Effects of Cooling Rate

Ideally, it would be preferable to operate Crystaf in conditions that fractionate the polymer chains according to their crystallizabilities at thermodynamic equilibrium in order to eliminate any crystallization kinetics effects. Practically, this idealized condition is imtenable because very long analysis times would be required. Recent investigations [29] have shown that the fractionation process in Crystaf is, in fact, very far from thermodynamic equilibrium. 

As the effect of crystallization kinetics becomes unavoidable, it is important to understand its impact on Crystaf profiles. Figme 36 shows how the Crystaf peak temperatures vary as a function of CR for three ethylene/1-hexene copolymers [29]. It is clear that the CR can have a dramatic effect on Crystaf peak temperatures even at very low CRs. The Crystaf profiles are significantly shifted to higher temperatures when slower CRs are used. Empirical linear relationships can be established between the Crystaf peak temperature of each polymer sample (Tp) and the natural logarithmic of the CR, as shown in Fig. 36. 

It is important to keep in mind that the typical CR used in Crystaf analysis, 0.1 °C/min, is in fact far from thermodynamic equilibrium. This can be easily noticed as further lowering of the CR can still significantly shift the Crystaf profiles. Notice that for sample B in Fig. 36, the peak temperature is still increasing even at the prohibitively slow CR of 0.001 C/min. Even though this should by no means be considered a limitation when comparing resins with different CCDs or measuring CCs in copolymers, it makes the development 

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Fig. 19. Effect of cooling rate on structure of a eutectoid steel. = austenitizing temperature > = austenite phase.

Haynie, F. H. and Ketcham, S. J., Electrochemical Behaviour of A1 Alloys Susceptible to Intergranular Corrosion. Electrode Kinetics of Oxide-covered Al , Corrosion, 19,403t (1963) Ketcham, S. J. and Haynie, F. H., Electrochemical Behaviour of Al Alloys Susceptible to Intergranular Corrosion. Effect of Cooling Rate on Structure and Electrochemical Behaviour in 202A Al Alloy , Corrosion, 19, 242t (1963)... 

Hodges, R. J., Intergranular Corrosion in High Purity Ferritic Stainless Steel. Effect of Cooling Rate and Alloy Composition , Corrosion, 27, 119 (1971)... 

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. 

Henry, M.A., Nodes, E.E., Gao, D., Mazur, P., Critser. J.K. (1993). Cryopreservation of human spermatozoa. IV. The effects of cooling rate and warming rate on the maintenance of motility, plasma membrane integrity, and mitochondrial function. Fertil. and Steril. 60,911-918. 

N. A. Williams, Y. Lee, G. P. Polli, and T. A. Jennings, The effects of cooling rate on solid phase transitions and associated vial breakage occurring in frozen mannitol solutions, J. Parenter. Sci. Technol., 40,135-141 (1986). 

Figure 5.64 Effect of cooling rate on Si02 polymorphic transitions. From Putnis and McConnell (1980). Reproduced with modifications by permission of Blackwell Scientific Publications, Oxford, Great Britain.

In 3.3 the effect of cooling rate on the free volume in the glassy state has been discussed. Rapidly cooled glassy polymers have a greater free volume, but they show volume retardation. This volume change, though very small, has a considerable effect on the creep behaviour all relaxation times for creep are shifted towards higher values. This phenomenon has been studied extensively by Struik (thesis Delft 1977). 

Effect of Cooling Rate on Milk Fat Crystallization and Rheology... 

Figure 7.17. Effect of cooling rate on the microstructure of milk fat cooled to 5°C slowly (0.1°C/min) (A) or quickly (5.0°C/min) (B).

Campos, R., Narine, S.S., Marangoni, A.G. 2002b. Effect of cooling rate on the structure and mechanical properties of milk fat and lard. Food Res. Int. 35, 971-982. 

Effects of cooling rate on the aluminate and ferrite phases... 

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