Phase Behavior and Rhythmically Grown Ring-Banded Spherulites in Blends of Liquid Crystalline Poly(aryl ether ketone) and Poly(aryl ether ether ketone)

Abstract

Phase behavior and rhythmically grown ring-banded spherulites in thin films of liquid crystalline poly(aryl ether ketone) (LC-PAEK) and poly(aryl ether ether ketone) (PEEK) blends have been investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and electron diffraction (ED) techniques. The results show that the composition of the blends has great effect on the phase behavior and structure. Thin films of pure LC-PAEK and PEEK crystallized from the melts exhibit typical mosaic and spherulitic structures, respectively. For the blends with higher LC-PAEK contents (>50%), the two components are miscible at the molecular level in the melting state, and a phase separation takes place during the cooling process, as a result of the competition between the phase separation and the LC-PAEK phase transition, resulting in an unusual ring-banded spherulite. The bright core and rings of the ring-banded spherulites under PLM are composed of the LC-PAEK phase, while the dark rings consist of a coexisting phase of PEEK with part of LC-PAEK. The formation of the ring-banded spherulites is attributable to structural discontinuity caused by a rhythmic radial growth. For the 50:50 LC-PAEK/PEEK blend, the ring-banded spherulites and individual PEEK spherulites coexist, which implies that a partial phase separation between the two components takes place in the melting state. In PEEK-rich blends, LC-PAEK is rejected into the boundary of PEEK spherulites. In addition, the effect of cooling rate and crystallization temperature on the phase behavior, especially the ring-banded spherulite formation in the blends, is discussed.

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) and poly(aryl ether ether ketone)

“…A similar phenomenon was also observed in our previous work on chloro‐poly(aryl ether ketone)/PEEK blends (see Fig. 2 in ref 18…”

“…In our previous works,17, 18 we have reported the phase behavior, morphology, and miscibility of the liquid crystalline chloro‐poly(aryl ether ketone)/PEEK blends, especially paying much attention on formation and development of the ring‐banded spherulite in the blends. The unusual concentric ringed structure can be found in thin films of chloro‐poly(aryl ether ketone)‐rich blends, which is different from the classical extinction bands in spherulites of polymers based on periodic twisting of lamellae along the radial growth direction of the spherulites 19–31.…”

Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review

“…Figure 3 give the typical examples to display the optical features and corresponding radial lamellar organizations of the two different types of polymer ring-banded morphologies, where Figure 3a,b are the CEBS of poly(trimethylene terephthalate) (PTT) and the non-birefringent concentric-ringed spherulites (ZBCRS) of isotactic polystyrene (iPS), respectively [33,34]. It should be noted that some extinction banded spherulites of polymer blends also possess an origin of the structural discontinuity deriving from an alternative stacking of lamellar crystals and the blended amorphous materials [35][36][37]. Unexpectedly, the two different kinds of ring-banded morphologies were seldom encountered in the same polymer as the crystallizable object.…”

Study on the crystal morphology and melting behavior of isothermally crystallized composites of short carbon fiber and poly(trimethylene terephthalate)

“…In general, the final properties of a polymer or its composite have close relationship with its crystallinity, crystal morphology, and crystal texture; so, it is very important to study the crystallization behavior of the system. It is generally believed that the extinction bands in banded spherulites are due to the periodic twisting of the lamella along the radial growth direction of the spherulites [6,8]. Chuang et al [6] studied the PTT spherulites during isothermal crystallization.…”