (T/TtIS) < 1 ... 

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