Non-associated Liquids Research Articles

The structure of overlapped epitropic LC

The proposed model of the structure of the wall-adjacent epitropic liquid crystalline layer considers it as an oligomeric system of thread-like associates in a non-associated liquid. The results of ELC studies of layers of aliphatic hydrocarbon - n-hexadecane are analyzed. The study of the ELC phase in n-alkanes is important both for the modification of the quantitative physical theory of this phenomenon, and in a practical sense, as it allows to solve practical problems related to the control of boundary friction in mechanisms and parts of machines. Previously, the results of rheological and structural-optical studies of the properties of these systems were considered separately, and the results obtained in the molecular-statistical model were not correlated in detail with the results of rheological measurements for the case of overlapped near-surface layers. To interpret the results of studies (by rheological and optical methods) of such a layer in interlayers of n-hexadecane, symmetrically limited by conductive substrates, it is proposed to take into account the increase in the concentration of the ordered component ("pile") under the condition that the wall layers of epitropic liquid crystals in the interlayer overlap. It will also allow to take into account the results obtained in the molecular statistical model in the processing of rheological data.

Temperature dependence of the Kirkwood correlation factor and linear dielectric constant of simple isotropic polar fluids.

The theory developed in an accompanying paper [Déjardin, Phys. Rev. E 105, 024109 (2022)10.1103/PhysRevE.105.024109] is used to compute the Kirkwood correlation factor of simple polar fluids of different nature. From this calculation, the theoretical static permittivity is readily obtained, which is compared with experimental values. This is accomplished by fitting only one parameter accounting for induction or dispersion forces and torques, which is necessarily connected with the individual molecular polarizability but not explicitly related to the physical properties due to the nonadditivity of such energies. Excellent agreement between theoretical and experimental static permittivities is obtained over a very broad temperature range for a number of associated and nonassociated liquids. Finally, limitations of the present theory are given.

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

We examined a series of structurally related glass-forming liquids in which a phenothiazine-based tricyclic core (PTZ) was modified by attaching n-alkyl chains of different lengths (n = 4, 8, 10). We systematically disentangled the impact of chemical structure modification on the intermolecular organization and molecular dynamics probed by broadband dielectric spectroscopy (BDS). X-ray diffraction (XRD) patterns evidenced that all PTZ-derivatives are not ‘ordinary’ liquids and form nanoscale clusters. The chain length has a decisive impact on properties, exerting a plasticizing effect on the dynamics. Its elongation decreases glass transition temperature with slight impact on fragility. The increase in the medium-range order was manifested as a broadening of the dielectric loss peak reflected in the lower value of stretching parameter βKWW. A disagreement with the behavior observed for non-associating liquids was found as a deviation from the anti-correlation between the value of βKWW and the relaxation strength of the α-process. Besides, to explain the broadening of loss peak in PTZ with the longest (decyl) chain a slow Debye process was postulated. In contrast, the sample with the shortest alkyl chain and a less complex structure with predominant supramolecular assembly through π–π stacking exhibits no clear Debye-mode fingerprints. The possible reasons are also discussed.

Thermodynamic, structural and dynamic properties of selected non-associative neat liquids

Non-associative neat liquids benzene, acetone and carbon tetrachloride have been examined via molecular dynamics simulations. Several models of each neat liquid have been simulated, and selected thermodynamic and structural results are presented. However, the models have been compared mainly in terms of their dynamic quantities. Since models are rarely parametrized with the dynamic properties in mind, the principal goal of this work is to present quantities such as the power spectra, rotational correlation functions and relaxation times, diffusion coefficients and self and distinct parts of the van Hove functions in relation to available experimental data. The general trends of the calculated data provide a benchmark for the behavior of neat simple liquids which will be built upon in the cases of mixtures with associative liquids.

Cohesive energy density and internal pressure of benzene and 1-alkanol binary mixtures

The internal pressure (Pint), cohesive energy density (ced), and free volume (vf) for liquid mixtures of benzene with (C6 to C10) 1-alkanol are calculated at 303.15 K and atmospheric pressure. Flory's statistical theory was employed to drive the internal pressure of five binary mixtures. The conductor-like screening model for real solutions (COSMO-RS), in combination with experimental densities was applied to calculate the cohesive energy density of the binary systems. The ‘structuredness’ of the fluids above was studied using the Pint/ced ratio. The values are between 0.7 and 1.2, as is the case for non-associated molecular liquids, and demonstrates the non-chemical dispersions and repulsion types for binary liquids. The variations of these parameters with mole fraction and length of alkyl chain in the studied 1-alkanol were explained from the perspective of intermolecular interactions. It is observed that increase in the methyl groups of alcohol creates additional steric hindrances, loosens the structural packing, and reduces the order of interactions in these mixtures. Also, experimental densities and viscosities at various temperatures were reported for liquid mixtures to verify the existing interactions among unlike molecules.

NMR Relaxometry: The Canonical Case Glycerol.

We present a quantitative description of the proton spin-lattice relaxation rate R1(T,ω) of glycerol including temperatures from 191 to 360 K and a frequency range 10 kHz < ω/2π < 20 MHz covered by the field-cycling technique. The analysis encompasses the data compiled by Noack and co-workers in 1971, so far, the most complete data set (10 kHz > ω/2π < 117 MHz). Applying frequency-temperature superposition, master curves are constructed extending over 15 decades in frequency/time. They are described by contributions reflecting translational and rotational dynamics mediated by inter- and intramolecular relaxation pathways. The rotational part of the spectral density/susceptibility shows high similarity with those reported by dielectric spectroscopy or photon correlation spectroscopy (PCS). In addition to a Cole-Davidson-like peak, a high-frequency "excess wing" has to be accounted for. Quantitative agreement with the PCS susceptibility is found which probes the same order of the rotational correlation function. The translational contribution is reproduced by applying the force-free hard sphere model, describing diffusion of dipolarly coupled spin systems. Rotational and translational time constants are compared to those from other techniques. Our approach is paradigmatic for the analysis of spin relaxation in glass-forming liquids. It also solves long-standing deficiencies regarding the analyses of deuteron relaxation. Moreover, the case of glycerol is special as its large separation of translation and rotation dynamics, probably because of its hydrogen bond network, is not found in nonassociated liquids.

Pressure densification of a simple liquid

The magnitude of the high frequency, static dielectric permittivity is used to determine the density of tetramethyl tetraphenyl trisiloxane, a non-associated glass-forming liquid, as a function of temperature and pressure. We demonstrate that the properties in the glassy state are affected by the pressure applied to the liquid during vitrification. This behavior is normal for hydrogen-bonded liquids and polymers, but unanticipated by models of simple liquids.

Influence of hydrogen bonds and temperature on dielectric properties.

Dielectric properties are evaluated by means of molecular dynamics simulations on two model systems made up of dipolar molecules. One of them mimics methanol, whereas the other differs from the former only in the ability to form hydrogen bonds. Static dielectric properties such as the permittivity and the Kirkwood factor are evaluated, and results are analyzed by considering the distribution of relative orientations between molecular dipoles. Dipole moment-time correlation functions are also evaluated. The relevance of contributions associated with autocorrelations of molecular dipoles and with cross-correlations between dipoles belonging to different molecules has been investigated. For methanol, the Debye approximation for the overall dipole moment correlation function is not valid at room temperature. The model applies when hydrogen bonds are suppressed, but it fails upon cooling the nonassociated liquid. Important differences between relaxation times associated with dipole auto- versus cross-correlations as well as their relative relevance are at the root of the Debye model breakdown.

The "anomalous" dynamics of decahyroisoquinoline revisited.

Decahydroisoquinoline (DHIQ) appears to be a unique material-the only non-associated, simple liquid with dynamics deviating from density scaling. To examine whether this anomaly is real, the density, ρ, of DHIQ was measured at temperatures, T, as low as 214 K and pressures up to ∼1.2 GPa. This enabled the equation of state (EoS) to be determined, without extrapolation, over the range of thermodynamic conditions for which the relaxation times had been reported. Using this less ambiguous EoS, we find that within the precision of the available relaxation times, the latter are a function of T/ρ(3.9), contrary to previous reports. Thus, the behavior of DHIQ is unexceptional; similar to every non-associated liquid tested to date, its dynamics comply with density scaling.

Dynamic correlation length scales under isochronal conditions.

The origin of the dramatic changes in the behavior of liquids as they approach their vitreous state-increases of many orders of magnitude in dynamic time scales and transport properties-is a major unsolved problem in condensed matter. These changes are accompanied by greater dynamic heterogeneity, which refers to both spatial variation and spatial correlation of molecular mobilities. The question is whether the changing dynamics are coupled to this heterogeneity; that is, does the latter cause the former? To address this, we carried out the first nonlinear dielectric experiments at elevated hydrostatic pressures on two liquids, to measure the third-order harmonic component of their susceptibilities. We extract from this the number of dynamically correlated molecules for various state points and find that the dynamic correlation volume for non-associated liquids depends primarily on the relaxation time, sensibly independent of temperature and pressure. We support this result by molecular dynamic simulations showing that the maximum in the four-point dynamic susceptibility of density fluctuations is essentially invariant along isochrones for molecules that do not form hydrogen bonds. Our findings are consistent with dynamic cooperativity serving as the principal control parameter for the slowing down of molecular motions in supercooled materials.

The solvent-induced interaction of spherical solutes in associated and non-associated liquids.

We propose an efficient method for studying the solvent-induced interaction of two solvophobic particles immersed in a liquid solvent. The method is based on the combination of the probabilistic hydrogen bond model with the density functional theory. An analytic expression for the number of hydrogen bonds per water molecule near two spherical hydrophobes is derived as a function of the molecule distance to both hydrophobes, distance between hydrophobes, and their radii. Using this expression, one can construct an approximation for the distribution of fluid (liquid water) molecules in the system which provides a reasonably good (much faster and accurate enough) alternative to a standard iteration procedure. Such an approximate density distribution constitutes an efficient foundation for studying the length-scale and temperature dependence of hydrophobic interactions. The model is applied to the interaction of solvophobic solutes in both associated and non-associated liquids. Of these two cases, the model predictions for the solvent-induced potential of mean force between two solutes in associated liquids are closer to the results of molecular dynamics simulation of hydrophobic interactions in the SPC/E model water. Our results suggest that the hydrogen bonding ability of water molecules may play a major role in hydrophobic phenomena.

Density of normal and associated liquids

A formula to evaluate the density of liquids was suggested on the basis of the molecular–statistical theory of liquids according to the distribution function. The regularities of changes in density were estimated in different ranks of normal (non-associated) liquids. It was shown that association leads to increase in density. Certain criteria were proposed, which allowed to assume the presence of association on the basis of density of a liquid. The characteristics of density of liquids consisting of molecules with intramolecular hydrogen bond were established. The density values were estimated for 36 compounds at 404K (or 445K).

New Semiempirical Equation Describing Evaporation and Condensation in Nonassociated Liquids

The consideration of the evaporating and condensing molecules’ interaction with the surface layer of nonassociated liquids made it possible to find an equation for relations between the saturated vapor pressure P, from one side, and surface tension, critical temperature, and molar volume of the liquids, from the other side. This equation takes into account the influence of intramolecular conformational transitions of evaporating molecules on the quantity of their energy barrier. There are two types of the condensation process for the nonassociated liquids: soft and hard molecular condensation. For some vapor molecules the surface layer of the liquids behaves as an impenetrable elastic film. In the case of evaporating molecules, their one‐particle potential barrier caused by the surface molecules vibration is essentially higher for the conformationally flexible molecules than that for rigid ones.

Connection between dynamics and thermodynamics of liquids on the melting line

The dynamics of a large number of liquids and polymers exhibit scaling properties characteristic of a simple repulsive inverse power-law potential, most notably the superpositioning of relaxation data as a function of the variable TV^{γ}, where T is temperature, V the specific volume, and γ a material constant. A related scaling law T{m}V{m}{Γ}, with the same exponent Γ = γ, links the melting temperature T{m} and volume V{m} of the model IPL liquid; liquid dynamics is then invariant at the melting point. Motivated by a similar invariance of dynamics experimentally observed at transitions of liquid crystals, we determine dynamic and melting-point scaling exponents γ and Γ for a large number of nonassociating liquids. Rigid, spherical molecules containing no polar bonds have Γ = γ; consequently, the reduced relaxation time, viscosity, and diffusion coefficient are each constant along the melting line. For other liquids γ > Γ always; that is, the dynamics is more sensitive to volume than is the melting point, and for these liquids the dynamics at the melting point slows down with increasing T{m} (that is, increasing pressure).

An empirical approach for predicting kinematic viscosities of biodiesel blends

Kinematic viscosity ( η) is an important property of diesel fuels, including biodiesels, which are marketed mostly as the blends in many countries around the world. In this study, the free energy of viscous flow (Δ G vis ) for a non-associated liquid mixture is assumed to be the summed of Δ G vis of individual components. Hence, the Eyring’s equation, η = Ae(−Δ G vis / RT), is transformed to ln η blend = a + bn 1 + c/ T + dn 1/ T (where, a, b, c and d, T and n 1 are thermodynamically related constants, absolute temperature and mole fraction of biodiesel, respectively). The transformed equation is used to predict kinematic viscosity of biodiesel blends ( η blend) of different degree of blending at any temperatures from pour point to 100 °C. The predicted kinematic viscosities are in good agreement with those reported in literatures at all temperatures. The highest deviation is ±5.4% and the average absolute deviation (AAD) is less than 2.86%. The transformed equation can also be used to predict kinematic viscosities of pure fatty acid methyl esters in diesel fuel. Methyl ricinoleate is an exception. The AAD is 4.50% and the deviation is as high as 12.80%. The high deviation suggests that molecular interactions between methyl ricinoleate and diesel fuel is high and cannot be ignored.

Conformational and dielectric relaxation studies on hydrogen bonded binary mixture of isopropyl alcohol in methyl benzoate and ethyl benzoate

The dielectric relaxation study for the hydrogen bonded binary system of polar liquid isopropyl alcohol in non-associated liquids – methyl benzoate and ethyl benzoate has been carried out, using the HP–LF impedance analyzer in static region, Plunger method in microwave frequency region and Abbe’s refractometer in optic region, at different temperature and mole fractions. The dielectric parameters viz. static, optic permittivity, excess permittivity, Bruggeman parameter, relaxation time, excess inverse relaxation time and thermodynamic parameters have been obtained. The dielectric parameters show systematic change with temperature and concentrations. Conformational analysis of the formation of hydrogen bond in the binary mixture systems isopropyl alcohol with methyl benzoate and ethyl benzoate is supported by FT-IR. Hamiltonian quantum mechanical calculations such as AM1, PM3 and MNDO optimized converged geometry operation is performed by using Spartan Modeling software for both pure and equi molar systems and thus the FT-IR spectra are obtained and further compared with the experimental values.

Assessment of undiscovered conventional oil and gas resources, onshore Claiborne Group, United States part of the northern Gulf of Mexico Basin

The middle Eocene Claiborne Group was assessed for undiscovered conventional hydrocarbon resources using established U.S. Geological Survey assessment methodology. This work was conducted as part of a 2007 assessment of Paleogene–Neogene strata of the northern Gulf of Mexico Basin, including the United States onshore and state waters (Dubiel et al., 2007). The assessed area is within the Upper Jurassic–Cretaceous–Tertiary composite total petroleum system, which was defined for the assessment. Source rocks for Claiborne oil accumulations are interpreted to be organic-rich, downdip, shaley facies of the Wilcox Group and the Sparta Sand of the Claiborne Group; gas accumulations may have originated from multiple sources, including the Jurassic Smackover Formation and the Haynesville and Bossier shales, the Cretaceous Eagle Ford and Pearsall (?) formations, and the Paleogene Wilcox Group and Sparta Sand. Hydrocarbon generation in the basin started prior to deposition of Claiborne sediments and is currently ongoing. Primary reservoir sandstones in the Claiborne Group include, from oldest to youngest, the Queen City Sand, Cook Mountain Formation, Sparta Sand, Yegua Formation, and the laterally equivalent Cockfield Formation. A geologic model, supported by spatial analysis of petroleum geology data, including discovered reservoir depths, thicknesses, temperatures, porosities, permeabilities, and pressures, was used to divide the Claiborne Group into seven assessment units (AUs) with three distinctive structural and depositional settings. The three structural and depositional settings are (1) stable shelf, (2) expanded fault zone, and (3) slope and basin floor; the seven AUs are (1) lower Claiborne stable-shelf gas and oil, (2) lower Claiborne expanded fault-zone gas, (3) lower Claiborne slope and basin-floor gas, (4) lower Claiborne Cane River, (5) upper Claiborne stable-shelf gas and oil, (6) upper Claiborne expanded fault-zone gas, and (7) upper Claiborne slope and basin-floor gas. Based on Monte Carlo simulation of justified input parameters, the total estimated mean undiscovered conventional hydrocarbon resources in the seven AUs combined are 52 million bbl of oil, 19.145 tcf of natural gas, and 1.205 billion bbl of natural gas liquids. This article describes the conceptual geologic model used to define the seven Claiborne AUs, the characteristics of each AU, and the justification behind the input parameters used to estimate undiscovered resources for each AU. The great bulk of undiscovered hydrocarbon resources are predicted to be nonassociated gas and natural gas liquids contained in deep (mostly 12,000-ft [3658 m], present-day drilling depths), overpressured, structurally complex outer shelf or slope and basin-floor Claiborne reservoirs. The continuing development of these downdip objectives is expected to be the primary focus of exploration activity for the onshore middle Eocene Gulf Coast in the coming decades.

Nonperturbative Effect of Attractive Forces in Viscous Liquids

We study the role of the attractive intermolecular forces in the viscous regime of a simple glass-forming liquid by using computer simulations. To this end, we compare the structure and the dynamics of a standard Lennard-Jones glass-forming liquid model with and without the attractive tail of the interaction potentials. The viscous slowing down of the two systems is found to be quantitatively and qualitatively different over a broad density range, whereas the static pair correlations remain close. The common assumption that the behavior of dense nonassociated liquids is determined by the short-ranged repulsive part of the intermolecular potentials dramatically breaks down for the relaxation in the viscous liquid regime.

Dynamics of glass-forming liquids. XIII. Microwave heating in slow motion

Using time-resolved nonlinear dielectric relaxation measurements at fields as high as 450 kV/cm, the nonthermal effects of energy absorption are studied for simple and associating polar liquids in their supercooled state. The experiment is a low frequency analog of microwave heating and facilitates tracking the flow of energy in time, as it accumulates in slow degrees of freedom and transfers eventually to the vibrational heat bath of the liquid. Most findings agree with a phenomenological model of heterogeneous relaxation regarding structure and configurational temperature. The relevant thermal behavior of monohydroxy alcohols differs considerably from the cases of simple nonassociating liquids due to their distinct origins of the prominent dielectric absorption mode for the two classes of liquids. Nonthermal effects are observed as dynamics that are accelerated without increasing sample temperature, but for the present low frequencies the changes remain too small to explain the high efficiencies reported for microwave chemistry. Limitations as to how rapidly the faster relaxation time constants are able to adjust to temperature separate the modes of the dispersive alpha-relaxation into a "relaxation" and an "aging" regime, thereby explaining the incompatibility of heterogeneous dynamics with common physical aging observations.

Analysis of Dielectric and Conductive Dispersion above Tg in Glass-Forming Molecular Liquids

Dynamics of the nonassociated supercooled liquids N-methyl-epsilon-caprolactam (NMEC) and glycerol in the frequency domain are investigated using full complex-nonlinear-least-squares fitting of immittance spectroscopy data for appreciable temperature ranges above the glass transition. Such fitting, not previously used for these materials, helps to identify physical processes responsible for the data and elements of their common behavior. Several different fitting models were applied to find a physically plausible best-fitting one to distinguish quantitatively between the dielectric effects of dipoles and the conductive effects of mobile ions. The utility of many composite fitting models was investigated, and although a pure conductive-system dispersive (CSD) fitting model led to good but physically unrealistic fits of all data sets, the dielectric-system dispersive (DSD) Davidson-Cole model best fitted the alpha-dispersion part of the responses. Nevertheless, the series combination of such a DSD model and a separate CSD model (one not associated with electrode effects) was found to yield much better fitting of the data for both materials. Although the CSD model plays somewhat the role of the conventional parallel DSD Johari-Goldstein beta-response, it is here in series and arises from mobile impurity-ion effects rather than from dipolar ones. Previous analyses of data of the present and other molecular materials have often involved two DSD models in parallel, but fitting with such a composite model led here to less physically plausible parameter values and ones with appreciably more uncertainties. Surprisingly, the series DSD and CSD composite-model fits led to comparable estimated values of the NMEC and glycerol dielectric strength parameters, as well as to the nearly equal small thermal activation energies of these parameters.