Lamellar Orientation Inversion under Dynamic Interplay between Crystallization and Phase Separation

Abstract

Crystallization dynamics and lamellar orientation are affected under the dynamic interplay between crystallization and phase separation. We carried out the experiment in a dynamically asymmetric blend of amorphous poly(methyl methacrylate) (PMMA) and crystalline poly-(ethylene oxide) (PEO). If phase separation is really weak, lamellae are normally grown in the radial direction within spherulites. Growth rate shows a bell-like curve with respect to temperature. However, when strong phase separation intervenes, the growth rate curve is characterized by double peaks, one of which is dominated by crystallization and the other by phase separation. Meanwhile, lamellae tend to orient in the tangential direction in concentric alternating structures, whose formation mechanism has been explained in previous studies. This lamellar orientation inversion is reflected by a negative to positive birefringence inversion under optical microscopy. Within lamellar stacks, more amorphous molecules tend to be pushed out under the effect of phase separation, leading to smaller long period.

Transition of spherulite morphology in a crystalline/crystalline binary blend of biodegradable microbial polyesters

“…SEM images of the blend films are illustrated in Figure 6. In these SEM polymethylmethacrylate, has been already reported [38]. However, this is the first observation of such behavior in crystalline/crystalline polymer blends.…”

“…However, this is the first observation of such behavior in crystalline/crystalline polymer blends. In the studies of spherulite crystals, such conversion indicates the formation of inordinate morphology caused by the increasing content of amorphous polymer [38] .…”

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

“…The inner and outer spherulites are templated by crystallization of different blocks. Lately, Shi et al [32] also reported a similar morphology in their study on PEG/PMMA blend and the formation was due to the different orientations of PEG crystal lamellae caused by the intervention of phase separation during crystallization process. Considering that the polymer's phase separation can also significantly affect the crystallization process of crystalline-amorphous block copolymers, double concentric spherulites may be expected to exist in crystalline-amorphous block copolymers.…”

“…Recently, Shi et al [43] reported the concentric structure which was caused by the lamellar orientation inversion of PEG crystals due to the intervention of phase separation. When phase separation occurred, due to the dynamic competition between phase separation and crystallization process, PEG lamellas tended to array along different directions and formed different spherulitic morphology forms [32,44]. As Block7800 was proved to be crystalline-amorphous, the resulting crystal morphologies can be significantly influenced by microphase separation [5,6].…”

Influence of thermal history on crystalline morphologies of isotactic polypropylene in its miscible blends with polybutene‐1

“…Further studies indicate that the extent of phase segregation depends on the relation between crystallization rate of the high T m component and the chain mobility of the low T m component . Meanwhile, primary nucleation of crystallization can be assisted by concentration fluctuation, especially at the interface boundaries of phase separated domains …”