ABSTRACT:The morphology and melting behavior of poly(e-caprolactone)-block-polystyrene (PCL-b-PS) copolymers, quenched from the melt or cast from the toluene solution, were investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) as a function of copolymer composition. The glass transition temperature of PS blocks is higher than the melting temperature of PCL blocks, T m.Pcu in this system, so that the molecular motion is extremely restricted when the PCL block crystallizes in temperatures below Tm.PCL· DSC results showed that the quenched PCL-b-PS did not crystallize at any temperature when PCL vol%, rf>PcL• was less than 26%, whereas it crystallized partially when and the crystallinity increased with increasing rf>PcL• suggesting that rf>PcL affects significantly the crystallizability of PCL blocks. However, crystallization was observed for all PCL-b-PS copolymers cast at 20°C, and the crystallinity decreased appreciably with increasing the casting temperature. SAXS results revealed that high crystallinity PCL-b-PS copolymers had an intensity peak arising from the lamellar morphology, an alternating structure consisting of crystalline lamellae and amorphous layers, whereas low crystallinity PCL-b-PS copolymers did not show any SAXS peak, indicating the morphological difference among crystallized PCL-b-PS copolymers. The morphology formed in PCL-b-PS is discussed as a function of rf>PcL in terms of the lamellar morphology observed for crystalline homopolymers.KEY WORDS Crystalline-Amorphous Diblock Copolymer I Morphology I Crystallization I Glass Transition IThe crystallization of block copolymers is very complicated since it starts from a homogeneous state or various microdomain structures existing in the melt. When the microdomain structure is weakly segregated, subsequent crystallization destroys this structure to result in a lamellar morphology, an alternating structure composed of crystalline lamellae and amorphous layers. 1 -10 This means that the driving force of crystallization is much larger than the stability ofmicrodomain structures. The lamellar morphology in equilibrium has been experimentally investigated 1 • 3 • 8 and also theoretically predicted, 11 • 12 in which crystalline blocks are folded rather than extended to accommodate amorphous blocks between lamellae. When the molecular weight of block copolymers increases, the stability of microdomain structures increases and subsequent crystallization cannot destroy these structures, and eventually the constituent block crystallizes without a morphological reorganization. 13 -16 The glass transition of amorphous blocks is another factor to enhance the stability of microdomain structures. That is, the crystalline block cannot move freely when it crystallizes in the bulk since the amorphous block, linked with the crystalline block by the covalent bond, is anchored into glassy regions. Crystallization is, therefore, extremely restricted and may occur, for example, within the microdomain structure. In other wo...

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In 0:53 Ga 0:47 As/GaAs 0:5 Sb 0:5 type-II multiple-quantum-well (MQW) light-emitting diodes were grown on (111)B InP substrates by molecular beam epitaxy. The peak wavelength of the electroluminescence (EL) was at 2.08 m at 11 K and at 2.28 m at 300 K. It was found that the EL intensity of the type-II MQW diode on (111)B substrates was about one order of magnitude stronger than that on (100) InP substrates, which can be explained by the improved crystal quality of the MQW diode on the (111)B InP substrate.

Coupling between a planar waveguide (PWG) mode in an organic single crystal and a surface plasmon polariton (SPP) mode is investigated in this paper. Anticrossing behavior appearing under the strong coupling regime was observed in the dispersion curves of the coupled modes. Although previous studies have utilized spin-coated organic waveguides, to date, there have been no reports on the use of single-crystalline waveguides. The so-called Fano line shapes have been observed in spectra in numerous studies related to PWG−SPP coupled systems, which are expected to find utility in surface plasmon resonance sensors. Meanwhile, transitions from Fano line shapes to Rabi splitting have been observed with increase in coupling and have attracted considerable attention in fundamental physics. As organic single crystals exhibit strong optical anisotropy, the influence of directional dispersions on coupling strength is expected to be significant. In the present study, we have developed angle-resolved transmission microspectroscopy that enables optical measurements of an organic single crystal with an in-plane dimension of hundreds of micrometers even in the nonradiative region. Because measuring such a small sample using conventional attenuated total reflection measurements is difficult, the transmission spectra in the nonradiative region were measured by rotating the sample in index-matching oil. Accordingly, dispersion curves reflecting the coupling between the PWG and SPP modes were obtained.

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