Development Of New Material Systems Research Articles

Organic cocrystals: From high‐performance molecular materials to multi‐functional applications

AbstractAdvancements in organic electronics are propelling the development of new material systems, where organic materials stand out for their unique benefits, including tunability and cost‐effectiveness. Organic single crystals stand out for their ordered structure and reduced defects, enhancing the understanding of the relationship between structure and performance. Organic cocrystal engineering builds upon these foundations, exploring intermolecular interactions within multicomponent‐ordered crystalline materials to combine the inherent advantages of single‐component crystals. However, the path to realizing the full potential of organic cocrystals is fraught with challenges, including structural mismatches, unclear cocrystallization mechanisms, and unpredictable property alterations, which complicate the effective cocrystallization between different molecules. To deepen the understanding of this promising area, this review introduces the mechanism of organic cocrystal formation, the various stacking modes, and different growth techniques, and highlights the advancements in cocrystal engineering for multifunctional applications. The goal is to provide comprehensive guidelines for the cocrystal engineering of high‐performance molecular materials, thereby expanding the applications of organic cocrystals in the fields of optoelectronics, photothermal energy, and energy storage and conversion.

Additive manufacturing of functionally gradient refractory coatings using substrate dilution and in-situ carbide formation

Enabling operations in extreme environments remains a top priority for the space, defense, and energy sectors, driving the demand for ultra-high-temperature materials. Traditional materials employed in these sectors have limited operating temperatures and thus novel alternatives are of interest. Refractory metals and carbides have excellent high-temperature properties, however, their high melting points and susceptibility to cracking during solidification make them challenging to process, especially through additive manufacturing (AM) technologies. In this work, Directed Energy Deposition (DED) was used to create a functionally graded refractory coating (W-WC-Nb system on a titanium substrate) by integrating titanium into the refractory matrix through substrate dilution. By developing a new W-based alloy then adding titanium from the substrate along the build direction, a crack-free microstructure was formed within layers closer to the substrate. Additionally, an in-situ carbide formation strategy was explored, creating titanium carbide and niobium carbide phases that could improve the high-temperature and corrosion properties without the need to overcome processing difficulties associated with these high-melting carbides. These strategies allow for the development of new material systems with tailored properties and improved processibility of refractory material systems.

Tailoring high-energy storage NaNbO3-based materials from antiferroelectric to relaxor states

Reversible field-induced phase transitions define antiferroelectric perovskite oxides and lay the foundation for high-energy storage density materials, required for future green technologies. However, promising new antiferroelectrics are hampered by transition´s irreversibility and low electrical resistivity. Here, we demonstrate an approach to overcome these problems by adjusting the local structure and defect chemistry, delivering NaNbO3-based antiferroelectrics with well-defined double polarization loops. The attending reversible phase transition and structural changes at different length scales are probed by in situ high-energy X-ray diffraction, total scattering, transmission electron microcopy, and nuclear magnetic resonance spectroscopy. We show that the energy-storage density of the antiferroelectric compositions can be increased by an order of magnitude, while increasing the chemical disorder transforms the material to a relaxor state with a high energy efficiency of 90%. The results provide guidelines for efficient design of (anti-)ferroelectrics and open the way for the development of new material systems for a sustainable future.

Overcoming the penetration–saturation trade-off in binder jet additive manufacturing via rapid in situ curing

Binder jetting (BJ) enables the production of green parts for structurally complex ceramic, metal, or composite parts. However, the existence of a penetration–saturation trade-off (PSTO) in conventional BJ 3D printing hinders its development. Since an increase in saturation is often accompanied by an increase in penetration distance of binder (P), it is difficult to produce high strength and high precision green parts; this limitation is not conducive to the development of new material systems. To overcome this limitation, a methacrylate-based, thermally activated free radical polymerization system was used in this study as a binder to produce green parts under in situ curing conditions, created by increasing the temperature of the powder bed. The penetration of the powder bed by the binder is controlled by regulating its curing status during printing. The proposed rapid in situ curing printing process overcomes the PSTO associated with conventional BJ and can inform the optimization of binder formulation, equipment design, and binder jet printing. • Acrylate-based binder cures by thermally activated free radical polymerization. • The binder cures rapidly in a heated powder bed, limiting penetration distance. • In situ cured green parts demonstrate high dimensional accuracy and strength.

Nanosphere Lithography: A Versatile Approach to Develop Transparent Conductive Films for Optoelectronic Applications.

Transparent conductive films (TCFs) are irreplaceable components in most optoelectronic applications such as solar cells, organic light-emitting diodes, sensors, smart windows, and bioelectronics. The shortcomings of existing traditional transparent conductors demand the development of new material systems that are both transparent and electrically conductive, with variable functionality to meet the requirements of new generation optoelectronic devices. In this respect, TCFs with periodic or irregular nanomesh structures have recently emerged as promising candidates, which possess superior mechanical properties in comparison with conventional metal oxide TCFs. Among the methods for nanomesh TCFs fabrication, nanosphere lithography (NSL) has proven to be a versatile platform, with which a wide range of morphologically distinct nanomesh TCFs have been demonstrated. These materials are not only functionally diverse, but also have advantages in terms of device compatibility. This review provides a comprehensive description of the NSL process and its most relevant derivatives to fabricate nanomesh TCFs. The structure-property relationships of these materials are elaborated and an overview of their application in different technologies across disciplines related to optoelectronics is given. It is concluded with a perspective on current shortcomings and future directions to further advance the field.

On the Constraint Factor Relating Uniaxial and Indentation Yield Strength of Polycrystalline Materials Using Spherical Microindentation

High-throughput (HT) material property characterization has become increasingly important for the rapid and cost-effective development of new material systems. In recent years, spherical indentation using the Pathak-Kalidindi (P-K) protocol has been shown to be a reliable and HT method for capturing the elastic-plastic properties of several different types of materials. However, because of the higher hydrostatic pressure under the indenter tip and the constraint of the surrounding elastically deforming material, the indentation yield strength is higher than the uniaxial yield strength and they can be related by a scaling factor, referred to as the constraint factor. For fully plastic indentation, the constraint factor was found by Tabor to be ~2.8. However, the constraint factor is not well defined for elastic-plastic indentation and depends on the strain induced. In this work, the application of the P-K indentation protocol is demonstrated on a set of aluminum 7050 samples that have undergone different solution and aging treatments. Conventional uniaxial tensile and compression tests were also conducted on the same material. The constraint factor at the 0.2 % offset yield point was determined from the indentation and uniaxial measurements to be ~1.4. Experimental observations from our work and a similar work on aluminum 6061 showed a dependence of the constraint factor at the 0.2 % offset yield point on the uniaxial plastic properties. To explain these experimental observations, further investigation was carried out using finite element simulations of spherical indentation on materials with different yield strengths and hardening parameters. New insights are provided on the constraint factor at the 0.2 % yield point, which show that it increases with the ratio of the plastic to elastic strain. It was also found that the effect of the hardening is much less than that of the yield strength on the constraint factor at the 0.2 % yield point.

Materials Science in the AI age: high-throughput library generation, machine learning and a pathway from correlations to the underpinning physics.

The use of advanced data analytics and applications of statistical and machine learning approaches ('AI') to materials science is experiencing explosive growth recently. In this prospective, we review recent work focusing on generation and application of libraries from both experiment and theoretical tools, across length scales. The available library data both enables classical correlative machine learning, and also opens the pathway for exploration of underlying causative physical behaviors. We highlight the key advances facilitated by this approach, and illustrate how modeling, macroscopic experiments and atomic-scale imaging can be combined to dramatically accelerate understanding and development of new material systems via a statistical physics framework. These developments point towards a data driven future wherein knowledge can be aggregated and used collectively, accelerating the advancement of materials science.

Thermophysical properties of multifunctional glass fibre reinforced polymer composites incorporating phase change materials

In this study novel multifunctional composites consisting of glass fibre/epoxy/microencapsulated phase change materials (micro-PCMs) were prepared and their thermophysical properties have been investigated. Test results showed that the phase change properties of micro-PCMs are not affected after incorporating these materials in fibre reinforced plastic composites. Results obtained from DSC demonstrated that the enthalpy (heat of fusion/crystallisation) is linearly proportional to the mass fraction of microcapsules incorporated into the composites. In addition, it was found that the thermal and dimensional stability of the multifunctional composites are significantly affected by increasing micro-PCMs concentration. The thermal decomposition temperature of the multifunctional composites was reduced while their coefficient of thermal expansion was increased due to the inclusion of micro-PCMs. Understanding the thermophysical properties of these composites pave the path for the development of new material systems that can simultaneously exhibit loading bearing and thermal storage capabilities.

Toughening of Photopolymers for Stereolithography (SL)

Additive Manufacturing (AM) received a lot of attention in the last years. Organizations are using AM systems for a range of applications such as prototypes for fitting an assembly, tooling components, patterns for prototype tooling, functional parts and many more. Nearly a third is applied for functional parts [1][2]. Hence, the SL method provides a smoother surface finish than other AMT[3]. Not only is the smoother surface a benefit but the good precision is also a positive feature. The ongoing development of new material systems and applications make them suitable alternatives for conventional series production like injection molding or machined-core fabrication for foundry use. Small to middle series cores for faucets with quantities from around 50,000 pieces produced using AM methods are already a reality [1]. From the economical point of view, the SL is a cheap and fast process in comparison to AM systems. The SL technology used in this work is based on an active mask exposure, the digital light processing (DLP). The term DLP refers to the digital mirror devices which are used for selectively tuning individual mirrors on and off in order to selectively expose a photosensitive resin with visible or ultraviolet light. The resin contains a photoinitiator which triggers radical polymerization when irradiated with light. The polymerization process leads to a solidification of the resin, leading finally to a solid polymer part [4]. A digital Mirror Device (DMD) chip acts as a dynamic mask to expose a defined area on the bottom of a transparent material vat above the optical system. The generated picture enables layer-wise polymerization of the photosensitive resin resulting in a 3-dimensional object. The light source radiates light with a wavelength of 460 nm which means blue visible light. At this wavelength the curing takes place. At the Institute of Materials Science and Technology at the Vienna University of Technology six generations of these Blueprinter machines have been developed and built to date. The largest parts that a Blueprinter can currently generate are 110 x 110 x 80 mm3 with a resolution of 25 x 25 x 25 μm3. The wall thickness can go down to four pixels which means one tenth of a millimetre.

Spontaneous Charge Transfer and Dipole Formation at the Interface Between P3HT and PCBM

AbstractIn the pursuit of developing new materials for more efficient bulk‐heterojunction solar cells, the blend poly (3‐hexylthiophene):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) serves as an important model system. The success of the P3HT:PCBM blend comes from efficient charge generation and transport with low recombination. There is not, however, a good microscopic picture of what causes these, hindering the development of new material systems. In this report UV photoelectron spectroscopy measurements on both regiorandom‐ (rra) and regioregular‐ (rr) P3HT are presented, and the results are interpreted using the Integer Charge Transfer model. The results suggest that spontaneous charge transfer from P3HT to PCBM occurs after heat treatment of P3HT:PCBM blends. The resulting formation of an interfacial dipole creates an extra barrier at the interface explaining the reduced (non‐)geminate recombination with increased charge generation in heat treated rr‐P3HT:PCBM blends. Extensive photoinduced absorption measurements using both above‐ and below‐bandgap excitation light are presented, in good agreement with the suggested dipole formation.

Characterizing the light guiding of fluorescent concentrators

Fluorescent concentrators have gained new research interest recently. The development of new material systems for this type of solar concentrator requires the testing of a wide range of materials. The most important characteristic to be tested is the ability of the concentrators to guide light to their edges where the solar cells are mounted. This ability depends on a large set of parameters and cannot be determined with one simple measurement. We present a method to determine this light guiding efficiency spectrally resolved with transmission, reflection, and centermount measurements using a photospectrometer and an integrating sphere. This method represents considerable progress in comparison to external quantum efficiency (EQE) measurements on systems with attached solar cells. The method is fast and flexible. Because no optical coupling and no solar cells with varying properties are involved, accuracy and reproducibility are higher. The method gives an area average of the light guiding efficiency, rather than the value for the point of excitation as does the EQE measurement. Reasonably similar samples can be compared without requiring corrections. For fully quantitative results on an absolute scale, for samples with large Stokes shifts and/or very different properties, additional corrections must be applied. These corrections use data from samples without luminescent material incorporated, which are measured as references. The information obtained for this correction can be also used to derive additional relevant data, such as the absorption of the dyes used and the fraction of light lost into the escape cone. For the tested materials, the measured spectral collection efficiency reached up to 60% at certain wavelengths.

自己修復,モルフィングなど先端的機能・構造実現のための新材料システム開発(OS10-4 複合材料・特性,OS10 インテリジェント材料の機能・特性および評価)

自己修復,モルフィングなど先端的機能・構造実現のための新材料システム開発(OS10-4 複合材料・特性,OS10 インテリジェント材料の機能・特性および評価)

Smaller--faster--brighter: developing optical probes of the future.

Optically brilliant: The fifth international topical conference on optical probes of conjugated polymers and organic and inorganic nanostructures was an exciting place to be and demonstrated three main directions of research: a move to do spectroscopy on individual molecules, application of ever faster coherent probes over an increasingly broad spectral range and the development of new material systems as well as enhancement of known ones. The graphic compares two different methods for studying such new materials, which contribute to models describing the role of excess energy in exciton dissociation processes.

High strain rate behavior of a SiC particulate reinforced Al 2O 3 ceramic matrix composite

The high strain rate deformation behavior of composite materials is important for several reasons. First, knowledge of the mechanical properties of composites at high strain rates is needed for designing with these materials in applications where sudden changes in loading rates are likely to occur. Second, knowledge of both the dynamic and quasi-static mechanical responses can be used to establish the constitutive equations which are necessary to increase the confidence limits of these materials, particularly if they are to be used in critical structural applications. Moreover, dynamic studies and the knowledge gained form them are essential for the further development of new material systems for impact applications. In this study, the high strain rate compressive deformation behavior of a ceramic matrix composite (CMC) consisting of SiC particles and an Al{sub 2}O{sub 3} matrix was studied and compared with its quasi-static behavior. Microscopic observations were conducted to investigate the deformation and fracture mechanism of the composite.

Ceramic Based Resistive Sensors

This paper reviews the current status and research trends of two types of ceramic based resistive sensors, thermistors and gas sensors. The issues and challenges associated with their development for high temperature applications are examined and discussed. Worldwide research efforts in ceramic based resistive sensors, devoted mostly to resolve the issues of selectivity and stability, are also reviewed. These efforts tend to integrate the results obtained from both empirical and basic science approaches, and focus on various stages of sensor development, including development of new material systems, sensor fabrication and manufacturing techniques, and smart sensor arrays.