Reversibility of structural phase transformations has profound technological implications in a wide range of applications from fatigue life in shape-memory alloys (SMAs) to magnetism in multiferroic oxides. The geometric nonlinear theory of martensite universally applicable to all structural transitions has been developed. It predicts the reversibility of the transitions as manifested in the hysteresis behaviour based solely on crystal symmetry and geometric compatibilities between phases. In this article, we report on the verification of the theory using the high-throughput approach. The thin-film composition-spread technique was devised to rapidly map the lattice parameters and the thermal hysteresis of ternary alloy systems. A clear relationship between the hysteresis and the middle eigenvalue of the transformation stretch tensor as predicted by the theory was observed for the first time. We have also identified a new composition region of titanium-rich SMAs with potential for improved control of SMA properties.

High cyclic stability of the elastocaloric effect in sputtered TiNiCu shape memory filmsVapor compression (VC) is by far the most dominant technology for meeting all cooling and refrigeration needs around the world. It is a mature technology with the efficiency of modern compressors approaching the theoretical limit, but its environmental footprint remains a global problem. VC refrigerants such as hydrochloroflurocarbons (HCFCs) and hydrofluorocarbons (HFCs) are a significant source of green house gas emissions, and their global warming potential (GWP) is as high as 1000 times that of CO 2 [Buildings Energy Data Book (Building Technologies Program, Department of Energy, 2009)]. There is an urgent need to develop an alternative high-efficiency cooling technology that is affordable and environmentally friendly [A. D. Little, Report For Office of Building Technology State and Community Programs, Department of Energy, 2001]. Here, we demonstrate that elastocaloric cooling (EC), a type of solid-state cooling mechanism based on the latent heat of reversible martensitic transformation, can have the coefficient of performance as high as %11, with a directly measured DT of 17 C. The solid-state refrigerant of EC completely eliminates the use of any GWP refrigerants including HCFCs/HFCs. V C 2012 American Institute of Physics. [http://dx.

We report the facile hydrothermal synthesis and surface functionalization of branched polyethyleneimine (PEI)-coated iron oxide nanoparticles (Fe3O4-PEI NPs) for biomedical applications. In this study, Fe3O4-PEI NPs were synthesized via a one-pot hydrothermal method in the presence of PEI. The formed Fe3O4-PEI NPs with primary amine groups on the surface were able to be further functionalized with polyethylene glycol (PEG), acetic anhydride, and succinic anhydride, respectively. The formed pristine and functionalized Fe3O4-PEI NPs were characterized via different techniques. We showed that the sizes of the Fe3O4-PEI NPs were able to be controlled by varying the mass ratio of Fe(II) salt and PEI. In addition, the formed Fe3O4-PEI NPs with different surface functionalities had good water dispersibility, colloidal stability, and relatively high R2 relaxivity (130-160 1/(mM·s)). Cell viability assay data revealed that the surface PEGylation and acylation of Fe3O4-PEI NPs rendered them with good biocompatibility in the given concentration range, while the pristine aminated Fe3O4-PEI NPs started to display slight toxicity at the concentration of 50 μg/mL. Importantly, macrophage cellular uptake results demonstrated that both PEGylation and acetylation of Fe3O4-PEI NPs were able to significantly reduce the nonspecific macrophage uptake, likely rendering the particles with prolonged circulation time. With the proven hemocompatibility and rich amine conjugation chemistry, the Fe3O4-PEI NPs with different surface functionalities may be applied for various biomedical applications, especially for magnetic resonance imaging and therapy.

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Elastocaloric cooling is a new alternative solid-state cooling technology undergoing early stage research and development. This study presents a comprehensive review of key issues related to achieving a successful elastocaloric cooling system. Fundamentals in elastocaloric materials are reviewed. The basic and advanced thermodynamic cycles are presented based on analogy from other solid-state cooling technologies. System integration issues are discussed to characterize the next generation elastocaloric cooling prototype. Knowledge acquired from the elastocaloric heat engines is provided as the basis for the design of cooling system configuration. Commercially available drivers enabling proper compression and tension are also presented. A few performance assessment indices are proposed and discussed as guidelines for design and evaluation of future elastocaloric cooling system. A brief summary of the up-to-date elastocaloric cooling prototypes is presented as well.

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise to quasi-linear stressstrain behaviors with extremely small hysteresis, leading to enhancement in the materials efficiency by a factor of five. Furthermore, despite being composed of more than 50% intermetallic phases, the reversible, repeatable elastocaloric performance of this material is shown to be stable over one million cycles. This result opens the door for direct implementation of additive manufacturing to elastocaloric cooling systems where versatile design strategy enables both topology optimization of heat exchangers as well as unique microstructural control of metallic refrigerants.One Sentence Summary: 3D printing produces highly efficient solid-state cooling nanocomposites with long fatigue life.