The effects of casting currents on the thermophysical behaviors, atomic and nanoscale structure, and mechanical properties of two Zr-based-bulk metallic glasses, i.e., Zr59Cu33A18 and Zr59（Cuo.55Feo.45）33A18, were s...The effects of casting currents on the thermophysical behaviors, atomic and nanoscale structure, and mechanical properties of two Zr-based-bulk metallic glasses, i.e., Zr59Cu33A18 and Zr59（Cuo.55Feo.45）33A18, were studied by using differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering, as well as compression tests. The casting currents can be tuned to change the casting initiative temperature. Results revealed that there is no anomalous structural change for the Zr59Cu33A18 molten liquid before crystallization during cooling with different casting currents. In contrast, liquid-state phase separation was suggested to occur in the Zr59（Cuo.55Feo.45）33A18 molten liquid prepared using lower casting current before crystallization during cooling. The position shift of the first sharp diffraction peak for the diffraction pattern of Zr59（Cuo.55Feo.45）33A18 shows that the density of the molten liquid may decrease upon cooling at different casting currents. The small-angle X-ray scattering results indicate that the heterogeneity of the Zr59（Cuo.55- Feo.gs）33A18 metallic glasses increases with decreasing the casting temperature. As a result, the metallic glasses with a liquid-state phase separation possess better mechanical properties, including higher-yielding stress and more significant compressive ductility. The increase in degree of heterogeneity formed by nanoscale liquid-state phase separation and their interactions with the shear bands for the Zr-Cu-Fe-Al bulk metallic glasses were suggested to be responsible for the enhanced mechanical properties.展开更多
Lipids exhibit an extraordinary polymorphism in self-assembled mesophases, with lamellar phases as the most relevant biological representative. To mimic lipid lamellar phases with amphiphilic designer peptides, seven ...Lipids exhibit an extraordinary polymorphism in self-assembled mesophases, with lamellar phases as the most relevant biological representative. To mimic lipid lamellar phases with amphiphilic designer peptides, seven systematically varied short peptides were engineered. Indeed, four peptide candidates （V4D, V4WD, V4WD2, I4WD2） readily self-assembled into lamellae in aqueous solution. Small-angle X-ray scattering （SAXS） patterns revealed ordered lamellar structures with a repeat distance of 4-5 nm. Transmission electron microscopy （TEM） images confirmed the presence of stacked sheets. Two derivatives （V3D and V4D2） remained as loose aggregates dispersed in solution; one peptide （L4WD2） formed twisted tapes with internal lameUae and an antiparaUel -type monomer aligrtment. To understand the interaction of peptides with lipids, they were mixed with phosphatidylcholines. Low peptide concentrations （1.1 mM） induced the formation of a heterogeneous mixture of vesicular structures. Large multilamellar vesicles （MLV, d-spacing - 6.3 nm） coexisted with oligo- or unilamellar vesicles （- 50 nm in diameter） and bicelle-like structures （- 45 nm length, - 18 nm width）. High peptide concentrations （11 mM） led to unilamellar vesicles （ULV, diameter - 260-280 nm） with a homogeneous mixing of lipids and peptides. SAXS revealed the temperature-dependent fine structure of these ULVs. At 25 ℃ the bilayer is in a fully Interdigitated state （headgroup-to-headgroup distance dH, -2.9 nm）, whereas at 50 ℃this interdigitation opens up （dtm- 3.6 nm）. Our results highlight the versatility of self-assembled peptide superstructures. Subtle changes in the amino acid composition are key design elements in creating peptide- or lipid- peptide nanostructures with richness in morphology similar to that of naturally occurrin~ lioids.展开更多
基金Si Lan would like to acknowledge the support from the National Natural Science Foundation of China （Grant Nos. 51501090 and 51520105001）, as well as the support from the Natural Science Foundation of Jiangsu Province （Grant No. BK20171425）, and the Fundamental Research Funds for the Central Universities （No. 30915015103）. Tao Feng acknowledges the support from the NSFC with Grant No. 51571119 and the Fundamental Research Funds for the Central Universities （No. 30916011106）. Bao-an Sun acknowledges the support from the NSFC with Grant No. 51671121 and the Fundamental Research Funds for the Central Universities （No. 30917015107）. Si Lan acknowledges the useful discussion with Prof. Hui-xing Song from the Nanjing Huaxing Vessel Pressure Manufacture Co., Ltd.
文摘The effects of casting currents on the thermophysical behaviors, atomic and nanoscale structure, and mechanical properties of two Zr-based-bulk metallic glasses, i.e., Zr59Cu33A18 and Zr59（Cuo.55Feo.45）33A18, were studied by using differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering, as well as compression tests. The casting currents can be tuned to change the casting initiative temperature. Results revealed that there is no anomalous structural change for the Zr59Cu33A18 molten liquid before crystallization during cooling with different casting currents. In contrast, liquid-state phase separation was suggested to occur in the Zr59（Cuo.55Feo.45）33A18 molten liquid prepared using lower casting current before crystallization during cooling. The position shift of the first sharp diffraction peak for the diffraction pattern of Zr59（Cuo.55Feo.45）33A18 shows that the density of the molten liquid may decrease upon cooling at different casting currents. The small-angle X-ray scattering results indicate that the heterogeneity of the Zr59（Cuo.55- Feo.gs）33A18 metallic glasses increases with decreasing the casting temperature. As a result, the metallic glasses with a liquid-state phase separation possess better mechanical properties, including higher-yielding stress and more significant compressive ductility. The increase in degree of heterogeneity formed by nanoscale liquid-state phase separation and their interactions with the shear bands for the Zr-Cu-Fe-Al bulk metallic glasses were suggested to be responsible for the enhanced mechanical properties.
文摘Lipids exhibit an extraordinary polymorphism in self-assembled mesophases, with lamellar phases as the most relevant biological representative. To mimic lipid lamellar phases with amphiphilic designer peptides, seven systematically varied short peptides were engineered. Indeed, four peptide candidates （V4D, V4WD, V4WD2, I4WD2） readily self-assembled into lamellae in aqueous solution. Small-angle X-ray scattering （SAXS） patterns revealed ordered lamellar structures with a repeat distance of 4-5 nm. Transmission electron microscopy （TEM） images confirmed the presence of stacked sheets. Two derivatives （V3D and V4D2） remained as loose aggregates dispersed in solution; one peptide （L4WD2） formed twisted tapes with internal lameUae and an antiparaUel -type monomer aligrtment. To understand the interaction of peptides with lipids, they were mixed with phosphatidylcholines. Low peptide concentrations （1.1 mM） induced the formation of a heterogeneous mixture of vesicular structures. Large multilamellar vesicles （MLV, d-spacing - 6.3 nm） coexisted with oligo- or unilamellar vesicles （- 50 nm in diameter） and bicelle-like structures （- 45 nm length, - 18 nm width）. High peptide concentrations （11 mM） led to unilamellar vesicles （ULV, diameter - 260-280 nm） with a homogeneous mixing of lipids and peptides. SAXS revealed the temperature-dependent fine structure of these ULVs. At 25 ℃ the bilayer is in a fully Interdigitated state （headgroup-to-headgroup distance dH, -2.9 nm）, whereas at 50 ℃this interdigitation opens up （dtm- 3.6 nm）. Our results highlight the versatility of self-assembled peptide superstructures. Subtle changes in the amino acid composition are key design elements in creating peptide- or lipid- peptide nanostructures with richness in morphology similar to that of naturally occurrin~ lioids.
