The stability of gold nanoparticles modified with heterobifunctional poly (ethylene glycol) (PEG) were investigated. An effective method for preparing hetero-bifunctional PEG by anionic ring-opening polymerization was...
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(纸本)1877040193
The stability of gold nanoparticles modified with heterobifunctional poly (ethylene glycol) (PEG) were investigated. An effective method for preparing hetero-bifunctional PEG by anionic ring-opening polymerization was also developed. Streptavidin-PEG gold nanoparticle showed extremely high response with biotinylated surface plasmon resonance (SPR) sensors. PEG-modified gold nanoparticles showed remarkable stability in physiological conditions, such as the solution of high ionic strength.
We have performed a detailed study of the magnetic and structural properties of the compound Nd5(Si0.6Ge0.4)4 by means of neutron powder diffraction, magnetization, linear thermal expansion, and magnetostriction exper...
We have performed a detailed study of the magnetic and structural properties of the compound Nd5(Si0.6Ge0.4)4 by means of neutron powder diffraction, magnetization, linear thermal expansion, and magnetostriction experiments. A coupled magnetic and crystallographic first-order transformation from a room-temperature monoclinic Gd5Si2Ge2-type paramagnetic state to a low-temperature orthorhombic Gd5Si4-type ferromagnetic structure takes place on cooling at ∼68K. This magnetostructural transition shifts towards higher temperatures by the application of an external magnetic field at a rate of 0.11(1)K∕kOe, which is lower than the ∼0.6to∼0.3K∕kOe observed in the Gd5(SixGe1−x)4 and Tb5(SixGe1−x)4 compounds. The magnetostructural transformation cannot be completed in the isothermal regime by a 120kOe magnetic field. It is suggested that the single-ion anisotropy of the Nd ions hinders the completion of the field-induced transformation. The existence of a simultaneous magnetic and crystallographic transformation in this alloy, which is in sharp contrast with other previously studied Nd5(SixGe1−x)4 alloys, is discussed in terms of the role of interstitial impurities in triggering and coupling/decoupling the crystallographic transition.
The room temperature crystal structures of Er5SixGe4−x alloys change systematically with the concentration of Ge from the orthorhombic Gd5Si4-type when x=4, to the monoclinic Gd5Si2Ge2 type when 3.5⩽x⩽3.9 and to the o...
The room temperature crystal structures of Er5SixGe4−x alloys change systematically with the concentration of Ge from the orthorhombic Gd5Si4-type when x=4, to the monoclinic Gd5Si2Ge2 type when 3.5⩽x⩽3.9 and to the orthorhombic Sm5Ge4 type for x⩽3. The Curie-Weiss behavior of Er5SixGe4−x materials is consistent with the Er3+ state. The compounds order magnetically below 30K, apparently adopting complex noncollinear magnetic structures with magnetization not reaching saturation in 50kOe magnetic fields. In Er5Si4, the structural-only transformation from the monoclinic Gd5Si2Ge2-type to the orthorhombic Gd5Si4-type phase occurs around 218K on heating. Intriguingly, the temperature of this polymorphic transformation is weakly dependent on magnetic fields as low as 40kOe (dT∕dH=−0.058K∕kOe) when the material is in the paramagnetic state nearly 200K above its spontaneous magnetic ordering temperature. It appears that a magnetostructural transition may be induced in the 5:4 erbium silicide at ∼18K and above by 75kOe and higher magnetic fields. Only Er5Si4 but none of the other studied Er5SixGe4−x alloys exhibit magnetic field induced transformations, which are quite common in the closely related Gd5SixGe4−x system. The magnetocaloric effects of the Er5SixGe4−x alloys are moderate.
The observed magnetoresistance of single crystalline Gd5Si2Ge2 is negative and strongly anisotropic. The absolute values measured along the [100] and [010] directions exceed those parallel to the [001] direction by mo...
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The observed magnetoresistance of single crystalline Gd5Si2Ge2 is negative and strongly anisotropic. The absolute values measured along the [100] and [010] directions exceed those parallel to the [001] direction by more than 60%. First principles calculations demonstrate that a structural modification is responsible for the anisotropy of the magnetoresistance, and that the latter is due to a significant reduction of electronic velocity in the [100] direction and the anisotropy of electrical conductivity.
Femtosecond laser ablation studies of silicon with and without the native oxide on the surface were conducted in an ultrahigh vacuum environment. SEM results show a clear difference in the laser intensity threshold fo...
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Optical coherence tomography (OCT), confocal, and multiphoton microscopy are used to nondestructively monitor in situ cell distribution and cell-matrix interaction in 3-D engineered tissues composed of chitosan scaffo...
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A series of linear polyethylenimines (LPEIs) with various molecular weights were synthesized and used for pH-dependent polypseudorotaxane formation with α- or γ-cyclodextrins (α-, γ-CDs). The polypseudorotaxane fo...
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A series of linear polyethylenimines (LPEIs) with various molecular weights were synthesized and used for pH-dependent polypseudorotaxane formation with α- or γ-cyclodextrins (α-, γ-CDs). The polypseudorotaxane formation was significantly dependent on the pH of the aqueous media. The maximum yield of the recovered polypseudorotaxane precipitates was observed at pH 11.0, whereas no complexation was observed in the pH range below 8.0 due to the protonation of secondary amine groups in LPEI backbones. This suggests that the ionization of the secondary amine groups leads to dethreading of CD molecules because PEI chains with cationic nature disfavor the hydrophobic cavities of CDs. The solid-state 13C CP/MAS NMR and X-ray diffraction measurements verified the successful formation of crystalline polypseudorotaxanes through the inclusion complexation. In addition, 1H NMR analysis showed that LPEI formed a 2:1 inclusion complex with α-CD ([EI]:[α-CD] = 2:1) and a 4:1 complex with γ-CD ([EI]:[γ-CD] = 4:1) as reported in the poly(ethylene glycol)-based polypseudorotaxane system. Such unique pH-controllable polypseudorotaxane formation may be useful in designing many building blocks for stimuli-responsive polyrotaxanes.
We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness...
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We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness dL increased as well as the reduced tethering density σ˜ of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at σ˜*∼3.7–3.8 as evidenced by an abrupt change in the slope between (dL)−1 and Tx. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.
Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic f...
Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic field of ∼8.4kOe is applied along the c direction, and irreversible metamagneticlike transitions when a 20 kOe or greater magnetic field is applied at 4.3 K along any of the three crystallographic axes are observed. Although Gd3+ ions have negligible single ion anisotropy, the metamagnetic transitions and magnetization of Gd5Ge4 in the ferromagnetic state depend on the crystallographic direction reflecting the anisotropy of the exchange interactions due to the distinctly layered Sm5Ge4-type crystal structure.
In this study, various thicknesses of Pd catalytic films were deposited on Ti/Si substrates and pretreated with NH/sub 3/. The effects of catalyst deposition parameters and NH/sub 3/ pretreatment time (0, 1, and 10 mi...
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In this study, various thicknesses of Pd catalytic films were deposited on Ti/Si substrates and pretreated with NH/sub 3/. The effects of catalyst deposition parameters and NH/sub 3/ pretreatment time (0, 1, and 10 minutes) on the size distribution of Pd catalytic particles, and subsequently, on the diameter and density of synthesized carbon nanotubes (CNTs) were investigated. The CNTs were synthesized by thermal CVD at 750/spl deg/C using methane (CH/sub 4/) as the carbon source, and a mixture of Ar/H/sub 2/ (80 vol.%/20 vol.%) as the carrier gas.
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