Developing a shape memory polyurethane with high mechanical properties, excellent self-healing has become a huge challenge for the development of smart materials. Herein, we report the design and fabrication of a shape memory polyurethane network terminated with coumarin units (HEOMC-PU) to address this conundrum. The synthesized HEOMC-PU exhibits exceptional mechanical performance with a breaking elongation of 746% and toughness of 55.5 MJ•m −3 . By utilizing the dynamically reversible behavior of coumarin units to repair the damaged network, the efficient self-healing performance (99.2%) of HEOMC-PU is obtained. In addition, the prepared network and light-induced dynamic reversibility endow the HEOMC-PU with both liquid-state remoldability and solid-state plasticity, respectively, enabling polyurethane to be recycled and processed multiple times. Furthermore, based on the fluorescence responsive characteristic of coumarin, HEOMC-PU with a fluorescent pattern can be deformed into specific threedimensional configurations by combining photolithography, self-healing, and the shape memory effect. Such a multilevel and multidimensional anti-counterfeiting platform with rewritable fluorescent patterns and reconfigurable shapes can open up a new encryption approach for future intelligent anti-counterfeiting.
Nowadays, polyurethanes with multifunctional and multiple shape memory effects, especially those without the use of toxic phosgene and isocyanate, have attracted significant attention. In this work, to prepare a kind of nonisocyanate polyurethane (NIPU) with triple shape memory effect, we introduced the behenic acid (BA) with good crystallinity into the NIPUs network, which combines glass transition of the cross-linked network and crystallization-melting of behenic acid, endowing the NIPUs with two independent transition temperatures: the glass transition temperature (T g ) and crystallization melting temperature (T m ). Specifically, the NIPUs were synthesized by the addition reaction of bi-functional cyclic carbonate and semicrystalline curing agent. The bi-functional cyclic carbonate was prepared by thiol-ene click reaction, and the BA was grafted onto polyethyleneimine to prepare semi-crystalline curing agent. By adjusting the ratio of BA to PEI and curing temperature, the crystallinity of NIPU can be tuned in a wide range, so that the NIPUs has tunable and superior triple shape memory performance, and the shape recovery rate is almost 100%.
The hot spot density is increased with the result that the Raman signals of molecules absorbed on the noble metallic nanostructures can be significantly enhanced. The noble metal Ag is an ideal candidate for electromagnetic enhancement in SERS because of its excellent SPR. However, the low stability of Ag is the largest challenge for electromagnetic enhancement, as it can be easily oxidized upon exposure to air, which reduces the detection limit of SERS. The noble metal Au exhibits a high stability and good biocompatibility although its SERS activity is inferior to that of Ag. [7] Thus, dual plasmonic structures combined with Ag and Au as SERS substrates are expected to improve the stability and sensitivity of SERS.Generally, dual plasmonic structures combined with Ag and Au are achieved by the galvanic replacement reaction of Ag with Au 3+ . The random distribution and inconsistent size of Au nanoparticles (AuNPs) on the Ag surface hinder the control of the adjacent gap. As a result, their SERS sensitivity is not effectively improved. In particular, the AuNPs on the surface of Ag nanowires (AgNWs) obtained by the galvanic replacement reaction weaken the propagating surface plasmon resonance (PSPR) effect of AgNWs, which is unfavorable for a high SERS sensitivity. [8] When rigid dual plasmonic SERS substrates are applied on uneven and irregular detecting surfaces, the dual plasmonic structures are destroyed, leading to decreased SERS sensitivity and reproducibility. By contrast, dual plasmonic structures incorporated into flexible substrates have excellent mechanical properties, antidamage characteristic, portability, and tailorability, which enable the detection of target molecules on an uneven and irregular surface. [9] Therefore, the development of strategies for the fabrication of dual plasmonic structures and introduction of flexible substrates are important for the development of sensitive and reproducible SERS detection.In this study, we demonstrate a flexible dual plasmonic SERS (FDPS) substrate with high SERS sensitivity and reproducibility, which is composed of aligned AgNWs and AuNP arrays separated by a thin polyurethane (PU) layer. The FDPS substrate achieved a high SERS activity with a detection limitThe fabrication of flexible surface-enhanced Raman scattering (SERS) substrates for sensitive detection on uneven or irregular surfaces is challenging. In this study, a flexible dual plasmonic SERS (FDPS) substrate rationally constructed using Au nanoparticle (AuNP) arrays/aligned Ag nanowires (AgNWs) and elastic polyurethane (PU) is demonstrated. It exhibits high sensitivity (detection limit of 10 −8 m for melamine and 10 −10 m for malachite green) and excellent reproducibility. The well-designed structure of AuNP arrays/aligned AgNWs fabricated using block copolymer self-assembly and oil-water-air interfacial self-assembly successfully enhances the electromagnetic field through plasmonic coupling. In addition, the FDPS substrate retains a high SERS sensitivity after exposure to air at room temperat...
The low tensile strength of ethylene/α-octene co-polymer (POE) limits its application as high-strength materials. In this study, 3-amino-1,2,4-triazole (ATA) was grafted onto maleic anhydride functionalized POE (PM) by melt reaction to obtain side chains capable of forming hydrogen bonding and metal coordination bonding, and then ferric chloride hexahydrate and POE are blended with them to obtain composite materials with high strength and fracture energy. The introduction of iron-based coordination bonding and hydrogen bonding double dynamic crosslinking network endow thermoplastic elastomers with excellent mechanical strength and high toughness. Fourier transform infrared spectroscopy, rheological tests, and X-ray photoelectron spectroscopy reveal the existence of non-covalent crosslinking networks. Based on the strengthening and toughening of non-covalent dynamic crosslinking network, the tensile strength of the modified POE elastomer composites achieves 12.5 MPa along with the elongation at break of 3540%. In addition, the modified POE elastomer composites exhibit improved melt elasticity and thermal stability.
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