Multiple and two-way reversible shape memory polymers (M/2W-SMPs) are highly promising for many fields due to large deformation, lightweight, strong recovery stress, and fast response rates. Herein, a semi-crystalline block poly(urethane-urea-amide) elastomers (PUUAs) are prepared by the copolymerization of isocyanate-terminated polyurethane (OPU) and amino-terminated oligomeric polyamide-1212 (OPA). PUUAs, composed of OPA as stationary phase and PTMEG as reversible phase, exhibit excellent rigidity, flexibility, and resilience, and cPUUA-C7 -S25 exhibits the best tensile property with strength of 10.3 MPa and elongation at break of 360.2%. Besides, all the PUUAs possess two crystallization/melting temperatures and a glass transition temperature, which endow PUUAs with multiple and reversible two-way shape memory effect (M/2W-SME). Physically crosslinked PUUA-C0 -S25 exhibits excellent dual and triple shape memory, and micro chemically crosslinked cPUUA-C7 -S25 further shows quadruple shape memory behavior. Additionally, both PUUA-C0 -S25 and cPUUA-C7 -S25 have 2W-SME. Intriguingly, cPUUA-C7 -S25 can achieve a higher temperature (up to 165 °C) SME, which makes it suitable for more complex and changeable applications. Based on the advantages of M/2W-SME, a temperature-responsive application scenario where PUUAs can transform spontaneously among different shapes is designed. These unique M/2W-SME and high-temperature SME will enable the applications of high-temperature sensors, actuators, and aerospace equipment.
Band structures of the photonic crystal slabs play a significant role in manipulating the flow of light and predicting exotic physics in photonics. In this Letter, we show that the key features of photonic band structures can be achieved experimentally by the polarization- and momentum-resolved photoluminescence spectroscopy utilizing the light emission properties of SiNx. The two-dimensional spectra clearly reveal the energy-momentum dispersion of band structures, which is in perfect agreement with the simulation results. The isofrequency contours can be measured easily by adding a bandpass filter with a desired photon energy. Furthermore, it is convenient to observe clearly and directly the optical singularity—the optical bound states in the continuum featured by dark point in three-dimensional photoluminescence spectra. The polarization-resolved isofrequency contours clearly show that this dark point is the center of an azimuthally polarized vortex. Finally, the helical topological edge states can be easily observed in photonic topological insulators with deformed hexagonal lattices. Our work provides a simple and effective approach for exploring topological photonics and other intriguing phenomena hidden in the photonic crystal slabs.
We have determined the angular distribution of the fluorescence at 1051 nm wavelength of the Nd3+-doped monoclinic La2CaB10O19 crystal, originating from Nd3+ ions located in the regular La3+ sites, for extraordinary polarization in the XZ principal plane. We have found that the highest emission intensity does not occurs the Z-axis direction but in a −7.1° around the Y=b-axis rotated direction. With a one-pump cavity we obtained simultaneous lasing at 1051 and 1069 nm in X and Z-polarizations from Nd3+ ions located in La3+ and Ca2+ sites, respectively. In the active Q-switch regime the two laser pulses are always simultaneous. With a two-pump setup based on an optical bifurcated fiber we obtained also simultaneous lasing at 1051 and 1069 nm. The relative power of the two laser channels is tuneable with the help of a beam-splitter. An adequate value of the relative pump power of the two channels leads to simultaneous pulses in the active Q-switch regime.
Anisotropic thermally conductive composites are very critical for precise thermal management of electronic devices. In this work, in order to prepare a composite with significant anisotropic thermal conductivity, polyamide 12/styrene-acrylic copolymer-boron nitride (PA12/SA-BN) composites with macro and micro double anisotropic structures were fabricated successfully using 3D printing and micro-shear methods. The morphologies and thermally conductive properties of composites were systematically characterized via SEM, XRD, and the laser flash method. Experimental results indicate that the through-plane thermal conductivity of the composite is 4.2 W/(m·K) with only 21.4 wt% BN, which is five times higher than that of the composite with randomly oriented BN. Simulation results show that the macro-anisotropic structure of the composite (caused by the selective distribution of BN) as well as the micro-anisotropic structure (caused by the orientation structure of BN) both play critical roles in spreading heat along the specified direction. Therefore, as-obtained composites with double anisotropic structures possess great potential for the application inefficient and controllable thermal management in various fields.
The development of semi-aromatic polyamides with excellent mechanical properties has always been a popular research avenue. In this work, the semi-aromatic polyamide 12T (PA12T) with the maximum tensile strength of 465.5 MPa was prepared after stretching at 210 °C 4.6 times. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) were used to characterize the structural evolution of semi-aromatic polyamide 12T (PA12T) after stretching at different stretching temperatures and stretching ratios. The formation mechanism of this change in mechanical properties was investigated from different aspects of the aggregated structure such as crystal morphology, crystal orientation and crystallinity. The relevant characterization results show that the crystal structure, crystal orientation and crystallinity of PA12T were the highest when the sample was pre-stretched at 210 °C, which is crucial for improving the mechanical properties of PA12T. These findings will provide important guidance for the preparation of polymer materials with excellent mechanical properties.
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