简立方格点自避行走所模拟的高分子链吸附和塌缩

采用复合Markov链法,针对简立方格点上的自避行走模型,研究了同时具有对壁的吸附作用ε1和最近邻相互作用ε2的高分子链的热力学性质.相互作用能量参数ε1和ε2分别联系于参数α和β.令链长N=100,由这种Monte Carlo方法可得出链的自由能FN (α ,β),热容2FN(α,β)/2α和2FN(α,β)/2β,吸附点平均数〈m〉/N,最近邻相互作用对平均数〈n〉/N和均方末端距对壁的垂直分量RZ2.除已有方法由热容数据可绘出α-β相图外,建议由结构参数〈m〉/N ,〈n〉/N和RZ2绘制相图,并发现二者基本一致.所得相图表明,存在4个相区,分别是解吸-膨胀相(DE),吸附-膨胀相(AE),解吸-紧密相(DC)和吸附 -紧密相(AC).在伸展区和塌缩区,随着吸附作用的增强,会出现吸附相转变.在解吸区和吸附区,随着自相互作用的增大,也将出现塌缩相转变.相图出现了两个三相点,即AE-AC-DC三相点和AE-DE-D C三相点.     

柔性高分子/液晶体系的相平衡理论

在Flory-HugginS柔性高分子溶液理论和Lebwohl-Lasher液晶模型的基础上;导出了柔性高分子/液晶复合体系的混合自由能和化学位,并计算了相应的相图。计算结果表明,体系可出现各向同性相(Ⅰ)和各向同性相(Ⅰ),以及各向同性相(Ⅰ)和向列相(N)间的相平衡。并且发现,高分子链段与液晶分子间的各向同性相互作用对I/N的相平衡有重要影响。与实验结果的比较表明,本理论能完整、正确地描述高分子/液晶体系的相平衡。     

三维吸附紧密高分子单链的力学性质研究

采用PERM(pruned-enriched Rosenbluth method)算法,研究了吸附在界面附近的紧密高分子链力学行为.发现当界面的吸附能比较大时,紧密高分子链从紧贴于吸附界面到逐渐远离的过程中,其外形会经历4种典型的变化.同时紧密高分子链的尺寸大小如/N、xy/N、z/N,形状参数<δ*>,热力学性质如每个键的平均自由能A/N,平均相互作用能/N等,甚至所受外力的大小都会同时做出相应的变化,其出现变化的位置也一致.特别是随着紧密高分子链离开吸附界面的过程中,作用于高分子链上的外力明显出现几个力学平台,这与实验得到的结果完全一致.同时还研究了弱吸附能的情况,在这种情况下实验是很难进行的.     

不对称Gemini表面活性剂在气/液界面的吸附动力学

合成出由1个亚甲基联接羟基和季铵基头基, 且带两根不同长度烷烃链的不对称Gemini表面活性剂CmH2m+1OCH2CH(OH)CH2N+(CH3)2C8H17Br(记为CmOhpNC8, m=10, 12, 14). 用最大泡压法研究了浓度低于临界胶团浓度时, CmOhpNC8在气/液界面上的吸附动力学. 结果表明, CmOhpNC8表现出很明显的吸附动力学效应. CmOhpNC8向新鲜气/液界面吸附时由扩散过程控制; 当界面上已具有一定吸附量时, 显示出吸附能垒Ea. 随着烷烃链的增长而明显降低, 表明长烷烃链的分子到达亚层后更容易插入表面层,这被归结为分子烷烃链间的疏水相互作用随着链增长而增强所致.     

聚合物PVP与表面活性剂AOT相互作用的介观模拟

用耗散颗粒动力学模拟(DPD)方法研究了聚乙烯吡咯烷酮(PVP)与2-乙基己基琥珀酸酯磺酸钠(AOT)之间的相互作用.在三维模拟格子中,聚合物链均方末端距〈r²〉随着表面活性剂浓度的增加呈现一种首先减小,接着增加,然后又减小的趋势.构型和结构分析表明,AOT的加入能够引起聚合物链的二面角分布发生改变,这意味着AOT与PVP产生了相互作用.同时表面活性剂/聚合物体系的聚集形态也可以在DPD三维模拟格子中直观显现出来.     

Al203-Si02-Ti02三元相图的数字化

用拟合曲线方程的方法得到了Al2O3-SiO2-TiO2三元相图液相面的方程,并由此得到了相界线的方程和三相点的坐标.利用这些数据可以绘制出等温截面和多温截面,还能模拟出结晶过程.     

二维HP格点模型中的紧密高分子链构象及其热力学性质的研究

采用二维HP模型用精确计数法和MonteCarlo方法研究了链长为N(≤ 2 2 )的紧密高分子链的构象和热力学性质 .发现不同HP序列的紧密高分子链的平均自由能和平均配分函数与链长N存在关系 :〈F〉=aN+b ,　ln〈Z〉=a′N +b′ .同时发现对于可折叠成基态且简并度为 1的紧密高分子链 ,其平均自由能和平均配分函数与链长N也存在相似的关系 .在HP模型中对于链长为N的紧密高分子链 ,存在着 2 N + 1 个不同的HP序列 .我们发现可以折叠成基态且简并度为 1的蛋白质分子的HP序列数目NS 为NS =a× 2 N+ 1 　 (a =0 0 2 5 ) ,对应的HP序列中 ,疏水基团 (H)数目的含量为 4 0 %～ 6 0 %的序列出现的几率最大 .同时在这些紧密高分子链中有些具有相同的结构 ,发现结构的‘简并度’为 3 3～ 4 0 (10≤N≤ 16 ) .在紧密高分子链折叠过程中 ,折叠的初期能量下降比较快 ,折叠的中期能量下降比较缓慢 ,折叠的后期能量下降也是比较快     

N_2O在Cu/t-ZrO_2(101)表面的吸附与解离

运用广义梯度密度泛函理论结合周期性平板模型方法研究了N2O在完整及负载Cu的四方相ZrO2(101)表面的吸附与解离.结果表明,N2O在完整ZrO2(101)表面的吸附均为物理吸附,Cu在其完整表面的次表层第一氧位为最稳定吸附位,且覆盖度为0.25ML时的吸附最为稳定,吸附能为155.8kJ/mol;N2O分子中O端弱物理吸附于Cu/ZrO2(101)表面,其N端及平行吸附方式得到的稳定吸附能分别为121.6和66.8kJ/mol.频率及电荷布居计算表明,吸附后对称和反对称伸缩振动频率均发生红移,电子由Cu负载底物表面转移给N2O分子.对N2O分子的解离考虑了N端垂直吸附和平行吸附两种解离反应过程,发现平行吸附过程的解离更易发生.     

Topological Studies on the П…П Interactions between OCS, CO2, N2O and Hydrocarbon

采用MP2/aug-cc-pVDZ方法对氧硫化碳（OCS）、二氧化碳（CO2）、一氧化二氮（N2O）与乙烯（C2H4）、乙炔（C2H2）、2-丁炔（C4H6）之间形成的平行构型复合物中的分子间相互作用进行了理论研究.复合物的相互作用能按照B…C2H4〈B…C2H2〈B…C4H6（B=OCS,CO2,N2O）的顺序依次增大,相互作用距离按照B…C2H4〉B…C2H2〉B…C4H6（B=OCS,CO2,N2O）的顺序依次减小.采用电子密度拓扑分析理论方法,讨论了复合物中π…π作用的成键特性.电子密度拓扑分析表明复合物中形成了弱的分子间相互作用,且以静电作用为主;π电子密度分子图与全电子密度分子图中键径方向是一致的,说明π…π作用在本文所讨论的体系中起着很重要的作用.NBO分析表明净电荷迁移从电子给体C2H4,C2H2,C4H6到电子受体OCS,CO2,N2O,迁移数按照B…C2H4〈B…C2H2〈B…C4H6（B=OCS,CO2,N2O）的顺序依次增大,与相互作用能的顺序一致.     

水杨酸型螯合吸附材料对重金属离子的吸附性能

将5-氨基水杨酸接枝到PGMA/SiO2微粒的聚甲基丙烯酸缩水甘油酯(PGMA)大分子链上,成功制备了一种新型螯合吸附材料ASA-PGMA/SiO2。采用静态法研究了ASA-PGMA/SiO2对重金属离子Cu2+、Cd2+、Zn2+、Pb2+的吸附性能,结果表明其对Cu2+、Cd2+、Zn2+、Pb2+具有很强的螯合吸附能力,吸附容量分别可以达到0.42、0.40、0.35、0.31mmol/g。体系的pH对吸附容量影响较大,吸附行为服从Langmuir和Freundlich吸附模型。使用0.1mol/L的盐酸溶液就可实现重金属离子的解吸。通过反复吸附-解吸实验证明ASA-PGMA/SiO2具有良好的重复使用性能。     

The oblique chiral nematic phase in calamitic bimesogens

ABSTRACT

The discovery of the oblique chiral (or, the twist-bend, N_TB) nematic phase predicted for bent-core mesogens has engendered much interest due to its unique structure and physical properties, and the possibility of use in the next generation of fast electro-optic technology. Bimesogenic calamitic as well as bent-core mesogens are found to form the N_TB phase. Here, we report direct measurements of the temperature dependence of the conical tilt and the evidence of volcano-like orientational distribution of molecules in the N_TB phase. Optical and x-ray scattering investigations of two single-component calamitic bimesogens and their mixtures show that, while the Maier–Saupe orientational distribution function (ODF) is valid for the higher temperature nematic phase, a generalised expansion in terms of even Legendre functions is needed for the N_TB phase. Temperature dependence of the ODFs and the order parameters 〈P₂(cosβ)〉, 〈P₄(cosβ)〉, and 〈P₆(cosβ)〉 has been measured in both phases. The parameters 〈P₂(cosβ)〉 and 〈P₄(cosβ)〉 increase/decrease in the N/N_TB phase with decreasing temperature, while 〈P₆(cosβ)〉 remains vanishingly small for all samples. The value of 〈P₄(cosβ)〉 becomes negative in the N_TB phase confirming a conical distribution of molecules as they follow a helical trajectory keeping the local director tilted at an angle α wrt the macroscopic director. The heliconical tilt calculated from ODFs, exhibits a power law behaviour with temperature, vanishing at the transition to the N phase.     

γ-Mo2N催化剂上H2及NO吸附性质的TPD-MS研究

采用TPD-MS方法研究了H2及NO在γ-Mo2N上的吸附状况．单独的H2-TPD结果表明,当H2在673K吸附时,在443K、573K及723K得到了三个H2脱附峰,表明γ-Mo2N上有三种不同能量的H2吸附位．NO－TPD结果表明,NO吸附后亦有三个脱附峰（383K、493K、543K）,对应着γ-Mo2N上三种不同能量的NO吸附位：低、中、高能吸附位．NO既可以以解离状态,又可以以一种NO三聚态（dimerordinitrosyl）的形式吸附在γ－Mo2N上,这些吸附物种在脱附过程中产生大量的N2及少量的N2O.对比NO吸附在不同处理条件的γ-Mo2N上的TPD结果可知,NO是吸附在γ-Mo2N上的MO的配位不饱和中心上,这些吸附中心既可通过还原催化剂,又可通过在773K抽空钝化态的γ－Mo2N而产生,H2和NO共吸附的结果表明,预吸附H2再吸附NO后,H2和NO的脱附量均大大减少,且只有两个脱附峰出现.NO只在363K及493K出现两个脱附峰,表明预吸附氢占据了NO的强吸附位,且NO很难取代它,从而使NO只能吸附在能量较低的吸附位上;而H2只在523K及723K出现两个脱附峰,且伴随着H2的脱出有N2和H2O的产生,表明在γ－Mo2N上NO可能与预吸附氢形成了一种复合相MoHx（NO）y,它在脱附时分解为H2、N2及H2O.     

Initial hydrogenations of pyridine on MoP(001): a density functional study

The initial hydrogenations of pyridine on MoP(001) with various hydrogen species are studied using self-consistent periodic density functional theory (DFT). The possible surface hydrogen species are examined by studying interaction of H(2) and H(2)S with the surface, and the results suggest that the rational hydrogen source for pyridine hydrogenations should be surface hydrogen atoms, followed by adsorbed H(2)S and SH. On MoP(001), pyridine has two types of adsorption modes, i.e., side-on and end-on; and the most stable η(5)(N,C(α),C(β),C(β),C(α)) configuration of the side-on mode facilitates the hydrogenation of pyridine. The optimal hydrogenation path of pyridine with surface hydrogen atoms in the Langmuir-Hinshelwood mechanism is the formation of 3-monohydropyridine, followed by producing 3,5-dihydropyridine, in which the two-step hydrogenations take place on the C(β) atoms. When adsorbed H(2)S is considered as the source of hydrogen, slightly higher hydrogenation barriers are always involved, while the energy barriers for hydrogenations involving adsorbed SH are much lower. However, the hydrogenation of pyridine should be suppressed by the adsorption of H(2)S, and the promotion effect of adsorbed SH is limited.     

(α/β)_8桶状蛋白质中紧密接触对的统计性质研究

在计算蛋白质分子中的氨基酸紧密接触对时采用以氨基酸的重心代替Cα 原子的新方法 ,通过计算(α/β) 8桶状蛋白质中的中程和远程紧密接触对的数目 ,研究了不同氨基酸在形成紧密接触对时所具有的不同能力以及在蛋白质结构稳定性中所起的不同作用 .发现在 (α β) 8桶状蛋白质中氨基酸形成的远程紧密接触对数目与它的Fauchere Pliska疏水性实验数值 (FPH)存在着非常好的线性关系 ,而对于氨基酸所形成的中程紧密接触对数目不存在这种关系 .同时还研究了 (α β) 8桶状蛋白质分子大小 ,发现其回转半径大小与表示远程接触对数目的远程次序值LRO存在着关系 .表明这一类 (α β) 8桶状蛋白质具有相似的结构 ,分子的远程接触对数目越多 ,分子越紧密 ,分子尺寸就越小 .同时还研究了不同氨基酸之间形成紧密接触对的能力 .     

Elastic behavior of single polymer chains adsorbed on rough surfaces

In this paper, elastic behaviors of single polymer chains adsorbed on the rough surfaces with a substrate and some periodically tactic pillars are investigated by the pruned-enriched-Rosenbluth method (PERM). In our simulation, a single polymer chain is firstly adsorbed on the substrate and then pulled along the z-axis direction, which is vertical to the substrate. We investigate the chain size and shape of polymer chains, such as mean-square radii of gyration per bond 〈S²〉_xy/N, 〈S²〉_z/N and shape factor 〈δ^∗〉 in order to show how the size and shape of adsorbed polymer chains change during the desorption process. Due to the occurrences of separation of the chains from the substrate, farther adsorption on the upper surfaces of pillars and complete separation from the whole rough surfaces in the elastic process, the changes of 〈S²〉_xy/N, 〈S²〉_z/N and 〈δ^∗〉 during the process are complicated. On the other hand, some thermodynamic properties such as average energy per bond, average Helmholtz free energy per bond, elastic force f are investigated, and our aim is to study the elastic behaviors of polymer chains adsorbed on the rough surface during the elasticity process. Elastic force f has some plateaus during the desorption process for strong adsorption interaction. If there is no adsorption interaction, the chains can get away from the rough surfaces spontaneously. These investigations can provide some insights into the elastic behaviors of polymer chains adsorbed on the rough surface.     

Quasiclassical Trajectory Study of Collisional Energy Transfer between Highly Excited C6F6 and N2 ,O2 and Ground State C6F6

Quasiclassical trajectory calculation (QCT) is used frequently for studying collisional energy transfer between highly vibrationally excited molecules and bath gases. In this paper, the QCT of the energy transfer between highly vibrationally excited C6F6 and N2 ,O2 and ground state C6F6 were performed. The results indicate that highly vibrationally excited C6F6 transferred vibrational energy to vibrational distribution of N2, O2 and ground state C6F6, so they are V-V energy transfer. Especially it is mainly V-V resonance energy transfer between excited C6F6 andground state C6F6, excited C6F6 transfers more vibrational energy to ground state C6F6 than to N2 and O2. The values of QCT, - (ΔEvib) of excited C6F6 are smaller than those of experiments.     

Semiempirical calculations of molecular polarizabilities and hyperpolarizabilities of polycyclic aromatic compounds

The correlation of 2D conjugation and the nonlinear properties of a series of polycyclic aromatic compounds were studied by performing semiempirical calculations using the MOPAC package. For linear polyacenes, both linear and nonlinear properties are found to be increased as the number of six-membered rings increases. In general, the polarizabilities, 〈α〉, and second hyperpolarizabilities, 〈γ〉, are found to correlate very well with total resonance energies. In the case of first hyperpolarizabilities, 〈β〉, symmetry is the dominating factor. © 1992 John Wiley & Sons, Inc.     

Second and third-order nonlinear optical properties and molecular parameters of azo chromophores: semiempirical analysis

The static and frequency dependent average polarizability (〈α〉), first- and second-hyperpolarizabilities (〈β〉 and 〈γ〉) and highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energies of nonlinear optical chromophores with nitro acceptors 1–5 have been investigated by using the Austin Model 1 (AM1), Modified Neglect of Diatomic Overlap (MNDO), MNDO with d orbitals (MNDO-d), Parameterization Method 3 (PM3), Recife Model 1 (RM1) and Parameterization Method 6 (PM6) methods within a time-dependent Hartree–Fock (TDHF) approaches. The electronic properties of chromophores 1–5 have been reported by employing two-state model calculated at Zerner's spectroscopic version of the Intermediate Neglect of Differential Overlap singly excited configuration interaction (ZINDO/S-SCI) method. Also, the molecular hardness (η) and electronegativity (χ) parameters have been obtained by using molecular frontier orbital energies. The 〈α〉, 〈β〉, 〈γ〉 HOMO, LUMO energies, η and χ parameters have been investigated with respect to the choice of different semiempirical methods.