Estimation of the critical properties of compounds using volume-based thermodynamics

The importance, yet scarcity of the critical constants of thermally unstable fluids warrants the development of reliable methods for the estimation of these essential thermodynamic properties. A thorough investigation undertaken in this study on 1,589 compounds belonging to 83 chemical classes, indicated that the ratio of critical temperature to critical pressure of both low and high molecular weight compounds could be well expressed in terms of their volumetric properties. In addition, two new methodologies are presented for estimating V_c, as well as an indirect approach for prediction of T_c from surface tension data, altogether allowing the calculation of Z_c. Moreover, comparative studies are made with five group contribution methods. It is also demonstrated that by employing the Peng-Robinson EOS, and without prior knowledge of the critical properties, it is possible to calculate various thermophysical properties including P^sat., T_b, , ∆H^vap. , C_p, and even the T_c and P_c themselves.     

Thermodynamic model for predicting phase equilibria of simple clathrate hydrates of refrigerants

In this communication, a thermodynamic model is presented for the study of the phase equilibria of clathrate hydrates of simple refrigerants. The van der Waals–Platteeuw solid solution theory is used to model the hydrate phase while it is assumed that vapor phase is an ideal gas of refrigerant ignoring its water content and the aqueous phase is considered as pure water (activity coefficient=1) ignoring aqueous solubility. The results through this model are successfully compared with the experimental data reported in the literature for clathrate hydrates of four refrigerants namely C₂H₂F₄ (1, 1, 1, 2-tetrafluoroethane or HFC-134a or R-134a), C₂H₄F₂ (1, 1-difluoroethane or HFC-152a or R-152a), CH₂F₂ (difluoromethane or HFC-32 or R-32), and C₂H₃Cl₂F (1,1-dichloro-1-fluoroethane or HCFC-141b or R-141b).     

Synthesis and properties of polyamide derived from piperazine and lower purity dimer acid as hot melt adhesive

Polyamide hot melt adhesive was synthesized from lower purity dimer acid (composition: ∼23% trimer acid, ∼75% dimer acid and ∼3% monomer acid), sebacic acid, ethylenediamine and piperazine. The effect of piperazine and dimer acid concentration on properties of polyamides such as thermal properties: fusion temperature (T_f), heat of fusion (H_f), crystallization temperature (T_c), heat of crystallization (H_c), softening point (T_s) and glass transition temperature (T_g), mechanical properties: tensile strength and hardness, adhesion properties like lap shear strength (LSS) and T-peel strength (TPS), and rheological properties were investigated. Concentration of piperazine was varied from 12.5 to 37.5 mol% while that of dimer from 37.5 to 42 mol%. Piperazine has one hydrogen atom on each of its two nitrogen atoms in the ring structure. When it undergoes reaction with acids to form polyamide, these hydrogen atoms get consumed, making the amide linkage unable to form hydrogen bonding with the neighboring polyamide polymer chains. This leads to decrease in crystallinity of the polyamide. Thus, as the mole percentage of piperazine in the polyamide increases, it becomes more amorphous, decreasing T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity. Dimer acid and trimer acid are bulky compounds. As their percentages in the polyamide increase, it becomes difficult for the neighboring polyamide chains to come closer. Thus, inter-molecular hydrogen bonding decreases. This leads to decrease in crystallinity of the polyamide, lowering T_f, H_f, T_c, H_c, T_s, T_g, tensile strength, hardness, LSS, TPS and viscosity.     

Structures of the (4S, 14S)-4, 14-Dimethyl-3,6,9,12,15-pentaoxa-21-azabicyclo[15.3.1] heneicosa-1(21) 17,19-Triene-2,16-dione Complexes of R-and S-α-(1-Naphthyl)ethylammonium Perchlorate

Crystal data for the more stable (R) and less stable (S) 1:1 macrocycle-cation complexes are as follows: R cation: M_r = 625.08, orthorhombic P2₁2₁2₁, a = 8.47(1), b = 11.78(1), c = 31.19(6) A, V = 3112.0(123) ų, Z = 4, D_x = 1.333 kg m⁻³, λ(Mo Kα) = 0.71073 μ = 1.90 cm⁻¹, F(000) = 1320, T = 295 K, R = 0.17 for 1680 reflections. S Cation: M_r = 625.08, monoclinic, P2₁, a = 8.654(2), b = 11.954(3), c = 15.130(4) Å, β = 97.39(2)°, V = 1552.2(12) ų, Z = 2, D_x = 1.337 kg m⁻³, λ(Mo Kα) = 0.71073, μ = 1.91 cm⁻¹, F(000) = 660, T = 295K, R = 0.081 for 2751 unique reflections. Crystals of the complexes were prepared by the authors. The greater thermodynamic stability of the R cation complex is consistent with the observation that this cation experiences less steric interaction with the methyl substituent of the ligand than does the S cation.     

Enhanced mechanical properties of poly(lactic acid) composites with ultrathin nanosheets of MXene modified by stearic acid

MXene modified by stearic acid (Ti₃C₂T_x-g-SA) is incorporated into poly(lactic acid) (PLA) matrix to prepare Ti₃C₂T_x-g-SA/PLA composites. The effects of Ti₃C₂T_x-g-SA to pure PLA are investigated, including crystallization, mechanical, and thermal properties. Fourier transform infrared spectroscopy and X-ray diffraction analyses confirm that Ti₃C₂T_x interlayer is successfully intercalated by SA, and the interlayer spacing of Ti₃C₂T_x is increased. Differential scanning calorimetry illustrates that the cold crystallization enthalpy (ΔH_cc), melting enthalpy (ΔH_m), and crystallinity (X_c) of Ti₃C₂T_x-g-SA/PLA composites are improved by the plasticization and heterogeneous nucleation effect of Ti₃C₂T_x-g-SA. Specially, the Ti₃C₂T_x-g-SA/PLA composites exhibit excellent mechanical properties at an appropriate content of the Ti₃C₂T_x-g-SA. Compared with pure PLA, the elongation at break of the Ti₃C₂T_x-g-SA/PLA composite is increased 5.9-fold (up to 131.6%) when only containing 0.5 wt % Ti₃C₂T_x-g-SA. Besides, the Ti₃C₂T_x-g-SA/PLA composites exhibit good thermal stability in the low loading (lower than 1 wt %) of Ti₃C₂T_x-g-SA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48621.     

Thermodynamic functions for 3-fluoropropene

Thermodynamic functions C_p°, S°, (H°-H₀°)/T, —(F°-H0°)/T have been calculated for 3-fluoropropene in the ideal gas state from 298.15° to 800°k. at 1 atm. pressure. The restricted rotational contribution has been treated by the conventional method of Pitzer and Gwinn.     

Analytical attractive functions and their derivatives in bulk and nanoconfined pores

In this paper, two new analytical attractive (alpha) functions and their derivatives in bulk and nanoconfined pores are developed based on the virial equation of state (EOS) and statistical thermodynamics and are evaluated at different conditions for the first time. A cubic EOS is modified to nanometer scale and applied to predict the thermodynamic and phase properties in bulk and nanoconfined pores coupled with the new analytical alpha functions. The nanoscale-extended EOS coupled with the analytical alpha functions are validated to be accurate by means of the experimental data for the thermodynamic and phase calculations. The alpha functions and dimensionless attractive term A for the O₂, Ar, CO₂, N₂, and C₁-C₁₀ are always positive and monotonically decrease with the temperature increases at T ≤ 2000 K in the bulk phase, whereas the second virial coefficients (B₂) are always negative and increase with the temperature increases. Moreover, the alpha functions, A, and B₂ for all of components remain constant with the decreasing pore radius until r_p = 50 nm, the former two of which decrease while the latter one increases by further reducing the pore radius. It should be noted that the intermolecular attractive force (ie, A) is a function of the pressure, which is gradually increased at P ≤ 10 MPa though drastically increases afterwards. Also, the enhanced confinement effects lead the same-component intermolecular attractive forces to be smaller. The analytical formulations in the SRK type slightly outperform in the gaseous or light component cases, while those in the PR type are better for the heavy component cases in terms of the thermodynamic property calculations, both of which are compatible with the modified EOS and analytical alpha functions.     

Effect of Piperazine Concentration on the Properties of Lower Purity Dimer Acid-Synthesized Polyamide Hot-Melt Adhesive

Abstract

Polyamide hot-melt adhesive was synthesized from lower purity, i.e., 75% purity dimer acid, sebacic acid, ethylenediamine and piperazine. The effect of piperazine content on the properties of polyamides, such as thermal properties: heat of fusion (H _f), heat of crystallization (H _c), softening point (T _s) and glass transition temperature (T _g); mechanical properties: tensile strength and hardness; adhesion properties: lap shear strength (LSS) and T-peel strength (TPS); and rheological properties was investigated. Concentration of piperazine was varied from 12.5 to 37.5 molar %. It was found that H _f, H _c, T _s, T _g, tensile strength, hardness, LSS, TPS and viscosity all increased with decrease in molar percentage of piperazine. This is due to increase in crystallinity of the polyamide with decrease in piperazine, giving better packing of molecules in the adhesive, thus giving better properties.     

Calculation of thermodynamic properties and vapor-liquid equilibria of refrigerants

Saturated state thermodynamic properties of refrigerants are predicted from critical coordinates and normal boiling points by using Soave's equation of state. Binary vapor-liquid equilibria are correlated by determining interaction parameters for the following six systems: CCl₂F₂/CH₃CHF₂, CCl₂F₂/CHClF₂, CHF₃/CClF₃, CClF₃/CCl₃F, CCl₂F₂/CClF₃, CF₄/CHF₃. On the whole the method gives reliable results over broad temperature and pressure ranges for practical engineering uses.     

A study of liquid molar volumes for some pure halogenated hydrocarbons and their binary mixtures

Liquid volume data have been measured at compressed liquid conditions for four pure refrigerants, CCl₃ F, CCl₂ F₂, CHClF₂ and C₂ Cl₂ F₄, and three mixtures, CCl₂ F₂/CCl₃ F, CCl₂ F₂/C₂ Cl₂ F₄, and CHClF₂/C₂ Cl₂ F₄. A comparison of measured data and data reported in the literature with calculated data by three methods is presented. The three methods are the Thomson-Brobst-Hankinson correlation, and two equations of state according to Carnahan-Starling-de Santis and Lee-Kesler-Plöcker. In general the Thomson-Brobst-Hankinson correlation shows a smaller deviation from experimental data than the two equations of state examined.     

Gas permeation properties of poly(2,5-dialkyl-p-phenyleneethynylene) membranes

Dipropynylbenzenes with alkyl groups (CH₃C ≡ CRC₆H₂RC≡CCH₃, R=n-C₆H₁₃, n-C₈H₁₇, n-C₁₀H₂₁, 1a–c, respectively) were polymerized with Mo(CO)₆ to afford solvent-soluble poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c). The polymers (2a–c) had high molecular weight over 3×10⁴, and gave free-standing membranes by solution casting method. According to thermogravimetric analysis (TGA), these poly(p-phenyleneethynylene)s showed high thermal stability (T₀ ≥380 °C). The densities of membranes of poly(2,5-dialkyl-p-phenyleneethynylene)s (2a–c) were 0.936–0.965, and their fractional free volume (FFV) were relatively large (ca. 0.14–0.15). The oxygen permeability coefficients (PO₂) of membranes of 2a–c were 4.88, 7.06, and 16.6 barrers, respectively.     

A novel unexpected seven-coordinated chain-like dysprosium coordination polymer of pyridine-4-carboxylate: structure and photophysical property

One novel dysprosium coordination polymer [Dy(PIC)₃(H₂O)₂]_n (HPIC = pyridine-4-carboxylic acid) has been synthesized. X-ray analysis reveals that it forms the chain-like molecular structure through the bridged oxygen atoms of the carbonyl groups. The title coordination polymer crystallizes in the monoclinic system, space group C2/c, with lattice parameters: a=20.243(9) Å, b=11.576(5) Å, c=9.834(4) Å, β=110.601(2)°, V=2078(2) ų, D_c=1.805 mg/m³, Z=4, F(000)=1100, GOF = 1.11, R1=0.0404. The photophysical property has been studied with ultraviolet absorption spectrum, excitation and emission spectrum. The luminescence spectra show the stronger blue emission than yellow emission.     

Non‐isothermal crystallization kinetics of Al2O3‐YAG amorphous ceramic coating deposited via plasma spraying

Crystallization kinetics of the newly developed Al₂O₃‐Y₃Al₅O₁₂ (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non‐isothermal conditions. The phase compositions and microstructure of the as‐sprayed coating were characterized by X‐ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature T_g, the onset temperature of crystallization T_c and the peak temperature of crystallization T_p presented heating rate dependence. The related kinetic parameters of activation energies (E_g, E_c, E_p) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis–Bennett, Ozawa and Matusita–Sakka, etc., to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (T_c, E_c), nucleation resistance E_c/RT_g and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al₂O₃‐YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing.     

Preparation and properties of plasma-deposited films with surface energies varying over a wide range

Polymer surfaces have been modified by chemical reaction or thin film deposition using a capacitatively coupled plasma RF-discharge system. This has allowed the production of a graded, reproducible series of surfaces with surface energies ranging from low to high. Three gases, hexafluoroethane (C₂F₆), perfluoropropane (C₃F₈), and hexafluoropropene (CF₃CF?CF₂), were used to prepare the low-energy surfaces. Ethylene oxide (C₂H₄O) was used to prepare the higher energy surfaces. Intermediate values of surface energy were obtained by using gas mixtures of perfluoropropane and ethylene oxide. The plasma-deposited films were characterized by ESCA and contact-angle studies. In the low-energy range, the critical surface tension (γ_c) values of the films prepared were found to be lower than those for Teflon. For the higher energy surfaces, values up to about 45 dyn/cm were obtained. Addition of oxygen to the plasma permitted the production of films with still higher γ_c values. ESCA studies indicate that, under the reaction conditions used, C₃F₈ and CF₃CF?CF₂ form a fluoropolymer deposit on glass that is at least 100 Å thick. For the same reaction parameters, C₂F₆ resulted in more etching and deposition of a much thinner film.     

High-temperature elastomers: A systematic series of linear poly(carborane-siloxane)s containing icosahedral (?CB10H10C?) cages. I. Thermomechanical behavior in nitrogen

An extensive study of structure–bulk property relations for a systematic series of well-defined linear poly(carborane-siloxane)s is reported. These polymers form the backbone components of the most recently developed high-temperature elastomers. The basic structure is where (1) x = 1, 3, 4, 5, ∞; (2) A = endgroups (reactive and inert); (3) Z = meta-, para-carborane (for x = 3); (4) R = ? CH₃, R = ? C₂H₄CF₃ (for x = 3), one in five R = ? C₆H₅ with the remainder ～CH₃ (for x = 4, randomly and regularly substituted); (5) molecular weight = ～10,000, ～50,000 (for x = 3). Thermomechanical spectra (～1 cps) from ?180°C to 625°C to ?180°C in nitrogen at 3.6°C/min and thermogravimetric data from 25°C to 800°C in argon are presented. Physical transitions (T_g, T_m, T_crys, T_sec) are discussed, including a correlation of T_g data with structure (for x = 1, 2, 3, 4, 5, ∞) using a copolymer equation. Thermostability is also discussed in terms of structure.     

Nonisothermal crystallization of s‐PP fractions

Syndiotactic polypropylene (s‐PP) was prepared by metallocene catalyst and was fractionated with the temperature rising elution fractionation (TREF) technique. The nonisothermal behavior of the obtained fractions was investigated. Fractions was first cooled at different rates and then heated at a constant rate. The parameters such as the peak crystallization temperature (T_c), the onset crystallization temperature (T_on), the difference between T_on and T_c (ΔT₁ = T_on − T_c), the crystallization enthalpy (ΔH), the peak melting temperatures (T_m1, T_m2), and the difference between the T_m1 and T_m2 (ΔT₂ = T_m2 − T_m1) were obtained. The dependence of these parameters on cooling rate, syndiotacticity, and molecular weight was discussed. It is found that T_c, T_on, ΔH, T_m1, and T_m2 systematically increase with increasing syndiotacticity and are depressed on increasing the cooling rate. Cooling rate, syndiotacticity, and molecular weight show different influences on ΔT₁. In the melting process of s‐PP, double peaks were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 897–901, 1999     

Achieving single domain in rhombohedral and tetragonal Mn-doped Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 crystals for infrared detecting applications

The [111]-oriented rhombohedral Mn-doped 0.15Pb(In_1/2Nb_1/2)-0.55Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (Mn:PIMNT(15/55/30)) crystal and the [001]-oriented tetragonal Mn-doped 0.29Pb(In_1/2Nb_1/2)-0.29Pb(Mg_1/3Nb_2/3)O₃-0.42PbTiO₃ (Mn:PIMNT(29/29/42)) crystal were poled under different conditions. The pyroelectric performance of the two crystals as a function of poling temperature, as well as the relationship with ferroelectric domain configuration and phase structure was investigated systematically. The pyroelectric properties of the two crystals enhance with rising the poling temperature, which can be attributed to the improvement of the single state. And for the rhombohedral Mn:PIMNT(15/55/30) crystal locating near morphotropic phase boundary (MPB), the increase of tetragonal phase induces the deterioration of pyroelectric properties. Due to more residual tetragonal phase, the pyroelectric coefficient of the Mn:PIMNT(15/55/30) crystal poled at 150°C is lower than that poled at 100°C. In general, both the crystals poled above T_C achieve nearly single state, exhibiting the best pyroelectric properties with relatively high Curie temperature (T_C), where P = 9.71 × 10⁻⁴ C m⁻² K⁻¹, F_i = 3.88 × 10⁻¹⁰ m V⁻¹, F_v = 0.068 m² C⁻¹ and F_d = 29.7 × 10⁻⁵ Pa^−1/2 for the rhombohedral Mn:PIMNT(15/55/30) crystal (T_C = 171°C) and P = 6.78 × 10⁻⁴ C m⁻² K⁻¹, F_i = 2.71 ×10⁻¹⁰ mV⁻¹, F_v = 0.1 m² C⁻¹, F_d = 23.54 × 10⁻⁵ Pa^−1/2 for the tetragonal Mn:PIMNT(29/29/42) single crystal (T_C = 251°C), meeting the stable operation of infrared detector at relatively high environmental temperatures.     

The magnetic,thermal transport properties,magnetothermal effect and critical behavior of Co3Sn2S2 single crystal

Through the magnetic/thermal transport measurements combined with the analyses of magnetocaloric effect and critical behavior of Co₃Sn₂S₂ single crystal, the main results we obtained are as follows: in the case of the magnetic field H//c-axis, Co₃Sn₂S₂ exhibits the phase-separation state below T_c in the low-field region (H < 500 Oe). T_c increases slightly from 174 to 177 K with an increase in H from 100 to 10 kOe. The second-order magnetic phase transition near T_c and the itinerant ferromagnetism below T_c are identified. The magnetization below T_c matches well with the three-dimensional Ising model, instead of the mean-field model. In the case of H//ab, T_c changes between 175 and 178 K with varying H. Noticeably, M above T_c exhibits a small positive value, instead of the null M as commonly expected in the paramagnetic region. An extra phase transition below 166 K is observed. The magnetic transition near T_c seems not to be the second-order phase transition. All results show a significant characteristic of anisotropic magnetic phase transition for the Co₃Sn₂S₂ single crystal. They support mutually those in previous reports, moreover, some new phenomena are also observed. They also provide the experimental evidences for the deep insight into the magnetic phase–transition behavior of Co₃Sn₂S₂.     

A novel equation of state (EOS) for prediction of solute solubility in supercritical carbon dioxide: Experimental determination and correlation

Solubility data of organophosphorous metal extractants in supercritical fluids (SCF) are crucial for designing metal extraction processes. We have developed a new equation of state (EOS) based on virial equation including an untypical parameter as BP/RT, reduced temperature and pressure for prediction of solute solubility in supercritical carbon dioxide (SC CO₂). Solubility experimental data (solubility of tributylphosphate in SC CO₂) were correlated with the two cubic equations of state (EOS) models, namely the Peng–Robinson EOS (PR‐EOS) and the Soave–Redlich–Kwong EOS (SRK‐EOS), together with two adjustable parameter van der Waals mixing and combining rules and our proposed EOS. The AARD of our EOS is significantly lower than that obtained from the other EOS models. The proposed EOS presented more accurate correlation for solubility data in SC CO₂. It can be employed to speed up the process of SCF applications in industry.