微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现:甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。     

石墨烯纳米通道中富勒烯纳米流体的压力驱动流动特性

采用分子动力学方法探索了水-富勒烯纳米流体在石墨烯纳米孔隙中Poiseuille流动特性。从富勒烯的微观运动及团簇行为的角度出发,考虑了驱动作用力、富勒烯体积分数和电场强度对纳米流体流动特性的影响机理。发现较大的压力驱动作用可以弱化纳米流体中富勒烯分子的团簇效应;富勒烯体积分数的增加会提高纳米流体剪切黏性,并促进富勒烯分子发生团簇,还会导致纳米流体边界滑移速度的增加;石墨烯壁面上的电场强度的增大,会使富勒烯纳米流体的边界滑移速度先减小后增大,阐明了电场强度对纳米流体边界滑移的影响是石墨烯-流体界面作用强度变化、疏水单分子层的形成和富勒烯团簇的运动行为三者协同作用的结果。     

高压静电场对海水蒸发和沸点的影响

研究了不同条件下高压静电场对海水蒸发速率和沸点的影响。实验结果表明:高压静电场下海水蒸发的速率是常态下的1.5~2.1倍;海水沸点随高压静电场强度的增大而降低。由实验现象和数据分析得出:水分子是极性分子,在高压静电场下易形成电偶极矩,电偶极矩使水分子之间的氢键断裂,从而水分更易蒸发;氢键断裂的能量来源于海水的内能,而不是电场能转化而来的能量。     

羧甲基纤维素钠在醇水混合溶剂中的流变性研究

采用Anton Paar MCR 302流变仪,研究了羧甲基纤维素钠在甘油质量分数分别为0%,20%,40%,60%和80%的甘油-水混合溶剂中的流变特性。发现甘油-水混合CMC溶液为无屈服力非牛顿流体,具有剪切稀化特性;随甘油质量分数的增加,CMC溶液黏度增大、剪切稀化特性逐渐明显、结构恢复变慢;溶液从黏弹性流体逐渐向黏弹性固体转变,内部结构增强,刚性增大。经高温处理后,CMC混合溶液的黏度均会显著增加,且增加值随甘油量增加而增大。亲水性多糖类聚合物的分子主链带有羟基,具有形成氢键的能力。甘油带3个醇羟基,与水形成氢键比水与水之间的氢键更强,可促进体系中羟基间氢键形成,增加氢键数量以及氢键作用力,增大了聚合物分子链缠绕、分子链段缠结。     

石墨烯纳米通道中富勒烯纳米流体的压力驱动流动特性

采用分子动力学方法探索了水-富勒烯纳米流体在石墨烯纳米孔隙中Poiseuille流动特性。从富勒烯的微观运动及团簇行为的角度出发,考虑了驱动作用力、富勒烯体积分数和电场强度对纳米流体流动特性的影响机理。发现较大的压力驱动作用可以弱化纳米流体中富勒烯分子的团簇效应;富勒烯体积分数的增加会提高纳米流体剪切黏性,并促进富勒烯分子发生团簇,还会导致纳米流体边界滑移速度的增加;石墨烯壁面上的电场强度的增大,会使富勒烯纳米流体的边界滑移速度先减小后增大,阐明了电场强度对纳米流体边界滑移的影响是石墨烯-流体界面作用强度变化、疏水单分子层的形成和富勒烯团簇的运动行为三者协同作用的结果。     

水在聚乙烯醇/水体系中的状态及氢键作用

水在聚乙烯醇(PVA)中的状态直接影响PVA的热塑加工.采用DSC和Raman光谱研究了水含量对其在PVA中的状态及氢键作用的影响.结果表明:水在PVA中以3种状态存在,随水含量增加,非冻结合水比例减小,可冻结合水和自由水比例增加.通过高斯分峰可将Raman光谱水的羟基伸缩振动峰分为5种羟基振动峰叠加,分别代表多氢键结合水分子的羟基对称与反对称伸缩振动,双氢键结合水分子羟基伸缩振动,单氢键结合水分子羟基伸缩振动,无氢键或弱氢键相互作用水分子的羟基伸缩振动.水含量增加,单氢键结合与多氢键结合水分子含量增加,而双氢键结合与无氢键结合水分子含量减少.     

电场作用下甲醇结构和扩散性质的分子动力学模拟

采用分子动力学模拟方法研究了外电场作用对甲醇的微观结构和动力学性质的影响.模拟得到了外电场作用下甲醇分子微观构型的物理图像,发现外电场的作用使甲醇分子的偶极向量沿电场作用方向有序排列.随着电场强度的增加,形成两氢键的甲醇分子的摩尔分数和氢键平均数目增加,O—H…O呈线形分布的概率增加,氢键的平均寿命延长,外电场增强了甲醇分子间的氢键作用.随着电场强度的增加,分子的平动自扩散系数降低.外电场作用的附加力阻碍了分子平动运动,分子的平动运动表现为各向异性.     

甲基苯丙胺在水溶液中第一性原理研究

本次设计研究了甲基苯丙胺在纯甲醇及9＋1水溶液中的分子荧光光谱,得到发生溶剂化作用的规律,并采用密度泛函计算验证了谱图的变化实质,得出了不同浓度、不同种类溶液中冰毒分子存在时所构成的团簇构型。比较了单溶剂体系和双溶剂体系对冰毒分子的影响效果,发现冰毒中N是与甲醇分子优先发生了力的作用,水则与甲醇作用,从而使混合溶剂的微观结构比单溶剂时趋于稳定的结构。通过比较不同种类,不同浓度的溶液中团簇分子的荧光强度和稳定性,说明了溶剂对冰毒的水溶性特性的影响。     

基于扫描电镜的三元复合溶液分子聚集体形态的研究

采用电镜扫描、分槽注入相结合的方法,研究了不同注入流量及分压注入工具槽数对三元复合体系中分子聚集态。结果表明:溶液配置条件相同的情况下,分注工具槽数相同时,随流量增大,三元体系中聚合物分子分子链发生断裂的程度增大;流量相同时,随槽数的增多,分子链断裂程度增大,在受到分注工具的剪切作用时,由于三元复合体系网络稀疏,包裹水分子的能力差,从而导致在流经分注工具时的抗剪切能力也变差。     

二乙醚、二异丙醚与水分子间相互作用的理论研究

为研究聚氧乙烯醚与聚氧丙烯醚的亲水与疏水效应,本文将两者合理简化为二乙醚和二异丙醚,并在高精度的B3LYP/6-311++G**水平上,对其与水分子形成的复合物体系进行了理论研究。计算结果表明,二乙醚可与2个水分子形成氢键,作用强度为-10.40kcal·mol-1,复合物形成时电荷转移的范围较大;而二异丙醚仅可与单个水分子形成氢键,作用强度为-7.78 kcal·mol-1,复合物形成时电荷转移的范围较小。聚氧乙烯醚分子中的醚氧原子形成的两氢键体系更为稳定,亲水性更强;而聚氧烯醚分子中,由于甲基的加入对水分子的接近形成空间阻碍作用,因此醚氧原子与水分子仅能形成单氢键结构,亲水性较弱。     

Interaction between water and polytrans-2,5-dimethylpiperazin thiofurazanamide films

Dense films of polytrans-2,5-dimethylpiperazin thiofurazanamide (DMP-TFZ) were characterized as to their physical properties and sorption isotherms. They appeared to be amorphous, endowed with high Tg (247°C), and high mechanical stiffness.Sorption and desorption equilibrium curves were obtained at 23°C for samples 26 and 36 μm thick; hysteresis phenomena were observed only in the desorption steps. BET and Burhoff-Pusch theories and best fit calculations allowed to find that the water layers on the active sorption centers are n = 5 and 1.6 respectively.The Zimm water cluster integral G₁₁/v₁ shows that water tends to be split in single adsorbed molecules in a large field of activities, but that cluster formation is unavoidable in the presence of liquid water. Infrared analysis of the OH stretching region of films conditioned at different relative humidity (RH), demonstrates that water hydrogen bonds in the sorbed state are weaker than in the liquid state and that the presence of big water clusters able to dissolve salts must be excluded. The close packing and high rigidity of the chains should be responsible for the free volume small size holes and uniform distribution, which does not allow big water clusters.     

热处理对木质纤维素Iβ结构及其力学性能影响的分子动力学模拟

采用分子动力学模拟方法对木材主要成分纤维素I_β在热处理环境下的结构和力学性能进行研究,建立了用于模拟的3×3×3纤维素超胞模型,得到350~550 K的体积、密度及氢键变化图,分析了纤维素微观结构的变化并计算了其力学性能。结果表明：升温过程中晶胞体积逐渐增大,由350 K的11.99 nm³增加至550 K的12.26 nm³,模型密度为1.581~1.617 g/cm³,与实验结果一致。氢键数量总数减小了24%,分子链内氢键部分断裂而形成了新的链间氢键,链内氢键与链间氢键的比值由2.1：1变成1：1.5,进而影响了其力学性能。随着温度的升高,杨氏模量逐渐降低,变化率约为13%。相比于杨氏模量,剪切模量和体积模量受温度影响较小,没有明显的变化趋势。     

Experimental verifications of Mpemba-like behaviors of clathrate hydrates

The exact mechanism of the Mpemba effect of water was recently investigated microscopically and explained on the basis of the cooperative relationship between intramolecular polar-covalent bonds (O-H) and intermolecular hydrogen bonds (O:H). We posited that this relationship might exist in clathrate hydrates since they consist of hydrogen-bonded host water frameworks and enclathrated guest molecules. The formation of tetrahydrofuran (THF) hydrate, which is the simplest clathrate hydrate, was investigated by using differential scanning calorimetry and Raman spectroscopy. THF hydrates show the Mpemba effect at lower initial temperatures, but formation times were delayed at higher initial temperatures because the evaporated THF molecules should be liquefied to correspond to the stoichiometric concentration of guest molecules to form sII clathrate hydrates. However, even though the formation time was delayed at higher initial temperatures, the rates of heat emission during THF hydrate formation, measured in a bulk state, roughly increased as the initial temperature increased. Moreover, we observed that the O: H stretching phonons of water in the THF hydrate showed a blue shift, and the O-H stretching mode showed a redshift as temperature decreased. Both the rate of heat emission and the Raman shift of these two bonds imply that a cooperative relationship between the covalent bond and the hydrogen bond exists in THF hydrate as pure water. The formation kinetics of THF hydrate therefore might depend on its initial temperature, thus showing Mpemba-like behavior.     

Vibrational spectroscopy of microhydrated conjugate base anions

Conjugate-base anions are ubiquitous in aqueous solution. Understanding the hydration of these anions at the molecular level represents a long-standing goal in chemistry. A molecular-level perspective on ion hydration is also important for understanding the surface speciation and reactivity of aerosols, which are a central component of atmospheric and oceanic chemical cycles. In this Account, as a means of studying conjugate-base anions in water, we describe infrared multiple-photon dissociation spectroscopy on clusters in which the sulfate, nitrate, bicarbonate, and suberate anions are hydrated by a known number of water molecules. This spectral technique, used over the range of 550-1800 cm(-1), serves as a structural probe of these clusters. The experiments follow how the solvent network around the conjugate-base anion evolves, one water molecule at a time. We make structural assignments by comparing the experimental infrared spectra to those obtained from electronic structure calculations. Our results show how changes in anion structure, symmetry, and charge state have a profound effect on the structure of the solvent network. Conversely, they indicate how hydration can markedly affect the structure of the anion core in a microhydrated cluster. Some key results include the following. The first few water molecules bind to the anion terminal oxo groups in a bridging fashion, forming two anion-water hydrogen bonds. Each oxo group can form up to three hydrogen bonds; one structural result, for example, is the highly symmetric, fully coordinated SO(4)(2-)(H(2)O)(6) cluster, which only contains bridging water molecules. Adding more water molecules results in the formation of a solvent network comprising water-water hydrogen bonding in addition to hydrogen bonding to the anion. For the nitrate, bicarbonate, and suberate anions, fewer bridging sites are available, namely, three, two, and one (per carboxylate group), respectively. As a result, an earlier onset of water-water hydrogen bonding is observed. When there are more than three hydrating water molecules (n > 3), the formation of a particularly stable four-membered water ring is observed for hydrated nitrate and bicarbonate clusters. This ring binds in either a side-on (bicarbonate) or top-on (nitrate) fashion. In the case of bicarbonate, additional water molecules then add to this water ring rather than directly to the anion, indicating a preference for surface hydration. In contrast, doubly charged sulfate dianions are internally hydrated and characterized by the closing of the first hydration shell at n = 12. The situation is different for the (-)O(2)C(CH(2))(6)CO(2-) (suberate) dianion, which adapts to the hydration network by changing from a linear to a folded structure at n > 15. This change is driven by the formation of additional solute-solvent hydrogen bonds.     

Properties of regenerated cellulose films plasticized with α‐monoglycerides

Regenerated cellulose (RC) films were plasticized with glycerol, glycerin α‐monobutyrate, glycerin α‐monocaproate, glycerin α‐monocaprylate, and glycerin α‐monocaprate. The structure and properties of the films were investigated by using Fourier transform IR, wide‐angle X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, and tensile tests. The experimental results showed that the addition of plasticizer enhanced the elongation at break, thermal stability, and crystallinity and lowered the tensile strength of the films. The formation of hydrogen bonds between the cellulose and plasticizers weakened the inter‐ and intra‐hydrogen bonds among cellulose molecules, leading to reduced tensile strength. These α‐monoglycerides have relatively good plasticizing effects. Compared with glycerol, the resistance against water washing of the synthesized compounds was significantly enhanced. With the increase of the carbochain length of the α‐monoglycerides, the plasticizing effect decreased but the resistance against water washing was enhanced. When the RC films were immersed in a 10% glycerin α‐monocaproate solution, the elongation at break increased to 15% and stayed at 14.8% after water washing. Glycerin α‐monocaproate might be better for plasticizing RC films than others. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3500–3505, 2003     

Puckered-boat conformation (H2O)14 cluster on the self-assembly of an inorganic-metal-architecture

BDC (phthalic acid) reacts with EuCl₃ to form 1D coordination polymer, in the presence of phen (1,10-phenanthroline) under hydrothermal conditions. Puckered-boat-shaped (H₂O)₁₄ water clusters resulted from four free water molecules and six coordinated water molecules, which join these chains to make a sheet. Of further interesting, the water clusters associate into an inorganic (carbon-free) sheet with chlorine anions by hydrogen bonds. This hybrid water–chlorine configuration acts as a “host” supporting the metal-organic “guest”.     

Atomistic simulation study of absorbed water influence on structure and properties of crosslinked epoxy resin

Absorbed water can generally degrade most polymer materials with many desired thermal and mechanical properties. In this work, a series of two-step molecular dynamics simulations have been carried out to study the moisture effects on an epoxy-amine polymer network. Copolymer of diglycidyl ether bisphenol A (DGEBA) and isophorone diamine (IPD) was investigated together with its four moist networks with concentrations of water 1.30, 2.54, 5.02 and 11.5 wt%. Simulated results clearly indicated that with addition of water molecules the density of the polymer system decreases whereas the mobility of the network chains increases at higher water concentration. However, at lower water concentration the results present the contrast trends. These differences resulting from water presence can be attributed to the interplay between the hydrogen bonding interactions and the free volumes, the former is responsible for antiplasticization whereas the latter leads to plasticization of the polymer materials. Further analysis confirms that the networks form hydrogen bonds with absorbed water molecules, which preferred to locate in the vicinity of polar groups on the polymer network, and water at higher concentration can cluster with each other. The diffusion coefficient increased with increasing water concentration; the same trend as the change in fractional free volume but contrary to that in density. These results from our simulations were in good agreement with the general experimental observations and the free volume theory.     

Formation and inhibition of free radicals in electrically stressed and aged insulating polymers

Previous work has shown that prebreakdown, electrical aging, and breakdown phenomena are directly associated with charge carriers injected from electrical contacts and their subsequent dissociative trapping and recombination. In addition, the energy released from each trapping or recombination event is dissipated in the breaking of the bonds of macromolecules, thus forming free radicals and new traps in the electrically stressed insulating polymers, as predicted by Kao's model. It is this gradual degradation process that leads to electrical aging and destructive breakdown. New experimental results are presented to confirm previous findings and a new approach to inhibit the degradation process by the incorporation of suitable dopants into the polymer. The concentration of free radicals in the polymer increases with an increasing electric field at a fixed stress time of 250 h and with increasing stress time at a fixed electric field of 833 kV cm^?1. The concentration of free radicals is directly related to the concentration of new traps created by stress. However, when suitable dopants are incorporated, the initiation voltage for the occurrence of electrical treeing and the breakdown strength are both increased. The dopants tend to create shallow traps and have little effect on the deep trap concentration. This implies that the dopants act as free‐radical scavengers that tend to satisfy the unpaired electrons of the broken bonds, which create new acceptor‐like electron traps and new shallow traps. By doing so, the shallow traps screen the deep traps, thereby reducing the energy released during trapping and recombination and the probability of breaking the macromolecular bonds and causing structural degradation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3416–3425, 2003     

氧化石墨烯膜间距对电渗析空气除湿特性影响的分子动力学研究

电渗析空气除湿技术利用高压电场为气体分子荷电,通过多孔氧化石墨烯膜实现水分子和其他带电分子,如氧气分子的分离。双层膜间距将影响到气体分子的传输特性和热力学性质,本文采用分子动力学研究了带电后的水分子和氧气分子在不同膜间距下通过膜的扩散及吸附现象。结果表明：膜层间距主要影响层间氢键形成方式,继而影响多孔氧化石墨烯膜与气体分子间吸附能,存在最佳层间距离1.25 nm,水分子渗透效果最佳,气体选择性达到最高,为1.14,较无电场时扩大了3倍。     

水分子对初始碳烟颗粒形成过程影响的分子动力学模拟

采用LAMMPS软件，基于ReaxFF，以十氢化萘、萘、2-甲基蒽、1-乙基芘为催化油浆的模型化合物研究了600～2500 K温度下催化油浆形成初始碳烟颗粒的过程，考察了2500 K时水分子对初始碳烟颗粒形成过程的影响。研究表明温度在600 K时模型化合物分子主要是物理聚集成核。温度在900～1700 K时模型化合物分子处于聚集和分离的动态过程，无法从单体向碳烟颗粒转变。温度高于2100 K时主要是化学成核，模型化合物分子碳氢键先断裂，然后碳碳键断裂产生大量短碳链，碳链经成键和环化形成初始碳烟颗粒。温度在2500 K时水分子抑制模型化合物分子化学成核，随着体系氢碳比的增加，抑制初始碳烟颗粒形成的作用增强。水分子产生氢自由基和氢氧自由基，这些基团会直接导致模型化合物分子的侧链断裂和碳碳键断裂形成大量短碳链。碳链继续与氢自由基和氢氧自由基作用形成一氧化碳、二氧化碳、氢气、甲烷等而被消耗，水分子的作用为促进短碳链形成和抑制短碳链向形成初始碳烟颗粒的方向进行。