Self-Nucleation Behavior

The technique of self-nucleation [75] can be very useful to study the nucleation and crystallization of block copolymer components, as already mentioned in previous sections. In block copolymers, factors like the voliunetric fraction and the degree of segregation affect the type of confinement and therefore modify the self-nucleation behavior. In the case of semicrystalline block copolymers, several works have reported the self-nucleation of either one or both crystallizable components in PS-fc-PCL, PS-h-PB-h-PCL, PS-h-PE-fo-PCL, PB-fo-PIB-fo-PEO, PE-fo-PEP-fc-PEO, PS-fc-PEO, PS-h-PEO-h-PCL, PB-fo-PEO, PB/PB-fc-PEO and PPDX-fo-PCL [29,92,98,99,101-103,134] and three different kinds of behavior have been observed. Specific examples of these three cases are given in the following and in Table 5  

Several block copolymer systems have shown only domains 1 and III upon self-nucleation. This behavior is observed in confined crystalhzable blocks as PEO in purified E24EP57EOi9 [29]. Crystallization takes place for the PEO block at - 27 °C after some weak nucleating effect of the interphase. Domain II is absent and self-nucleation clearly starts at Tg = 56 °C when annealed crystals are already present, i.e., in domain III (Fig. 17b). The absence of domain II is a direct consequence of the extremely high 

In those cases where the injection of self-nuclei in every MD is most difficult in view of the very large number of MDs, domain III is split into two domains. Evaluation of the self-nucleation of the PE block within SasEisCso shows that not only domain II is absent, but upon decreasing Ts, the PE block is annealed before any detectable self-nucleation occurs (Eig. 17c). Therefore two subdomains were defined [98] domain IIIa, where annealing without previous self-nucleation occurs and domain IIIsa, where self-nucleation and annealing are simultaneously observed for Ts 88 °C. Domain IIIsa would be the exact equivalent to the standard domain III established by Fillon et aL [75]. 

Avrami indexes of the order of 1 or lower) unless the crystallization occurs at temperatures very close to the Tg of the crystallizing phase. 

Chen et al. [92] also performed self-nucleation experiments by DSC in PB-fo-PEO diblock copolymers and PB/PB-fc-PEO blends. The cooling scans presented in their work showed that a classical self-nucleation behavior was obtained for PEO homopolymer and for the PB/PB-fo-PEO blend where the weight fraction of PEO was 0.64 and the morphology was lamellar in the melt. For PB/PB-fo-PEO blends with cylinder or sphere morphology, the crystallization temperature remained nearly constant for several self-seeding temperatures evaluated. This observation indicates that domain II or the self-nucleation domain was not observable for these systems, as expected in view of the general trend outlined earlier. 

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Table 5 Self-nucleation behavior for diblock and triblock copolymers ...

Fig. 17 a Classical self-nucleation behavior for polyethylene (PE) within E18EP57EO25133 triblock copolymer [101]. b Self-nucleation behavior for PEO within purified E24EP57EO1964 triblock copolymer [29], c Self-nucleation behavior for PE within S35E15C50219 triblock copolymer [29,98]. (a, c from [98,101] with permission, b Reprinted with permission from [29], Copyright 2002 American Chemical Society)... 

Figure 5.5 presents the self-nucleation behavior of an isotactic polypropylene (PP). Figure 5.5a shows the cooling runs after thermal conditioning at the indicated temperatures and Figure 5.5b shows the subsequent heating scans. 

This equation represents a simple way to quantify the nucleating action of an additive in relative terms to its self-nucleation behavior. 

SCH Schwalm, D., Richter, D., Wight, P.J., Symon, C., Fetters, L.J., and Lin, M., Self-assembhng behavior in decane solution of potential wax crystal nucleators based on poly(co-oleGns), Macromo/ecu/es, 35, 861, 2002. 

In order to obtain an ideally nucleated polymer, it is heated to just above its melting point so that large number of residual crystal fragments exist in the melt and act as nuclei. This method is referred to as self-seeding or self-nucleation (Blundell 1966). Zhao et al. have evaluated crystallization behavior of propylene/ethylene copolymer by self-seeding approach (Zhao et al. 2001), which was found in good agreement with the earlier published DSC data (Laihonen et al. 1970,1997). 

The inverse problems discussed in Sections 6.1 and 6.2 were addressed in the absence of nucleation and growth processes. In this section we investigate inverse problems for the recovery of the kinetics of nucleation and growth from experimental measurements of the number density. It is assumed, however, that particle break-up and aggregation processes do not occur. Determination of nucleation and growth rates is of considerable practical significance since the control of particle size in crystallization and precipitation processes depends critically on such information. We will dispense with the assumption of self-similar behavior, as it is often not observed in such systems. Also, we provide here only a preliminary analysis of this problem, as it is still in the process of active investigation by Mahoney (2000). 

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