Data driven temperature dependence of EOS parameters

Using three kinds of experimental data (p_c, V_c and T_c at the critical state or P_s, V_s^v and V^sL at different temperatures for saturation data) three parameters of the EOS may be directly determined and the temperature dependence of the parameters may be established from thermodynamic conditions of vapour-liquid critical point or vapour-liquid phase equilibria respectively. The principle was demonstrated on the BACK EOS. Examples of argon and n-alkanes were used to demonstrate the idea. It was found, that there are two parameter sets of the BACK equation that satisfy the critical or saturation conditions for certain pure compounds. The BACK equation is able to reproduce experimental Z_c values for compounds above Z_c = 0.2764 (that is, for argon, methane, ethane), but it is improper for higher alkanes. In case of n-alkanes we found that there is no simple function for T dependence of BACK parameters. Parameter values obtained in the way demonstrated may be useful to give initial values for parameter estimation from experimental (e.g., VLE) data.     

Analysis to obtain precise density fluctuation of supercritical fluids by small-angle X-ray scattering

A procedure of analysis for small-angle X-ray scattering (SAXS) data has been established to obtain density fluctuation of supercritical fluids near the critical point. It is indispensable for the certain analysis to utilize both of high-quality SAXS data measured under stable thermodynamic condition and accurate P–ρ–T data in supercritical region. As a standard example, SAXS measurements have been performed for supercritical CO₂, which is a suitable sample satisfying the condition for both experiment and analysis. The measurements were carried out along four isothermal conditions at reduced temperature of T_r = T/T_c = 1.020, 1.022, 1.043 and 1.064. Comparing the experimental density fluctuation with calculated one from the most reliable equation of state, the differences are within 8% at most.     

Influence of hydrostatic pressure on the phase transition in Ni(NH3)6I2: EPR studies

Electron paramagnetic resonance techniques are used to determine the phase transition temperature T_c of Ni(NH₃)₆I₂ as a function of hydrostatic pressure. The hydrostatic pressure causes T_c to increase and the value of the pressure coefficient dT_c/dp is (10 ± 2) K/GPa. T_c and dT_c/dp for hexammine halides is calculated on the basis of the “rigid-sphere model” and good agreement with the experimental data is obtained.     

快速扫描量热法研究聚对苯二甲酸-1,4-环己烷二甲醇酯的结晶和熔融行为

采用快速扫描量热法(FSC)结合传统的差示扫描量热仪(DSC)考察了聚对苯二甲酸-1,4-环己烷二甲醇酯(PCT)聚酯在接近玻璃化转变(T_g)和熔融温度(T_m)范围(100~270 ℃)的结晶和熔融行为。 较大过冷度时PCT聚酯结晶较快,FSC有效地抑制降温过程结晶的发生,而较低过冷度下传统DSC可以避免样品降解对实验结果的影响,二者的结合能很好地对PCT聚酯结晶动力学进行测量,实验结果表明在175 ℃时结晶速率最快。 并且利用Flash DSC对等温结晶温度下形成的片晶熔点进行加热速率的相关测量,在熔融动力学建模的基础上进行校准,以确定零加热速率下片晶的熔点。 Hoffman-Weeks方程中T_m与结晶温度(T_c)的线性关系与T_c=T_m的交点给出了PCT晶体的平衡熔融温度$T_m^o$为315 ℃。     

The low-lying electronic states of YCu

The spectroscopic constants for the singlet and tripletstates of YCu below about 15 000 cm⁻¹ are determined using an internally contracted multireference configuration-interaction approach. These calculations are calibrated by studies of fewer states using higher levels of correlation treatment and/or basis sets. The computed T_c values and radiative lifetimes are in reasonable agreement with experiment. The calculations confirm the previous experimental assignment for all but one state, where theory helps resolve between two possible assignments.     

Calculation of critical temperature Tc in high temperature superconductivity using grand canonical ensemble

In this paper we use the grand canonical ensemble to calculate the T_c of superconductivity for the compound YBa₂Cu₃O₇ under one dimensional Cu–O chain model. The results are consistent with experiments.     

Mesomorphic behaviour of forty benzylidene-aniline-p,p′-dialkoxy derivatives

The transition temperatures of forty mesomorphic homologous benzylidene-aniline-p,p′-dialkoxy derivatives are reported.

The transition diagrams show different paths for heating and cooling for most of the compounds. Moreover, some compounds with higher length-breadth ratios, show very complicated thermal cycles with some monotropic phases. In any case, the clearing temperatures (T_c) alternate within every series.

The experimental data are discussed briefly and some general considerations on the structure and mesomorphic behaviour are suggested.     

Magnetic investigation of Cu(NH3)4(NO3)2

The magnetic properties of Cu(NH₃)₄(NO₃)₂ have been measured at low temperatures. Broad maxima in both the susceptibility and specific heat are observed and are consistent with linear chain behavior of a Heisenberg antiferromagnet, with J/k = 3.9 ± 0.1 K. Long-range order sets in at T_c = 0.15 ± 0.01 K, and the ratio kT_c/|J| = 0.038 is the lowest observed as yet for a one-dimensional, S = 1/2 antiferromagnet.     

Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures (T_c) below the maximum glass transition of the fully cured epoxy (T_g∞=85.8°C). Initially, the modulus of the complex heat capacity, |C^*_p|, increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of |C^*_p|, due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in |C^*_p| at vitrification decreases with the increase of T_c becoming zero at temperature T_g∞. This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network.

The decay of |C^*_p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor.     

Determination of absorptivity and formation constant of a chalcone association complex

A UV spectrometric method was developed to determine the molar absorptivity (_C) and formation constant (K_c) of the association complex of unsubstituted chalcone in cyclohexane, in the concentration range from 4.00·10⁻⁴ to 2.00·10⁻² mol dm⁻³. The thermodynamic and spectroscopic magnitudes such as K_c and _C contribute to the understanding of the physicochemical behavior of several ,β-unsaturated carbonylic compounds, of low solubility in water, as it is the case of numerous flavonoids of chemical and biological importance. The studied association complex, formed by two chalcone molecules, is characterized by the constants _C (300.8 nm)=4.98·10⁴ dm³ mol⁻¹ cm⁻¹ and K_c=5.58·10³. The method proposed is convenient for the study of solute–solute molecular associations particularly those due to dipole–dipole interactions.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XIII. 4-(4-Substituted phenylazo)phenyl 4-alkoxybenzoates

Five homologous series of 4-(4-substituted phenylazo)phenyl 4-alkoxybenzoates (Ia-e) were prepared in which the substituent (X) was taken from CH₃O, CH₃, Cl, NO₂, and CN, while, within each homologous series, the length of the terminal alkoxy group varied between 6 and 16 carbon atoms. Compounds prepared were characterized by infrared spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and polarizing optical microscopy. The results are discussed in terms of mesomeric and polarizability effects. In each group of compounds bearing the same alkoxy group, the mesophase - isotropic transition temperatures (T_c) were successfully correlated with the polarizability anisotropy of bonds to the substituent X.     

Study of initiation reactivity of some plastic explosives by vacuum stability test and non-isothermal differential thermal analysis

On the basis of measurements of 18 high explosives by means of the Czech Vacuum Stability Test (VST) STABIL, a relationship has been specified between the results of this test and those of Russian manometric method. The said relationship was used to predict the Arrhenius parameters (E_a and log A values) of four plastic explosives based on RDX and one high explosive based on PETN (Semtex). The slopes E_aR⁻¹ of Kissinger's equation were specified by means of non-isothermal differential thermal analysis (DTA) and evaluation of the measurement results by means of the Kissinger method. The role played by binders and plasticizers in thermal decomposition of nitramines was pointed out on the basis of relationship between the E_a values obtained from VST and the E_aR⁻¹ values obtained from DTA, both for plastic explosives, eight nitramines, Composition B and PETN. The relationships between the E_aR⁻¹ values and thermostability threshold was specified for the given group of explosives. The relationship classify some of the studied plastic explosives as belonging to nitramines with steric hindrance in the molecule (CPX, TNAZ and HNIW). The relationship between E_aR⁻¹ values and drop energies, E_dr, sharply differentiates between plastic explosives and individual nitramines. From the relationship between the E_dr and D² values it was found that the increasing performance of the studied nitramines and plastic explosives is connected with the decrease in their impact sensitivity. Also specified are the approximate linear dependences between the peak temperatures of exothermic decomposition of all the explosives studied and their ignition temperatures, T_ig, or critical temperatures, T_c; these dependences were applied to prediction of T_ig and T_c of both the studied plastic explosives and some of the nitramines.     

Hm and Vm thermodynamic surfaces for binary mixtures in the near critical region

Even for such simple mixtures as (argon+methane), the excess enthalpy H^E_m and the excess volume V^E_m in the near critical region are about two orders of magnitude higher than for the liquid mixture at low temperatures and pressures near ambient conditions. Mixtures for which the critical temperatures are close together, and for which the critical pressures are far apart, have similar H^E_m (x,p,T) and V^E_m (x,p,T) surfaces, and near critical isotherms show double maxima in the supercritical fluid region. Mixtures for which the critical pressures are close together, and the critical temperatures are far apart, also have similar H^E_m (x,p,T) and V^E_m (x,p,T) surfaces, but isobars on the surfaces are ‘S’ shaped. The shapes of these near-critical excess-function surfaces can be understood from an inspection of the enthalpy, or residual enthalpy curves of the mixture and of the pure components. Examples of both are given. Attention is drawn to the large value that these excess functions can have close to a pure component critical point.     

Novel glassy nematic and chiral nematic oligomers derived from 1,3,5-cyclohexanetricarboxylic and (1R,3S)-( )-camphoric acids

Novel nematic and chiral nematic liquid crystals capable of vitrification have been synthesized using 1,3,5-cyclohexanetricarboxylic and (1R,3S)-(+)-camphoric acids as the base structures to which cyanotolan, cyanobiphenyl, methoxybiphenylbenzoate nematogenic groups, (S)-(-)-1-phenylethylamine and (S)-(+)-1,3-butanediol chiral moieties are attached. Once the glassy state is induced by quenching or controlled cooling from the isotropic state, these liquid crystals showed no detectable tendency towards crystallization upon heating through the glass transition temperature. In all cases, the ΔC_p and ΔH_c values resulting from the DSC heating scans are comparable to those previously reported for polymer analogues and other low molar mass glassy liquid crystals. In the nematic series with varying spacer lengths, both T_g and T_c are consistently lower than the linear polymer counterparts, in contrast to the siloxane-based systems. It was also demonstrated that cholesteric mesomorphism can be induced following one of the three approaches: chiral nematic mixture, chiral nematic cyclic cooligomer, and pendant nematogenic groups attached to a chiral ring.     

Phase transitions and critical phenomena in strongly chemisorbed adlayers: Influence of defects

Phase diagrams and, more severely, critical properties of continuous phase transitions in two-dimensional systems can strongly be changed by the presence of defects on the surface. We focus on the example of adsorbed atomic hydrogen on Ni(111). Although strongly chemisorbed, the phase diagram of this system is sensitive to isotopic mixtures. Finite energies of mixing and changes of the order-disorder phase transition of the (2 × 2) phase from continuous to first order were found. The critical properities of this order-disorder transition are changed by the presence of preadsorbed oxygen concentrations of 0.3% to 3% of a monolayer. The result is a crossover from 4-state Potts exponents far away from T_c to Ising-like exponents closer to T_c. These effects can well be separated from finite size effects, which are present in addition. The influence of steps on the critical properties is particularly interesting, if the order of the adsorbate is not interupted by steps. In this case, a similar change of critical exponents is seen, as for O/Ru(0001)−p(2 × 2). These results are discussed in the framework of random disorder.     

The conformation of N-nitroso-N-methylaniline from microwave spectroscopy

The low resolution microwave spectrum of N-nitro,N-methylaniline shows only one series of μ_a R-branch bands. The value of B + C = 1584.6 MHz is consistent with this being the rotamer in which the benzene ring is exo to the nitroso group. The high resolution microwave spectra of the normal. CD₃ and two meta-D species show conclusively that this rotamer has a non-polar heavy atom skeleton. The rotational constants, the quantity Δ_c (= I_a + I_b − I_c) and the substitution coordinates are well reproduced by a molecular model based on the structures of aniline and N,N-dimethylnitrosamine in which the plane of the benzene ring is twisted by 30° relative to the heavy atom plane of the rest of the molecule.     

Application of the ISM EoS for polymer solutions and blends

A method for predicting an analytical equation of state for polymer mixtures and blends from surface tension and liquid state density at normal (ordinary) temperature (γ_n, ρ_n), as scaling constants, is presented. B₂(T) follows a promising corresponding-states principle. Calculation of (T) and b(T), the two other temperature-dependent constants of the equation of state, are made possible by scaling. As a result, γ_n and ρ_n are sufficient for determination of thermophysical properties of polymer mixtures and blends.

We applied the procedure to predict liquid density of poly(ethylene glycol) (PEG-200) + 1-octanol solutions and poly(propylene glycol) (PPG) + poly(ethylene glycol) (PEG-200) blends at compressed state with temperature range from 298.15 to 338.15 K and pressures up to 40 MPa. In this work, the ISM EoS is extended to polymer mixtures and blends as well as pure case without proposing any mixing rule.     

Elastic, dielectric and optical constants of 4'-pentyl-4-cyanobiphenyl

4'-n-Pentyl-4-cyanobiphenyl (5CB) is a room temperature nematic liquid crystal with a high positive dielectric anisotropy and a high chemical stability. Many experimental results concerning the elastic and dielectric constants of 5CB are available in the literature, although there is often no satisfactory agreement between the experimental data obtained by different groups, especially as far as the dielectric constants are concerned. Furthermore, no detailed investigation of the temperature dependence of the elastic and dielectric constants close to the nematic-isotropic transition temperature T_NI has yet been reported. In this paper, we report the measurement of the elastic and dielectric constants of 5CB, and the temperature behaviour close to T_NI has been investigated in detail. The experiment consists in the measurement of the director deformation induced by an electric field using simultaneously both a dielectric and an optical method. The simultaneous use of these two methods provides an indirect check on the reliability of the measurements. Special attention has been devoted to control possible sources of uncertainty. In particular, the effects of finite anchoring energy and of finite pretilt angle have been considered. The temperature dependence of the anisotropy of the refractive indices is also obtained in the experiment.     

Induced smectic C* phases

Induced ferroelectric S*_C phases are formed by non-chiral S_C host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization P_s and the tilt angle Θ has been investigated as a function of the mole fraction x_G of the chiral dopant. In most cases the reduced polarization P₀ = P_S/ sin Θ has been found to depend linearly on x_G. The polarization power which is defined by δ_P=(∂P₀/∂x_G)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P₀(x_G) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P₀. By assuming a local field of Lorentz type a theoretical relation for P₀(x_G) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large.     

Predicted radiolysis yield in a Fricke solution irradiated with various heavy ions

Experimental data on the spatial distribution of the energy deposited around an energetic heavy ion, from 1 MeV proton to 5.9 MeV/n uranium ion, which have been reported in the literature were documented to obtain a scaled radial dose distribution; (β/Z*)² D(Z*, β,t)=200 (for t=0–1), 200/t² (for t=1t_c), and 200 t_c/t³ (for t>t_c) where Z* and β are the effective charge and velocity relative to c, the velocity of light, of the incident ion, respectively, D the dose in unit of Gy, t the radial distance in unit of nm, t_c the critical distance empirically determined.

Then, if we know the yield of any chemical reaction as a function of dose from the results of experiments using γ-radiations or fast electrons or theoretical calculations, we can calculate the probability for the yield of the chemical reaction in the system bombarded with a heavy ion of the effective charge Z* and velocity β. The results of the present calculation of the LET-values and of G(Fe³⁺) in the ferrous sulfate acidic solution are presented and compared with reported experimental results.