Solvent phase behavior and the interaction of uniform and patterned solutes

Isotropic and anisotropic hypernetted-chain (HNC) integral equation theories are used to obtain the interaction of solutes both near and far from the solvent liquid-vapor coexistence. Spherically symmetrical and chemically patterned (patched) solutes are considered, and the influences of particle and patch sizes are investigated. Solvophilic and solvophobic solutes (or patches) are examined. Near coexistence, in the solvophobic case drying-like behavior occurs for solutes (patches) of sufficient size. This gives rise to relatively long ranged attractive forces that are strongly orientation dependent for the patched solute particles. We also report grand canonical Monte Carlo results for a pair of spherically symmetric solutes. This demonstrates that the anisotropic HNC theory gives qualitatively correct solvent structure in the vicinity of the solutes. Comparison with previous simulations also shows that the solute-solute potentials of mean force given by the anisotropic theory are more accurate (particularly at small separations) than those obtained using the isotropic method.     

Spontaneous "phase separation" of patterned binary alkanethiol mixtures

This article describes novel phase-separation behavior by a binary mixture of alkanethiols when deposited onto a gold surface using micro- and nanodeposition tools, such as microcontact printing (muCP) and dip-pen nanolithography (DPN). This behavior is significantly different than that observed in the bulk. We demonstrate this behavior using three model compounds: 16-mercaptohexadecanoic acid (MHA), 1-octadecanethiol (ODT), and CF3(CF2)11(CH2)2SH (PFT). The identity of the resulting segregated structure is confirmed by lateral force microscopy (LFM) and by selective metal-organic coordination chemistry. Importantly, this phenomenon can be exploited to print sub-100 nm wide alkanethiol lines via conventional muCP and to form sub-15 nm features using DPN, which is below the ultimate resolution of both these techniques. We also demonstrate that these nano-patterned materials can serve as templates for constructing more complex architectures.     

Infrared study of 6-methylcoumarin in binary solvent mixtures

The infrared absorption spectra of the carbonyl stretching vibrations of 6-methylcoumarin (6MC) have been investigated in CCl4/ROH mixtures (CCl4/C2H5OH, CCl4/n-C3H7OH, CCl4/i-C3H7OH, and CCl4/t-C5H11OH). Two types of carbonyl stretching vibration bands for 6MC are found with the change of the mole fraction of the aprotic solvent CCl4(X CCl4 in binary solvent mixtures. The dependencies of the frequencies of carbonyl stretching vibrations upsilon(C=O) on X CCl4 allow a distinction and assignment of all species resulting from the solvent-solute interactions. Linear correlations between the upsilon(C=O) of each species and X CCl4 are found. The influence on the transformation of some species caused by the self-associated alcohols is discussed.     

The gelation rule of the polyol acetal derivatives in binary solvent mixtures

The tendency of a gelator to gel in mixed solvents is strongly correlated with its gelation behaviors in the corresponding single solvents.     

Raoult's law as applied to binary solvent mixtures

The inapplicability of the original statement of Raoult's law to binary solvent mixtures has been known for many years. An appropriate form for binary solvent mixtures is developed from the fundamental thermodynamic concept of fugacity, and is shown to be quantitatively applicable to the water+tetrahydrofuran solvent system and qualitatively applicable to the results which have been obtained for other aqueous organic solvent mixtures.     

Thermochemistry of 1-bromoadamantane in binary mixtures of water-aprotic solvent

Solution enthalpies of 1-bromoadamantane in the mixed solvents water-N,N-dimetylformamide, water-N,N-dimethylacetamide and water-acetone were determined at 298.15 K, within the range of solubility of 1-bromoadamantane (1-BrAd) in the mixed solvents. The solution enthalpy of 1-bromoadamantane in water was determined based on extrapolation from the three mixtures. Enthalpies of transfer from the mixed solvents to cyclohexane were calculated. The effect of the composition of the mixtures on the thermochemical values obtained was also investigated.     

The entropy effects in binary mixtures of polar mesogenic solvent/nonpolar solute

The paper concerns two aspects of the entropy in mesogenic systems: (i) the entropy jump (Delta S (0) NI) at the phase transition from the isotropic liquid (I) to the nematic liquid crystalline state (N), and (ii) the entropy increment (Delta S) caused by the ordering action of the probing electric field applied to the dipolar system. The system studied are the mixtures of strongly polar mesogenic solvent n-hexylcyanobiphenyl (C 6H 13PhPhCN, 6CB) and the nonpolar nonmesogenic admixture 4-ethylcyclohexyl-4'- n-nonylphenyl (C 2H 5CyHxPhC 9H 19, 2CyPh9). The entropy jump at the I-N phase transition in pure 6CB [Delta S (0) NI= 1.52 J/(mol K)] was evaluated from the analysis of the phase diagram of the mixture 6CB + 2CyPh9 with use of the Landau-Lifshitz theory; the resulting value of the transition enthalpy (Delta H (0) NI = T NIDelta S (0) NI = 0.50 kJ/mol) agrees well to that obtained with the calorimetric methods. The field-induced entropy increment (Delta S) was calculated, at the given temperature, from the static dielectric permittivity derivative value (depsilon s/d T), with use of the Fr?hlich theory. The singularities in dependence of the entropy increment on the temperature and on the mixtures composition are discussed in terms of the prenematic molecular self-organization extent in mesogenic liquids of different density of dipoles.     

Primary photoprocesses in molecules of carbocyanine dyes in binary solvent mixtures

The effect of the composition of the dimethyl sulfoxide (DMSO)-toluene mixture on the photophysical processes of thia-, indo-, and imidacarbocyanine dyes was studied. In the mixtures with the DMSO content of more than 20 vol %, the dyes representing solvated cations are characterized by high efficiency of trans → cis photoisomerization and fluorescence, in contrast to the extremely low efficiency of intersystem crossing to the triplet state. With growing the toluene content in the mixture, ion pairs between the dye cation and Cl⁻, Br⁻, I⁻, or BF⁴⁻ anion are formed. In the cases when the dye counterions are Br⁻ or I⁻, a sharp increase in the yield of the triplet molecules and a decrease in their lifetime take place. The results are discussed in terms of “the external heavy atom effect” in ion pairs.     

Solubility of carbazole in binary chloroalkane + dibutyl ether solvent mixtures

Solubilities are reported for carbazole in three binary chloroalkane + dibutyl ether solvent mixtures at 25°C. Results of these measurements are compared with solution models developed for solubility in systems containing specific solute-solvent interactions. A simple model based on a single 1:1 carbazole:dibutyl ether complex described the solubility data, though the calculated equilibrium constant was about one-half of values published previously. A more sophisticated solution model, which assumes both carbazole:dibutyl ether and carbazole:chloroalkane complexes, was needed to thermodynamically describe the systems studied. Equilibrium constants for three presumed carbazole:chloroalkane complexes are calculated from measured carbazole solubilities.     

Solvatochromic study of 1,2-dihydroxyanthraquinone in neat and binary solvent mixtures

Preferential solvation of a solvatochromic probe has been studied in binary mixtures comprising of a non-protic and a protic solvent. The non-protic solvents employed are carbon tetrachloride (CCl(4)), acetonitrile (AcN) and N,N-dimethyl formamide (DMF) and the protic solvents are methanol (MeOH) and ethanol (EtOH). The probe molecule exhibits different spectroscopic characteristics depending upon the properties of the solubilizing media. The observed spectral features provide an indication of the microenvironment immediately surrounding the probe. Solvatochromic shifts of the ground and excited states of the probe were analysed by monitoring the charge transfer absorption band and the fluorescence emission spectra in terms of the solute-solvent and solvent-solvent interactions. Fluorescence emission spectra show the dual emission due to excited state proton transfer nature of the probe molecule. The effect of solvent and the excitation energy on dual emission are also studied. The observed magnitude of the Stokes shift in the above solvents has been used to deduce experimentally the dipole moment ratio of the probe molecule for the excited state to the ground state. The dipole moment of excited state is higher than the ground state.     

Molecular interaction in binary surfactant mixtures containing alkyl polyglycoside

Surface tensions were measured for several binary mixtures of a multidegree polymerized alkyl polyglycoside, C12G1.46' with different types of surfactants in 0.1 M NaCl at 25 degrees C. Based on regular solution theory, using a dimensional crystal model and a phase separation model, the molecule exchange energy in mixed monolayer formation (epsilon) and mixed micellization (epsilon(m)) were determined. Surfactants used in the mixtures with C12G1.46 in this study are C12E3S (trioxyethylenated dodecyl sulfonate), C12TAC (dodecyl trimethylammonium chloride), BE-6 (hexaoxyethylenated trisiloxane surfactant), and TMN-6 (hexaoxyethylenated-2,6,8-trimethylnonanol). The mixtures show exchange energy in mixed monolayer formation (epsilon) and mixed micellization (epsilon(m)) ranging from -660 to -1410 J/mol, indicating a decrease in surface energy upon mixing. The decreases in surface energy are in the order C12G1.46/C12E3S > C12G1.46/C12TAC, C12G1.46/C12TAC > C12G2/C12TAC and C12G1.46/BE-6 > C12G1.46/TMN-6. The ability of the mixed monolayer formation relative to the mixed micelle formation of the same binary mixture, measured by the (epsilon-epsilon(m)) values, is in the order C12G1.46/BE-6 > C12G1.46/TMN-6 > C12G1.46/C12E3S-->0 > C12G1.46/C12TAC.     

Molecular interaction studies in hydrogen bonded polar binary mixtures

The molecular interactions between the polar systems of propan-1-ol (1PN) with alkyl benzoates (methyl benzoate and ethyl benzoate) for various mole fractions at different temperatures are studied by determining the dielectric permittivity in radio, microwave and optic frequency regions, respectively. Dipole moment, excess dipole moment, excess Helmholtz free energy, excess permittivity, relaxation time, excess inverse relaxation time and excess thermodynamical values are calculated using experimental data. Hamiltonian quantum mechanical calculations are performed on both pure and equimolar binary systems of 1PN with alkyl benzoates for the measurement of dipole moment from the ab initio Hartree–Fock and density functional theory (B3LYP) methods with 6-31?+?G* and 6-311?+?G** basis sets using Spartan 08 modelling software and these theoretical values are in good agreement with the experimental values.     

Enhancement of solid solubility in binary solvent mixtures. The systemo-toluic acid-cyclohexane+methylene iodide

solubilities of solid o-toluic acid in five binary mixtures of cyclohexane with methylene iodide were measured in the temperature range from 290 to 350 K. All systems studied were found to exhibit a synergetic effect of solubility. The data were fitted by the two-parameter h equation with root mean square deviations not greater than 1.3 K.     

Solubility of polycyclic aromatics in binary solvent mixtures using activity coefficient models

Polycyclic aromatic hydrocarbons (PAHs) precipitation is one of the major problems in the hydrocracking units. In this investigation, pyrene and phenanthrene were selected because they were found to be in higher concentrations in the feed to hydrocracking units. Their solubilities were investigated in toluene solvent mixture of iso-octane and heptane over a temperature range from 293 to 323 K. The experimental solubility data were used to predict the interaction parameters for seven different solid–liquid equilibrium models. The following activity coefficient models were used; Wilson, NIBS/Redlich–Kister, UNIQUAC, modified UNIFAC, modified UNIFAC (Dortmund), Flory–Huggins and Sheng. The interaction parameters were expressed as a second-order polynomial function in temperature. In order to test the models, the average absolute deviation percentage (AADP) was used. The overall AADP was found to range from approximately 7 to 14%. The models can be arranged according to their accuracy in a descending order based on AADP as follows: NIBS/Redlich–Kister, Wilson, UNIQUAC, Sheng, Flory–Huggins, modified UNIFAC (Dortmund) and finally modified UNIFAC. All models used in this work gave reasonable results; however, the group contribution models can also be used as a predictive tool for the solubility measurement of pyrene and phenanthrene in other solvents containing the same groups of the solvents used in this study.