均匀电场对冰晶结构及生长的影响

Homogeneous crystallization of supercooled water under electric field with strength ranging from 4.0 to 40.0 V·nm^-1 was investigated by using molecular simulation technique. The liquid-solid transition was successfully obtained based on ice component analysis using the CHILL algorithm. The analysis suggested that the produced crystalline was cubic ice dominant. The influence of the field strength on the structure and the growth rate of the ice was studied. The results revealed that the presence of an electric field drove the system to crystallize rapidly into dense and distorted cubic ice. The density of the crystals increased as a function of the field strength, from 0.98 to 1.08 g·cm^-3. The growth rate of the ice nucleus increased along with the field strength according to the characteristic time derived from the Avrami equation which ranged from 0.254 to 5.513 ns. This type of acceleration can be partially attributed to the enhancement of the rotational dynamics of the water molecules. Moreover, by monitoring the formation history of the cubic ice, we found that the defective ice acted as a transition state linking the liquid water and the cubic ice.     

甘油对冰晶生长抑制作用的分子动力学模拟

采用分子模拟方法研究了正交晶系冰晶(020)生长面在不同浓度甘油水溶液中的生长情况. 通过统计分析氢键数、 密度分布函数、 均方根偏差和原子间径向分布函数研究了水分子和甘油分子的动态行为. 结果表明, 甘油分子在水溶液中可与水分子形成大量氢键, 这使水分子间的氢键作用受到抑制, 降低了水分子的扩散性, 致使冰晶不易成核和生长; 另外, 一些甘油分子可代替水分子吸附在晶面上, 甚至占据晶格位点, 这种行为打破了冰晶的对称性并且降低了冰晶的生长速率. 因此, 甘油可同时在晶面和液相中抑制冰晶的生长.     

均匀电场对冰晶结构及生长的影响（英文）

采用分子动力学模拟方法研究了强度为4.0-40.0 V·nm-1的均匀电场对过冷水冰晶结构和冰晶生长速率的影响.文中通过CHILL算法来识别不同的冰相结构,通过拟合Avrami公式来得到冰晶生长所需的特征时间.结果表明,在所施加的电场强度范围内生成的冰相以立方冰为主.随着电场强度的增加,形成的立方冰的变形程度逐渐增大,冰晶的密度从0.98 g·cm-3增加到1.08 g·cm-3,同时冰晶生长的特征时间从5.153 ns减小到0.254 ns,冰晶生长的速率逐渐增长.对水分子的动力学分析表明,冰晶生长速率增加的部分原因是电场能够促进水分子运动到形成冰晶所需要的取向.此外,对冰相分子形成过程的分析表明缺陷冰分子在冰晶的生长过程中扮演着中间态的角色.随电场强度的增加,由缺陷冰转变为立方冰的比例增长的速率逐渐提高.     

径向电场对纳米管中水分子通量的影响

水分子在纳米通道中的运动对于生命活动、纳米器件的设计等都有着重要的意义. 现在已经证实, 在(6,6)的碳纳米管中, 水分子会以单分子水链的形式协同通过碳纳米管. 但是如何控制水分子的流量仍然是一个困难的课题. 本文研究了在径向电场作用下, 碳纳米管中水分子通量的变化趋势和碳纳米管的开关行为.发现在碳纳米管两端存在200 MPa的压力差时, 电场强度从1 V·nm^-1增加到3 V·nm^-1, 水分子通量线性减小. 当径向电场强度增加到3 V·nm^-1时, 碳纳米管处于关闭状态, 水分子无法通过碳纳米管. 进一步, 我们发现水偶极与碳纳米管管轴夹角的平均值的概率分布和翻转频率都与水分子在纳米管中的个数有很大关系.     

电场下离子型聚合物复合囊泡结构变化的分子动力学模拟

利用粗粒化分子动力学模拟研究了电场作用下离子型聚合物复合囊泡形变与破裂的过程.定量分析了囊泡破裂过程中的结构变化,包括囊泡的形变程度、破裂速度、组分分布以及破裂后的结构.研究表明,电场强度较弱时,囊泡表面所吸附的聚电解质首先脱落,囊泡由球形结构转变为椭球结构.随着电场强度增大,离聚物的离子侧基发生重新排布,囊泡表面电荷的有序结构被破坏,导致囊泡的结构无法维持而破裂,囊泡塌缩,分裂形成离聚物团簇,并进一步破裂为小尺寸的离聚物聚集体,均匀分散于溶液中.本文利用分子动力学模拟明确了电场中离子型高分子复合囊泡破裂过程的分子机理,为药物释放技术的优化及发展提供了理论支持.     

表面电荷及外电场对液固界面热阻的影响

采用非平衡分子动力学方法模拟了外电场及固体表面电荷对水与固体间界面热阻的影响. 结果表明,外加电场平行于界面时, 其对界面热阻几乎没有影响, 而垂直于界面时, 界面热阻将随着电场强度的增大而减小. 壁面带正电荷或负电荷都将使得界面热阻减小. 界面热阻与表面电荷密度及电场强度均满足二次函数关系. 模拟结果表明施加外电场和表面电荷是控制液固界面热阻的有效方法.     

非均匀电场的电堆积理论研究

基于样品区非均匀电场电势分布的测试结果并利用异性双点电荷电场的理论模型,研究了非均匀电场电堆积效应,提出了非均匀电场电堆积作用的理论模型.采用一种改进的非均匀电场电堆积系统,以矿泉水中痕量Cr(Ⅵ)和Pb(Ⅱ)为考察对象,同时对其进行分离富集和测定,为理论模型提供了实验依据.     

外电场对甲醛分子的结构与电子光谱的影响

采用密度泛函理论(DFT)在B3LYP/6-311++G(d,p)基组水平上,计算了不同外加电场(-8.22×10~9~8.22×10~9 V/m)下甲醛分子基态稳定构型、分子键长、电荷分布、能级分布、能隙、红外光谱、拉曼光谱和分子的总能量.在此基础上利用TDDFT/B3LYP/6-311++G(d,p)方法研究了甲醛分子由基态跃迁到前25个激发态的激发能E、谐振强度f、吸收波长λ受外电场的影响.结果表明:随着C=O连线方向外电场的增加,C=O键键长、氢原子电荷、偶极矩和能隙递增;C—H键键长、C,O原子电荷递减,总能量降低.振动频率与红外强度及拉曼强度由于不同振动有不同变化.甲醛分子UV-Vis光谱随外电场的增加,不同的吸收峰发生了不同程度的蓝移或者红移;外电场对甲醛分子的激发能、谐振强度和吸收波长的强度有一定影响,但随电场变化比较复杂.     

电场对聚肽液晶相行为的影响

聚合物液晶的相转变不仅可以通过溶液温度或聚合物的浓度的改变来实现,也可以通过施加外电场、磁场等取向场来达到．在二氧六环、氯仿、间甲酚等支持聚肽a一螺旋构象的溶剂中,当PBLG(聚L-谷氨酸γ-苯甲酯)达到一定的浓度会形成胆甾型溶致液晶．对这种液晶施加强度足够     

外电场作用下离子液体振动光谱变化的分子动力学模拟研究

Vibrational spectroscopy is a powerful tool for studying the microstructure of liquids, and anatomizing the nature of the vibrational spectrum (VS) is promising for investigating changes in the properties of liquid structures under external conditions. In this study, molecular dynamics (MD) simulations have been performed to explore changes in the VS of 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF₆]) ionic liquid (IL) under an external electric field (EEF) ranging from 0 to 10 V·nm^-1 at 350 K. First, the vibrational spectra for [Emim][PF₆] IL as well as its cation and anion are separately obtained, and the peaks are strictly assigned. The results demonstrate that the VS calculated by MD simulation can well reproduce the main characteristic peaks in the experimentally measured spectrum. Then, the vibrational spectra of the IL under various EEFs from 0 to 10 V·nm^-1 are investigated, and the intrinsic origin of the changes in the vibrational bands (VBs) at 50, 183, 3196, and 3396 cm^-1 is analyzed. Our simulation results indicate that the intensities of the VBs at 50 and 183 cm^-1 are enhanced. In addition, the VB at 50 cm^-1 is redshifted by about 16 cm^-1 as the EEF is varied from 0 to 2 V·nm^-1, and the redshift wavenumber increases to 33 cm^-1 as the EEF is increased to 3 V·nm^-1 and beyond. However, the intensities of the VBs at 3196 and 3396 cm^-1 show an obvious decrease. Meanwhile, the VB at 3396 cm^-1 is redshifted by about 16 cm^-1 when the EEF increases to 3 V·nm^-1, and the redshift increases to 33 cm^-1 with an increase in the EEF beyond 4 V·nm^-1. The intensity of the VB at 50 cm^-1 increases because of the increase in the total dipole moment of each anion and cation (from 4.34 to 5.46 D), and the redshift is attributed to the decrease in the average interaction energy per ion pair (from -378.7 to -298.0 kJ·mol^-1) with increasing EEF. The intensity of the VB at 183 cm^-1 increases on account of the more consistent orientations for cations in the system with increasing EEF. The VB at 3196 cm^-1 weakens visibly because a greater number of hydrogen atoms appear around the carbon atoms on the methyl/ethyl side chains and the vibrations of the corresponding carbon-hydrogen bonds are suppressed under the action of the EEF. Furthermore, the intensity of the VB at 3396 cm^-1 decreases due to the decrease in the intermolecular ⁺C-H···F^- hydrogen bonds (HBs), while the relaxation effect that is beneficial for the formation of HBs simultaneously exists in the system under the varying EEF, thus causing a redshift of the VB at 3396 cm^-1.     

分子动力学模拟研究外电场对咪唑类离子液体振动谱的影响

本文利用分子动力学模拟研究了外电场对咪唑类离子液体1-乙基-3-甲基咪唑六氟磷酸盐(EMIMPF₆)从0到4000 cm⁻¹范围内振动谱的影响。研究结果表明,在没有外电场时利用分子动力学模拟计算得到的从400到4000 cm⁻¹的振动带可以重现实验测得的谱。当外电场从0到9 V·nm⁻¹变化时,在50.0和199.8 cm⁻¹处的振动带强度持续增强然后趋于饱和,而从400到4000 cm⁻¹的振动带强度明显减弱并最终消失。此外,在外电场从0变到2 V·nm⁻¹时,50.0 cm⁻¹的振动带红移了16.7 cm⁻¹,然后当外电场变化到3 V·nm⁻¹及更大时,该振动带红移增大到33.3 cm⁻¹。在外电场从0变到3 V·nm⁻¹时,3396.6 cm⁻¹的振动带红移大约16.7 cm⁻¹,然后当外电场增大到4 V·nm⁻¹甚至更大时,该振动带红移33.3 cm⁻¹,但是从0到4000 cm⁻¹的其他振动带的位置几乎没有变化。基于对模拟结果和先前报道文献的进一步分析,对于50.0 cm⁻¹的振动带,增加的外电场增强了阳离子和阴离子之间的极性使阳离子和阴离子间的偶极矩增大,因此该振动带的强度不断增大然后达到饱和。对于199.8 cm⁻¹的振动带增加的外电场增强了乙基链的扭转,使该振动带的强度增大并达到饱和。对于从400到4000 cm⁻¹的其他振动带,增加的外电场使EMIMPF₆中的阳离子和阴离子的取向更一致,并且可以推测这种更一致的取向可能会削弱振动带的强度甚至使它们消失。50.0 cm⁻¹处振动带的红移可能是由于外电场破坏了EMIMPF₆内部的静电场分布进而减弱了阳离子和阴离子间的相互作用。3396.6 cm⁻¹处振动带的红移可归功于外电场减弱了氮原子与阳离子咪唑环上酸性氢原子间形成的氢键的拉伸振动。对于其他的振动带,由于官能团固有的拉伸、弯曲、转动振动不受外电场的影响,外电场没有改变振动带的位置。     

Molecular Dynamics Simulation: Influence of External Electric Field on Bubble Interface in Air Flotation Process

Molecular dynamics(MD) simulation was performed to investigate the influence of external electric field on the vapour-liquid interface of the bubble during the process of toluene separation by air flotation. The physicochemical properties of vapour-liquid interface, surface tension, probability of a hydrogen bonding near the vapour-liquid interface and the viscosity of liquid phase caused by external electric field were analyzed. The results show that the angle between the water molecule dipole moment and the normal z axis in the vapour phase changes smaller when the external electric field is applied. The surface tension and the probability of hydrogen bonding near the vapour-liquid interface increase with the increase of electric field strength. And the viscosity also increases under an external electric field. The results confirm that the external electric field has a positive effect on the performance of bubbles in air flotation, which may provide useful guidance for the combination of electric field and air flotation technology.     

广义簇合物在均匀几率密度场下的生长

通过对广义簇合物生长的自调整模型的解析,得出了粒子在均匀几率密度场下簇合物生长形态的变化特征,揭示了表征其生长形态结构分式维数D的物理意义,同时考查了格子模型对簇合物生长形态的影响以及自调整模型的动力学行为。     

微晶碳电活化过程中离子尺寸效应研究

以石油焦基微晶碳作为电极材料,并由N2吸附,X射线衍射(XRD)表征其孔结构和微晶结构.研究了4种电解液Et4NBF4/PC(四乙基铵四氟硼酸盐/碳酸丙烯酯)、Et4NBF4/AN(四乙基铵四氟硼酸盐/乙腈)、Bu4NBF4/PC(四丁基铵四氟硼酸盐/碳酸丙烯酯)和Bu4NBF4/AN(四丁基铵四氟硼酸盐/乙腈)的微晶碳电容器特性.结果表明:电解质离子与溶剂AN的溶剂化半径较小,容易嵌入类石墨微晶碳层,其于AN的电活化电位比在PC中的低,致使电活化程度更深,材料的表面利用率更高,电容量较大.电解质阳离子(Et4N+,Bu4N+)大小对电活化影响不大.电活化使材料类石墨微晶层间距(d002)变大,离子尺寸越大,层间距增加越明显.