Induced nuclei

Fig. 14 A sequence of AFM phase images of a BA-C8 film obtained at room temperature showing the formation and growth of induced nuclei. The time interval between each consecutive image is approximately 5.8 min [61]...

The appearance and disappearance of some of the induced nuclei suggest that they are formed at the surface as a result of a trapped polymer chain in the parent lamellae. In addition when a polymer crystallizes very quickly, stresses... 

Fig. 17 AFM phase image obtained on a BA-C12 film. Three induced nuclei are observed at about 15 nm away from the parent lamella [83]...

The flow-induced nuclei number takes the following form as suggested by Eder and Janeschitz-Kriegl (1997) ... 

One form of spherulite nucleation is illustrated in Figure 3.61. The single lamella in the first image (a) contains an induced nucleus that appears as a barely visible dot slightly below the midpoint. From this grow two lamellae in panel (b). As these new lamellae are on the same side of the parent lamella, they do not correspond to a screw dislocation. Additional induced nuclei... 

Figure 3.61 Formation of a small lamellar stack in PBA-C8 at room temperature. A I M images are at time intervals of 10.6 minutes. New lamellae are formed by induced nuclei that are just visible as dots at this resolution in panels (a) and (c). Each image is 3 pm wide. From Lei et al. [89] with permission of Elsevier.

The real number of flow-induced nuclei per unit volume A/eai and the real total shish length per unit volume Ltot,reai cau be found directly with the following expressions ... 

Custodio et al. [74] added the parameter 5 to circumvent numerical problems. They did not adopt the dependence of the characteristic nucleation time on the strain rate from Steenbakkers and Peters [135] (see Table 14.1), but instead they took Zp = 0 under all conditions. The reptation and Rouse times of the HMW fraction were made linearly dependent on the number density of flow-induced nuclei. The parameter 6 was set to one for all nonzero strain rates and to zero when the strain rate was zero. Thus, no more nuclei are created after the flow stops, mimicking the model of Steenbakkers and Peters. 

Figure 14.13 Distribution across half of the normalized slit thickness of the total shish length Lioifsai, the number of flow-induced nuclei per unit volume and the average shish length for ail MPR flow conditions [74].

A major interest of the differential forms is that they are more suitable for numerical simulation. Both Schneider et al. [66] and Haudin and Chenot [67] approaches have been extended to integrate flow effects [68, 69]. Flow introduces additional nuclei. Two types of morphologies can be considered spherulites (point-like nuclei) or shish-kebabs (thread-like nuclei).The number density Nf of flow-induced nuclei is given by the following type of equation ... 

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