Self-nucleation domains

The technique of self-nucleation can be very useful to study the nucleation and crystallization of block copolymers that are able to crystallize [29,97-103]. Previous works have shown that domain II or the exclusive self-nucleation domain disappears for systems where the crystallizable block [PE, PEO or poly(e-caprolactone), PCL] was strongly confined into small isolated MDs [29,97-101]. The need for a very large number of nuclei in order to nucleate crystals in every confined MD (e.g., of the order of 1016 nuclei cm 3 in the case of confined spheres) implies that the amount of material that needs to be left unmolten is so large that domain II disappears and annealing will always occur to a fraction of the polymer when self-nucleation is finally attained at lower Ts. This is a direct result of the extremely high number density of MDs that need to be self-nucleated when the crystallizable block is confined within small isolated MDs. Although this effect has been mainly studied in ABC triblock copolymers and will be discussed in Sect. 6.3, it has also been reported in PS-fc-PEO diblock copolymers [29,99]. 

Chen et al. [92] also performed self-nucleation experiments by DSC in PB-fr-PEO diblock copolymers and PB/PB-b-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-b-PEO blend where the weight fraction of PEO was 0.64 and the morphology was lamellar in the melt. For PB/PB-fr-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. 

Figure 5.6 provides a schematic diagram to illustrate at a molecular level the different self-nucleation domains. 

Self-nucleation can be used as the basis of comparison to determine the nucleation power of additives, nanofillers, or nucleating agents. This is a very useful application in order to quantify the efficiency of nucleation of a foreign additive into any polymer. The idea was proposed by Fillon et al. [34], The first step would be to self-nucleate the polymer of interest, just like in Figure 5.4, to determine its self-nucleation domains. 

DSC isothermal scans were also recorded in order to study the crystallization kinetics of PPDX after self-nucleating the sample at 117 °C. This self-nucleation temperature was determined by analyzing the self-nucleation domains and choosing an intermediate temperature within Domain II (more on the self-nucleation protocol can be found in Ref [52,60,91]). 

Figure 1 shows the DSC cooling scan of iPP in the bulk after self-nucleation at a self-seeding temperature Ts of 162 °C (in domain II). The self-nucleation process provides a dramatic increase in the number of nuclei, such that bulk iPP now crystallizes at 136.2 °C after the self-nucleation process this means with an increase of 28 °C in its peak crystallization temperature. In order to produce an equivalent self-nucleation of the iPP component in the 80/20 PS/iPP blend a Ts of 161 °C had to be employed. After the treatment at Ts, the cooling from Ts shows clearly in Fig. 1 that almost every iPP droplet can now crystallize at much higher temperatures, i.e., at 134.5 °C. Even though the fractionated crystallization has disappeared after self-nucleation, it should also be noted that the crystallization temperature in the blend case is nearly 2 °C lower than when the iPP is in the bulk this indicates that when the polymer is in droplets the process of self-nucleation is slightly more difficult than when it is in the bulk. In the case of block copolymers when the crystallization is confined in nanoscopic spheres or cylinders it will be shown that self-nucleation is so difficult that domain II disappears. 

Several block copolymer systems have shown only domains I and III upon self-nucleation. This behavior is observed in confined crystallizable blocks as PEO in purified E24EP57EO1969 [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 Ts = 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 S35E15C50219 shows that not only domain II is absent, but upon decreasing Ts, the PE block is annealed before any detectable self-nucleation occurs (Fig. 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]. 

Fillon et al. [30] have defined the so-called domains of self-nucleation for isotactic polypropylene (PP) and we will follow their definitions ... 

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