Lamellar Assembly Mechanism on Dendritic Ring-Banded Spherulites of Poly(ε-caprolactone)

The self-assembly structures of lamellae in optical ring bands have a critical effect on their optical and physical arrangements. Two different types of dendritic banded spherulites (namely ring-banded and zigzag ring-banded) are formed in poly(ε-caprolactone)/poly (phenyl methacrylate) blend at crystallization temperatures of 42 and 46 °C, respectively. The difference in optical birefringence of ring bands in two types of spherulites is resolved by means of direct morphological comparison. Banded spherulites are fractured carefully to facilitate lamellar orientation analyses of both the top surface and the interior surface. The results have revealed the existence of tree-like dendritic fractal growth lamellar assemblies in both banded spherulites. The optical ring patterns of the banded spherulites are differentiated mainly by the fractal orientation of the edge-on crystal branches in the ridge region. On the basis of detailed morphological analysis, 3D-lamellar assembly mechanisms are proposed to explain the growth of dendritic ring-banded spherulites at 42 °C and dendritic zigzag ring-banded spherulites at 46 °C.

Formation of well-organized, concentric-ringed spherulites of four-arm star symmetric PEO-b-PCL via confined evaporative crystallization

Toluene solvent-assisted topology confinement facilitates PCL block templated rhythmic crystallization into concentric-ringed spherulites of star symmetric P(EO_2.5k-b-CL_2.7k)₄.

Formation of aligned periodic patterns during the crystallization of organic semiconductor thin films

Self-organizing patterns with micrometre-scale features are promising for the large-area fabrication of photonic devices and scattering layers in optoelectronics. Pattern formation would ideally occur in the active semiconductor to avoid the need for further processing steps. Here, we report an approach to form periodic patterns in single layers of organic semiconductors by a simple annealing process. When heated, a crystallization front propagates across the film, producing a sinusoidal surface structure with wavelengths comparable to that of near-infrared light. These surface features initially form in the amorphous region within a micrometre of the crystal growth front, probably due to competition between crystal growth and surface mass transport. The pattern wavelength can be tuned from 800 nm to 2,400 nm by varying the film thickness and annealing temperature, and millimetre-scale domain sizes are obtained. This phenomenon could be exploited for the self-assembly of microstructured organic optoelectronic devices.