Solvent-Polymer Interaction. II. Measurements of Liquid Solvent Molecules Associating with Polymer Sites and of Their Transport Behavior in Polymer Membrane by Thermogravimetry,GLC, and Mass Spectrometry

The measurement of sorption and diffusion behavior of liquid ethanol and water solvent mixtures in polyurethane membrane were made simultaneously by thermogravimetry. The individual amounts of sorbed water and ethanol in the polymer membrane were estimated by thermogravimetry and differentiated by mass spectrometry. In addition, from a single dynamic thermogravimetric experiment the activation energy for solvent molecules desorbing from the polymer membrane was also determined. The thermodynamic activity of ethanol vapor in equilibrium with the ethanol-water-polyurethane system was determined by gas-liquid chromatography. The clustering functions, the mean numbers of solvent molecules in the clusters, and those associating with polymer sites were evaluated by applying simplified mathematical derivatives using the experimentally determined values of activity and volume fraction of solvent molecules. It was found that at lower ethanol concentration the tendency for ethanol molecules to cluster together is high. At higher ethanol activity, ethanol-polymer site interactions predominantly occurred.

Similar results were observed for ethanol-water molecules. However, water molecules in this particular system did not exhibit a self-associating tendency nor interact with the polymer sites. It was concluded that the Zimm-Lundberg clustering theory can be adequately applied to the interpretation of sorption and diffusion behavior of liquid ethanol-water mixtures in the polymer membrane.     

Coordination Networks Self-assembled by Transition Metal Salts With 4,4′-oxydianiline (4,4′-oda). Syntheses and Structures of ∞ 1 [Ni(NCS) 2 (4,4′-oda) 2 ], ∞ 2 [Co(NCS) 2 (4,4′-oda) 2 ] and ∞ 2 [M(N 3 )(4,4′-oda) 2 ]NO 3 (M=Cd II or Co II )

Four infinite complexes X 1 [Ni(NCS) 2 (4,4'-oda) 2 ], X 2 [Co(NCS) 2 (4,4'-oda) 2 ] and X 2 [M(N 3 )(4,4'-oda) 2 ]NO 3 [M=Cd II ( 3 ) or Co II ( 4 )] were obtained by reactions 4,4'-oxydianiline (4,4'-oda) with Ni(SCN) 2 , Co(SCN) 2 , Cd(N 3 ) 2 and Co(N 3 ) 2 , respectively which have been structurally established by single-crystal X-ray diffraction. Complex 1 contains one-dimensional double-stranded chains comprising 24-membered Ni 2 (4,4'-oda) 2 macrocycles, each formed by two 4,4'-oda ligands and two octahedral Ni II centers. Complex 2 exhibits two-dimensional non-interpenetrating networks consisting of large 48-membered macrocycles each formed by four 4,4'-oda ligands and four octahedral Co II centers. The crystal structures of 3 and 4 are isomorphous and both contain one-dimensional double-stranded chains comprising 24-membered M 2 (4,4'-oda) 2 macrocycles, which are interlinked by w -1,3-azide groups to generate cationic two-dimensional sheets. These sheets are further connected by hydrogen bonds between the amine groups and nitrate ions to furnish three-dimensional networks. Crystal data: complex 1 crystallizes in the monoclinic space group P 2 1 / c with a =11.990(4) Å, b =9.413(4) Å, c =12.827(4) Å, g =116.32(2), V =1297.6(8) Å 3 and Z =2; complex 2 crystallizes in the orthorhombic space group Pbca with a =9.583(2) Å, b =12.738(3) Å, c =21.039(4) Å, V =2568.2(9) Å 3 and Z =4; complex 3 crystallizes in the monoclinic space group C 2/ c with a =23.036(5) Å, b =5.920(1) Å, c =17.800(4) Å, g = 92.67(3), V =2424.8(9) Å 3 and Z =4; complex 4 crystallizes in the monoclinic space group C 2/ c with a = 22.861(5) Å, b =5.812(1) Å, c =17.720(4) Å, g =93.00(3), V =2351.2(8) Å 3 and Z =4.     

Calculations of dynamic dipole polarizabilities of Li and Na atoms in debye plasma using the model potential technique

The effects of Debye plasma on the frequency‐dependent polarizabilities of Li and Na atoms are investigated using symplectic algorithm within the framework of the pseudostate summation technique. Dynamic dipole polarizabilities of Li (2s ²S) and Na(3s ²S) as functions of scaled number density of the plasma electrons for arbitrary plasma temperature are presented. Screening effects on the resonance frequencies are also presented. In free‐atomic cases, our calculated results are comparable with the reported theoretical and experimental predictions. © 2012 Wiley Periodicals, Inc.     

Sulfur-linked cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase

ABSTRACT

The synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4?-[1,ω-alkanediylbis(thio)]bis-[1,1?-biphenyl]-4-carbonitriles (CBSnSCB), and 4?-({ω-[(4?-cyano[1,1?-biphenyl]-4-yl)oxy]alkyl}thio)[1,1?-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 3⁴-{6-[(4?-cyano[1,1?-biphenyl]-4-yl)thio]-hexyl}[1¹,2¹:2⁴,3¹-terphenyl]-1⁴-carbonitrile (CT6SCB), is also reported and shows enantiotropic N_TB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-N_TB transition corresponds to 4 longitudinal molecular distances.     

Codimension-4 resonant homoclinic bifurcations with orbit flips and inclination flips

The paper studies a codimension-4 resonant homoclinic bifurcation with one orbit flip and two inclination flips, where the resonance takes place in the tangent direction of homoclinic orbit.Local active coordinate system is introduced to construct the Poincar′e returning map, and also the associated successor functions. We prove the existence of the saddle-node bifurcation, the perioddoubling bifurcation and the homoclinic-doubling bifurcation, and also locate the corresponding 1-periodic orbit, 1-homoclinic orbit, double periodic orbits and some 2n-homoclinic orbits.     

Model based prediction of the trap limited diffusion of hydrogen in post‐hydrogenated amorphous silicon

The diffusion of hydrogen within an hydrogenated amorphous silicon (a‐Si:H) layer is based on a trap limited process. Therefore, the diffusion becomes a self‐limiting process with a decreasing diffusion velocity for increasing hydrogen content. In consequence, there is a strong demand for accurate experimental determination of the hydrogen distribution. Nuclear resonant reaction analysis (NRRA) offers the possibility of a non‐destructive measurement of the hydrogen distribution in condensed matter like a‐Si:H thin films. However, the availability of a particle accelerator for NRR‐analysis is limited and the related costs are high. In comparison, Fourier transform infrared spectroscopy (FTIR) is also a common method to determine the total hydrogen content of an a‐Si:H layer. FTIR spectrometers are practical table‐top units but lack spatial resolution. In this study, an approach is discussed that greatly reduces the need for complex and expensive NRR‐analysis. A model based prediction of hydrogen depth profiles based on a single NRRA measurement and further FTIR measurements enables to investigate the trap limited hydrogen diffusion within a‐Si:H. The model is validated by hydrogen diffusion experiments during the post‐hydrogenation of hydrogen‐free sputtered a‐Si. The model based prediction of hydrogen depth profiles in a‐Si:H allows more precise design of experiments, prevents misinterpretations, avoids unnecessary NRRA measurements and thus saves time and expense. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Non-linear scission/recombination kinetics of living polymerization

Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization (one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution. Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M ^* (M^* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find that: 1) for M ^* ≪ M ≪ M ^*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t₁, t₂, t₃ and t^*; 2) there are transient regimes (t ₁ ≲ t ≲ t ₃) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter than t₂. The chain growth is auto-accelerated for t ₁ ≲ t ≲ t ₂ : the cut-off chain length (= polymerization degree 〈n〉_w N ₁ ∝ t ² in this regime. 4) For t ₂ < t < t ₃ the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N₁ is decreasing with time in this regime, while the length scale N₂ of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t^*, shows a sharp maximum in the vicinity of M^*; the effective exponent is as high as ∼ σ^-1/3 just above M^*.     

线性响应和两种态特定方法模拟AF350电子跃迁的溶剂效应

在极化连续模型框架下比较了线性响应与两种不同态特定方法计算的溶液中Alexa Fluor 350(AF350)分子激发能和光谱移动值的差异. AF350的第一激发态S0→S1电子跃迁属于π→π^*跃迁, 主要对应于最高占据分子轨道(HOMO)到最低空轨道(LUMO)的跃迁. 该分子激发态偶极矩大于基态偶极矩, 激发态时溶质溶剂相互作用比基态时更强, 随着溶剂极性增大, 会发生光谱红移的现象. 与实验值相比, 线性响应和两种态特定方法均高估了激发能, 其中以IBSF(Improta-Barone-Scalmani-Frisch)方法得到的激发能最小, 矫正的基态反应场方法(cGSRF)得到的激发能最大. 对于光谱移动值, 3种方法与实验值相比都偏小, 线性响应方法(LR)计算出的误差最大, 而IBSF方法得到的结果与实验值最吻合, 是预测溶液中AF350分子激发能和光谱移动值最准确的方法. 对比了Marcus传统理论和基于约束平衡的非平衡溶剂化理论的结果, 发现后者得到的激发能和光谱移动值更接近于实验值.     

利用选择共振作用实现相位门

提出一个在高品质腔中实现相位门方案.该方案通过控制原子和腔之间的相互作用,选择所需要的共振作用,而让其它的原子跃迁由于大失谐可以绝热去除.由于仅原子基态参与作用,该方案有效抑制了原子自发辐射的影响;同时,不需要对腔中原子独立寻址,进一步降低了实验难度.     

低能小型医用回旋加速器谐振腔的有限元分析

应用有限元方法分析了一台小型医用回旋加速器的谐振腔.以PC机为平台,采用ANSYS软件进行建模,对腔体的谐振频率、空载品质因数进行了研究,探讨了微调电容间距、网格剖分精度以及建模方法对计算结果的影响.回旋加速器谐振腔不是一个严格的封闭腔体,结构复杂.为减少计算量,根据其物理特性对腔体做了封闭处理,研究发现,这一简化的模型对计算精度的影响不大.计算结果和实际测量结果的误差在工程允许的范围之内,表明基于有限元的软件能够很好地计算类似回旋加速器高频谐振腔这样具有复杂边界的腔体结构,可用于加速器的物理设计及工程设计.