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We demonstrate how addition of polyvinylpyrrolidone (PVP, a non-adsorbing polymer) affects the rheology of concentrated aqueous suspensions of colloidal alumina particles.

 

The rising interest in 3D-printing of concrete structures for use in marine environments requires development of concrete mixtures with adequate mechanical and durability characteristics. The incorporation of alternative cementitious materials, combined with careful selection of printing parameters has emerged as an effective way of controlling not only the fresh properties and printability of mixtures, but also their mechanical and durability properties. This paper presents the results of various durability related tests performed on 3D-printed mortars, including density, porosity, rate of water absorption and resistance to chloride penetration. Results of these tests indicate that the performance of mortar elements 3D-printed using controlled overlap process was similar to the performance of conventionally cast mortar elements with the same composition. Moreover, the results of the chloride transport related tests obtained from all specimens evaluated during the course of the study indicate low chloride ion penetrability, thus re-affirming that combination of the proposed material and 3D-printing method of fabrication have a potential for producing structural elements for applications in marine environments. 

There is an increasing interest in hierarchical design and additive manufacturing (AM) of cement‐based materials. However, the brittle behavior of these materials and the presence of interfaces from the AM process currently present a major challenge. Contrary to the commonly adopted approach in AM of cement‐based materials to eliminate the interfaces in 3D‐printed hardened cement paste (hcp) elements, this work focuses on harnessing the heterogeneous interfaces by employing novel architectures (based on bioinspired Bouligand structures). These architectures are found to generate unique damage mechanisms, which allow inherently brittle hcp materials to attain flaw‐tolerant properties and novel performance characteristics. It is hypothesized that combining heterogeneous interfaces with carefully designed architectures promotes such damage mechanisms as, among others, interfacial microcracking and crack twisting. This, in turn, leads to damage delocalization in brittle 3D‐printed architectured hcp and therefore results in quasi‐brittle behavior, enhanced fracture and damage tolerance, and unique load‐displacement response, all without sacrificing strength. It is further found that in addition to delocalization of the cracks, the Bouligand architectures can also enhance work of failure and inelastic deflection of the architectured hcp elements by over 50% when compared to traditionally cast elements from the same materials.

 

Vanadium dioxide (VO₂) is a well‐studied Mott‐insulator because of the very abrupt physical property switching during its semiconductor‐to‐metal transition (SMT) around 341 K (68 °C). In this work, through novel oxide‐metal nanocomposite designs (i.e., Au:VO₂and Pt:VO₂), a very broad range of SMT temperature tuning from≈323.5 to≈366.7 K has been achieved by varying the metallic secondary phase in the nanocomposites (i.e., Au:VO₂and Pt:VO₂thin films, respectively). More surprisingly, the SMTT_ccan be further lowered to≈301.8 K (near room temperature) by reducing the Au particle size from 11.7 to 1.7 nm. All the VO₂nanocomposite thin films maintain superior phase transition performance, i.e., large transition amplitude, very sharp transition, and narrow width of thermal hysteresis. Correspondingly, a twofold variation of the complex dielectric function has been demonstrated in these metal‐VO₂nanocomposites. The wide range physical property tuning is attributed to the band structure reconstruction at the metal‐VO₂phase boundaries. This demonstration paved a novel approach for tuning the phase transition property of Mott‐insulating materials to near room temperature transition, which is important for sensors, electrical switches, smart windows, and actuators.