Development of shape memory polymer materials with integrated self-healing ability, shape memory property, and outstanding mechanical properties is a challenge. Herein, isophorone diisocyanate, polytetramethylene ether glycol, dimethylglyoxime, and glycerol have been used to preparation polyurethane by reacting at 80 C for 6 h. Then, graphene oxide (GO) was added and the reaction keep at 80 C for 4 h to obtain polyurethane/GO composite with selfhealing and shape memory properties. Scanning electron microscopy shows that the GO sheets were dispersed uniformly in the polyurethane matrix. The thermal stability was characterized by thermogravimetric analyses. The tensile test shows that the Young's modulus of the composites increases from 38.57 ± 4.35 MPa for pure polyurethane to 95.36 ± 10.35 MPa for the polyurethane composite with a GO content of 0.5 wt%, and the tensile strength increases from 6.28 ± 0.67 to 15.65 ± 1.54 MPa. The oxime carbamate bond and hydrogen bond endow the composite good self-healing property. The healing efficiency can reach 98.84%. In addition, the composite has excellent shape memory property, with a shape recovery ratio of 88.6% and a shape fixation ratio of 55.2%. This work provides a promising way to fabricate stimulusresponsive composite with versatile functions.
Broadband multilayer dielectric gratings (MDGs) with rectangular HfO2 grating profile were realized for the first time using a novel fabrication process that combines laser interference lithography, nanoimprint, atomic layer deposition and reactive ion-beam etching. The laser-induced damage initiating at the grating ridge was mitigated for two reasons. First, the rectangular grating profile exhibits the minimum electric-field intensity (EFI) enhancement inside the grating pillar compared to other trapezoidal profiles. Second, our etching process did not create nano-absorbing defects at the edge of the HfO2 grating where the peak EFI locates, which is unavoidable in traditional fabrication process. The fabricated MDGs showed a high laser induced damage threshold of 0.59J/cm2 for a Ti-sapphire laser with pulse width of 40 fs and an excellent broadband diffraction spectrum with 95% efficiency over 150 nm in TE polarization.
We introduce a novel concept for the design of functional surfaces of materials: Spatial surface charge engineering. We exploit the concept for an all-solid-state, epitaxial InN/InGaN-on-Si reference electrode to replace the inconvenient liquid-filled reference electrodes, such as Ag/AgCl. Reference electrodes are universal components of electrochemical sensors, ubiquitous in electrochemistry to set a constant potential. For subtle interrelation of structure design, surface morphology and the unique surface charge properties of InGaN, the reference electrode has less than 10 mV/decade sensitivity over a wide concentration range, evaluated for KCl aqueous solutions and less than 2 mV/hour long-time drift over 12 hours. Key is a nanoscale charge balanced surface for the right InGaN composition, InN amount and InGaN surface morphology, depending on growth conditions and layer thickness, which is underpinned by the surface potential measured by Kelvin probe force microscopy. When paired with the InN/InGaN quantum dot sensing electrode with super-Nernstian sensitivity, where only structure design and surface morphology are changed, this completes an all-InGaN-based electrochemical sensor with unprecedented performance.
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