High-power UV Irradiation Research Articles

Enhancing the fracture toughness of aerospace-grade carbon fibre/epoxy composites by interlaying surface-activated low-melt polyaryletherketone (LMPAEK) meshes

This study proposed an innovative method for enhancing the interlaminar fracture resistance of carbon fibre/epoxy composites by incorporating structured low-melt polyaryletherketone meshes (LMPAEK) meshes. LMPAEK films were machined into structured hollow meshes and then surface-treated using high-power UV-irradiation. These treatments significantly increased the contact area and interface adhesion between the LMPAEK inserts and the composite matrix, leading to substantial improvement in the interlaminar fracture performance of the composite. Fracture test results demonstrated that the mode-I and mode-II fracture propagation energies of the LMPAEK-inserted composite at 22 °C were 1.04 times and 13.92 times higher, respectively, than those of the reference composite. Similarly, at 130 °C, their mode-I and mode-II fracture propagation energies were 1.36 times and 8.56 times higher, respectively. The remarkable fracture performance of the LMPAEK-inserted composites were attributed to the substantial plastic deformation and damage of the LMPAEK resins, which possessed exceptional mechanical properties and thermal resistance.

High Power Sunlight‐Simulated UV‐Induced Radical Polymerization: Self‐Initiation and Self‐Crosslinking

AbstractUnder high power UV irradiation, radicals can be generated from double bonds through photodissociation, H‐abstraction, or oxygen initiation mechanisms. This eliminates the need for externally added initiators in photopolymerization. This study investigates high‐power sunlight‐simulated UV‐induced free radical polymerization under various experimental conditions, including the presence of inhibitors, open or closed systems, and partial degassing. Additionally, high‐power sunlight‐simulated UV‐induced atom transfer radical polymerization is explored by externally adding CuBr2/ligand (1:2) catalyst at 100 or 1000 ppm molar concentration of copper. Delicate fabrication of real‐world thin films, coatings, and delicate 3D composites further demonstrates the high reliability and versatility of this technology.

One-step fast fabrication of multi-layer quantum dot diffusion plate for stable display and ultra-long life, a novel quantum dot packaging strategy

Quantum dots (QDs), renowned for their distinctive optical and physical attributes, are extensively employed in diverse fields such as lighting, displays, electronics, sensors, and solar cells. Nonetheless, the susceptibility to light, oxygen, and moisture is a major obstacle to the development of QDs. Achieving simple, efficient, and universal modification or encapsulation for enhanced stability remains a challenge. Herein, a one-step fast fabrication of multi-layer quantum dot diffusion plate (QD-DP) with excellent barrier and optical properties was proposed, which is alternately stacked by MS-EVOH and MS-QDs layers. The barrier phase morphology undergoes a fiber-flake transition induced by the bidirectional tensile force field during multiplication, and layer-by-layer encapsulation synergistically enhances the barrier performance, photo-oxygen stability, thermal-oxygen stability, and fluorescence lifetime of QD-DP in backlight applications. Under high-power UV irradiation, the fluorescence intensity ofMS/MS-QD 128L dropped to 90 % (T90) in only about 10 minutes, while the T90 of MS-E/MS-QD 128L was close to 216 hours, improved more than 1200 times. Concurrently, the quantum dot diffusion plate (QD-DP), characterized by an alternating multi-layer structure, demonstrated an elevated backlight color gamut value of ∼ 120 % NTSC, outperforming conventional quantum dot light emitting diodes (QLED). Compared with existing QDs backlight modules, a simpler structure, more efficient preparation process, and longer fluorescence lifetime of QD-DP were achieved.Moreover, unlike prevalent modification or packaging technologies that only target specific QD types, our alternating multilayer coextrusion packaging technology is applicable to all kinds of QDs and is simple, efficient, and universal.It was believed that this work could provide new opportunities for all kinds of QDs encapsulation and application in many fields and will be the dawn of large-scale commercialization of QDs.

The development of high performance hybrid joints between epoxy composites and PEEK/PPS composites: The mode-II and mix mode-I/II fracture behaviour

The development of effective methods for the bonding of Poly-etherether-ketone (PEEK) and Polyphenylene-sulphide (PPS) composites to thermoset composites is appealing to expand their applications in aerospace industry. Herein, the surfaces of PEEK and PPS composites were treated by a high-power UV-irradiation technique for 6 s, that proved to significantly improve their intrinsically low surface activities. Carbon fibre reinforced epoxy composites were then directly cured onto the PEEK and PPS composites with or without an aerospace film adhesive at the joining interfaces. The mode-II and mix mode-I/II fracture behaviour of the hybrid joints were studied using an end notched flexural test and a fixed-ratio mixed-mode test, respectively. It was observed that the failure of the hybrid joints without adhesives mainly took place at the joining interfaces. In this case, the lack of resins at the fracture plane resulted in relatively low fracture toughness. Encouragingly, a cohesive failure was observed for the hybrid joints with adhesives in all the cases, owing to the enhanced adhesion between the adhesive and the PEEK/PPS composites upon the UV-treatment. This phenomenon indicated that optimal fracture resistance of the hybrid adhesive joints was obtained for the given material systems.

On the fracture behaviour of aerospace-grade Polyether-ether-ketone composite-to-aluminium adhesive joints

The inherently low surface energy of carbon fibre reinforced Polyether-ether-ketone (CF/PEEK) composites results in an extremely low compatibility with adhesives. This subsequently causes significant challenges in the adhesive joining of them to other dissimilar materials. Herein, the bonding surfaces of the CF/PEEK composites were treated by a high-power UV-irradiation technique prior to the adhesive bonding, with an attempt to develop hybrid composite-to-aluminium joints with excellent fracture resistance. The mode-I, mode-II and mix-mode fracture behaviour of CF/PEEK-to-aluminium joints bonded by two commercial aerospace adhesives was evaluated. Cohesive failure within the adhesive layers or substrate damage to the CF/PEEK composites were observed in all the cases. This indicated that the adhesion between the CF/PEEK composites and the adhesives was sufficient to prevent an adhesive failure at the composite/adhesive interfaces under different fracture modes. This study explored an effective route to develop strong and tough CF/PEEK-to-aluminium joints for aerospace applications. Additionally, it revealed that the form of the adhesive supporting carrier was a key factor affecting the fracture behaviour and fracture energies of the adhesive joints.

Alumina‐Protected, Durable and Photostable Zinc Sulfide Particles from Scalable Atomic Layer Deposition

AbstractZinc sulfide has unique and easily modifiable photophysical properties and is a promising candidate for photocatalysis and optoelectronic devices. However, ZnS suffers from corrosive decomposition during excitation processes like UV irradiation, which drastically limits its field of potential applications. For the first time, complete photostabilization of individual ZnS particles by a dense, durable, and only 3‐nm‐thick Al2O3 layer, produced by rotary atomic layer deposition (ALD) is reported. In contrast to bare ZnS, the coated particles do not suffer from photocorrosive degradation even under long‐term or high power UV irradiation. The presence of a protection layer covering the entire ZnS surface is additionally confirmed by microscopic and spectroscopic investigations of particle cross‐sections. Further, complete inhibition of the reaction between Ag+ ions added as the analyte and the ZnS surface is observed. Durability tests of the as‐prepared Al2O3 layer upon prolonged exposure to water reveal a significant decrease in the protection capability of the layer, which is ascribed to the hydrolysis of the amorphous Al2O3. A calcination step at 1000 °C after the ALD treatment, which leads to crystallization of the amorphous Al2O3 layer, successfully suppresses this hydrolysis and produces an insulating, dense, and inert protection layer.

Significantly enhanced structural integrity of adhesively bonded PPS and PEEK composite joints by rapidly UV-irradiating the substrates

A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites, aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiated for a duration of between 2–30s, and then bonded using an aerospace film adhesive to produce joints. Tensile lap-shear strength and mode-I and mode-II fracture energies of the adhesive joints were investigated. It was observed that the application of a short-time UV-irradiation to the substrates transformed the failure mode of the specimens from adhesion failure to substrate damage in all cases. This consequently resulted in remarkable improvements in the mechanical and fracture performance of the adhesive joints. For example, the lap-shear strength increased from 11.8MPa to 31.7MPa upon UV-irradiating the PPS composites for 3s, and from 8.3MPa to 37.3MPa by applying a 5s UV-irradiation to the PEEK composites. Moreover, the mode-I and mode-II fracture energies significantly increased from ∼50J/m2 to ∼1500J/m2 and from <300J/m2 to ∼7000J/m2, respectively for both of the adhesively bonded PEEK and PPS composite joints.

Rapid surface activation of carbon fibre reinforced PEEK and PPS composites by high-power UV-irradiation for the adhesive joining of dissimilar materials

Carbon fibre reinforced poly-etherether-ketone (PEEK) and poly-phenylene-sulfide (PPS) composites were rapidly surface-treated by high-power UV light, and then adhesively bonded to aluminium 2024-T3 and carbon fibre/epoxy composites. The results of a single lap-shear joint test demonstrated that a UV-treatment lasting for 5 s was sufficient to prevent joint failure occurring at the composite/adhesive interfaces in all cases, e.g. it increased the failure strength of the PPS composite/aluminium joints from 11.1 MPa to 37.5 MPa. Moreover, the composite/adhesive interfaces performed well upon an exposure of the joints to an environment of high humidity and temperature for 8 weeks. Additionally, an investigation lasting for 6 months showed no degradation of the surface functionalisation from UV-irradiation. Overall, this work highlights high-power UV-irradiation a very promising method for surface preparation of thermoplastic composites (TPCs) for adhesive joining, i.e. TPC adhesive joints with excellent structural integrity can be obtained by using this rapid, eco-friendly and low-cost surface-treatment method.

Rapid surface activation of carbon fibre reinforced PEEK and PPS T composites by high-power UV-irradiation for the adhesive joining of dissimilar materials

Rapid surface activation of carbon fibre reinforced PEEK and PPS T composites by high-power UV-irradiation for the adhesive joining of dissimilar materials

Co-cure joining of epoxy composites with rapidly UV-irradiated PEEK and PPS composites to achieve high structural integrity

Efficient joining of hybrid thermoset/thermoplastic composite joints is critical to produce high performance lightweight structures while keeping the cost low. Herein, a high-power UV-irradiation technique was proposed to rapidly active the surfaces of PEEK and PPS composites for the following co-cure joining with epoxy composites. A single lap-shear joint test and a double cantilever beam test were used to evaluate the mechanical and fracture performance of the hybrid joints. The experimental results revealed that high structural integrity of the hybrid joints was achieved upon applying a 6 s UV-treatment to the thermoplastic composites. For example, the lap-shear strength and fracture energy of the adhesive bonded hybrid joints were above 25 MPa and 800 J/m2, respectively. Overall, high-power UV-irradiation proved a highly efficient, rapid and low-cost method to treat thermoplastic composites for the co-cure joining with epoxy composites, and hence it demonstrated significant promise in industrial mass production.

High Power UV-Light Irradiation as a New Method for Defect Passivation in Degraded Perovskite Solar Cells to Recover and Enhance the Performance

Although the power conversion efficiency (PCE) of perovskite solar cells (PSCs) reached up to 23%, their short lifetime and fast degradation still remain as the main challenges. In this work, a new facile optical method based on the high power UV-irradiation is presented for the recovery of the degraded PSCs. Addition to the full recovery of the performance, about 20% PCE enhancement and hystersis reduction are also achieved by UV-irradiation. UV-treatment causes modifications in both the bulk properties of the perovskite layer and the energy equilibrium at the interfaces. It is shown that UV-treatment effectively passivates the surface and grain boundaries defects in different types of the devices comprising normal and inverted configurations that is confirmed by the reduction of the density of defect states (DOS). It is proposed that UV-light passivates the shallow and deep defects by dissociation of adsorbed hydroxyl groups and water molecules during the device storage.

Preparation of nanoporous graphene sheets via free radical oxidation of graphene oxide and their application in lithium ion battery

Graphene is an attractive candidate for use as an electrode material in electrochemical energy storage due to its unique structure and excellent properties. Compared with graphene, nanoporous graphene is a superior electrode material, owing to the porous structure of its graphene sheets, which facilitates cross-plane lithium ion transportation and provides more binding sites for the lithium ions during the lithiation/delithiation process. In this work, we demonstrate a simple and efficient strategy for obtaining nanoporous graphene on a large scale. Nanoporous graphene can be generated through the oxidation of graphene oxide by H2O2 under high-power UV irradiation with a subsequent reduction process. The morphology, chemical composition and defects of the as-generated nanoporous graphene were studied. The electrochemical evaluation of the nanoporous graphene sheets showed that it delivered higher specific capacity and better charge/discharge rate capability compared with chemically reduced graphene sheets for use as an anode material in lithium ion batteries.

High-Adhesion Plating on ABS Resin using High-Power UV Irradiation

High-Adhesion Plating on ABS Resin using High-Power UV Irradiation

One-Dimensional Fluorescent Silicon Nanorods Featuring Ultrahigh Photostability, Favorable Biocompatibility, and Excitation Wavelength-Dependent Emission Spectra.

We herein report a kind of one-dimensional biocompatible fluorescent silicon nanorods (SiNRs) with tunable lengths ranging ∼100-250 nm, which can be facilely prepared through one-pot microwave synthesis. In addition to the strong fluorescence (quantum yield value: ∼15%) and negligible toxicity, the resultant SiNRs exhibit excitation wavelength-dependent photoluminescence whose maximum emission wavelength ranges from ∼450 to ∼600 nm under serial excitation wavelengths from 390 to 560 nm, providing feasibility for multicolor biological imaging. More significantly, the SiNRs are ultrahighly photostable, preserving strong and nearly unchanged fluorescence under 400 min high-power UV irradiation, which is in sharp contrast to severe fluorescence quenching of organic dyes (e.g., FITC) or II-VI quantum dots (QDs) (e.g., CdTe QDs and CdSe/ZnS QDs) within 15 or 160 min UV treatment under the same experiment conditions, respectively. Taking advantage of these attractive merits, we further exploit the SiNRs as a novel type of color converters for the construction of white light-emitting diodes (LED), which is the first proof-of-concept demonstration of LED device fabricated using the one-dimensional fluorescent silicon nanostructures.

Facile, Large-Quantity Synthesis of Stable, Tunable-Color Silicon Nanoparticles and Their Application for Long-Term Cellular Imaging.

We herein introduce a facile, low-cost photochemical method capable of rapid (<40 min) and large-quantity (∼10 g) production of highly fluorescent (quantum yield: 25%) silicon nanoparticles (SiNPs) of tunable optical properties (peak emission wavelength in the range of 470-560 nm) under ambient air conditions, by introducing 1,8-naphthalimide as a reducing agent and surface ligands. The as-prepared SiNPs feature robust storage stability and photostability preserving strong and stable fluorescent during long-term (>3 h) high-power UV irradiation, in contrast to the rapid fluorescence quenching within 2 h of conventional organic dyes and II-VI quantum dots under the same conditions. The as-prepared SiNPs serving as photostable nanoprobes are workable for cellular imaging in long-term manners. Our findings provide a powerful method for mild-condition and low-cost, large-quantity production of highly fluorescent and photostable SiNPs for various promising applications.

Ultra-photostable, non-cytotoxic, and highly fluorescent quantum nanospheres for long-term, high-specificity cell imaging

A new class of fluorescent quantum nanospheres (QNs) is directly achieved in aqueous phase through a facile one-pot microwave irradiation (MWI) strategy. Multi-color QNs with maximum emission wavelengths ranging from 525 to 610 nm and PLQY of 30–60% are facilely prepared through this new MWI strategy. In addition to strong fluorescence, these QNs possess excellent photostability, preserving ∼90% of the original intensity after 70 min high-power UV irradiation (100 W Xeon lamp). In sharp contrast, the fluorescence of CdTe/CdS/ZnS core-shell-shell quantum dots (QDs), recognized as established fluorescent probes with robust photostability, decrease to ∼50% under the same conditions. Besides, cytotoxicity assessment demonstrates that the prepared QNs exhibit favorable cytocompatibility to K562 cells with high concentration (3 μmol) and long-time incubation (24 h). Furthermore, cellular imaging results demonstrate that the as-prepared QNs are remarkably efficacious for long-term and high-specificity immunofluorescent cellular labeling, and multi-color cell imaging. Our systematical investigation clearly shows that these high-performance QNs may serve as practical and powerful tools for various biological researches, such as in vivo and in vitro imaging.

Functional Perovskite Hybrid of Polyacetylene Ammonium and Lead Bromide: Synthesis, Light Emission, and Fluorescence Imagining

A highly photoresponsive perovskite hybrid containing an electroactive organic component (H1) was fabricated. A disubstituted polyacetylene (PA) with a hidden amino functionality (P3) was synthesized, hydrolysis and quaternization of which afforded the desired PA ammonium salt (P5). Mixing P5 with lead bromide readily yielded H1, which was stable, soluble, and film-forming. The inorganic framework induced the polymer chains to align in an ordered fashion, which helped to populate the chain segments with long conjugation lengths. The hybrid emitted a blue light (457 nm) in a high quantum yield (62%), thanks to the enhanced electronic conjugation, the weakened interaction between the layer-segregated chains, and the efficient energy transfer from the inorganic sheets to the organic layers. P3 exhibited a half-discharge time as short as approximately 0.7 s, representing the first example of an efficient photoconductive disubstituted PA. While stable to normal light illumination, H1 was rapidly bleached upon exposure to high-power UV irradiation, enabling facile generation of two-dimensional luminescent photopatterns. After the UV irradiation, the emissions of P9 and P9/H12 were enhanced and weakened, respectively, proving that the inorganic perovskite framework works as a photocatalyst for accelerating the bleaching process of the conjugated PA chains.

EPR study of spin-trapped free radical intermediates formed in the heterogeneously-assisted photodecomposition of acetaldehyde †

Electron paramagnetic resonance spectroscopy is used to detect radical adducts of PBN (α-phenyl N-tert-butyl nitrone) generated by exposure of solutions and suspensions to ambient or high power UV at 300 K. Exposure of acetaldehyde to direct sunlight generates a different PBN radical adduct to high power UV irradiation. Direct sunlight irradiation of deoxygenated acetaldehyde generates PBN–acetyl adducts whereas direct sunlight exposure of oxygenated acetaldehyde produces PBN–acetoxyl adducts. High power UV irradiation of TiO2/acetaldehyde suspensions yields the same radical adduct generated when no TiO2 is present—this adduct (assigned to trapped formyl radicals or PBN degradation products) is produced irrespective of the state of oxygenation of solution. Direct sunlight irradiation of deoxygenated TiO2/acetaldehyde suspension results in the production of PBN–acetyl adducts as the primary species. In oxygenated TiO2/acetaldehyde suspension, PBN–acetyl adducts are again produced as the primary species, together with a weakly adducted secondary species—assigned to PBN–acetoxyl adducts. TiO2 band gap transitions are observed to play no part in the production of radical intermediates in sunlight irradiated acetaldehyde/TiO2 suspension. The extent of non-band gap dependent processes is shown to be sensitive to the surface basicity of the metal oxide. Band gap mediated radical production is demonstrated to arise when acetaldehyde photoreduction is coupled to the concomitant photooxidation of ethanol. Ethanol derived PBN–ethoxy adducts are detected as the primary species arising from sunlight irradiation of both oxygenated and deoxygenated TiO2/acetaldehyde/ethanol suspensions.

Bleaching and diffusion of laser dyes in solution under high power UV irradiation

Bleaching experiments in some laser dyes under high power UV irradiation from a nitrogen laser are described. Very high bleaching quantum efficiencies, of the order of 10 -3 molecules bleached/photon absorbed, and a dependence of this efficiency on intensity have been found. The diffusion coefficients for the dyes in ethyl alcohol were also measured.