Concentration Of Polar Solvent Research Articles

The polar solvent effect of transparent conductive films composed of graphene/PEDOT:PSS nanohybrids

Abstract Novel transparent conductive films were successfully fabricated by forming graphene/PEDOT:PSS nanohybrids and then spin-coating the mixture onto glass substrates. The mechanism and characterization of graphene nanosheets dispersed at various concentrations of polar solvents (isopropanol, IPA) to improve the conductivity of the nanohybrids are evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), four-point probe sheet resistance measurements, and UV/vis spectroscopy. The results show that the conductivity of the graphene/PEDOT:PSS nanohybrids significantly improves upon addition of 50 wt.% IPA (the optimum conditions). The sheet resistance of the nanohybrids was reduced by ~ 95% from 16.6 kΩ/□ by addition of 0 wt.% IPA to 0.85 kΩ/□ by addition of 50 wt.% IPA, whereas the transparency still remained up to 82%. The conductivity could then be rapidly enhanced (from 0.85 kΩ/□ to 0.64 kΩ/□) by a second treatment of H2SO4, with a concomitant loss of transmittance. The correlations among the roughness, hydrophilicity, conductivity, and transparency also are investigated in detail in this paper. It is anticipated that graphene/PEDOT:PSS nanohybrids can be potentially used in an electronic and biomedical platform, such as biosensors.

Biofiltration of paint solvent mixtures in two reactor types: Overloading by polar components

Steady-state performances of a trickle bed reactor (TBR) and a biofilter (BF) in loading experiments with increasing inlet concentrations of polar solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone and n-butyl acetate, were investigated, along with the system's dynamic responses. Throughout the entire experimentation time, a constant loading rate of aromatic components of 4 gc·m−3·h−1 was maintained to observe the interactions between the polar substrates and aromatic hydrocarbons. Under low combined substrate loadings, the BF outperformed TBR not only in the removal of aromatic hydrocarbons but also in the removal of polar substrates. However, increasing the loading rate of polar components above the threshold value of 31–36 gc·m−3·h−1 resulted in a steep and significant drop in the removal efficiencies of both polar (except for butyl acetate) and hydrophobic components, which was more pronounced in the BF; so the relative TBR/BF efficiency became reversed under such overloading conditions. A step-drop of the overall OLPOLAR (combined loading by polar air pollutants) from overloading values to 7 gc·m−3·h−1 resulted in an increase of all pollutant removal efficiencies, although in TBR the recovery was preceded by lag periods lasting between 5 min (methyl ethyl ketone) to 3.7 h (acetone). The occurrence of lag periods in the TBR recovery was, in part, due to the saturation of mineral medium with water-soluble polar solvents, particularly, acetone. The observed bioreactor behavior was consistent with the biological steps being rate-limiting.

Contact Mechanics of Nanometer-Scale Molecular Contacts: Correlation between Adhesion, Friction, and Hydrogen Bond Thermodynamics

Using a scanning force microscope, adhesion forces have been measured between carboxylic acid terminated self-assembled monolayers in different nonpolar solvents or in two-component liquid mixtures consisting of a polar solvent (ethyl acetate or acetone) in heptane. The adhesion forces measured in pure acetone and ethyl acetate were small (0.24 nN) but increased logarithmically as the concentration of the polar solvent decreased to reach a maximum value (2.77 nN), equal to that measured in pure heptane, and for lower concentrations of polar solvent, the adhesion force remained constant. This behavior is identical to that observed for association constants measured for the formation of 1:1 H-bonded complexes between dilute solutes in solvent mixtures. The transition between the solvent-dependent and -independent regimes occurs at a polar solvent concentration corresponding to 1/K(S), where K(S) is the equilibrium constant for solvation of a carboxylic acid by the polar solvent in heptane. A simple model, in which the solvation of the carboxylic acid groups may be estimated by considering the concentration and polarity of functional groups in the liquid, accurately predicts values of K(S) that were found to correlate very well with the observed solvent-dependence of the adhesion force. Friction-load relationships were measured using friction-force microscopy. In pure acetone and ethyl acetate, a linear friction-load relationship was observed, in agreement with Amontons' law. However, as the concentration of polar solvent was reduced, a nonlinear relationship was observed and the friction-load relationship was found to fit the Derjaguin-Müller-Toporov (DMT) model for single asperity contacts. For pure heptane and a range of other nonpolar liquids with identical dielectric constants, the friction-load relationship was described by DMT mechanics. Exceptionally, for perfluorodecalin, Johnson-Kendall-Roberts mechanics was observed. These observations may be rationalized by treating the friction force as the sum of load-dependent and shear contributions. Under conditions of low adhesion, where the carboxylic acid surface is solvated by polar solvent molecules, the shear term is negligible and the sliding interaction is dominated by load-dependent friction. As the degree of solvation of the carboxylic acid groups decreases and the adhesion force increases, the shear friction contribution increases, dominating the interaction for media in which the adhesion force is greater than ca. 0.6 nN.

Interactions between Crown Ethers and Water, Methanol, Acetone, and Acetonitrile in Halogenated Solvents

The interactions between crown ethers and water, methanol, acetone, and acetonitrile molecules in halogenated solvents are studied by means of calorimetric measurements. The results reveal the formation of 1:1 complexes between crown ethers and water in chloroform. The hydrogen bonding and ion–dipole interactions are responsible for the complex formation between the water molecules and crown ethers. For a better understanding of the influence of chloroform upon the complexation between crown ethers and water, chloroform is replaced by dichloromethane, 1,2-dichloroethane, and carbon tetrachloride. Since the hydrogen bonds are responsible for the complex formation between crown ethers and water in the halogenated solvents, further investigations are performed with methanol, acetone and acetonitrile. The interactions, the ligand nature, the concentrations of polar solvents, and the nature of nonpolar solvents involved in complexation are analyzed and discussed.

A flash photolysis and optoacoustic calorimetry study of the cis—trans isomerization of 1,3-diphenyltriazene

The trans-to-cis photoisomerization of 1,3-diphenyltriazene occurs with similar quantum yields in polar and non-polar media. The cis-to-trans thermal isomerization is much faster in polar (hydrogen bonding) than non-polar media, and studies in mixed solvents reveal a quadratic dependence with the concentration of polar solvent. A study of the reaction using the technique of laser-induced optoacoustic calorimetry leads to a Δ H value for the trans-to-cis isomerization of 34.6±2.8 kcal mol −1 in toluene and of 19.9±2.3 kcal mol −1 in methanol; the fact that the cis-to-trans thermal isomerization is faster when the energetics are less favorable ( i. e. alcohols) is attributed to a change in mechanism involving solvent-assisted isomerization.

Solution behavior of Na sulfonated polystyrene: Dipole moment determinations

Solution behavior of Na sulfonated polystyrene (NaSPS) ionomers with different percentages of sulfonate was studied by viscosity and dipole moment measurements. Two solvents of different character were chosen, i.e. dioxane (ϵ = 2.22) and dimethyl formamide (DMF, ϵ = 36) and their mixtures. The reduced viscosity as a function of concentration in polar solvents reflects the ‘polyelectrolyte’ behaviour of the ionomers. Mean-squared dipole moment ( /x) values were calculated over a temperature range of 20–100°C, in dioxane and in a mixture of 4% DMF in dioxane. The results confirm the ‘polyelectrolyte’ behavior of ionomers by the addition of a small amount of polar cosolvent. The effect of increasing temperature on /x in the DMF-dioxane mixture is attributed to the formation of a coordination complex.

Secretion of albumin and alpha-foetoprotein by dimethylsulphoxide-stimulated hepatocellular carcinoma cells

Exposure of BW77-1 and BW77-2 mouse hepatic tumour cells to the polar solvent dimethylsulphoxide (DMSO) altered extracellular accumulation of albumin and alpha-foetoprotein (AFP) and perturbed their cell cycle kinetics. The amount of albumin secreted into the culture growth medium was dependent on the concentration of DMSO used. Hepatic tumour cells cultured in 1 and 2% DMSO accumulated 50% and 111% more albumin, respectively, than non-DMSO-stimulated cells during the final 24 h of a 4-day exposure to the polar solvent. Commitment of mouse hepatoma cells to increased albumin secretion was temporally dependent, requiring a minimum of 48 h in the presence of DMSO. The AFP level in 1% DMSO-treated cultures was also significantly increased, compared with control cells. Unlike albumin secretion, however, exposure of hepatic tumour cells to 2% DMSO did not further increase (but slightly decreased) extracellular AFP accumulation. Treatment of BW77-1 cells with DMSO resulted in a gradual decline in the percentage of 2C DNA content cells (diploid G1 population) and in a corresponding increase in the proportion of cells with a 4C DNA content (generation of either a G2 or tetraploid G1 population). The extent of this shift directly reflected the concentration of polar solvent in the medium and paralleled the DMSO-induced stimulation in albumin secretion. DMSO-stimulated hepatic tumour cells, therefore, may prove useful in the elucidation of specific regulatory events underlying control of gene expression during the hepatocyte cell cycle.

Simple relationship concerning mobile and stationary phases in normal- and reversed-phase chromatography

For normal-phase chromatography on aminoproply-bonded silicas, the adsorption of the polar modifier of various mixtures of hexane with n-alkanols, benzyl alcohol, acetone, dimethylformamide, nitromethane, chloroform and diisopropyl ether were measured. One to three molecules of the polar solvent per bonded aminopropyl chain can be fixed. Simple calculations allow the determination of the relative proportions of amino groups free or bonded with one, two or three modifier molecules for each mobile phase composition. The amount of the polar modifier in the stationary phase increases with its ability to form hydrogen bonds with the amino groups for a given composition of the mobile phase. The amount is larger with any alcohol than with nitromethane, acetone or dimethylformamide. The capacity factor ( k′) of various polar solutes (phenols, amines and pyridines) and non-polar solutes (polyaromatic hydrocarbons) decreases when the concentration of polar solvent in the mobile phase increases. When the average number of molecules of the polar modifier in the stationary phase remains less than one per amino group, a linear relationship exists between 1/ k′ and the volume fraction of the polar solvent in the mobile phase. When more than one molecule per amino chain is fixed, the variations of 1/ k′ are not easily linked to the eluent composition. For reversed-phase chromatography on alkyl-bonded silicas, the ln k′ and the selectivity for non-polar and polar solutes vary linearly with NS ( N being the total number of chains bonded on the silica surface and S the hydrocarbonaceous surface area of a chain). For instance, the retention time of a solute will be the same using C 8, C 12 or C 22 bonded phases with the same value of NS and consequently the same carbon content. Retention of polar and non-polar solutes were measured with five different water-miscible organic modifiers (methanol, ethanol, 1-propanol, acetonitrile and tetrahydrofuran). The variation of k′ can be related to the volume fraction ( x) of water by ln k′ = ax n + b (O < x < 0.85), n depending on the organic solvent nature and a on the solute properties. For each organic modifier, a linear relationship exists between a and the molar volume of the solute. The solubility of solutes was measured in the same mixtures used as mobile phases. The solubility of a given solute in any water-modifier mixture is related to x by ln s = − ax n + b′, a and n having the same values as those obtained for the retention variation. This equation is verified for x values corresponding to 1 < k′ < 200. Hence a very simple relationship between k′ and s ( k′ s = C) is valid for all mobile phase compositions.

Excited state solvation dynamics of 2-anilinonaphthalene

Nanosecond fluorescence spectroscopy has been used to study the interaction of 2-anilinonaphthalene with polar solvent molecules which is shown to result in stoichiometric complex formation at low polar solvent concentrations. This is followed by reorientation of the solvent cage when the concentration of polar solvent is high.

Solute interactions with the mobile and stationary phases in liquid—solid chromatography

A dynamic equation for the distribution coefficient is proposed that accounts for the different solute—phase interactions in liquid chromatography. The validity of the basic form of the equation is experimentally verified and the effect of solvent composition on retention is shown to be dependent on the probability of solute—solvent interaction and thus the concentration of polar solvent in the mobile phase. Using the equation, the change in retention volume with polar solvent concentrations can be accurately predicted. Where polar forces between solute and solvent are weak, it is shown that dispersive interactions are proportional to the density of the dispersing solvent. The magnitude of the polar interactive effects of both solute and solvent are shown to be proportional to the exponent of the polarizability per milliliter of the respective solute or solvent for a limited number of solutes and solvents.

Investigations on the relationship between molecular structure and chromatographic parameters : VII. Partition of phenols in systems of the type cyclohexane + polar solvent—formamide

Relatonships between R M values and the concentration of polar solvents in the mobile phase were determined for a group of halogenophenols, xylenols and several other derivatives of phenol. Three alcohols, olcic acid and chloroform were used as the polar component (S). It was found that alcohols, in spite of their auto-association, have high extration strengths relative to phenols. 1:1 solvation complexes being easily formed. Hindered solvation due to internal hydrogen bonding or steric shielding of the hydroxyl group resulted in less steep R M versus log % S lines.