Set Of Molecular Parameters Research Articles

Tuning Cocrystallization, Microphase Separation, and Optical Property of All-Conjugated Triblock Copolymers by Molecular Engineering

Compared to the widely studied classical coil–coil block copolymers (BCPs) with well-established phase diagram and recent advances achieved in all-conjugated diblock copolymers, the investigation into the phase behavior of all-conjugated triblock copolymers is rather limited. In this work, we prepare a series of triblock copolymers containing various poly(3-alkylthiophene)s (P3ATs), interrogate their phase transition between cocrystallization and microphase separation adjusted by a set of molecular parameters (alkyl side chains, block ratios, and block sequences), and correlate these different structures strongly to their optical properties. Poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene) (P3HT), poly(3-(2′-ethyl)hexylthiophene) (P3EHT), poly(3-octylthiophene) (P3OT), and poly(3-dodecylthiophene) (P3DDT) are selected, in which P3EHT has a much less crystalline capability than the other four components. Interestingly, when the P3EHT block is situated in the BCP middle position (P3BT-b-P3EHT-b-P3AT), a smaller side chain difference between the two outer P3BT and P3AT blocks and the P3EHT with a shorter main chain length favor cocrystallization in the triblock copolymers over microphase separation. Moreover, when changing the block sequence to place the P3EHT block at two terminals (P3OT-b-P3BT-b-P3EHT and P3BT-b-P3OT-b-P3EHT), they display stronger cocrystalline capability than P3BT-b-P3EHT-b-P3OT with the P3EHT in the central. At last, these various crystalline structures are related to their optical properties. This work demonstrates the tuning of the phase transition between cocrystalline and microphase-separated structures in conjugated triblock copolymers via molecular engineering, which correlate closely to their optical properties and may underpin their applications in optoelectronic devices.

SAFT-VR modelling of the surface and bulk properties of imidazolium and pyridinium based ionic liquids with ten different anions

Statistical associating fluid theory for potential of variable range has been used to provide an accurate thermophysical properties for 26 imidazolium and pyridinium-based families of ionic liquids (ILs) with different cationic structures combined with [PF6]−, [BF4]−, [NTf2]−, [Cl]−, [dca]−, [Triflate]−, [EtSO4]−, [lactate]−, [C(CN)3]− and [MeSO4]− anions. An appropriate set of molecular parameters were obtained by means of fitting the model predictions to experimental liquid densities over a wide temperature and pressure ranges. The overall absolute average relative deviation (AARD) between the calculated and experimental liquid densities is 0.12% over a wide range of temperature and pressure from 283 to 472K and 0.1–200MPa. The reliability and physical significance of the parameters were tested by calculation of thermodynamic derivative properties including isobaric thermal expansivity and isothermal compressibility of ILs. Moreover, the interfacial surface tension of ILs was calculated by density gradient theory (DGT) coupled with the SAFT-VR model. The results are in excellent agreement with the available experimental data.

A molecularly based theory for electron transfer reorganization energy.

Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule's permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory.

Modeling the [NTf2] Pyridinium Ionic Liquids Family and Their Mixtures with the Soft Statistical Associating Fluid Theory Equation of State

In this work, the soft statistical associating fluid theory (soft-SAFT) equation of state (EoS) has been used to provide an accurate thermodynamic characterization of the pyridinium-based family of ionic liquids (ILs) with the bis(trifluoromethylsulfonyl)imide anion [NTf(2)](-). On the basis of recent molecular simulation studies for this family, a simple molecular model was proposed within the soft-SAFT EoS framework. The chain length value was transferred from the equivalent imidazolium-based ILs family, while the dispersive energy and the molecular parameters describing the cation-anion interactions were set to constant values for all of the compounds. With these assumptions, an appropriate set of molecular parameters was found for each compound fitting to experimental temperature-density data at atmospheric pressure. Correlations for the nonconstant parameters (describing the volume of the IL) with the molecular weight were established, allowing the prediction of the parameters for other pyridiniums not included in the fitting. Then, the suitability of the proposed model and its optimized parameters were tested by predicting high-pressure densities and second-order thermodynamic derivative properties such as isothermal compressibilities of selected [NTf(2)] pyridinium ILs, in a large range of thermodynamic conditions. The surface tension was also provided using the density gradient theory coupled to the soft-SAFT equation. Finally, the soft-SAFT EoS was applied to describe the phase behavior of several binary mixtures of [NTf(2)] pyridinium ILs with carbon dioxide, sulfur dioxide, and water. In all cases, a temperature-independent binary parameter was enough to reach quantitative agreement with the experimental data. The description of the solubility of CO(2) in these ILs also allowed identification of a relation between the binary parameter and the molecular weight of the ionic liquid, allowing the prediction of the CO(2) + C(12)py[NTf(2)] mixture. The good agreement with the experimental data shows the excellent ability of the soft-SAFT EoS to describe the thermophysical properties of ILs as well as their phase behavior. Results prove that this equation of state can be a valuable tool to assist the design of ILs (in what concerns cation and anion selection) in order to obtain ILs with the desired properties and, consequently, enhancing their potential industrial applications.

Critical Micelle Concentration of Micelles with Different Geometries in Diblock Copolymer/Homopolymer Blends

AbstractIt is well‐known that A‐B diblock copolymers in selective solvents or A‐homopolymers can form micelles of different shapes. The critical micelle concentration (CMC) of three basic micelle shapes (lamellar, cylindrical, and spherical) are calculated using the self‐consistent field theory formulated in the grand canonical ensemble. For a given set of molecular parameters, the stable micelle morphology is determined by a comparison of the CMC. The results confirm that micelles undergo a sequence of shape transitions, lamellar → cylindrical → spherical, when the A‐block of the diblock copolymer becomes longer. The results also reveal details about the micelle structure, such as the core radius and corona thickness. This information can be used to understand the effect of homopolymer molecular weight and monomer–monomer interaction on the micelle morphologies.magnified image

Modeling Complex Associating Mixtures with [Cn-mim][Tf2N] Ionic Liquids: Predictions from the Soft-SAFT Equation

In a previous work (Andreu and Vega, J. Phys. Chem.B2008, 111, 16028), we presented a simple model for the imidazolium-based ionic liquids (ILs) with the bis(trifluorosulfonyl)imide anion [Tf(2)N](-) in the context of the soft-SAFT equation of state. The model was successfully used to predict the solubility of several gases in these ILs. However, the small amount of experimental data made the predictions less accurate when going into more complex mixtures and one or two fitted binary parameters were needed in some cases. In this work, we have reparameterized our previous model and evaluated its reliability to predict the behavior of these ionic liquids in binary mixtures with other associating compounds. Model parameters for the ionic liquids were estimated using new experimental density data at atmospheric pressure in an extended range of temperatures, from 273 until 473 K, consistent within the range of temperatures previously measured by other authors. The new set of molecular parameters has been tested to predict the density of several members of the family at higher pressures up to 60 MPa with the same degree of accuracy than at atmospheric values. In addition to density-temperature data, interfacial tensions and the isothermal compressibility of some compounds were predicted in reasonable good agreement with experimental data. The molecular parameters of the pure compounds were used then, in a predictive manner, to describe the behavior of binary mixtures with other imidazolium ionic liquids, changing either the cation or the anion. Predictions for some mixtures with methanol, ethanol, and water were compared with experimental data, providing an excellent description of the systems, with no fitting to mixture data in almost all the cases. The excellent results obtained in this work reinforce the need to have accurate data, showing that molecular based models can be used to assess the validity of these data. In addition, this work also shows that a simple model in which the physics of the system is kept is good enough to describe the complex behavior of associating mixtures of ionic liquids, without the need of additional parameters that may obscure the real physics of the system.

A Density Functional Theory for Lennard-Jones Fluids in Cylindrical Pores and Its Applications to Adsorption of Nitrogen on MCM-41 Materials

A density functional theory (DFT) constructed from the modified fundamental-measure theory and the modified Benedict-Webb-Rubin equation of state is presented. The Helmholtz free energy functional due to attractive interaction is expressed as a functional of attractive weighted-density in which the weight function is a mean-field-like type. An obvious advantage of the present theory is that it reproduces accurate bulk properties such as chemical potential, bulk pressure, vapor-liquid interfacial tension, and so forth when compared with molecular simulations and experiments with the same set of molecular parameters. Capabilities of the present DFT are demonstrated by its applicability to adsorption of argon and nitrogen on, respectively, a model cylindrical pore and mesoporous MCM-41 materials. Comparison of the theoretical results of argon in the model cylindrical pore with those from the newly published molecular simulations indicates that the present DFT predicts accurate average densities in the pore, slightly overestimates the pore pressure, and correctly describes the effect of the fluid-pore wall interaction on average densities and pressures in the pore. Application to adsorption of nitrogen on MCM-41 at 77.4 K shows that the present DFT predicts density profiles and adsorption isotherms in good agreement with those from molecular simulations and experiments. In contrast, the hysteresis loop of adsorption calculated from the mean-field theory shifts toward the low pressure region because a low bulk saturated pressure is produced from the mean-field equation of state. The present DFT offers a good way to describe the adsorption isotherms of porous materials as a function of temperature and pressure.

Solid–liquid phase behavior of ternary mixtures

AbstractThe Gibbs Duhem integration technique is extended to calculate ternary phase diagrams at constant temperature and pressure. The technique is used to calculate solid–liquid–vapor phase equilibria for a system selected to roughly model a mixture of two diastereomeric molecules of similar melting point and diameter immersed in a solvent with a lower melting point and a slightly smaller diameter. The cross‐species well‐depth and diameter between the two diastereomers are varied to determine their impact on the phase equilibria. We find that when the interspecies well‐depth is lowered to less than that of either of the diastereomers, the solid phase separates into two solid solutions and consequently there is a region of three‐phase coexistence in the ternary phase diagram. We then calculate ternary phase diagrams at a series of temperatures for one set of molecular parameters. For an equimolar mixture of diastereomers, there is a range of temperature and solvent concentration at which only one of the diastereomers will precipitate, thus effecting a separation of the diastereomers. As the temperature is decreased the purity of the precipitate increases. © 2008 American Institute of Chemical Engineers AIChE J, 2008

High resolution rotation–inversion spectroscopy on doubly deuterated ammonia, ND 2H, up to 2.6 THz

Frequency multiplication of phase locked, high power backward wave oscillators (BWO) permitted to record high accuracy spectra of ND 2H up to frequencies of 2.6 THz. Novel superlattice (SL) devices were used as key-element to generate higher order harmonics for the first time in spectroscopic applications. In total, 240 measured ground state transitions of the pure rotation and inversion–rotation spectra of ND 2H were measured with accuracies of several kilohertz in the frequency region between 0.08 and 2.58 THz. Energy levels up to quantum numbers J=18 and K a=9 have been accessed. A greatly extended experimental dataset was obtained with significantly improved accuracies. Two sets of molecular parameters have been determined from which predictions can be generated that can be regarded as a reliable basis for future astronomical high resolution observations throughout the microwave to terahertz regions. These predictions are available in the Cologne database for molecular spectroscopy ( www.cdms.de).

Investigation of the Phase Equilibria and Interfacial Properties for Non‐polar Fluids

AbstractA self‐consistent density‐functional theory (DFT) was applied to investigate the phase behavior and interfacial properties of non‐polar fluids. For the bulk phases, the theory was reduced to the statistical associating fluid theory (SAFT) that provides accurate descriptions of vapor‐liquid phase diagrams below the critical region. The phase diagrams in the critical region were corrected by the renormalization group theory (RGT). The density profile in the surface was obtained by minimizing the grand potential. With the same set of molecular parameters, both the phase equilibria and the interfacial properties of non‐polar fluids were investigated satisfactorily.

Search for an interstellar Si2C molecule: A theoretical prediction

We suggest that Si2C molecule may be identified in astronomical objects through its transitions 414 → 505, 515 → 606, 212 → 303, 313 → 404, and 111 → 202 at 15.9, 5.1, 33.6, 24.9, and 42.3 GHz in absorption even against the cosmic 2.7 K background, in a region having low temperature. The absorption phenomenon is found rather large in the first two transitions. Dependence of results on the set of molecular parameters is discussed.

Vapor−Liquid Equilibria and Interfacial Tensions of Associating Fluids within a Density Functional Theory

A self-consistent density functional theory is applied to investigating the phase behavior and interfacial tensions of water and low-molecular-weight normal alkanols. For the bulk phases, the density functional theory is reduced to an equation of state that provides an accurate description of saturation pressures as well as vapor-liquid phase diagrams. Near the critical region, the long-range fluctuations are taken into account using a renormalization group theory. With the same set of molecular parameters, the theory yields satisfactory results for both bulk properties and surface tensions of the associating fluids investigated at all temperatures.

A self-consistent approach for modelling the interfacial properties and phase diagrams of Yukawa, Lennard-Jones and square-well fluids

A self-consistent density-functional approach is presented for describing the phase behaviour and interfacial tensions of van der Waals fluids represented by the hard-core Yukawa (HCY), Lennard-Jones (LJ) and square-well (SW) potentials. The excess Helmholtz energy functional is formulated in terms of a modified fundamental measure theory (MFMT) for the short-ranged repulsion and a density-gradient expansion for the van der Waals attractions. Analytical expressions for the direct correlation functions of uniform fluids are utilized to take into account the effect of van der Waals’ attraction on intermolecular correlations. For bulk phases, the density functional theory is reduced to an equation of state (EOS) that provides accurate saturation pressures and vapour–liquid phase diagrams. Near the critical region, the long-range fluctuations can be corrected by using the renormalization group (RG) theory. With the same set of molecular parameters, the theory also yields satisfactory surface tensions and interfacial density profiles at all relevant temperatures.

On the dipole moments of some excited electronic states of HfS and HfO

Stark measurements of the dipole moments in excited states of hafnium mono-sulfide, 180Hf 32S, and hafnium mono-oxide, 180Hf 16O, have been performed. The molecules were produced using a laser ablation source combined with a time-of-flight mass spectrometer, where a static electric field was applied. From the first order Stark effect splitting the permanent electric dipole moments, μ, were determined to be 3.416(23) D and 3.478(25) D for the HfS D 1 Π v=0 and v=1 states, respectively, and 2.665(29) D for the HfO b 3 Π 1 v=0 state. The e- and f-parity mixing due to the Stark effect was examined. Field-free low temperature spectra for the (0,0), (1,0), and (2,0) bands of the D 1 Π – X 1 Σ + transition of HfS and the (0,0) band of the b 3 Π 1 – X 1 Σ + transition of HfO were recorded and analyzed. Term-value calculations were performed, including most previously reported spectra, and potential energy curves and sets of molecular parameters were extracted.

The Phosphidogen Radical, PH2: Terahertz Spectrum and Detectability in Space

Abstract Pure rotational transitions of phosphidogen, PH2, in its ground electronic ( X 2B1) and ground vibrational states have been observed with the Cologne terahertz spectrometer using backward wave oscillators as radiation sources in the frequency region between 458 and 951 GHz. The PH2 radical was generated by immersing solid red phosphorus in a dc glow discharge of molecular hydrogen buffered with helium, with a ratio He/H2∼3. A total of 107 new lines have been measured, comprising 21 distinct sets of rotational transitions through N and Ka of 7 and 6, respectively. These include four important sets of R-branch transitions with N=2←1 and N=3←2. In addition to the fine structure splitting, all measured rotational transitions exhibit smaller splittings due to hyperfine interactions involving the three nuclei. The achieved frequency accuracy of the measurements ranges between 30 and 500 kHz, but is typically 50–100 kHz. The newly measured PH2 transitions were analyzed together with existing field-free data to derive highly accurate molecular parameters, which are considerably more extensive than those reported in the existing literature. Among the determined parameters are the rotational constants A=273 783.512 (38) MHz, B=242 347.640 (42) MHz, C=126 343.827 (34) MHz, centrifugal distortion constants through eighth order, and fine and hyperfine constants with distortion corrections up to and including sextic and quartic terms, respectively. This new set of molecular parameters allows highly accurate and reliable frequency predictions of the rotational spectrum up to about 2 THz. The strongest transitions, both measured and predicted, should be the basis of future astronomical searches. Abundance estimates indicate PH2 to be detectable in young hot-molecular-core regions of interstellar clouds or in circumstellar envelopes of oxygen-rich or carbon-rich stars.

Predictions of the Joule−Thomson Inversion Curve for the n-Alkane Series and Carbon Dioxide from the Soft-SAFT Equation of State

In this work, we use a molecular based equation of state, the Soft-SAFT equation, to predict complete Joule−Thomson inversion curves for carbon dioxide and the n-alkane series, including heavy n-alkanes up to octatetracontane (n-C48H98). Comparisons with available experimental and correlation data, for carbon dioxide and the lighter n-alkanes, show good quantitative agreement. We observe a strong dependence of the inversion curve on the set of molecular parameters used in the calculations, especially near the inversion point and in the high-temperature region. The equation is able to predict the general trend of inversion curves even for extreme conditions, with reduced pressure, Pr = P/Pc, values up to 40, and reduced temperatures, Tr = T/Tc, of almost 5.

The microwave spectrum of cobalt monoxide: Hyperfine interactions in the X 4Δ state

The rotational spectrum of CoO in the Δ4 ground state was observed using a source-modulated submillimeter-wave spectrometer. A direct current sputtering method using cobalt powder placed in the hollow cathode electrode was used to generate the CoO radical in an atmosphere of oxygen and helium. In total 84 spectral lines were precisely measured in the frequency region of 255–465 GHz for eight rotational transitions of the two lowest spin substates. Each rotational transition consists of eight components due to the Co59 (I=7/2) hyperfine interaction. A least squares analysis of the measured frequencies gave a new set of molecular parameters: rotational constant, hyperfine coupling constants, a, bF, c, and eQq, centrifugal distortion corrections to rotation and spin–orbit interaction, and the less well known higher-order spin–orbit distortion term to the Fermi contact interaction, bS. A comparison of the determined molecular hyperfine coupling constants was made with those of atomic/ionic Co in order to assess the inherent characteristics of the molecular orbitals around the Co nucleus.

A Study of the (2–0) Overtone Bands of the FO, BrO, and IO Free Radicals by Laser Magnetic Resonance

The (2–0) overtone bands of the FO, BrO, and IO free radicals in their ground electronic state X2Π3/2 have been detected by laser magnetic resonance. The data obtained from this work have been fitted together with data from previous work. A set of molecular parameters, including vibrational, rotational, centrifugal distortion, spin–orbit, lambda-doubling, hyperfine, and Zeeman terms, has been determined for each molecule.

Transitions between Hund's coupling cases for the X 2Π state of NO

The submillimetre-wave spectra of 14N16O, 15N16O, and 14N18O in both the X 2Π1/2 and X 2Π3/2 states have been measured in the frequency region 773 GHz to 1.1 THz and assigned. Transitions involving J values between 6.5 and 10.5 have been recorded for the first time. The higher J values display an uncoupling of the electronic spin S and the angular momentum L from the rotor axis. The S-uncoupling leads to an intermediate coupling condition between Hund's case (a) and (b), whereas the L-uncoupling causes a coupling scheme intermediate between Hund's case (a) and (d). An improved set of molecular parameters has been obtained for these isotopic species, including magnetic dipole and electric quadrupole constants.

Regulation of the start of DNA replication in Schizosaccharomyces pombe.

Cells of Schizosaccharomyces pombe were grown in minimal medium with different nitrogen sources under steady-state conditions, with doubling times ranging from 2.5 to 14 hours. Flow cytometry and fluorescence microscopy confirmed earlier findings that at rapid growth rates, the G1 phase was short and cell separation occurred at the end of S phase. For some nitrogen sources, the growth rate was greatly decreased, the G1 phase occupied 30-50% of the cell cycle, and cell separation occurred in early G1. In contrast, other nitrogen sources supported low growth rates without any significant increase in G1 duration. The method described allows manipulation of the length of G1 and the relative cell cycle position of S phase in wild-type cells. Cell mass was measured by flow cytometry as scattered light and as protein-associated fluorescence. The extensions of G1 were not related to cell mass at entry into S phase. Our data do not support the hypothesis that the cells must reach a certain fixed, critical mass before entry into S. We suggest that cell mass at the G1/S transition point is variable and determined by a set of molecular parameters. In the present experiments, these parameters were influenced by the different nitrogen sources in a way that was independent of the actual growth rate.