Transparent ceramics are usually polycrystalline materials, which are wildly used in many optical applications, such as lasers. As of today, the fabrication of transparent ceramic structures is still limited to conventional fabrication methods, which do not enable the formation of complex structures. A new approach for 3D printing of micrometer-size, transparent ceramic structures is presented. By using a solution of metal salts that can undergo a sol–gel process and photopolymerization by two-photon printing, micrometer-sized yttrium aluminum garnet (YAG) structures doped with neodymium (Nd) are fabricated. The resulting structures are not only transparent in the visible spectrum but can also emit light at 1064 nm due to the doping with Nd. By using solution-based precursors, without any particles, the sintering can be performed under air at ambient pressure and at a relatively low temperature, compared to conventional processes for YAG. The crystalline structure is imaged at atomic resolution by ultrahigh-resolution scanning transmission electron microscopy (STEM), indicating that the doped Nd atoms are located at the yttrium positions. Such miniaturized structures can be used for diverse applications, e.g., optical components in high-intensity laser systems, which require heat resistance, or as light sources in optical circuits.
Ordered mesoporous silica materials gain high interest because of their potential applications in catalysis, selective adsorption, separation, and controlled drug release. Due to their morphological characteristics, mainly the tunable, ordered nanometric pores, they can be utilized as supporting hosts for confined chemical reactions. Applications of these materials, however, are limited by structural design. Here, we present a new approach for the 3D printing of complex geometry silica objects with an ordered mesoporous structure by stereolithography. The process uses photocurable liquid compositions that contain a structure-directing agent, silica precursors, and elastomer-forming monomers that, after printing and calcination, form porous silica monoliths. The objects have extremely high surface area, 1900 m2/g, and very low density and are thermally and chemically stable. This work enables the formation of ordered porous objects having complex geometries that can be utilized in applications in both the industry and academia, overcoming the structural limitations associated with traditional processing methods.
4D printed objects are 3D printed structures whose shape, property, and functionality are able to self-transform when exposed to a predetermined stimulus. The emerging field of 4D printing has attracted wide interest from both academia and industry since first introduced in 2013. Stimuli-responsive hydrogels have become a competitive and versatile group of materials for 4D printed devices due to their good deformability, promising biocompatibility, simple manufacturing, and low cost. This review aims to provide a summary of the current progress of hydrogel-based 4D printed objects and devices based on their fabrication techniques, materials, and applications. Herein, presented are: the characteristics of different additive manufacturing methods such as direct ink writing, fused deposition modeling, and stereolithography; the properties of various stimuli-responsive hydrogels such as poly(N-isopropylacrylamide) and poly(N,N-dimethylacrylamide), alginate, etc.; and diverse applications of 4D printed hydrogels such as actuators, cellular scaffolds, and drug release devices. Opportunities and challenges for 4D printed hydrogels are discussed and prospects for future development are elaborated.
Despite the abundance of data concerning single-photon double ionization of methanol, the spin state of the emitted electron pair has never been determined. Here we present the first evidence that identifies the emitted electron pair spin as overwhelmingly singlet when the dication forms in low-energy configurations. The experimental data show that while the yield of the CH2O+ + H3+ Coulomb explosion channel is abundant, the metastable methanol dication is largely absent. According to high-level ab initio simulations, these facts indicate that photoionization promptly forms singlet dication states, where they quickly decompose through various channels, with significant H3+ yields on the low-lying states. In contrast, if we assume that the initial dication is formed in one of the low-lying triplet states, the ab initio simulations exhibit a metastable dication, contradicting the experimental findings. Comparing the average simulated branching ratios with the experimental data suggests a \textgreater3 order of magnitude enhancement of the singlet:triplet ratio compared with their respective 1:3 multiplicities.
Jin He, Jeff Armstrong, Peixi Cong, Barak Menagen, Lior Igaher, Andrew M Beale, Lioz. Etgar, and David Avnir. 1/10/2020. “Affecting an Ultra-High Work Function of Silver.” Angewandte Chemie International Edition, 2020, doi.org/10.1002/anie.201912293.
Costly investor-state dispute settlement (ISDS) cases have led several developing countries to take far-reaching steps to distance themselves from the global investment regime, such as the denunciation or renegotiation of international investment agreements (IIAs) or the withdrawal from the International Centre for Settlement of Investment Disputes (ICSID). Despite facing the highest number of investment claims worldwide and despite being very vocal about the shortcomings of the current regime, Argentina has neither denounced a single IIA nor renounced ICSID. This article addresses this puzzle. It first shows that under the Kirchners’ governments (2003‒2015), Argentina adopted a dual approach: maintaining its IIAs and membership in ICSID on the one hand, but vigorously fighting ISDS awards on the other. Using in-depth interviews, news reports, and secondary sources, it then demonstrates that this ‘neither-in-nor-out’ approach is best explained by a unique Argentinian identity, which combines Latin American and Western dimensions, conditioned by external political and economic constraints, especially in the immediate aftermath of the 2001 financial crisis. As such, this study underscores the need to account for both material and ideational factors when striving to grasp development-related foreign policy.
