Breakout crystallization

Zhu et al. and Huang et al. employed a block copolymer/homopolymer system (poly(ethylene oxide)-h-polystyrene/polystyrene) in order to study the crystallization of PEO under hard and soft confinement [180, 244]. In a related work, Xu et al. prepared blends of poly(oxyethylene)-h-poly(oxybutylene) and polystyrene/poly(oxybutylene) and compared confined versus breakout crystallization [249, 308]. Guo et al. studied a block copolymer/thermoset blend constituted by poly(ethylene)-h-poly(ethylene oxide)/bisphenol A type epoxy resin. The authors reported the nanoconfinement effect on the crystallization kinetics of the PE block [309]. 

The block copolymers with cylindrical microdomains also show confined and breakout crystallization and the expected crystallization kinetics. There is, however, an intermediate region for this class of copolymer. In this region small-angle x-ray scattering patterns indicated that the crystallization was confined to the cylindrical domains, yet sigmoidal type kinetics resulted.(65) This intermediate rate region is defined approximately by 1.5 < (xM)c/(xM)odt- Here, so-called templated... 

Weakly segregated systems, Todt > Tc > Tg with soft confinement. In this case, crystallization often occurs with little morphological constraint, enabling a breakout from the ordered melt MD structure and the crystallization overwrites any previous melt structure, usually forming lamellar structures and, in many cases, spherulites depending on the composition [10-18],... 

From this section we can summarize the general behavior of confined crystallizable MDs. These generalizations apply to block copolymers that are in the strong segregation regime and that can crystallize within their specific MD without breakout. When a block copolymer component crystallizes within isolated MD structures like spheres, cylinders or lamellae it may nucleate homogeneously. For homogeneous nucleation to take place, several requirements should be met ... 

Ueda et al. [26] recently investigated a flow-oriented PE-fr-aPP diblock copolymer with Mw = 113 000 (Mn/Mw = 1.1) and a PE volume fraction of 0.48. This diblock copolymer is in the strong segregation regime (i.e., estimated xN = 10.5 and Todt = 290 °C) and has a lamellar morphology in the melt. They found a breakout phenomenon with the formation of spherulites in an intermediate crystallization temperature range 95 < Tc < 101 °C. At crystallization temperatures above 101 °C or below 95 °C spherulites were not formed and the crystallization was confined within the lamellar MD. Ueda et al. report that lamellar MD and spherulites do not co-exist when the material crystallizes from the melt which is separated in lamellar MDs. In other words, in this particular case, breakout or confined crystallization within lamellar MDs depends on the crystallization conditions. 

Any secondary explosive can be used over the bridge, but in practice only PETN is used, usually pressed to 50% crystal density ( 0.88 g/cm ). In most cases, an output pellet of higher density is added over the PETN initial pressing to enhance the breakout pressure. 

Weakly segregated systems (low xN values) Tour The crystallization destroys previous melt structure (by breakout) and crystalline lamellae are formed... 

Loo Y.-L., Register R. A., and Ryan A. J. (2002) Modes of crystallization in block copolymer microdomains Breakout, templated, and confined. Macromolecules 35 2365-2374. 

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