Enrichment of Luminescence via Incorporation of Fluxes in La2Zr2O7:Tb3+ Nanophosphors: One Material, Many Possibilities-Latent Fingerprint Visualization, Anti- counterfeiting, Luminescent Flexible Films

Engineering of single material with multidirectional applications is of crucial for improving the productivity, low cost, flexibility and least power consumption, etc. To achieve these requirements, novel design structures and high performance materials are in urgent need. Lanthanide-doped nanophosphors have greatest strengths and ability in order to tuning its applications in various dimensions. However, nanophosphor applications in latent fingerprints visualization, anti-counterfeiting and luminescent gels/films are still in its infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb3+ doped (1-11 mol %) La2Zr2O7 nanophosphors by conjugating the fluxes via simple solution combustion route. The photoluminescence spectra reveal intense peaks at ~ 491, 546, 587 and 622 nm arises from 5D4◊7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions, respectively. The highest emission intensity was achieved in the NH4Cl flux assisted nanophosphor as compared to NaBr and NH4F. The colorimetric images of fingerprints visualized using optimized nanophosphor on forensic related surfaces exhibit level –III ridge details, including sweat pores, width of the ridges, bifurcation angle, successive distance between sweat pores, etc. These results are decisive parameters which clearly supports the statement “no two persons have ever been found to have the same fingerprints”. The anti-counterfeiting security ink was formulated using nanophosphor and designed various patterns by simple screen printing and dip pen technology. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are not just what it looks/feels like and how it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the fabricated green-emissive films display excellent flexibility, uniformity and transparency in the normal and ultraviolet 254 nm light illumination. Aforementioned results revealed that prepared NH4Cl flux assisted La2Zr2O7: Tb3+(7 mol %) NPs are considered to be best candidate for multi-dimensional applications.

Mechanically Reinforced, Flexible, Hydrophobic and UV Impermeable Starch-Cellulose Nanofibers (CNF)-Lignin Composites with Good Barrier and Thermal Properties

Bio-based composite films have been widely studied as potential substitutes for conventional plastics in food packaging. The aim of this study was to develop multifunctional composite films by introducing cellulose nanofibers (CNF) and lignin into starch-based films. Instead of costly and complicated chemical modification or covalent coupling, this study optimized the performance of the composite films by simply tuning the formulation. We found that starch films were mechanically reinforced by CNF, with lignin dispersing as nanoparticles embedded in the matrix. The newly built-up hydrogen bonding between these three components improves the integration of the films, while the introduction of CNF and lignin improved the thermal stability of the starch-based films. Lignin, as a functional additive, improved hydrophobicity and blocked UV transmission. The inherent barrier property of CNF and the dense starch matrix provided the composite films with good gas barrier properties. The prepared flexible films were optically transparent, and exhibited UV blocking ability, good oxygen-barrier properties, high hydrophobicity, appreciable mechanical strength and good thermal stability. These characteristics indicate potential utilization as a green alternative to synthetic plastics especially for food packaging applications.

Absorption-dominant Microwave Shielding Properties of Sn0.2Fe2.8O4-Graphite-PVDF Ternary Nanocomposite Films

Absorption-dominant microwave shields are in high demand for mitigating the effect of electromagnetic interference on devices and the environment. In this paper, we describe the development of absorption enhanced ternary nanocomposites and their electromagnetic interference shielding capability. Polymer based shields have been fabricated by dispersing conducting graphite and magnetic spinel ferrite Sn0.2Fe2.8O4 nanoparticles in electroactive polymer PVDF. Shielding effectiveness (SE) values in the expected range of 10 - 30 dB in the X-band region, were achieved with as low as 30 – 50 wt% of pristine graphite and 1 – 10 wt% of Sn0.2Fe2.8O4. The industrial standard of 99% shielding (SE ≥ 20 dB) was obtained with 50 wt% of graphite. The composites exhibit absorption as the dominant mechanism of shielding. The percentage shielding effectiveness due to absorption is about 70% and is tuned upwards by the increase in ferrite concentration. The composites were characterized by XRD and VSM; thermal analysis confirms their stability. The thin, flexible films fabricated by the simple and cost-efficient technique of solution casting will be extremely valuable as wrap-on shields for X-band microwave attenuation.

Development and Characteristics of Multipurpose Transparent Polyurethane Film

In industry, recent research developments include flexible films and foldable films. The next step is the development of stretchable films, and studies are being intensively carried out. Research on the development of stretchable and transparent materials is also increasing greatly. Currently, polydimethylsiloxane (PDMS) is the most commonly used film in the industry. However, PDMS surfaces are hydrophobic, so their use is limited to making materials and compounds with hydrophilic properties. In this study, we developed a transparent polyurethane film that can be used for multiple purposes. A transparency comparison between the transparent polyurethane film and the general polyurethane film was used to verify their future application. The conventional polyurethane films showed a transmittance rate of 2.2 percent, but the transparent polyurethane films achieved a high transmittance rate of 85 percent. To determine whether the film can be realized, we produced a conductive paste using resin for the transparent polyurethane film. In addition, a conductive paste was made based on the material used in the transparent polyurethane film to verify the hardness and reliability of the adhesion of electrodes, and we confirmed this with thermogravimetric analysis (TGA). The transparent polyurethane based paste was made with stretchable electrodes through a screen printing method. The manufactured stretchable electrodes were demonstrated by mechanical and adhesion tests. Finally, a permittivity test was conducted to determine the suitability of the film for application to printed electrodes for antennas in the future. The genetic rate of transparent polyurethane films was better than that of conventional polyurethane films. Moreover, the adhesion of the transparent polyurethane film and stretchable electrodes was as good as that of conventional polyurethane film and stretchable electrodes, and observation by optical microscopy confirmed that the printing performance was also excellent. In addition, the conductive paste made based on the transparent polyurethane film material was cured for 1 hour at 120 °C, and TGA analysis confirmed that both the binders and curing agent responded well in the test for curing the developed stretchable electrodes and transparent polyurethane.

Flexible Ag Microparticle/MXene-Based Film for Energy Harvesting

Ultra-thin flexible films have attracted wide attention because of their excellent ductility and potential versatility. In particular, the energy-harvesting films (EHFs) have become a research hotspot because of the indispensability of power source in various devices. However, the design and fabrication of such films that can capture or transform different types of energy from environments for multiple usages remains a challenge. Herein, the multifunctional flexible EHFs with effective electro-/photo-thermal abilities are proposed by successive spraying Ag microparticles and MXene suspension between on waterborne polyurethane films, supplemented by a hot-pressing. The optimal coherent film exhibits a high electrical conductivity (1.17×104 S m−1), excellent Joule heating performance (121.3 °C) at 2 V, and outstanding photo-thermal performance (66.2 °C within 70 s under 100 mW cm−1). In addition, the EHFs-based single-electrode triboelectric nanogenerators (TENG) give short-circuit transferred charge of 38.9 nC, open circuit voltage of 114.7 V, and short circuit current of 0.82 μA. More interestingly, the output voltage of TENG can be further increased via constructing the double triboelectrification layers. The comprehensive ability for harvesting various energies of the EHFs promises their potential to satisfy the corresponding requirements.

Colorless Polyimides Derived from an Alicyclic Tetracarboxylic Dianhydride, CpODA

An alicyclic tetracarboxylic dianhydride having cyclopentanone bis-spironorbornane structure (CpODA) was polycondensated with aromatic dianhydrides to form the corresponding poly(amic acid)s which possessed logarithmic viscosities in the range 1.47–0.54 dL/g. The poly(amic acid) was imidized by three methods: a chemical, a thermal, and a combined chemical and thermal process. In a thermal method, imidization temperature markedly influenced the film quality and molecular weight of the polyimide. When the poly(amic acid) was cured over the Tg of the corresponding polyimide, the flexible polyimide films were obtained and the molecular weights increased several times, which means that the post-polymerization took place. In spite of low-temperature cure below Tg flexible films with the imidization ratio of 100% were fabricated by a combined chemical and thermal imidization technique. The films possessed the decomposition temperatures in a range of 475–501 °C and Tgs over 330 °C. The high Tg results from a dipole–dipole interaction between the keto groups of the polymer chains as well as development of the rigid polyalicyclic unit. The polyimide films exhibited CTE between 17 and 57 ppm/K. All the films fabricated were entirely colorless and possessed the λcut-offs shorter than 337 nm. Notably, the films prepared by a chemical method exhibited outstanding optical properties.