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Abstract Thermal insulation materials reduce heat transfer and are typically made from materials like fiberglass, foam, or mineral wool, which are engineered to trap air and hinder heat conduction and convection. The traditional manufacturing processes of thermal insulation materials are often energy-intensive and result in significant greenhouse gas emissions. In the current global drive for sustainability, these energy-intensive manufacturing processes raise environmental concerns and need to be addressed. In this work, with the objective of addressing both material sustainability and manufacturing sustainability, we present an additive manufacturing strategy to fabricate biomass materials for thermal insulation applications. We propose utilizing wheat straw as a biomass feedstock for manufacturing sustainable thermal insulation. This approach captures carbon during growth and stores it within the insulation structure. In the presented work, we first demonstrate the formulation of a 3D-printable ink using chopped straw fibers. We conduct comprehensive rheological characterizations to reveal the shear-thinning properties and the printability of the straw fiber ink. Utilizing the direct ink writing (DIW) process, the straw fiber material is deposited into 3D structures. Through material characterization tests, which include microstructure, mechanical, and thermal analyses, we demonstrate the low thermal conductivity and robust mechanical properties. This paper marks the first work of 3D printing of wheat straw fibers for thermal insulation structures. The discoveries in this pilot work demonstrate the potential to leverage additive manufacturing technologies and sustainable biomass materials to create both functional and value-added wheat straw parts tailored for thermal insulation applications. 

Thermal insulation materials reduce heat transfer and are typically made from materials like fiberglass, foam, or mineral wool, which are engineered to trap air and hinder heat conduction and convection. The traditional manufacturing processes of thermal insulation materials are often energy-intensive and result in significant greenhouse gas emissions. In the current global drive for sustainability, these energy-intensive manufacturing processes raise environmental concerns and need to be addressed. In this work, with the objective of addressing both material sustainability and manufacturing sustainability, we present an additive manufacturing strategy to fabricate biomass materials for thermal insulation applications. Firstly, we propose to use biomass materials, such as wheat straw, as the primary feedstock materials for manufacturing. Such biomass materials offer the unique capacity to sequester carbon dioxide during their growth, and when incorporated into thermal insulation structures, they effectively capture and store carbon inside the structure. Concurrently, our pursuit of manufacturing process sustainability is driven by using a cost-effective additive manufacturing technology to fabricate durable thermal insulation structures. In the presented work, we first demonstrate the formulation of a 3D-printable ink using chopped straw fibers. We conduct comprehensive rheological characterizations to reveal the shear-thinning properties and the printability of the straw fiber ink. Utilizing the direct ink writing (DIW) process, the straw fiber material is deposited into 3D structures. Following bulk material characterization tests, including microstructure, mechanical, and thermal tests. We unveil the low thermal conductivity and robust mechanical properties. This paper marks the first work of 3D printing of wheat straw fibers for thermal insulation structures. The discoveries in this pilot work demonstrate the potential to leverage additive manufacturing technologies and sustainable biomass materials to create both functional and value-added wheat straw parts tailored for thermal insulation applications. 

Micro Projection-based Stereolithography (µPSL), also known as micro vat photopolymerization, is a promising technology that could revolutionize microfabrication by providing benefits similar to traditional lithography while reducing production time and cost. However, it faces a significant challenge in the form of the "proximity effect." This effect occurs when adjacent features are too close together, causing undesirable artifacts and limiting the achievable fabrication resolution. The proximity effect is caused by interactions between adjacent pixels of light and affects both the spatial and temporal domains of the fabrication process. Although researchers have been aware of this issue for some time, there has been little progress in understanding and addressing the proximity effect in micro vat photopolymerization. Existing models developed for laser-based systems can explain the effect to some extent, but they do not fully account for the impact of large area projection or explain how local threshold changes affect part size. This research aims to fill this knowledge gap by using in-situ observation systems to experimentally study the spatial and temporal proximity effects in single-shot vat photopolymerization microfabrication. We also investigate the role of oxygen in the proximity effect and lay the groundwork for better understanding how the effect impacts periodic structures with micronic inter-feature distances. In conclusion, while micro vat photopolymerization offers significant advantages over traditional lithography, the proximity effect remains a significant obstacle. This research represents an important step forward in addressing this challenge and improving the accuracy and resolution of vat photopolymerization in microfabrication. 

The selection of electronically-different thiolate-based photosensitizers is employed to achieve a precise and specific C–F bond defluorination of a broad range of trifluoromethylarenes, enabling the synthesis of 88 α,α-difluoromethyl compounds. 

Abstract Direct ink writing (DIW) process is a facile additive manufacturing technology to fabricate three-dimensional (3D) objects with various materials. Its versatility has attracted considerable interest in academia and industry in recent years. As such, upsurging endeavors are invested in advancing the ink flow behaviors in order to optimize the process resolution and the printing quality. However, so far, the physical phenomena during the DIW process are not revealed in detail, leaving a research gap between the physical experiments and its underlying theories. Here, we present a comprehensive analytical study of non-Newtonian ink flow behavior during the DIW process. Different syringe-nozzle geometries are modeled for the comparative case studies. By using the computational fluid dynamics (CFD) simulation method, we reveal the shear-thinning property during the ink extrusion process. Besides, we study the viscosity, shear stress, and velocity fields, and analyze the advantages and drawbacks of each syringe-nozzle model. On the basis of these investigations and analyses, we propose an improved syringe-nozzle geometry for stable extrusion and high printing quality. A set of DIW printing experiments and rheological characterizations are carried out to verify the simulation studies. The results developed in this work offer an in-depth understanding of the ink flow behavior in the DIW process, providing valuable guidelines for optimizing the physical DIW configuration toward high-resolution printing and, consequently, improving the performance of DIW-printed objects. 

Abstract Stimuli-responsive elastic metamaterials augment unique subwavelength features and wave manipulation capabilities with a degree of tunability, which enables them to cut across different time scales and frequency regimes. Here, we present an experimental framework for robust local resonance bandgap control enabled by enhanced magneto-mechanical coupling properties of a magnetorheological elastomer, serving as the resonating stiffness of a metamaterial cell. During the curing process, ferromagnetic particles in the elastomeric matrix are aligned under the effect of an external magnetic field. As a result, particle chains with preferred orientation form along the field direction. The resulting anisotropic behavior significantly boosts the sensitivity of the metamaterial’s elastic modulus to the imposed field during operation, which is then exploited to control the dispersive dynamics and experimentally shift the location and width of the resonance-based bandgap along the frequency axis. Finally, numerical simulations are used to project the performance of the magnetically-tunable metamaterial at stronger magnetic fields and increased levels of material anisotropy, as a blueprint for broader implementations of in situ tunable active metamaterials. 

Abstract As a facile and versatile additive manufacturing technology, direct ink writing (DIW) has attracted considerable interest in academia and industry to fabricate three-dimensional structures with unique properties and functionalities. However, so far, the physical phenomena during the DIW process are not revealed in detail, leaving a research gap between the physical experiments and the underlying theories. Here, we presented a comprehensive simulation study of non-Newtonian ink flow during the DIW process. We used the computational fluid dynamics (CFD) method and revealed the shear-thinning behavior during the extrusion process. Different nozzle geometry models were adopted in the simulation. The advantages and drawbacks of each syringe-nozzle geometry were analyzed. In addition, the ink shear stress and velocity fields were investigated and compared in the case studies. Based on these investigations and analysis, we proposed an improved syringe-nozzle geometry towards high-resolution DIW. Consequently, the high-resolution and high shape fidelity DIW could enhance the DIW product performance. The results developed in this work offer valuable guidelines and could accelerate further advancement of DIW. 

Achieving a mesoporous structure in superinsulation materials is pivotal for guaranteeing a harmonious relationship between low thermal conductivity, high porosity, and low density. Herein, we report silica-based cryogel and aerogel materials by implementing freeze-drying and ambient-pressure-drying processes respectively. The obtained freeze-dried cryogels yield thermal conductivity of 23 mW m −1 K −1 , with specific surface area of 369.4 m 2 g −1 , and porosity of 96.7%, whereas ambient-pressure-dried aerogels exhibit thermal conductivity of 23.6 mW m −1 K −1 , specific surface area of 473.8 m 2 g −1 , and porosity of 97.4%. In addition, the fiber-reinforced nanocomposites obtained via freeze-drying feature a low thermal conductivity (28.0 mW m −1 K −1 ) and high mechanical properties (∼620 kPa maximum compressive stress and Young's modulus of 715 kPa), coupled with advanced flame-retardant capabilities, while the composite materials from the ambient pressure drying process have thermal conductivity of 28.8 mW m −1 K −1 , ∼200 kPa maximum compressive stress and Young's modulus of 612 kPa respectively. The aforementioned results highlight the capabilities of both drying processes for the development of thermal insulation materials for energy-efficient applications.