The possibility of controlling light emission and propagation by exploiting periodic structures of dielectric media has attracted interest in the last decade. These photonic-bandgap materials, so-called photonic crystals, have generated considerable interest due to their wide applicability in optoelectronic and microwave devices.[1] In particular, emission control and lasing action in optically active photonic crystals can offer new applications for low-threshold lasers from small-size devices. [2][3][4] Currently an intensive effort is underway in molecular crystallography to develop photonic-bandgap materials with lattice parameters comparable to the wavelengths from visible to infrared light. This approach involves using liquid-crystalline materials that naturally form helical structures with a helical pitch in the optical-wavelength range.[5] The relevant optical property of the cholesteric phases of liquid crystals is the selective reflection of light over a range of wavelengths, that is, the photonic stop band. Previous studies have readily demonstrated that the lasing action of cholesteric liquid crystals can be attributed to the band-edge effect of the photonic stop band. These studies further explore mechanically, electrically, and chemically tunable photonic-stop-band responses [6][7][8] and a defect mode for a low-laser-threshold application. [9][10][11] Cholesteric liquid crystals can be regarded as one-dimensional photonic crystals, whereas the liquid-crystalline blue phases are three-dimensional cubic structures with lattice periods of several hundred nanometers, which give rise to selective Bragg reflections.[12] Therefore, probing light confinement in the blue phases and using them as novel molecularly assembled photonic crystals is of great interest. Although selective light reflections in the blue phases have already been studied for quite some time, [12][13][14] such three-dimensional extensions in molecular self-assembly are normally much more difficult to produce. A practical limitation of blue phases is their narrow temperature occupation (∼ 1-2°C) at the transition between the isotropic and cholesteric phases. The potential photonic application of the blue phases has been recently demonstrated by measuring the laser emission in three dimensions.[15]However, lasing action was still limited to a very narrow temperature range. Therefore, improving the temperature stability has been required for practical application of blue phases. [16,17] In this study, we describe the preparation of polymer-stabilized blue phases and the demonstration of laser emission attributed to the photonic effect of the blue-phase photonic crystal. The polymer network that forms in the blue phase leads to restriction of the deformation of the photonic crystal in a wide temperature range. We confirm the thermal stability of the polymer-stabilized blue phase by measuring laser emission over a wide range of temperature above 35°C. Pulsed excitation gives rise to laser emission with the low threshold excitation energy of a...

The deformation behavior of polythiourethane (PTU) elastomers was investigated using in situ small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and X-ray absorption fine structure (XAFS) methods. Two PTUs were prepared from poly­(oxytetramethylene) glycol, 1,4-bis­(isocyanatomethyl) cyclohexane, and 1,4-butanedithiol (PTU-B) or 1,5-pentanedithiol (PTU-P). The effect of methylene length of the chain extender on molecular aggregation structure of PTU during the elongation process was evaluated. SAXS measurement revealed that the spacing of hard segment domains of PTUs increased and decreased in the directions parallel and perpendicular to the elongation direction and showed a constant value of strain above 2. The strain calculated from the spacing of the hard segment domains for PTU-B was larger than that for PTU-P, suggesting that well-developed hard segment domains were formed for PTU-B. WAXD measurement showed that strain-induced crystallization of the soft segment occurred at around the strain of 2. XAFS measurement showed that at the strain of 2 or 3, atoms in the vicinity of sulfur became more ordered, which is confirmed by the decrement of the extended XAFS Debye–Waller factor. It seems reasonable from these SAXS, WAXD, and XAFS results that the hard segment domains orientation occurred for both PTUs during the deformation process, followed by strain-induced crystallization of the soft segment. In addition, PTU-B exhibits more ordered hard segment domains that maintain their aggregation structure upon uniaxial deformation in comparison with PTU-P.

The structure of the polymer-stabilized blue phase I with a cubic structure of the order of optical wavelength was observed by the confocal laser scanning microscope. The spacing of a striped pattern observed in the (110) plane of the polymer-stabilized blue phase I was a couple of hundred nm, which agreed to the interval of the ordered double twisted cylinders estimated based on a well-known model of blue phase I with O 8 symmetry.

Isotactic polypropylene sheets were uniaxially stretched and observed with a frequency-modulation atomic force microscope operated in phenyloctane liquid. Crystalline lamellae were seen in fibrils with their axis parallel to the stretched direction. Individual CH 3 side-chains of threefold helices were identified in the lamellae. Fragmentation of the lamellae was induced by further stretching. The real-space features observed with the microscope were successfully compared with X-ray scattering results obtained in a synchrotron radiation facility.

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