Surface Modification of Hetero-phase Nanoparticles for Low-Cost Solution-Processable High-k Dielectric Polymer Nanocomposites

The surface modification of nanoparticles (NPs) is crucial for fabricating polymer nanocomposites (NCs) with high dielectric permittivity. Here, we systematically studied the effect of surface functionalization of TiO2 and BaTiO3 NPs to enhance the dielectric permittivity of polyvinylidene fluoride (PVDF) NCs by 23 and 74%, respectively, measured at a frequency of 1 kHz. To further increase the dielectric permittivity of PVDF/NPs-based NCs, we developed a new hetero-phase filler-based approach that is cost-effective and easy to implement. At a 1:3 mixing ratio of TiO2:BaTiO3 NPs, the dielectric constant of the ensuing NC is found to be 50.2, which is comparable with the functionalized BaTiO3-based NC. The highest dielectric constant value of 76.1 measured at 1 kHz was achieved using the (3-aminopropyl)triethoxysilane (APTES)-modified hetero-phase-based PVDF composite at a volume concentration of 5%. This work is an important step toward inexpensive and easy-to-process high-k nanocomposite dielectrics

Spectroscopic Identification of Active Sites of Oxygen-Doped Carbon for Selective Oxygen Reduction to Hydrogen Peroxide

The electrochemical synthesis of hydrogen peroxide (H2O2) via a two-electron (2 e−) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst for H2O2 electrochemical production. The optimized PCC900 material exhibits remarkable activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H2O2 selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2 e− ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis

Scalable high-efficiency multilayered anti-icing/de-icing coating: Superhydrophobic upper layer boosts the performance of the electrothermal system

The formation and accumulation of ice can easily cause serious safety issues and damage. The superhydrophobic surface can delay ice formation due to its liquid repellence feature, but does not work very well under super cold temperatures. The electrothermal coating can effectively prevent ice formation, while it is very energy-consuming. In this work, a multilayered system that combined electrothermal layer (ET) with energy-saving superhydrophobic layer (SH) (SH@ET system) was fabricated to improve the energy efficiency of anti-icing/de-icing coatings. A programmable automatic spraying machine was used to prepare the graphene nanoplates (GNP)-based electrothermal coating with controllable electrical resistance and excellent electrothermal performance. After spraying the SH layer, the SH@ET coating showed excellent water repellency, superior anti-icing performance, and extremely low ice adhesion strength (15 kPa). During the anti-icing test, there was no ice accumulation on the surface of assembled SH@ET system even under low power (0.5 W) at −19 °C for 20 min, confirming its practical application prospects. The SH@ET system also exhibited superior deicing performance than the ET coating. An obvious difference appeared at the low applied voltage range, under which ice continuously formed on the surface of ET coating, while no ice formed on the SH layer. The results can be ascribed to the better water repellency and low ice adhesion strength of the SH layer. This work provides a feasible approach for designing multilayer anti-/de-icing systems for practical large-area applications

4D printing of reprogrammable liquid crystal elastomers with synergistic photochromism and photoactuation

4D printing of liquid crystal elastomers (LCEs) via direct ink writing has opened up great opportunities to create stimuli-responsive actuations for applications such as soft robotics. However, most 4D-printed LCEs are limited to thermal actuation and fixed shape morphing, posing a challenge for achieving multiple programmable functionalities and reprogrammability. Here, a 4D-printable photochromic titanium-based nanocrystal (TiNC)/LCE composite ink is developed, which enables the reprogrammable photochromism and photoactuation of a single 4D-printed architecture. The printed TiNC/LCE composite exhibits reversible color-switching between white and black in response to ultraviolet (UV) irradiation and oxygen exposure. Upon near-infrared (NIR) irradiation, the UV-irradiated region can undergo photothermal actuation, allowing for robust grasping and weightlifting. By precisely controlling the structural design and the light irradiation, the single 4D-printed TiNC/LCE object can be globally or locally programmed, erased, and reprogrammed to achieve desirable photocontrollable color patterns and 3D structure constructions, such as barcode patterns and origami- and kirigami-inspired structures. This work provides a novel concept for designing and engineering adaptive structures with unique and tunable multifunctionalities, which have potential applications in biomimetic soft robotics, smart construction engineering, camouflage, multilevel information storage, etc.Agency for Science, Technology and Research (A*STAR)National Research Foundation (NRF)This study was supported by the RIE2020 Industry Alignment Fund–Industry Collaboration Projects (IAF-ICP) Funding Initiative, Singapore, the cash and in-kind contributions from the industry partner, HP Inc., and the National Research Foundation, Prime Minister's Office, Singapore under its Medium-Sized Centre funding scheme through the Marine and Offshore Program

Recent progress in black phosphorus nanosheets for improving the fire safety of polymer nanocomposites

The application of black phosphorus (BP) nanosheets to improving the fire safety of polymers has been intensively explored in recent years. The phosphorus-rich construction, inherent layered structure, and ease of surface modification contribute to the highly efficient flame-retardant performance of BP nanosheets. Reported results confirmed that BP nanosheets and BP-based hybrids could reduce the release of heat, suppress fire spreading, and reduce the emission of smoke and toxic gases during the combustion of polymers. However, the poor air and moisture stability, severe synthesis conditions, and difficulty to scale up limit their wide application. Up to date, there is no review about BP-based flame retardants for improving the fire safety of polymer nanocomposites. In this review, we summarize the proposed, preparation approaches, surface modification methods and improved air stability, and flame-retardant mechanisms of BP nanosheets and flame-retardant BP nanosheets/polymer composites. The fire safety of polymer nanocomposites is discussed to specifically illustrate the functions of BP nanosheets. Lastly, the limitations and the outlook of using BP nanosheets as flame retardants are presented.The work was financially supported by the National Natural Science Foundation of China (51874266). This study was also supported under the RIE2020 Industry Alignment Fund – Industry Collaboration Projects (IAF-ICP) Funding Initiative

Surface modification of oriented glass fibers for improving the mechanical properties and flame retardancy of polyamide 12 composites printed by powder bed fusion

The orientation of glass fibers (GF) introduced by powder bed fusion (PBF) imparts enhanced mechanical properties to polyamide 12 (PA12). However, there is still much room for reinforcement of PBF-printed GF/PA12 composites. In addition, no studies have addressed the flame retardancy of PBF-printed GF/PA12 composites impaired by the candlewick-like effect of GF. This work presents a feasible and practical approach for addressing these two issues, by surface modification of GF with layered double hydroxide (LDH) to synthesize LDH@GF hybrids. Compared with the ultimate tensile strength, Young's modulus, flexural strength, and flexural modulus of the GF/PA12 composites, those of the LDH@GF/PA12 composites increased by 21.3%, 54.3%, 31.8%, and 36.7%, respectively. Meanwhile, LDH weakened the candlewick-like effect of GF and thus improved the flame retardancy of the PA12 composites. Compared with the peak heat release rate and total heat release of the GF/PA12 composites, those of LDH@GF/PA12 composites were reduced by 17.7% and 12.7%, respectively. The mechanisms for mechanical reinforcement and flame retardancy of LDH@GF hybrids were investigated and proposed. This work paves the way for PBF to prepare flame-retardant high-strength PA12 composites and provides a new solution to boost the performance of additively manufactured products.This study was supported by the RIE2020 Industry Alignment Fund – Industry Collaboration Projects (IAF-ICP) Funding Initiative, Singapore and the cash and in-kind contributions from our industry partner, HP Inc

Magnetic Fe₃O₄ nanoparticle/ZIF-8 composites for contaminant removal from water and enhanced flame retardancy of flexible polyurethane foams

In order to separate heavy-metal ions from contaminated wastewater and further realize the reutilization of waste adsorbent, magnetic composites with flowerlike structure were successfully synthesized. After the absorption of Cu2+ions, hybrids can be used as effective coatings to enhance the fire safety of flexible polyurethane foam (FPUF) through a dip-coating method. As-fabricated metal-organic framework (MOF)-based composites exhibited a core-shell and flowerlike structure with high thermal stability. The maximum adsorption capacity for Cu2+could reach 292.13 mg·g-1, calculated from the Langmuir isotherm model. In order to reutilize the adsorbed Cu2+ions, the CuO-loaded MOF-derived Fe3O4@ZnO@CuO (MO) was obtained with a simple heat treatment. The effectivity of MO as a fire-safety coating for inhibiting the release of heat and toxic gases of FPUF was satisfactory. The application of this MOF-based composite will provide useful insights into the design of bifunctional materials for efficient wastewater remediation and fire-safety coatings.The research was financially supported by the National Natural Science Foundation of China (Grant 51874266), the Fundamental Research Funds for the Central Universities (WK2320000054) and the Open Project Program of Engineering Laboratory of Non halogen Flame Retardants for Polymers Beijing Technology and Business University, China(BTBUFR20-1)

Vertically Aligned Nickel 2‑Methylimidazole Metal–Organic Framework Fabricated from Graphene Oxides for Enhancing Fire Safety of Polystyrene

In this work, flowerlike nickel 2-methylimidazole metal–organic framework (Ni-MOF) was prepared by a solvothermal method. Vertically aligned Ni-MOF was fabricated from graphene oxide (GO) solution in the same way. The combination of GO and Ni-MOF (GOF) obviously suppressed the agglomeration of Ni-MOF sheets. As-synthesized, GOF has bigger pore volume and specific surface area, which are beneficial for volatile degradation products adsorption. It is noteworthy that the addition of GOF obviously reduced the fire hazard of polystyrene (PS). More than 33% decrease in the peak heat release rate for the PS/GOF composite was obtained when the content of the additives is only 1.0 wt %. Meanwhile, the reductions of total smoke and CO production were also prominent during the combustion of PS/GOF, respectively 21% and 52.3% decreases compared with that of pure PS. The synergism effects between layered GO and porous Ni-MOF realized the improved performances of PS. Thus, this work paves a feasible pathway to design efficient flame retardants for enhancing fire safety of polymers

Investigation of the mechanical properties of polyimide fiber/polyamide 12 composites printed by Multi Jet Fusion

Multi Jet Fusion (MJF) has attracted extensive attention because of its ability to print support-free complex structures. However, the mechanical properties of MJF-printed polymer parts are still unsatisfactory for certain industrial requirements. Herein, by leveraging the fibre reinforcement effect and high specific strength of polyimide (PI) fibres, this work developed PI/polyamide 12 (PA12) composites with largely enhanced mechanical performance via MJF. Specifically, the tensile strength and modulus were increased by 43% and 42%, and the flexural strength and modulus were improved by 39% and 46%, respectively, compared to those of the neat PA12 parts. Furthermore, the incorporation of lightweight PI fibres endowed the composites with high specific tensile strength (67.60 kN·m/kg) and specific flexural strength (93.70 kN·m/kg), which are superior to those of MJF-printed PA12 composites reinforced with other fibres. This work provides new insights into enhancing the mechanical performance of lightweight parts printed by MJF and other powder-based techniques