Polymer modifies the critical region of the coexisting liquid phases

Several recent conceptual advances, which take advantage of the polymer conformation in the near critical point of coexisting liquid phases and practical techniques of some unique molecular interactions between polymer chain and the solvent molecules, have been made to allow the investigation of the effect of the well-defined polymer in phase separation of binary mixtures. The behavior of a flexible linear or branched chain polymer (polyethylene oxide, PEO, MW = 9 x 10(5), as an impurity) in the critical binary mixture of isobutyric acid (I) + water (W) was studied by the refractive index (n) measurements using a very accurate and sensitive refractometer. The refractive index in each phase of IW as well as three different PEO concentrations (C = 0.395, 0.796, and 1.605 mg/cm(3)) in the near critical composition of IW have been measured at temperatures below the system's upper critical point. We observed that the polymer was significantly affected in the critical region of IW and these various concentrations of PEO show an important behavior on the critical exponents (beta), the critical temperatures (T(c)), and critical composition (phi(c)), which are depicting the shape of the coexistence curve. The phase-transition region of coexisting phases of IW shifts down with the addition of PEO and T(c) decreases linearly with increasing PEO concentrations. This may indicate that the polymer chain entangles with each phase, thereby the polymer monomers strongly interact with neighbor solvent particles and also intrachain interaction between the polymer segments. At such conditions, the collapse of polymer chain is possible in the vicinity of the critical point. At temperatures T close enough to T(c), the critical exponent beta (defined by the relation (n(1) - n(2)) proportional, variant (T(c) - T)(beta), with n(1) and n(2) being the refractive indices of the coexisting phases) was found to decrease from 0.382 to 0.360 when the PEO concentration changes from 0.395 to 1.605 mg/cm(3). These values are higher than that of 0.326 +/- 0.005 of pure IW, which is compatible with the three-dimensional Ising value beta = 0.325. The observed critical exponents for the PEO in IW are fully renormalized Ising critical exponents. Besides, the phi(c) values decrease with increasing the C values in the mixture of IW. It appears that the shape of the PEO in IW coexistence curves is similar from that of pure IW.     

Critical phenomenon of nonaqueous microemulsion (AOT/DMA/decane)

The critical phenomenon of nonaqueous microemulsion was studied for the first time. The coexistence curves of (T,n), (T,phi), and (T,psi) (n and phi are refractive index and volume fraction, respectively; psi is defined as psi=phi/[phi+phi(c)(1-phi)/(1-phi(c))]) for a ternary microemulsion [phi (AOT-DMA)+(1-phi) decane] at constant pressure and a constant molar ratio (omega=2.86) of DMA to AOT have been determined within about 7 K from the critical temperature T(c) by measurements of refractive index. The critical exponent beta has been deduced from (T,n), (T,phi), and (T,psi) coexistence curves within 1 K below T(c). They all were 0.329+/-0.005 and were consistent with the 3D Ising value. The experimental results in a temperature range of (T(c)-T)<7 K also have been analyzed to obtain critical amplitudes and the Wegner correction terms, to examine the diameters of the coexistence curves.     

2,6-二甲基哌啶+水体系临界性质的氘代同位素影响

用等体积法分别确定2,6-二甲基哌啶+水和2,6-二甲基哌啶+重水体系的临界组成, 并测定各自的临界温度. 采用折射率法在较宽温度范围内测定两个体系的温度-折射率(T-n)共存曲线, 利用标φ曲线法将其转化为温度-摩尔分数(T-x)和温度-体积分数(T-φ)共存曲线, 求得临界指数β、指前因子B、Wegner校正项因子B1及与共存曲线直径ρd相关的参数. 研究结果表明, 氘代后, 体系低临界温度下降了约3.2 K, 临界组成和共存曲线形状不变, 在近临界点临界指数β仍符合三维伊辛模型(3D-Ising)的理论值(0.327).     

Tricritical phenomena in quasi-ternary mixtures of water + n-decane + n-undecane + tert-butanol

Coexistence curves for the quasi-ternary system of water + n-decane + n-undecane + tert-butanol have been determined by measurements of the refractive index in three coexisting liquid phases. The binary mixtures of n-decane + n-undecane constructed the quasi-pure components in which the mass fraction beta of n-decane controls the approach to the tricritical point. The coexistence curves can be fitted to Scott's extended theory and can be extrapolated to a tricritical point at (44.1 +/- 0.3) degrees C and beta = 0.77 +/- 0.02 corresponding to an average n-alkane-carbon number of 10.19 +/- 0.02. The nonclassical critical amplitude ratio has been confirmed to be 4-5% smaller than the classical value, which is consistent with Fisher's prediction.     

Finite-size scaling analysis on the phase transition of a ferromagnetic polymer chain model

The finite-size scaling analysis method is applied to study the phase transition of a self-avoiding walking polymer chain with spatial nearest-neighbor ferromagnetic Ising interaction on the simple cubic lattice. Assuming the scaling M2(T,n) = n(-2beta/nu)[phi0 + phi1n(1/nu)(T-T(c)) + O(n(2/nu)(T-T(c))2)] with the square magnetization M2 as the order parameter and the chain length n as the size, we estimate the second-order phase-transition temperature T(c) = 1.784 J/k(B) and critical exponents 2beta/nu approximately 0.668 and nu approximately 1.0. The self-diffusion constant and the chain dimensions (R2) and (S2) do not obey such a scaling law.     

Blends of POSS-PEO(n=4)(8) and high molecular weight poly(ethylene oxide) as solid polymer electrolytes for lithium batteries

Solid polymer electrolyte blends were prepared with POSS-PEO(n=4)8 (3K), poly(ethylene oxide) (PEO(600K)), and LiClO4 at different salt concentrations (O/Li = 8/1, 12/1, and 16/1). POSS-PEO(n=4)8/LiClO4 is amorphous at all O/Li investigated, whereas PEO(600K) is amorphous only for O/Li = 8/1 and semicrystalline for O/Li = 12/1 and 16/1. The tendency of PEO(600K) to crystallize limited the amount of POSS-PEO(n=4)(8) that could be incorporated into the blends, so that the greatest incorporation of POSS-PEO(n=4)(8) occurred for O/Li = 8/1. Blends of POSS-PEO(n=4)(8)/PEO(600K)/LiClO4 (O/Li = 8/1 and 12/1) microphase separated into two amorphous phases, a low T(g) phase of composition 85% POSS-PEO(n=4)(8)/15% PEO(600K) and a high T(g) phase of composition 29% POSS-PEO(n=4)(8)/71% PEO(600K). For O/Li = 16/1, the blends contained crystalline (pure PEO(600K)), and two amorphous phases, one rich in POSS-PEO(n=4)(8) and one rich in PEO(600K). Microphase, rather than macrophase separation was believed to occur as a result of Li(+)/ether oxygen cross-link sites. The conductivity of the blends depended on their composition. As expected, crystallinity decreased the conductivity of the blends. For the amorphous blends, when the low T(g) (80/20) phase was the continuous phase, the conductivity was intermediate between that of pure PEO(600K) and POSS-PEO(n=4)(8). When the high T(g) (70/30, 50/50, 30/70, and 20/80) phase was the continuous phase, the conductivity of the blend and PEO(600K) were identical, and lower than that for the POSS-PEO(n=4)(8) over the whole temperature range (10-90 degrees C). This suggests that the motions of the POSS-PEO(n=4)(8) were slowed down by the dynamics of the long chain PEO(600K) and that the minor, low Tg phase was not interconnected and thus did not contribute to enhanced conductivity. At temperatures above T(m) of PEO(600K), addition of the POSS-PEO(n=4)(8) did not result in conductivity improvement. The highest RT conductivity, 8 x 10(-6) S/cm, was obtained for a 60% POSS-PEO(n=4)(8)/40% PEO(600K)/LiClO4 (O/Li = 12/1) blend.     

硝基苯与正十六烷在临界区域的液-液共存曲线

用折射率法在离临界温度10.5K范围内测定了硝基苯+正十六烷的温度-折射率(T, n)共存曲线, 通过标准曲线法转化得到温度-摩尔分数(T, x)和温度-体积分数(T, φ)共存曲线, 进而求得临界指数, 与理论值一致。分析实验数据, 给出描述三条共存曲线的方程, 并讨论了选定的序参量的有效性。     

Nonasymptotic critical behavior of a ternary ionic system

Refractive indices n and salt concentrations ms of coexisting phases of the ternary system 1,4-dioxane + water + potassium chloride were measured along the liquid-liquid-solid coexistence curve near the liquid-liquid critical end point. Refractive index measurements were carried out in the range 0.689 x 10-3 < t = (T - Tc)/Tc < 0.118 while salt concentrations were determined for the temperature range 1.84 x 10-3 < t < 8.07 x 10-2. From these experimental results, compositions fD (mass fraction of dioxane on a salt-free basis) and densities rho of coexisting phases were obtained. The shape of the coexistence curve was analyzed using alternatively n, ms, fD, and rho as order parameters. In all cases, the obtained coexistence curve displays, asymptotically, Ising behavior. Outside the asymptotic critical domain, n, ms, and rho show significant deviations of the effective critical exponent from its Ising value, while the concentration variable fD requires no corrections to simple scaling. On the basis of the present results, we conclude that this system shows no indication of multicritical behavior.     

Determination of critical indices by "slow" spectroscopy: NMR shifts by statistical thermodynamics and density functional theory calculations

The temperature dependencies of NMR shifts in the critical region of two coexisting phases have been simulated using statistical thermodynamics and graph-theory consideration of equilibrium processes of molecular association. Microparameters of magnetic screening of various water and water/pyridine structures used in the statistical averaging have been evaluated by density functional theory calculations (PBE1PBE and B3PW91 functionals in the 6-311++G** basis set). The gauge-including atomic orbital (GIAO) approach has been applied to ensure gauge invariance of the results. Solvent effects were taken into account by a polarized continuum model (PCM). NMR shifts "order parameters" (Deltadelta = |delta+ - delta-|) and "diameters" (phidelta = |(delta+ + delta-)/2 - deltaC|, where delta+, delta-, and deltaC are the chemical shifts of coexisting phases and at the critical point respectively) have been calculated in each case close to the lower critical solution point (TL) and processed using linear regression analysis of Deltadelta approximately |T - TL| and phidelta approximately |T - TL| in the log-log plot. It has been shown that the critical index beta can be evaluated with high precision from the slope of Deltadelta = f(T - TL) at any realistic set of model input parameters. The slope of diameter has been found to depend on both input beta and alpha values. The obtained phidelta slopes (0.58-0.63) are very close to 2beta values. The results are discussed within the concept of complete scaling. Results of simulation are compared and supported by experimental NMR data for water/2,6-lutidine, acetic anhydride/n-heptane, and acetic anhydride/cyclohexane systems.     

反离子对全氟辛酸盐与高聚物的相互作用的影响

通过表面张力和电导率测定, 研究了全氟辛酸铵/四烷基铵(C7F15COON(CnH2n＋1)4, n＝0, 1, 2, 3, 4)与聚氧乙烯(PEO, 分子量20000)和聚氧乙烯聚氧丙烯三嵌段共聚物(Pluronic F68)的相互作用. 结果表明, 对PEO-C7F15COON(CnH2n＋1)4混合体系, 只有全氟辛酸铵、全氟辛酸四甲铵与PEO之间有明显的相互作用. 对F68-C7F15COON(CnH2n＋1)4混合体系, 只有全氟辛酸四丁铵未发现与F68有明显的相互作用. 说明全氟辛酸盐的反离子越大, 其与高聚物间的相互作用越弱. 增加高聚物的疏水性可以增强表面活性剂与高聚物的相互作用.     

DMA+AOT+正辛烷三组分非水微乳体系的临界现象

采用折射率法在离临界温度7 K的范围内测定N,N-二甲基乙酰胺(DMA)与二-(2-乙基己基)琥珀酸酯磺酸钠(AOT)摩尔比为3.46的非水微乳体系(DMA+AOT+正辛烷)的温度-折射率(T-n)共存曲线, 利用标准曲线转化为温度-体积分数(T-φ)共存曲线和温度-有效体积分数(T-ψ)共存曲线, 进而求得临界指数β. 研究结果表明, 该体系的临界指数β与已经报道的微乳液不同, 在较宽的温度范围内均符合Fisher重整化理论值0.365. 分析实验数据, 获得指数因子B、Wegner校正项因子B1和共存曲线的直径籽d, 并讨论所选择的序参量的优劣性.     

DMA/AOT摩尔比对非水微乳体系临界现象的影响

采用折射率法测定了非水微乳体系{N,N-二甲基乙酰胺(DMA)/二(2-乙基己基)琥珀酸酯磺酸钠(AOT)/正辛烷}在不同DMA与AOT摩尔比ωs时的温度-折射率(T-n)共存曲线, 并根据曲线推导出临界指数β和指前因子B. 结果表明, 临界组成φc(即DMA和AOT的体积之和在总体积中所占的分数)随ωs的增加而降低, 而临界温度Tc随ωs增加而增大; 临界指数β与ωs无关, 其数值趋近于Fisher重整化理论值(0.365); 与体系有关的指前因子B随ωs的增加而增大.     

Cyclotriphosphorus complexes: solid-state structures and dynamic behavior of monoadducts with carbonyl fragments

Treatment of the cyclo-P3 complexes [(triphos)MP3] [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane; M = Co (1), Rh (2)] with stoichiometric amounts of [M'(CO)5(thf)]n+ (n = 0, M' = Cr, Mo, W; n = 1, M' = Re) and [W(CO)4(PPh3)(thf)] yields the compounds [[(triphos)M](mu,eta 3:1-P3) [M'(CO)5]] [M = Co; M' = Cr (3a), Mo (3b), W (3c). M = Rh; M' = W (4)], [[(triphos)Co](mu,eta 3:1-P3)[Re(CO5)]]BF4.C7H8 (5) and [[(triphos)Rh](mu,eta 3:1-P3)[W(CO)4PPh3]].2CH2Cl2 (6). The X-ray structures of 5 and 6 have been determined. Crystal data: 5, monoclinic space group P2(1)/n, a = 14.754(2) A, b = 24.886(4) A, c = 15.182(2) A, beta = 103.38(1) degrees, Z = 4; 6, monoclinic space group P2(1)/n, a = 14.872(3) A, b = 27.317(6) A, c = 16.992(4) A, beta = 111.75(5) degrees, Z = 4. The effects of eta 1 coordination on the MP3 core are discussed by comparing the MP3 skeletons in the above structures with those of the previously characterized bis and tris end-on adducts of organometallic fragments of 1. Variable temperature NMR data for the compounds provide evidence for fluxional processes in solution that may be interpreted as [(triphos)M] rotation about its C3 axis and [M'(CO)5] or [M'(CO)4PPh3] scrambling over the P3 cycle. The activation parameters of the fragment scrambling process are determined.     

聚氧乙烯-镧系金属盐(Ln3+)的络合对聚氧乙烯形态结构的影响

采用偏光显微镜(POM)、差示扫描量热(DSC)和X 射线衍射,对聚氧乙烯(PEO)的形态结构和热物理行为随6种镧系盐对PEO的摩尔比变化的规律进行了系统的探讨.结果表明,随六合水氯化镧系盐摩尔比的增加,PEO球晶行为、熔点和熔融热均逐渐减弱,当盐对PEO的摩尔比达到一定值时(如YbCl3·6H2 O :PEO =2 0 ) ,则PEO完全不结晶.不同的镧系盐对PEO结晶的影响程度不同.X 射线衍射分析的结果也表明PEO晶面衍射峰随Ln3+ 盐摩尔比的增加而下降,与POM和DSC结果一致的.结果还表明较高的干燥温度(6 0℃)对PEO与Ln3+ 的相互作用有促进作用.对比二次降温的试样与原始试样的结晶行为,降温后结晶试样的特征表明络合在降温结晶后还存在.红外结果表明PEO与Ln3+ 的相互作用是络合作用.     

Highly Accurate CCSD(T) and DFT–SAPT Stabilization Energies of H‐Bonded and Stacked Structures of the Uracil Dimer

The CCSD(T) interaction energies for the H‐bonded and stacked structures of the uracil dimer are determined at the aug‐cc‐pVDZ and aug‐cc‐pVTZ levels. On the basis of these calculations we can construct the CCSD(T) interaction energies at the complete basis set (CBS) limit. The most accurate energies, based either on direct extrapolation of the CCSD(T) correlation energies obtained with the aug‐cc‐pVDZ and aug‐cc‐pVTZ basis sets or on the sum of extrapolated MP2 interaction energies (from aug‐cc‐pVTZ and aug‐cc‐pVQZ basis sets) and extrapolated ΔCCSD(T) correction terms [difference between CCSD(T) and MP2 interaction energies] differ only slightly, which demonstrates the reliability and robustness of both techniques. The latter values, which represent new standards for the H‐bonding and stacking structures of the uracil dimer, differ from the previously published data for the S22 set by a small amount. This suggests that interaction energies of the S22 set are generated with chemical accuracy. The most accurate CCSD(T)/CBS interaction energies are compared with interaction energies obtained from various computational procedures, namely the SCS–MP2 (SCS: spin‐component‐scaled), SCS(MI)–MP2 (MI: molecular interaction), MP3, dispersion‐augmented DFT (DFT–D), M06–2X, and DFT–SAPT (SAPT: symmetry‐adapted perturbation theory) methods. Among these techniques, the best results are obtained with the SCS(MI)–MP2 method. Remarkably good binding energies are also obtained with the DFT–SAPT method. Both DFT techniques tested yield similarly good interaction energies. The large magnitude of the stacking energy for the uracil dimer, compared to that of the benzene dimer, is explained by attractive electrostatic interactions present in the stacked uracil dimer. These interactions force both subsystems to approach each other and the dispersion energy benefits from a shorter intersystem separation.     

Characterization of the potential energy surfaces of two small but challenging noncovalent dimers: (P2)2 and (PCCP)2

This work characterizes eight stationary points of the P₂ dimer and six stationary points of the PCCP dimer, including a newly identified minimum on both potential energy surfaces. Full geometry optimizations and corresponding harmonic vibrational frequencies were computed with the second‐order Møller–Plesset (MP2) electronic structure method and six different basis sets: aug‐cc‐pVXZ, aug‐cc‐pV(X+d)Z, and aug‐cc‐pCVXZ where X = T, Q. A new L‐shaped structure with C₂ symmetry is the only minimum for the P₂ dimer at the MP2 level of theory with these basis sets. The previously reported parallel‐slipped structure with C_2h symmetry and a newly identified cross configuration with D₂ symmetry are the only minima for the PCCP dimer. Single point energies were also computed using the canonical MP2 and CCSD(T) methods as well as the explicitly correlated MP2‐F12 and CCSD(T)‐F12 methods and the aug‐cc‐pVXZ (X = D, T, Q, 5) basis sets. The energetics obtained with the explicitly correlated methods were very similar to the canonical results for the larger basis sets. Extrapolations were performed to estimate the complete basis set (CBS) limit MP2 and CCSD(T) binding energies. MP2 and MP2‐F12 significantly overbind the P₂ and PCCP dimers relative to the CCSD(T) and CCSD(T)‐F12 binding energies by as much as 1.5 kcal mol^?1 for the former and 5.0 kcal mol^?1 for the latter at the CBS limit. The dominant attractive component of the interaction energy for each dimer configuration was dispersion according to several symmetry‐adapted perturbation theory analyses. © 2014 Wiley Periodicals, Inc.     

What is the role of the complexant in the large first hyperpolarizability of sodide systems Li(NH3)(n)Na (n = 1-4)?

To explore the coordination number (around the cation) dependence of the nonlinear optical (NLO) properties in alkalides, this paper studies the structures and large NLO responses of model alkalides, Li(NH3)(n)Na (n = 1-4). At the MP2/aug-cc-pVDZ level, the structural characteristic is determined to be that the Li-Na distance increases (from 3.030 to 4.646 angstroms) with the increasing of the number of NH3 (n from 1 to 4). Results show that Li(NH3)(n)Na (n = 1-4) have considerably large first hyperpolarizabilities (beta0). Especially, a prominent coordination number dependence of the beta0 value is found as follows: beta0 = 13 669 (n = 1) < 26,840 (n = 2) < 39 764 (n = 3) < 77 921 au (n = 4) at the MP2 level. With the same coordination number (four N atoms) of Li+ cations, the beta0 value (77,921 au) of this "small" inorganic molecule Li(NH3)(n)Na is over five times larger than that of the "big" organic molecule Li@Calix[4]pyrrole-Na (14,772 au). This indicates that the beta0 value is strongly related to the flexibility of the complexant. Obviously, the flexibility of (NH3)4 is much greater than that of the cup-like shaped Calix[4]pyrrole. This work suggests that two important factors should be taken into account to enhance the first hyperpolarizability of alkalide, i.e., the coordination number around the cation and the flexibility of the complexant.     

聚氧乙烯／聚酚氧共混体系的结晶行为及相容性研究

对聚氧化乙烯/聚酚氧(PEO/PH)共混体系的研究表明,随共混体系中非晶组份PH含量的增加,Avrami指数n值由2.0～2.3变为1.5～2.0,体系的结晶由盘状生长转化为纤维状生长;成核方式由方式Ⅰ转化为方式Ⅱ.PEO/PH共混体系的平衡熔点随PH含量的增加而降低,相互作用能量密度B=-1.46cal/mol,说明体系是互容的。     

Revealing the physical nature and the strength of charge‐inverted hydrogen bonds by SAPT(DFT), MP2, SCS‐MP2, MP2C,and CCSD(T) methods

The physical nature of charge‐inverted hydrogen bonds in H₃XH YH₃ (X = Si, Ge; Y = Al, Ga) dimer systems is studied by means of the SAPT(DFT)‐based decomposition of interaction energies and supermolecular interaction energies based on MP2, SCS‐MP2, MP2C, and CCSD(T) methods utilizing dimer‐centered aug‐cc‐pCVnZ (n = D, T, Q) basis sets as well as an extrapolation to the complete basis set limit. It is revealed that charge‐inverted hydrogen bonds are inductive in nature, although dispersion is also important. Computed interaction energies form the following relation: . It is confirmed that the aug‐cc‐pCVDZ basis set performs poorly and that very accurate values of interaction and dispersion energies require basis sets of at least quadrupole‐ζ quality. Considerably large binding energies suggest potential usefulness of charge‐inverted hydrogen bonds as an important structural motif in molecular binding. Terminology applying to σ‐ and π‐hole interactions as well as to triel and tetrel bonds is discussed. According to this new terminology the charge‐inverted hydrogen bond would become the first described case of a hydride‐triel bond. © 2017 Wiley Periodicals, Inc.