微液滴在不同能量表面上润湿状态的分子动力学模拟

微小液滴在不同能量表面上的润湿状态对于准确预测非均相核化速率和揭示界面效应影响液滴增长微观机理具有重要意义. 通过分子动力学模拟, 研究了纳米级液滴在不同能量表面上的铺展过程和润湿形态. 结果表明, 固液界面自由能随固液作用强度增加而增加, 并呈现不同液滴铺展速率和润湿特性. 固液作用强度小于1.6的低能表面呈现疏水特征, 继续增强固液作用强度时表面变为亲水, 而固液作用强度大于3.5的高能表面上液体呈完全润湿特征. 受微尺度条件下非连续、非对称作用力影响, 微液滴气液界面存在明显波动, 呈现与宏观液滴不同的界面特征. 统计意义下, 微小液滴在不同能量表面上铺展后仍可以形成特定接触角, 该接触角随固液作用强度增加而线性减小, 模拟结果与经典润湿理论计算获得的结果呈现相似变化趋势. 模拟结果从分子尺度为核化理论中的毛细假设提供了理论支持, 揭示了液滴气液界面和接触角的波动现象, 为核化速率理论预测结果和实验测定结果之间的差异提供了定性解释.     

非晶碳氧化硅纳米线的合成与光致发光

利用直流电弧放电合成非晶碳氧化硅(SiCO)纳米线,不使用催化剂和模板,独立的SiCO 纳米线沉积在石墨锅的表面．通过XRD、SEM、TEM、XPS、FTIR等对SiCO纳米线进行了表征．结果表明,纳米线长度为20～100 μm,直径为10～100 nm,Si原子同C原子和氧原子分享成键组成SiCO单元．SiCO纳米线的光致发光谱在454和540 nm呈现了强而稳定的白色发光峰． SiCO纳米线的生长机制为等离子辅助气―固生长机制．     

Extended s-wave pairing symmetry on the triangular lattice heavy fermion system

We investigate the pairing symmetry of the Kondo-Heisenberg model on triangular lattice, which is believed to capture the core competition of Kondo screening and local magnetic exchange interaction in heavy electron compounds. On the dominant background of the heavy fermion state, the introduction of the Heisenberg antiferromagnetic interaction (J _H ) leads to superconducting pairing instability. Depending on the strength of the interactions, it is found that the pairing symmetry favours an extended s-wave for small J _H and high conduction electron density but a chiral \(d_{x^2 - y^2 } + id_{xy}\)-wave for large J _H and low conduction electron density, which provides a phase diagram of pairing symmetry from the calculations of the ground-state energy. The transition between these two pairing symmetries is found to be first-order. Furthermore, we also analyze the phase diagram from the pairing strengths and find that the phase diagram obtained is qualitatively consistent with that based on the ground-state energy. In addition, we propose an effective single-band BCS Hamiltonian, which is able to describe the low-energy thermodynamic behaviors of the heavy fermion superconducting states. These results further deepen the understanding of the antiferromagnetic interaction which results in a geometric frustration for the model studied. Our work may provide a possible scenario to understand the pairing symmetry of the heavy fermion superconductivity, which is one of active issues in very recent years.     

Ultrafast solvation dynamics at internal sites of staphylococcal nuclease investigated by site-directed mutagenesis

Internal solvation of protein was studied by site-directed mutagenesis,with which an intrinsically fluorescent probe,tryptophan,is inserted into the desired position inside a protein molecule for ultrafast spectroscopic study.Here we review this unique method for protein dynamics research.We first introduce the frontiers of protein solvation,site-directed mutagenesis,protein stability and characteristics,and the spectroscopic methods.Then we present time-resolved spectroscopic dynamics of solvation dynamics inside cavities of active sites.The studies are carried out on a globular protein,staphylococcal nuclease.The solvation at sites inside the protein molecule’s cavities clearly reveals characteristics of the local environment.These solvation behaviors are directly correlated to enzyme activity.     

Microwave-Assisted Synthesis,Structure and Properties of a Nano-Double-Bowl-Like Heptanuclear Nickel(II) Cluster

A nano-double-bowl-like heptanuclear nickel cluster [Ni₇(mmp)₆(OH)₆]₂·(ClO₄)₂·12H₂O (1, Hmmp is 2-methoxy-6-methyliminomethyl-phenol) has been synthesized through the microwave-assisted reaction of Ni(ClO₄)₂·6H₂O with 2-hydroxy-3-methoxy-benzaldehyde (Hhmb) and methylamine in distilled water only 29 min. The core of the complex 1 can be described as a double-bowl-like, while the dodecanuclear water cluster stands on the bowl. The magnetic investigation shows that 1 displays very weak ferromagnetic coupling between Ni^II ions.     

生长溶液配比对MnTeMoO6晶体形态的影响

采用顶部籽晶溶液法生长Mn Te Mo O6晶体,研究了在不同配比生长溶液中Mn Te Mo O6晶体的实际生长形态,模拟计算了Mn Te Mo O6晶体的理想生长形态,探讨了生长溶液配比对晶体形态的影响,选择的3种生长溶液中Mn Te Mo O6∶Te O2∶Mo O3摩尔比分别为1∶2∶2、1∶3∶2和1∶3∶3。结果表明,在3种配比的生长溶液中Mn Te Mo O6晶体的(110)面具有最大的面网密度和最小的生长速率;生长溶液中Te O2和Mo O3的含量和比例影响了晶体在不同方向的生长速率,从而影响到Mn Te Mo O6晶体的实际生长形态。     

Thermal study of HNIW(CL-20) and mixtures containing aluminum powder

The thermal behavior of the energetic material 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-tetracyclo-[5.5.0.0^5,9.0^3,11]-dodecane (HNIW or CL-20) and its mixtures with aluminum under linear temperature control condition and adiabatic condition were investigated by DSC-TG-MS-FT-IR and ARC. Two different particle sizes of aluminum powder (10 μm and 50 nm) were added into CL-20. The influence of particle size on the thermal behavior of CL-20 was studied by using of these apparatuses. The enthalpies of reaction and onset temperatures were determined for various heating rates. The kinetic parameters were found according to Kissinger method, Ozawa method, and Friedman method based on DSC data. The gaseous products from the decomposition of CL-20 and its mixtures were determined by simultaneous MS-FT-IR experiments. ARC measurements were performed to investigate the thermal stability of the samples. The onset temperature, adiabatic temperature rise, self-heat rate, time to maximum rate, and pressure–temperature profile were found from the data measured by ARC. Based on these results, the catalytic effect of aluminum powder was studied.     

超声法合成CePO4纳米线及发光性能研究

用CeO2作为铈源,采用可重复利用的H3PO4及非模板剂的情况下,用低温超声法成功合成了六方结构的CePO4一维纳米线材料。用X-射线粉末衍射(XRD)、透射电镜(TEM)和荧光分光光度计(FL)测试样品的物相结构、微观形貌、颗粒尺寸和发光性能;并研究超声时间和PO3-4/Ce3+摩尔比对产物的形貌和荧光性能的影响。结果表明:实验所做出的样品全部是六方晶系的结构,形貌都为一维纳米线,其纳米线长50~200nm,宽5~40nm左右;不同超声时间和PO3-4/Ce3+摩尔比的纳米线长径比不同,随超声时间的延长和PO3-4/Ce3+摩尔比增大纳米线出现团聚现象,产物在250~300nm处有宽的激发峰,在378nm处有一个发射峰,是属于Ce3+的5d-4f能级跃迁。     

Following Solid‐Acid‐Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase—Zeolite‐Catalyzed Conversion of Cyclohexanol in Water

A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid–liquid–gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The ¹³C spectra show that dehydration of 1‐¹³C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the ¹³C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐¹³C‐cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2‐hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl‐1‐cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100‐fold faster per proton.     

Restraint of stress in fabricating the large areas of crack-free porous silica films in the presence of composite polydimethylsiloxane

To present a new method of fabricating the large areas of crack-free porous silica films by introduction of composite polydimethylsiloxanes (PDMS). We employed two kinds of side-chain polyether modified by PDMS terminated with Si–CH₃ and Si–OC₂H₅ groups in preparation of large areas of porous silica films. The porous film presents a mesopore structure with a porosity of 58.0 %, which is fit for thermal-isolating layer applied in pyroelectric devices. The stress evolution on gel-to-ceramic film conversion has been investigated. The results reveal that a slow decrease in tensile stress before 250 °C and a slow increase after 250 °C can be observed, which is closely related to the alteration of chemical composition in the heat-treatment process. It is clear that the stress has been restrained with the addition of composite PDMS.