Isothermal crystallization temperatur

Turnbull and Cech [58] analyzed the solidification of small metal droplets in sizes ranging from 10 to 300 xm and concluded that in a wide selection of metals the minimum isothermal crystallization temperature was only a function of supercooling and not of droplet size. Later, it was found that the frequency of droplet nucleation was indeed a function of not only crystallization temperature but also of droplet size, since the probability of nucleation increases with the dimension of the droplet [76]. However, for low molecular weight substances the size dependence of the homogeneous nucleation temperature is very weak [77-80]. 

Figure 3 shows a plot of the volume normalized nucleation time constant as a function of isothermal crystallization temperature for PEO droplets, taken from the work of Massa and Kalnoki-Veress [84]. As expected, droplets of different volumes have the same value of r V. The inset in Fig. 3 is a plot consistent with classical nucleation theory (see Eqs. 1, 4) only the last four data points correspond to the work of Massa and Kalnoki-Veress. The first... 

Fig. 9 Inverse of the crystallization half-time as a function of isothermal crystallization temperature for PCL11 homopolymer and for the PCL block of the indicated copolymers. All experiments were performed after the PPDX block had been previously crystallized until saturation. Solid lines are fits to the Lauritzen and Hoffman theory. (From [103]. Reproduced with permission of the Royal Society of Chemistry)...

The non-isothermal crystallization dynamics were performed using DSC, employing cooling rates of 2.5, 5, 10, 20, 25, 30, 35 and 40°C/min. The isothermal crystallization dynamics were studied for each sample heated to 290 °C, with a 5 min hold time, and cooled to the isothermal crystallization temperature using a cooling rate of 200°C/min, and then holding for 40 min to obtain the crystallization exotherm. 

The effects of different rates of cooling down to isothermal crystallization temperature, different crystallization temperatures and different rates of heating during melting, on polymorph formation and transformation are easily studied by DSC. However, it is not possible unequivocally to identify polymorphs by DSC this must be done by X-ray diffractometry (Rossell, 2003 see below). 

Figure 18.7 Time evolution of degree of crystallinity of SPS of various Mw. Isothermal crystallization temperature T = 245 °C. Numbers on curves represent M of SPS...

Figure 20.2 sPS/PPE blends (75 25 wt%) at different isothermal crystallization temperatures. (a) DSC thermograms (b) WAXD patterns. Reprinted from Polymer, vol. 39, Hong B. K., Jo W. H., Lee S. C., Kim J., Correlation between melting behavior and polymorphism of sPS and its blends with PPE , p. 1793, Copyright 1998, with permission from Elsevier Science... 

Fig. 7. Schematic diagram showing the effect of cooling rate on the lamellar organization of TAG and the t,. T is the initial temperature and is the isothermal crystallization temperature.

Another, less important factor, is the isothermal crystallization temperature, T, j, when the crystallization is carried out at a constant temperamre (Table 3.16). When a crystallization experiment is performed at lower temperatures, the activation energy for nucleation of several types of heterogeneities can be overcome. At that T, j, more nuclei become active, leading to the formation of a larger number of smaller spherulites. 

The observed melting temperature of blended PP, T, appeared to linearly increase with its isothermal crystallization temperature. The experimental data could be fitted by the Hoffmann equation (see Eq. 6.6). The extrapolated values were influenced... 

Figure 7.2 Morphological phase boundary for the sPP/POE blends at several isothermal crystallization temperatures and compositions (S, A, and P correspond to single crystal, single-crystal aggregate, and spherulite of sPP, respectively).

Figure 8.6 Half-time of crystallization (tl/2) of PLLA as a function of isothermal crystallization temperature reproduced with permission from [45]. Copyright Wiley-VCH Verlag GmbH Co. KGaA.

Relaxed permittivity of PDS against time for a series of selected isothermal crystallization temperatures at a frequency of 25 kHz. 

Crystallization properties were determined using a differential scanning calorimeter (DSC, Du Pont Thermal Analyser 2000). Isothermal crystallization was carried out by heating the sample up to 200°C at a rate of 125°C/min, where they were held for 10 min to remove the previous thermal history. The specimens were then quenched to the appropriate isothermal crystallization temperature. 

Avrami exponent Tensile modulus MPa DSC and microscopy, octene-1 46 CHa/LOOOC Isothermal crystallization temperature range 319-325K 327-334 K D 1708, quenched Octene-1, density = 0.8702gcm 25mmmin draw D 412, 5mmmin draw, (octene-1, density range = 0.856-889 gcm ) 2.0 1.0 7.0 12.5 1.5-12.5 (11) (3) (5) (2)... 

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