Miscibility and phase structure of binary blends of polylactide and poly(methyl methacrylate)

Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (T_g) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated T_g's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The T_g composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003     

Ab-initio molecular dynamics simulation on nano-system under external pressure

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.

     

Synthesis and Crystal Structure of Organocobalt(III) Complexes with Secondary Alkyls or Bulky Schiff Base Equatorial Ligands

Alkylcobalt(III) Schiff base B(12) model complexes with secondary alkyls or a bulky diamine in the equatorial position were synthesized and characterized. Structures have been first determined by X-ray diffraction analysis for i-C(4)H(9)Co(salen)(gamma-pic) (I), n-C(3)H(7)Co(salen)(gamma-pic) (II) and C(2)H(5)Co(SB) (III), where salen = N,N'-ethylenebis(salicylideneamine) dianion; SB = 1,1,2,2-tetramethyl-N,N'-ethylenebis(salicylideneamine) dianion, gamma-pic = gamma-picoline. Crystal data for I (CoC(26)N(3)O(2)H(30)): space group P2(1)/c with a = 6.661(5) ?, b = 18.612(2) ?, c = 19.533(3) ?, beta = 98.93(1) degrees, V = 2392.10 ?(3), D(calcd) = 1.320 g.cm(-3), Z = 4, and R = 0.048 for 4469 measured reflections. Crystal data for II (CoC(25)N(3)O(2)H(28)): space group P2(1)/c, a = 9.609(6) ?, b = 19.169(8) ?, c = 12.995(9) ?, beta = 106.9(7) degrees, V = 2290.4 ?(3), D(calcd) = 1.332 g.cm(-1), Z = 4, and R = 0.048 for 4358 measured reflections. Crystal data for III (CoC(22)N(2)O(2)H(27)): space group P2(1)/c, a = 8.318(3) ?, b = 21.579(2) ?, c = 11.572(2) ?, beta = 93.35(1) degrees, V = 2073.7 ?(3), D(calcd) = 1.314 g.cm(-1), Z = 4, and R = 0.060 for 3954 measured reflections. The crystal structure data reveal that complexes I and II display six-coordinate octahedral geometry; their Co-C, Co-N bond lengths, as well as the Co-C-C angles, are very close to those in 5'-deoxyadenosylcobalamin. Complex III is one of the very few compounds having five-coordinate square pyramidal geometry and observed instability of the Co-C bond.     

Rationally Designed Three-Layered Cu2S@Carbon@MoS2 Hierarchical Nanoboxes for Efficient Sodium Storage

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three-layered Cu₂S@carbon@MoS₂ as anode materials for sodium-ion batteries is reported. Through a facile multistep template-engaged strategy, ultrathin MoS₂ nanosheets are grown on nitrogen-doped carbon-coated Cu₂S nanoboxes to realize the Cu₂S@carbon@MoS₂ configuration. The design shortens the diffusion path of electrons/Na⁺ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three-layered Cu₂S@carbon@MoS₂ hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life.     

Fabrication of Heterostructured Fe2TiO5–TiO2 Nanocages with Enhanced Photoelectrochemical Performance for Solar Energy Conversion

Photocatalysts with well‐designed compositions and structures are desirable for achieving highly efficient solar‐to‐chemical energy conversion. Heterostructured semiconductor photocatalysts with advanced hollow structures possess beneficial features for promoting the activity towards photocatalytic reactions. Here we develop a facile synthetic strategy for the fabrication of Fe₂TiO₅–TiO₂ nanocages (NCs) as anode materials in photoelectrochemical (PEC) water splitting cells. A hydrothermal reaction is performed to transform MIL‐125(Ti) nanodisks (NDs) to Ti–Fe–O NCs, which are further converted to Fe₂TiO₅–TiO₂ NCs through a post annealing process. Owing to the compositional and structural advantages, the heterostructured Fe₂TiO₅–TiO₂ NCs show enhanced performance for PEC water oxidation compared with TiO₂ NDs, Fe₂TiO₅ nanoparticles (NPs) and Fe₂TiO₅–TiO₂ NPs.     

Rationally Designed Three‐Layered Cu2S@Carbon@MoS2 Hierarchical Nanoboxes for Efficient Sodium Storage

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three‐layered Cu₂S@carbon@MoS₂ as anode materials for sodium‐ion batteries is reported. Through a facile multistep template‐engaged strategy, ultrathin MoS₂ nanosheets are grown on nitrogen‐doped carbon‐coated Cu₂S nanoboxes to realize the Cu₂S@carbon@MoS₂ configuration. The design shortens the diffusion path of electrons/Na⁺ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three‐layered Cu₂S@carbon@MoS₂ hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life.     

α‐Chlorination of Acetophenones Using 1,3‐Dichloro‐5,5‐Dimethylhydantoin

A novel method for the synthesis of α‐chloroacetophenones using 1,3‐dichloro‐5,5‐dimethylhydantoin (DCDMH) and p‐toluenesulfonic acid in methanol at 30–35°C is described. Substituted acetophenones at the para position or meta position of aromatic ring give α‐chloroacetophenones in high yield. However, reaction of o‐nitroacetophenone does not take place under the same condition.     

聚对苯二甲酸乙二酯的非等温结晶行为

用付里叶变换红外光谱法、示差扫描量热、广角Ｘ 射线衍射和密度法等手段，研究了聚对苯二甲酸乙二酯（ＰＥＴ）的非等温结晶行为．在１１０℃以上，ＰＥＴ的结晶度随温度的升高而增加；在１６０～２３０℃温度区间，ＰＥＴ的结晶度随温度的升高变化不大．但在其后的降温过程中，其结晶度显著增加．从高温缓冷试样的结晶度明显地比淬火试样的高．实验结果有力地支持了高聚物在结晶前链的折叠就已经形成的观点．     

Atomistic simulations of nonequilibrium crystal-growth kinetics from alloy melts

Nonequilibrium kinetic properties of alloy crystal-melt interfaces are calculated by molecular-dynamics simulations. The relationships between the interface velocity, thermodynamic driving force, and solute partition coefficient are computed and analyzed within the framework of kinetic theories accounting for solute trapping and solute drag. The results show a transition to complete solute trapping at high growth velocities, establish appreciable solute drag at low growth velocities, and provide insights into the nature of crystalline anisotropies and solute effects on interface mobilities.     

Temperature dependent photoluminescence properties of needle-like ZnO nanostructures deposited on carbon nanotubes

The structural and optical properties of the needle-like ZnO nanostructure grown on the carbon nanotubes (ZnO/CNTs) have been studied by scanning electron microscope (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectra. It can be seen that there is about tens of nanometers in diameter of the single ZnO nanorod from the SEM picture. The XRD analysis shows that the prepared film is of typical wurtzite hexagonal phase without impurity. Temperature dependence of electronic transitions in the ZnO/CNTs has been investigated by PL in detail. The emission features in near band gap at 10 K reveal a redshift trend compared to ZnO single crystal, which is associated with the strong interfacial connection between ZnO and CNTs. Moreover, the intensities of all transitions in near band gap and visible regions decrease with increasing the temperature but increase with the excitation power. It can be concluded that the combined effect from ZnO and CNTs plays an important role in the PL response. The emission variations with the temperature for the ZnO/CNTs are the result of the electron–phonon interaction and the lattice thermal expansion.