Crystallinity cooling rate effect

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Other than in their mean compositions. Slow cooling produces relatively large crystals of each phase, while fast cooling produces close intergrowths textures are discussed further in Section 4.2.1. Zoning occurs readily in the ferrite (Section 2.3.1), and may also occur in the aluminate. The distribution of atoms between octahedral and tetrahedral sites in the ferrite depends on the temperature at which internal equilibrium within the crystal has been achieved (Section 1.5.1). The degree of crystallinity of both phases appears to vary with cooling rate (V3). All these effects, and perhaps others, may affect the behaviour of the interstitial material on hydration. 

Figure 13.7 Effect of cooling rate on crystalline microstructure (polarized light microscopy) of a milk fat model system (50% high-melting and 50% low-melting component of milk fat) crystallized at 25 °C and agitation rate of 200RPM. Cooling rate (a) 0.20°C/min and (b) 5.50°C/min. (From Herrera and Hartel 2000c with permission.)...

It is well established that most metallic and ionic materials undercool to approximately 80% of the equilibrium melting point before crystallisation commences. The cooling rate is also large ranging form 10 — 10 K/s. These effects may result in the formation of metastable phases as discussed in detail by McPherson for alumina. The crystalline structure formed may be influenced by a second component. For example Al Oj favours the formation of rutile form of TiO rather than anastase... 

Figure 6.17 Specific volume versus temperature curves (a) a crystalline solid with a melting point T , (b) a glass, with a glass transition temperature T, and (c) the effects of cooling rate on glass transition temperature...

The key factors influencing the purity drop phenomena are considered at first. They must be the factors which enh ce primary nucleation or growth of attached tiny crystalline particles on the seed crystals therefore a list of factors would include solution supercooling (or supersaturation), agitation speed, suspension density, mass of seed crystals, pretreatment of seed crystals, cooling rate and phase equilibria of given systems. Effects of these factors investigated in literature are examined separately. 

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