Enthalpic Interaction Parameters Research Articles

Thermoresponsive liquid desiccants for dehumidification cycles

We describe a liquid desiccant dehumidification cycle that regenerates via liquid–liquid phase separation instead of the typical liquid–vapor phase separation. Liquid-liquid phase separation is enabled by the use of thermoresponsive liquid desiccants that exhibit a “U-shaped” immiscibility curve in their phase diagram with water. Crossing this immiscibility curve causes a single-phase liquid to transform into a two-phase liquid mixture, which then facilitates the liquid-state removal of the absorbed humidity. In order to systematically explore this cycle’s dehumidification coefficient of performance (COPdeh), we employ the Flory-Huggins theory of mixing to systematically vary the immiscibility curve. The Flory-Huggins theory uses two key parameters, the lower critical solution temperature (LCST) and the enthalpic interaction parameter (χH) to define the position and shape of the immiscibility curve, respectively. We show that LCST temperatures close to the cycle’s heat rejection temperature improve COPdeh by reducing the necessary sensible heat during regeneration. We also show that enthalpic interaction parameters with larger negative magnitudes lead to flatter immiscibility curves that improve COPdeh. This improves COPdeh by better directing regeneration heat toward liquid–liquid demixing as opposed to increasing temperature. Our modeling indicates that COPdeh values up to ∼4 are possible using this cycle whereas traditional non-thermoresponsive liquid desiccant cycles would achieve COPdeh values of <1. This large increase in COPdeh is due to the fact that the demixing enthalpy associated with liquid–liquid phase separations is much smaller than the enthalpy of vaporization associated with liquid–vapor phase separations.

Thermodynamics of bicyclic compound + n-alkane mixtures

Mixtures formed by a cyclic molecule A, namely cyclohexane, or benzene, or bicyclohexyl ((1,1′-bi(cyclohexane)), or cis-decalin (cis-bicyclo[4.4.0]decane), or trans-decalin (trans-bicyclo[4.4.0]decane), or cyclohexylbenzene, or tetralin (1,2,3,4-tetrahydronaphthalene) and a n-alkane have been investigated by means of excess molar functions, enthalpies (HmE) and volumes (VmE), available in the literature, and of isochoric excess properties determined in this work, internal energies (UVmE) and heat capacities (CVmE). The behaviour of the systems with respect to the GmE(excess molar Gibbs energy) vs. HmE is discussed. The mixtures have been also studied using the zeroth approximation of DISQUAC and the Flory model. Dispersive interactions are dominant in the considered systems. The HmE values increase with n, the number of C atoms in the n-alkane, along each homologous series. Mixtures containing shorter n-alkanes and a bicyclic compound are characterized by large negative VmE values, which remark the existence of large structural effects. It is shown that longer n-alkanes are poorer breakers of the A-A interactions, which leads to decreased values of UVmE when n increases in systems with a given cyclic compound. The disruption of the short orientational order of longer n-alkanes by the A molecules lead to increased values ofUVmE. This effect is predominant in systems with cyclohexane, or benzene from n = 8, and UVmE decreases up to this alkane and then increases. However, the mentioned effect seems to be only predominant in systems with a bicyclic compound for n = 16. Thus, UVmE decreases up to n = 12 and increases for n = 16. The different behaviour of the treated systems is described by the Flory model through a X12 parameter which increases with n in solutions with cyclohexane or benzene, and that changes similarly to UVmE in the remainder solutions. In terms of DISQUAC, the enthalpic interaction parameter for the aromatic/aliphatic contact is independent of the n-alkane in systems with tetralin. For solutions with bicyclohexyl or cis-decalin, the variation with n of the mentioned parameter for the aliphatic/cyclic contact is similar to that observed for cyclohexane systems.

A molecular interaction-diffusion framework for predicting organic solar cell stability.

Rapid increase in the power conversion efficiency of organic solar cells (OSCs) has been achieved with the development of non-fullerene small-molecule acceptors (NF-SMAs). Although the morphological stability of these NF-SMA devices critically affects their intrinsic lifetime, their fundamental intermolecular interactions and how they govern property-function relations and morphological stability of OSCs remain elusive. Here, we discover that the diffusion of an NF-SMA into the donor polymer exhibits Arrhenius behaviour and that the activation energy Ea scales linearly with the enthalpic interaction parameters χH between the polymer and the NF-SMA. Consequently, the thermodynamically most unstable, hypo-miscible systems (high χ) are the most kinetically stabilized. We relate the differences in Ea to measured and selectively simulated molecular self-interaction properties of the constituent materials and develop quantitative property-function relations that link thermal and mechanical characteristics of the NF-SMA and polymer to predict relative diffusion properties and thus morphological stability.

Structure and properties of Polylactide/Poly(butylene succinate)/Organically Modified Montmorillonite nanocomposites with high-efficiency intercalation and exfoliation effect manufactured via volume pulsating elongation flow

The Polylactide (PLA)/Poly(butylene succinate)(PBS)/Organically Modified Montmorillonite (OMMT) nanocomposites with different ratio were manufactured via intense volume pulsating elongation flow. The nanostructure, microscopic morphology, crystallization property, thermostability, mechanical properties were well investigated. The processing mechanism was well discussed. The OMMT (C30B) was well dispersed, intercalated, and exfoliated in all the nanocomposites. The interlayer spacing doubled in all the nanocomposites. The clay mainly dispersed in PBS and located at the interface of PLA/PBS in all samples, which could be predicted by the interfacial tension, enthalpic interaction, and wettability parameter. Diameter of the in situ formed PBS fiber decreased as the C30B content increased. Nanocomposites with PBS content range from 30% to 70% displayed the co-continuous structure. The Young's modulus and elongation at break of the blend increased significantly by adding the clay.

Structural Elucidation of the Binary Mixtures of [EMIM][BF4] and [BMIM][BF4] in Ethyl‐Substituted Solvents by Isothermal Titration Calorimeter

AbstractIn order to address the issue whether both ionic liquids and solvents influence the enthalpy of their solutions, highly accurate excess partial molar enthalpy, values have been measured using Isothermal Titration Calorimeter (ITC). Therefore, thermodynamic behavior has been observed in the mixtures containing ionic liquids. It essentially depends on the molecular structure of the constituents of the mixture. The hydrogen bonding between ionic liquids and ethyl‐substituted solvents (2‐ethoxyethanol, ethylene glycol, diethylamine, ethyl acetate and N,N‐ diethylacetamide) may lead to strong ion‐solvent interactions. In the present study, an effort has been made to quantify various interactions between ionic liquid and solvent, based on the values. Linear solvation free relation shows dependence of limiting excess partial molar enthalpies, upon the solvent properties. Structural orientation of solvent molecules and ionic liquids also described by the values. The ion‐ion, ion‐solvent interactions have also been investigated in terms of the enthalpic interaction parameters, and relative apparent molar enthalpy, φL of ionic liquid‐ethyl‐substituted solvent systems.

Enthalpic interactions in aqueous strong electrolytes upon addition of ionic liquids.

The present study deals with the inter-ionic interactions between strong electrolytes and ionic liquids based on the thermodynamic properties such as excess partial molar enthalpy, HEIL, relative apparent molar enthalpy, φL, and the enthalpic interaction parameters. The thermodynamic properties of the systems are the key indicators to understand the interionic interactions. We have conducted a systematic investigation of the enthalpic behavior of aqueous solution of salts and ionic liquids and their mixtures. The present study also emphasizes how the HEIL values for the mixture of aqueous solution of ionic liquids and salts deviate from linearity as compared to those of the constituent aqueous ionic liquid or salt. This deviation from linearity for the HEIL values has been discussed here.

Self-assembly of gradient copolymers synthesized in semi-batch mode by nitroxide mediated polymerization.

The effect of diffuse compositional interfaces on copolymer self-assembly was studied via gradient copolymers (GCP). Poly(methyl methacrylate)-grad-(styrene) (PMMA-grad-PSt) copolymers were synthesized in semi-batch mode using nitroxide-mediated polymerization (NMP) with varied monomer injection protocols to produce varied diffuse interfaces (number average molecular weights (Mn) ranged from 62 000 g mol-1 to 94 000 g mol-1 with dispersities (Đ) between 1.35 and 1.59). The GCPs were spun into thin films on substrates made neutral by (St-ran-MMA-ran-hydroxyethyl methacrylate) terpolymers and annealed at elevated temperature to produce vertically oriented microphase-separated domains. The GCPs were found to have domain spacing larger than equivalent monodisperse BCPs, due to their polydisperse nature. This effect was partially offset by the decrease in χ due to the gradient. GCPs synthesized with a single-injection protocol (i.e. less diffuse interfaces) were found to self-assemble into ordered domains. However, GCPs synthesized with long injection times (i.e. more diffuse interfaces) exhibited poor self-assembly attributed to their predicted statistical-copolymer-like middle sequence, which caused a reduction of the effective enthalpic interaction parameter.

Isothermal Titration Calorimetric Study of Ionic Liquid Solutions in Alcohols at Extreme Dilutions: An Investigation of Ion–Solvent Interactions

In this work an effort has been made to show the effect of an alcohol-rich environment on imidazolium-based ionic liquids at 298.15 K using an isothermal titration calorimeter. It is divulged from this study that the thermal behavior expressed in terms of excess partial molar enthalpy, \( H_{\text{IL}}^{\text{E}} \), of ionic liquids in various linear alcohols is governed by the increasing hydrophobicity of the residual alkyl group attached to the cation of an ionic liquid and to the alcohol molecules. An interesting observation about the systems consisting of ethylated residuals on both the cations of the ionic liquid and the alcohol molecules is that these systems do not follow the trend exhibited by other ionic liquid–alcohol systems. Interesting information on ionic interactions is obtained by using a simple methodology that gives the enthalpic interaction parameter \( H_{{I{\text{L - IL}}}}^{\text{E}} \).

Calorimetric and Theoretical Study of the Interaction between Some Saccharides and Sodium Halide in Water

Dilution enthalpies and mixing enthalpies of sodium halide and some saccharides (glucose, galactose, xylose, arabinose, fructose, and sucrose) in aqueous solution were determined by calorimetric measurements at 298.15 K. The values were used to determine enthalpic pair interaction parameters. Combined with Gibbs energy pair parameters, entropic pair interaction parameters were also obtained. Theoretical calculations at the B3LYP/6-311++G(d,p) level were carried out to provide the information of structures and thermodynamic functions. The information reveals the thermodynamic essence of the interactions between sodium halide and saccharides in aqueous solutions. The experimental results and theoretical calculations show that the sign of enthalpic pair interaction parameter 2υh(ES) is determined by the direct interaction between saccharides and ions, whereas the difference in value of 2υh(ES) for different saccharides or electrolytes depends on the partial dehydration of saccharides or anions in aqueous solution. The difference in value of entropic pair interaction parameters depends partly on the different dominant interactions in the process of partial dehydration of saccharides or ions. An enthalpy-entropy compensation relationship was observed for the sodium bromide-aldopyranose-water systems. Remarkably, it can be conjectured that the hydration entropy of glucose is lower than for other monosaccharides. Perhaps it is one of the reasons why glucose plays an important role in living organisms rather than other monosaccharides.

Mean-Field Modeling of the Encapsulation of Weakly Acidic Molecules in Polyelectrolyte Dendrimers

The unique architecture of dendrimers has attracted interest in a wide variety of biomedical applications such as drug delivery. In order to gain insight into the solubilization of drugs inside dendrimer architectures, we have developed and numerically implemented a self-consistent field theory model for the equilibrium characteristics of charged dendrimer molecules in the presence of weakly acidic drug molecules. Using such a model, we examine the relative influence of excluded volume, electrostatic, and local enthalpic interactions upon the solubilization of drugs in dendrimers. When only excluded volume interactions are accounted, there is no driving force for drug solubilization inside the dendrimer, and hence depletion of the drug from the dendrimer molecule (relative to the bulk drug concentration) is observed. The inclusion of electrostatic interactions within the model results in solubilization of drugs within the dendrimer. The solubilization of the drugs is shown to increase with increasing drug charge density and increasing dendrimer generation number. We probe the effect of enthalpic interactions and demonstrate that the number of drug molecules encapsulated through enthalpic interaction is dependent upon the number of dendrimer monomers, the enthalpic interaction parameters between the dendrimer and drug (χPD), and the drug and solvent (χDS). We also analyze the combined effects of the preceding interactions to identify the synergism in their influence and delineate the relative importance of different parameters such as pOH, size of the drugs, and the Bjerrum length of the solution in influencing the encapsulation of drugs by dendrimer molecules.

Order and anti-order in olivine III: Variation of the cation distribution in the Fe,Mg olivine solid solution series with temperature and composition

The structures of four Fe,Mg olivine crystals Fa11.6, Fa22.3, Fa27.6 and Fa27.8 have been investigated by ex situ and in situ experiments using single-crystal X-ray diffractometry. For the ex situ experiments, the crystals were quenched after equilibration at temperatures between 500 °C and 900 °C. Resetting effects were only observed for samples quenched from 900 °C. The in situ experiments were performed at temperatures up to 750 °C. With increasing equilibration temperature, Fe 2+ was found to progressively segregate into the octahedral M1 site, i.e. the degree of anti-order increases with rising temperature. Thus, contrary to the results of Rinaldi et al. (2000) and Redfern et al. (2000), no indication of an ordering reversal at high temperatures is found. Incorporation of the results of Heinemann et al. (2006) on olivine Fa47.9 into the present study allows for the first time to systematically investigate the compositional variation of the temperature dependence of the Fe 2+ ,Mg site occupancies. The formulation of Thompson (1969, 1970) for solid solutions undergoing non-convergent disordering processes, (1) \[{-} RTln K_{D} = [{\Delta}H_{exch}^{0} {-} (L_{M1}^{H} {-} L_{M2}^{H})X] {-} T[{\Delta}S_{exch}^{0} {-} (L_{M1}^{S} {-} L_{M2}^{S})X],\] yielded \begin{eqnarray*}&&{\Delta}H_{exch}^{0} = 1153 ({\pm}67) J/mol{ }{ }{\Delta}S_{exch}^{0} = 3.743({\pm}0.072) J/molK\\&&L_{M1}^{H} {-} L_{M2}^{H} = 973 ({\pm}211) J/mol{ }{ }L_{M1}^{S} {-} L_{M2}^{S} = {-} 0.89 ({\pm}0.24) J/molK.\end{eqnarray*} ΔH exch 0 and ΔS exch 0 are the exchange enthalpy and entropy, respectively, related to the Fe 2+ ,Mg site exchange, L M1,M2 H and L M1,M2 S denote enthalpic and entropic intrasite interaction parameters. The compositional parameter X varies between −1 for forsterite (Fa0) and +1 for fayalite (Fa100). The magnitudes and signs of the four refined quantities can be rationalized in terms of thermodynamic and crystal-chemical considerations. (L M1 H − L M2 H ) > 0 indicates that the interactions between the M1 sites are stronger than those between the M2 sites, conforming with the M1-M1 distances being shorter than the M2-M2 distances. (L M1 S − L M2 S ) exch 0 increases towards the Mg endmember while ΔS exch 0 decreases. Since ΔH exch 0 > 0 stabilizes the ordered state whereas ΔS exch 0 >0 stabilizes the anti-ordered state, it follows that the ordered state is progressively favoured with increasing Mg content. Consequently, ordered site distributions should occur only in slowly cooled Mg-rich olivines, whereas olivines with Fa > 25 mol% should be found in their anti-ordered states frozen during cooling. This conclusion is supported by structure refinements and ordering path simulations for a metamorphic olivine Fa12.4 as well as two volcanic olivines Fa25.6 and Fa27.8.

Gas transport in surface‐modified low‐density polyethylene films with acrylic acid as a grafting agent

AbstractThe modification of polyethylene by the grafting of poly(acrylic acid) onto the surface of one of the faces of low‐density polyethylene films with UV radiation is reported. The transport of oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane, ethylene, propane, and argon across surface‐modified films containing 3.7% poly(acrylic acid) has been investigated at several temperatures. The layer of poly(acrylic acid) grafted onto the surface of one of the faces of the films reduces the permeability coefficient of the gases by a factor of about 1/6. The sharp drop in the gas permeability as a result of the poly(acrylic acid) layer may arise either from the formation of ordered structures of the grafted chains or from the development of highly crosslinked structures. The values of the polymer–gas enthalpic interaction parameter for the modified film are higher than those for the unmodified one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2828–2840, 2006

Enthalpic interactions between some amino acids and cyclohexanone in aqueous solutions at 298.15 K

The enthalpies of mixing of glycine, l-α-alanine, l-γ-aminobutyric acid, l-α-valine, l-α-serine and l-α-threonine with cyclohexanone in aqueous solutions and their respective enthalpies of dilution have been measured by calorimetry at 298.15 K. Experimental enthalpies of dilution and mixing have been correlated with the virial expansion equation that was obtained with the McMillan–Mayer theory. The enthalpic interaction parameters h xy , h xxy and h xyy of the amino acids studied with cyclohexanone in aqueous solutions have been evaluated, and the heterotactic enthalpic pair interaction coefficients ( h xy ) are discussed in terms of solute–solute interactions.

Enthalpic Pair Interaction of Rubidium Chloride with α‐Amino Acid in Water at 298.15 K

AbstractThe mixing enthalpies of aqueous heavy rare alkali metal chloride RbCl solutions with aqueous α‐amino acid (L‐glycine, L‐alanine and α‐aminobutyric acid) solutions, as well as the dilution enthalpies of RbCl and α‐amino acid solutions in pure water had been measured at 298.15 K. The transfer enthalpies of RbCl from pure water to aqueous α‐amino acid solutions could be obtained from these data. The enthalpic pair interaction parameters of RbCl with α‐amino acid in water have been evaluated according to the McMillan‐Mayer theory and discussed in terms of the electrostatic interaction, structure interaction and Savage‐wood group additivity mode.

Temperature dependence of the interaction between two hydrophobic solutes: a calorimetric study

The enthalpies of tetraethyl- and tetrabutylammonium bromides solution in water and its mixtures with hexamethyl phosphoric triamide (HMPT) in the “water-rich” region of the mixed solvent were measured at 277.15, 288.15 and 313.15 K. The standard enthalpies of solution are computed and compared with previously determined values at 298.15 K. The enthalpic and heat capacity coefficients of solute–HMPT pair interactions in water and the temperature changes of the entropic pair interaction coefficients were computed and compared with those for other organic non-electrolytes. It was shown that bromide-ion and cosolvent nature influenced strongly both enthalpic interaction parameters and their temperature dependence, the last one in particular. The enthalpy of methylene group interaction with HMPT was found to be large, positive and independent of the temperature. It was pointed out that the energetics of non-polar solute transfer from water to various highly aqueous water-organic mixtures at room temperature is defined to a great extent by dimensions of cosolvent molecules and packing effects of solvent molecules in the solute solvation shell.

Enthalpic interaction for a‐amino acid with alkali metal halides in water

AbstractThe studies of the enthalpic interaction parameters, hxy, hxyy and hxyy of alkali metal halides with glycine, α‐alanine and a‐aminobutyric acid were published. Synthetic considering of the results of the studies, some interesting behaviors of the interaction between alkali metal halides and the a‐amino acids have been found. The values of hxy will increase with the increase of the number of carbon atoms in alkyl side chain of amino acid molecules and decrease with the increase of the radius of the ions. The increasing of the salt's effect on the hydrophobic hydration structure as the radii of anion is more obvious than as that of cation. The value of hxxy will regularly decrease with the increase of the number of carbon atoms in the alkyl chain of amino acids and linear increase with the increase of the radius. But the relation of hxxy with the radius of cations is not evident. The value of hxyy will increase with the increase of the radii of the ions. As the increase of the number of carbon atom of amino acids, hxyy is decreas for the ions which have lager size and there is a maximum value at α‐aniline for the ions which have small she. The behaviors of the interaction mentioned above were further discussed in view of electrostatic and structural interactions.

Hierarchic Structure Formation in Binary and Ternary Polymer Blends

The phase morphology of multi-component polymer blends is governed by the interfacial interactions of its components. We discuss here the domain morphology in thin films of model binary and ternary polymer blends containing polystyrene, poly(methyl metacrylate), and poly(2-vinylpyridine) (PS, PMMA, PVP). When sandwiched between two non-polar surfaces, characteristic lateral phase morphologies are observed after the film formation by spin-coating. We discuss here two techniques, by which hierarchical lateral structures in polymer films can be made. The first method makes use of two simultaneously occurring interfacial instabilities. The second technique employs the effect of a variation of the enthalpic interaction parameters in a ternary polymer mixture on its lateral polymer phase morphology.

The enthalpic interaction parameters of α-aminobutyric acid and alkali metal halides in water at 298.15 K

The enthalpies of solution have been measured for α-aminobutyric acid in LiCl, NaCl, KCl and NaBr aqueous solutions at 298.15 K. The enthalpic interaction parameters h xy, h xxy and h xyy of α-aminobutyric acid with these salts have been evaluated. Combining the previous studies for the enthalpic interaction parameters of glycine and α-alanine with alkali metal halides, the experimental results are discussed in view of electrostatic and structural interactions.

The enthalpic interaction parameters of acetamide with some alkali-metal chlorides in water at 298.15 K

The enthalpies of solution have been measured for acetamide in LiCl and KCl aqueous solutions at 298.15 K. The enthalpic interaction parameters h xy, h xyy and h xxy of acetamide with these salts have been evaluated. Combining the previous studies for other alkali-metal halides, the experimental results are discussed in views of electrostatic interaction and structural interaction.

The enthalpic interaction of α-alanine with alkali metal halides in water at 298.15 K

The enthalpies of solution have been measured for α-alanine in NaBr, KBr and KI aqueous solutions at 298.15 K. The enthalpic interaction parameters h xy , h xyy and h xxy of α-alanine with these salts have been evaluated. Combining the previous studies for other alkali metal halides, the experimental results are discussed in view of electrostatic and structural interactions.