Form and Object Garcia, Tristan; Ohm, Mark Allan; Cogburn, Jon
03/2014
eBook
What is a thing? What is an object? Tristan Garcia decisively overturns 100 years of Heideggerian orthodoxy about the supposedly derivative nature of objects to put forward a new theory of ontology ...that gives us deep insights into the world and our place in it.
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Biopolymer nanofibrils exhibit exceptional mechanical properties with a unique combination of strength and toughness, while also presenting biological functions that interact with the ...surrounding environment. These features of biopolymer nanofibrils profit from their hierarchical structures that spun angstrom to hundreds of nanometer scales. To maintain these unique structural features and to directly utilize these natural supramolecular assemblies, a variety of new methods have been developed to produce biopolymer nanofibrils. In particular, cellulose nanofibrils (CNFs), chitin nanofibrils (ChNFs), silk nanofibrils (SNFs) and collagen nanofibrils (CoNFs), as the four most abundant biopolymer nanofibrils on earth, have been the focus of research in recent years due to their renewable features, wide availability, low-cost, biocompatibility, and biodegradability. A series of top-down and bottom-up strategies have been accessed to exfoliate and regenerate these nanofibrils for versatile advanced applications. In this review, we first summarize the structures of biopolymer nanofibrils in nature and outline their related computational models with the aim of disclosing fundamental structure-property relationships in biological materials. Then, we discuss the underlying methods used for the preparation of CNFs, ChNFs, SNFs and CoNFs, and discuss emerging applications for these biopolymer nanofibrils.
Voxelated liquid crystal elastomers Ware, Taylor H.; McConney, Michael E.; Wie, Jeong Jae ...
Science (American Association for the Advancement of Science),
02/2015, Letnik:
347, Številka:
6225
Journal Article
Recenzirano
Dynamic control of shape can bring multifunctionality to devices. Soft materials capable of programmable shape change require localized control of the magnitude and directionality of a mechanical ...response. We report the preparation of soft, ordered materials referred to as liquid crystal elastomers.The direction of molecular order, known as the director, is written within local volume elements (voxels) as small as 0.0005 cubic millimeters. Locally, the director controls the inherent mechanical response (55% strain) within the material. In monoliths with spatially patterned director, thermal or chemical stimuli transform flat sheets into three-dimensional objects through controlled bending and stretching. The programmable mechanical response of these materials could yield monolithic multifunctional devices or serve as reconfigurable substrates for flexible devices in aerospace, medicine, or consumer goods.
Additive manufacturing (AM) is the process of printing 3D objects in a layer‐by‐layer manner. Polymers and their composites are some of the most widely used materials in modern industries and are of ...great interest in the field of AM due to their vast potential for various applications, especially in the medical, aerospace, and automotive industries. Many studies have been conducted to develop new polymer materials for AM techniques, which include vat photopolymerization, material jetting, powder bed fusion, material extrusion, binder jetting, and sheet lamination. Although several reviews on the development of polymer materials for AM have been published, most of them only focus on a specific application, process, or type of material. Therefore, this article serves to provide a comprehensive review on the progress in polymer material development for AM techniques. It begins with an introduction to different AM techniques, followed by highlighting the progress of their development. Material requirements, notable advances in newly developed materials and their potential applications are discussed in detail and summarized. This review concludes by identifying the major challenges currently encountered in using AM for polymer materials and providing insights into the valuable opportunities it presents, in hopes of spurring further development in this field.
Additive manufacturing (AM) has emerged as a disruptive technology that is utilized to fabricate products with complex geometries to enable great design freedom. This article reviews the recent progress on polymer materials for various AM techniques. Material requirements, notable advances in new AM polymer materials, and their potential applications are discussed and major challenges and future research directions are identified.
Biological materials, such as bones, teeth and mollusc shells, are well known for their excellent strength, modulus and toughness
. Such properties are attributed to the elaborate layered ...microstructure of inorganic reinforcing nanofillers, especially two-dimensional nanosheets or nanoplatelets, within a ductile organic matrix
. Inspired by these biological structures, several assembly strategies-including layer-by-layer
, casting
, vacuum filtration
and use of magnetic fields
-have been used to develop layered nanocomposites. However, how to produce ultrastrong layered nanocomposites in a universal, viable and scalable manner remains an open issue. Here we present a strategy to produce nanocomposites with highly ordered layered structures using shear-flow-induced alignment of two-dimensional nanosheets at an immiscible hydrogel/oil interface. For example, nanocomposites based on nanosheets of graphene oxide and clay exhibit a tensile strength of up to 1,215 ± 80 megapascals and a Young's modulus of 198.8 ± 6.5 gigapascals, which are 9.0 and 2.8 times higher, respectively, than those of natural nacre (mother of pearl). When nanosheets of clay are used, the toughness of the resulting nanocomposite can reach 36.7 ± 3.0 megajoules per cubic metre, which is 20.4 times higher than that of natural nacre; meanwhile, the tensile strength is 1,195 ± 60 megapascals. Quantitative analysis indicates that the well aligned nanosheets form a critical interphase, and this results in the observed mechanical properties. We consider that our strategy, which could be readily extended to align a variety of two-dimensional nanofillers, could be applied to a wide range of structural composites and lead to the development of high-performance composites.
The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design ...strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.
A photoresponsive hydrogel was constructed by using a supramolecular design strategy. A red‐shifted anthracene group furnishes the system with fast photo‐actuation. Hydrogen bonding, π–π interactions, and anthracene photodimerization results in an actuator with high mechanical strength, fast self‐healing, and recyclability.
A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a ...single ultraviolet‐light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up‐conversion (UC)PL of these CDs is also observed. Moreover, flexible full‐color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light‐emitting diodes, full‐color displays, and multiplexed (UC)PL bioimaging.
On the dot: A facile approach to photoluminescent carbon dots (CDs) that can be excited by a single wavelength and demonstrate emission of the three primary colors (red, green, and blue) is reported. The resulting CDs can be potentially used in the fabrication of flexible full‐color emission films and in multicolor cellular imaging.
Continuous liquid interface production of 3D objects Tumbleston, John R.; Shirvanyants, David; Ermoshkin, Nikita ...
Science (American Association for the Advancement of Science),
03/2015, Letnik:
347, Številka:
6228
Journal Article
Recenzirano
Odprti dostop
Additive manufacturing processes such as 3D printing use time-consuming, stepwise layer-by-layer approaches to object fabrication. We demonstrate the continuous generation of monolithic polymeric ...parts up to tens of centimeters in size with feature resolution below 100 micrometers. Continuous liquid interface production is achieved with an oxygen-permeable window below the ultraviolet image projection plane, which creates a "dead zone" (persistent liquid interface) where photopolymerization is inhibited between the window and the polymerizing part. We delineate critical control parameters and show that complex solid parts can be drawn out of the resin at rates of hundreds of millimeters per hour. These print speeds allow parts to be produced in minutes instead of hours.
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