Apolar Liquids Research Articles

Wetting properties of microfiltration membrane: determination by means of the capillary rise technique and incidence on the adsorption of wine polysaccharide and tannins

Polysaccharides and tannins adsorption take part in irreversible fouling of microporous membranes during the cross-flow microfiltration of wine. This adsorption is dependent on the membrane surface properties, especially its surface free energy, and could be minimized by the development of adequate materials. The aim of this work was to study the incidence of surface free energy of microfiltration membranes on wine polysaccharides and tannins adsorption. Four different capillary organic microporous membranes (M102, M202, M302 and M402) were used. As usual methods to determine solid surface free energy were unapplicable to such microporous materials, we investigated the possibility of using a capillary rise method to characterize them. Adsorption tests were carried out from a Carignan red wine to correlate polysaccharides and tannins adsorption to membrane surface properties. Capillary rise experiments, performed on membranes using apolar and polar test liquids, allowed to classify them with regard to the apolar Lifshitz-van der Waals and polar Lewis acid/base components of their surface free energy. The four membranes differed from one another by their polarity: M102, M302 and M302 were characterized as polar materials, M102 showing a higher hydrophilicity then M202 and M302, while M402 was found to be apolar. This ordering was in fair qualitative agreement with the chemical composition of the membranes, indicating that the capillary rise method is appropriate to the characterization of such materials. Polysaccharides and tannins adsorption was observed on the four membranes. Adsorbed polysaccharides were mainly grape arabinogalactan-proteins and yeast mannoproteins, and their amount depended on the membrane surface properties: it decreased (from 0.959 to 0.336 mg g−1 of anhydrous material) as surface polarity increased, due to unfavourable polar interactions. Contrary to polysaccharides, the maximum tannins adsorption occurred on the most polar membrane M102 (8 mg g−1 of anhydrous material). It was lower on the M202, M302 and M402 membranes (2–3 mg g−1). The structure of the adsorbed molecules on the M102 membrane was also different comparing to the others, indicating that interactions implied in tannins adsorption were different in nature.

Wettability of psoralen powders: influence of bile salts on their contact angles and surface free energy components

The purpose of this work was to assess the surface free energy (SFE) of bare and bile-salt-precontacted pellet surfaces of psoralens (lipophilic molecules). This study was carried out according to the approach of van Oss et al. to the solid-liquid interfacial free energy using the Lifshitz-van der Waals component, electron acceptor and electron donor parameters of the SFE. With the help of a hydraulic press, powders of 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP) and 4,5',8-trimethylpsoralen (TMP) were compacted sufficiently to obtain smooth and glossy disc surfaces. One set of pressed discs was used directly after preparation and another set was treated with a bile salt (sodium cholate/sodium deoxycholate mixture) aqueous solution of 0.1 mol l −1 for 2 h at 37°C before droplet deposition. The surface free energies of bare and bile-salt-treated discs were determined by advancing contact angles using polar (water and formamide) and apolar (diiodomethane) standard liquids. The measurements were carried out at 21.5 ± 1.5°C using a surgical microscope fitted with a slanted mirror and equipped with a video camera linked to a computer. In addition, the surface and interfacial tensions of a biphasic system of octanol and water in which psoralens were solubilized were measured using the De Noüy ring method. The results were correlated with the lipophilicity and solubility of these drugs. The data of contact angle values of psoralen bare surfaces indicated the hydrophobicity order 8-MOP < 5-MOP < TMP. The percentages of Lifshitz-van der Waals ( γ s LW) components corroborated this. 8-MOP showed the same acidic and basic values ( γ s AB = 6.5 mJm −2, while γ s AB was equal to 1.8 and 0.4 mJm −2 for 5-MOP and TMP respectively. However, when the psoralens were treated with sodium cholate sodium deoxycholate ( NaC NaDC ) mixture, the presence of micelles on the surface modified the previous data by decreasing the contact angles with polar solvents and γ s LW. In contrast, the total surface free energy of all the psoralens increased, especially the electron onor component ( γ −) and γ s AB. When comparing the three psoralens, 5-MOP behaved peculiarly as it had the lowest γ s − (29.5 mJm −2) and γ s AB (21.4 mJm −2). Theoretical explanations concerning the reactivity of the psoralens vis à vis standard liquids were assumed. The results of this work enabled us to understand qualitatively and quantitatively the types of interaction between the molecules of each studied psoralen and to predict their behaviour when they permeate through a given biological membrane (e.g. human skin). From this work the adsorption of bile salts on to the hydrophobic surface was confirmed for the psoralen case. This result could constitute the beginning of a physicochemical explanation of the digestion step for orally taken psoralens.

The Usefulness of the Equation of State for Interfacial Tensions Estimation in Some Liquid–Liquid and Solid–Liquid Systems

Using the values of water–apolar liquid, glycerol–apolar liquid, formamide–apolar liquid, and ethylene glycol–apolar liquid surface or interfacial tension taken from the literature, the relationships between φ parameter of interfacial interactions and interfacial tensions were determined both graphically and mathematically. Next, the so-called “α” and “β” values obtained in this way were used for the solution of the equation of state for interfacial tensions for liquid–liquid and polymer–liquid systems. The results obtained from the calculations have shown that the α and β values are not constant, but depend on the kind of polar–apolar liquid system and the way the values are determined. The values of α and β differ from 0.0075 and 1, respectively. It has been found that it is impossible to predict the interfacial tensions of polar–apolar liquids as well as polymer–liquid systems with good accuracy on the basis of α = 0.0075 and β = 1, and α and β values have also been determined from polar–apolar liquid interfacial tensions.

Application of Flory-Huggins theory to ternary polymer-solvents equilibria: A case study

The ternary equilibrium data of the following systems: benzene/heptane/NBR at 60 °C (system 1), heptane/isooctane/PE at 25 °C (system 2), ethanol/water/CA at 20 °C (system 3) and ethanol/water/ P(E-co-VAc) at 32 °C (system 4), already reported in the literature, have been used and experimental results compared to predictions offered by the Flory-Huggins theory applied to ternary mixtures (one polymer and two liquids), with constant interaction parameters and negligible elastic contribution. Polymer-solvent interaction parameters have been determined from swelling in pure liquid, while liquid-liquid interaction parameters have been estimated from liquid-vapour equilibrium data curve fitting. It is shown that the Flory-Huggins theory offers reasonable prediction in the case of apolar liquids in an elastomeric matrix (system 1), while approximate isotherm patterns with significant discrepancies are obtained with apolar liquids in a thermoplastic (system 2). The equilibrium data of polar liquids in either homopolymer or copolymer (systems 3 and 4) can hardly be achieved by Flory-Huggins theory, even when a variable liquid-liquid interaction parameter is used. Implications in ternary diagram simulations and possible prediction improvements are discussed.

Solvent crazing as a stress‐induced surface adsorption and bulk plasticization effect

AbstractIn solids with low bulk modulus, like polymer glasses, concentration of stress due to surface defects and other kinds of inhomogeneities can induce substantial surface tension reduction and bulk plasticization in extremely localized regions. This effect becomes important in the presence of organic liquids. As a liquid comes into contact with the polymer surface and as stress is applied, a point is reached when the work to draw new surface area becomes minimal. In addition, at least up to a diffusion limited extent, bulk solvation can also take place locally. At this point, solvent crazing initiates in the presence of a triaxial stress field, and craze fibrils are easily drawn with additional deformation. For van der Waals (WL) interactions between polymer and solvent, two different expressions for solvent craze initiation have been derived. The first is derived assuming interfacial tension reduction (ITR) is the dominant mechanism for solvent craze initiation. The second is derived assuming that flaw tip bulk plasticization (BP) is the main mechanism for solvent craze initiation. Existing experimental data on six different glassy polymers was also examined with respect to the above two expressions. A relatively good functional relation (straight line passing near the origin) was found for a wide spectrum of glassy polymers and apolar (WL) liquids, for both the (ITR) and (BP) cases. Additional assumptions made in this analysis, especially about the stress concentration factor and the bulk modulus of the materials, indicate a better correlation with interfacial tension reduction data, in the case of (WL) liquids. However, better controlled experiments would be necessary to properly identify the mechanisms of environmental crazing, even in the case of (WL) liquids. © 1995 John Wiley &amp; Sons, Inc.

Surface modification of a polypropylene film by microwave plasma and the adhesion of a vacuum‐deposited aluminium layer

AbstractIn order to improve the adhesion properties of polypropylene on a thin aluminium layer deposited under vacuum, a superficial modification of the polymer has been carried out by exposing the polymer surface to a microwave plasma from gas of different nature and composition.The concentration of the present species in the sample proximity (downstream) has been measured by emission spectroscopy.Superficial polymer modifications have been analysed by ESCA and by measuring contact angles with polar and apolar liquids. The adhesion measurements have been performed by pull‐off tests.The wettability increase has been attributed to the creation of a very thin superficial layer which is partially soluble in methanol and includes carboxylic and ethylenic functions being observed by ESCA.Wettability and adhesion depend on the composition of the gas mixture used. They increase with the atomic oxygen quantities which are created in the discharge and carried away in post‐discharge by the gas flow. A relationship has been established between the tensile stress values obtained by the pull‐off test and the polar interaction values measured during dewetting.

Comparison between Direct Contact Angle Measurements and Thin Layer Wicking on Synthetic Monosized Cuboid Hematite Particles

Contact angles (θ wicking ) with apolar and polar liquids on monosized synthetic cuboid hematite particles were obtained by thin layer wicking. Contact angles (θ adv ) of these liquids on films of hematite particles were also measured by the advancing drop method. The values of θ wicking and θ adv coincided within a few degrees. Thus, the thin layer wicking method and the direct contact angle approach appear equally valid

Examination of Neumann's Equation-of-State for Interfacial Tensions

Advancing contact angles for water, glycerol, diiodomethane, and ethylene glycol on polytetrafluoroethylene, polyethylene, Asphalt Ridge bitumen, Circle Cliffs bitumen, Whiterocks bitumen resins, and Whiterocks bitumen asphaltenes were measured and the "surface tension" of these low energy solids was calculated using Neumann's equation-of-state. Also, the surface tension of several polymers and self-assembled monolayers was analyzed based on Neumann's approach and using advancing contact angle values reported in the literature. It is demonstrated that the equation-of-state for surface tension determination may only be used for systems with apolar liquids involving interactions of a physical nature. Reasonable surface tension values were obtained for polymers when advancing contact angles for diiodomethane were used in the calculations. Nevertheless, there appears to be an inconsistency in the surface tension values determined for self-assembled monolayers as calculated with the equation-of-state using contact angle data for different apolar liquids, diiodomethane and hexadecane.

Fragmentation, amorphisation et propriétés superficielles de minéraux. Comminution, amorphization and surface properties of minerals

Comminution, amorphization and surface properties of minerals The comminution of minerals involves energetic, mechanical, structural and superficial phenomena. According to the principles of fracture mechanics, the propagation of cracks can be favoured by lowering the surface free energy of their walls (Rebinder's effect). It is also possible to promote breaking by modifying the electrical surrounding of discontinuities, for example by increasing the surface charge (Westwood's principle). However both these theories give only a partial explanation of experimental facts. Here it is proposed to consider that the elasticity of strongly structured layers of the medium to the solid-liquid interface protects the structure and spreads the stresses. Then, the mineral breaks according to its intrinsic weak strength directions. If the structured layers do not exist (apolar liquids) or are disordered (using hydrogen bond disruptors), the material amorphizes without breaking and the formation of amorphous substances can generate aggregation. The variation of surface properties of minerals resulting from grinding can be described by measuring the dispersive component of the surface free energy ; this measurement is achieved using inverse gas chromatography.

Physicochemical and structural studies onAcinetobacter calcoaceticus RAG-1 and MR-481—Two standard strains in hydrophobicity tests

Acinetobacter calcoaceticus RAG-1 and MR-481, two standard strains used in microbial adhesion to hydrocarbons (MATH), were characterized by contact angles, pH-dependent zeta potentials, elemental surface composition by X-ray photoelectron spectroscopy (XPS), and molecular composition by infrared spectroscopy (IR). Negatively stained (methylamine tungstate) and ruthenium red-stained cells were studied by transmission electron microscopy to reveal the absence or presence of surface appendages. Despite the fact thatA. calcoaceticus RAG-1 is known to be extremely hydrophobic in MATH, whereas MR-481 is a completely non-hydrophobic mutant, neither XPS nor IR indicated a significant difference in chemical composition of the cell surfaces. Contact angles with polar liquids, water and formamide, were considerably higher on RAG-1 than on MR-481, in accordance with their relative hydrophobicities as measured by MATH. However, no significant differences in contact angles were observed between the two strains with apolar liquids like diiodomethane,α-bromonaphthalene, and hexadecane. Fibrous extensions on RAG-1, observed after ruthenium red staining, were absent on the non-hydrophobic mutant MR-481. Tentatively, these extensions could be held responsible for the hydrophobicity ofA. calcoaceticus RAG-1.

Electrophoresis of small particles and fluid globules in weak electrolytes

The electrical double layer plays an essential role in the electrokinetic behavior of both rigid and fluid spheres. One of the assumptions woven into the formulation of the classical balance laws of electrokinetics is that the ionogenic solutes are fully ionized. In aqueous media, common inorganic electrolytes such as KCl and NaOH dissociate completely into their constituent ions; the high dielectric constant of water favors dissociation by lowering the energy required to ionize a solute. Not all ionic solutions are aqueous, however, and electrokinetic effects are important in these media, too. Less polar liquids have a much lower dielectric constant, and so they are unable to sustain a high degree of solute ionization; in fact ionogenic solutes may dissociate less than a percent. Here we examine the influence of partial ionization on the electrophoresis of small particles and fluid globules, with a view toward understanding how, and under what conditions, dissociation-association alters the electrokinetics. We find generally that mass-action, consistent with Le Chatelier's principle, works to minimize disturbances to the electrical double layer, resisting polarization of the diffuse ion cloud. Thus, dissociation-association processes are quantitatively important in cases where double layer polarization and relaxation would otherwise prevail. Consequently, the predicted impact on the electrophoretic mobility is greatest for drops and bubbles, since their surfaces are fluid and convection within the interface is a factor. Mass-action can reduce the mobility of a conducting drop by an order of magnitude, and sizeable decreases (50% and more) in drop mobility are even found at ζ-potentials below 50 mV. Rigid particles are affected less dramatically and quantitative effects rarely exceed 10%; particles are markedly insensitive to partial solute ionization unless the ζ-potential is high (above ca. 100 mV) and aκ > 1. The computation scheme employed applies strictly to situations in which the magnitude of the forcing-field is small. Nevertheless, the results imply that for electrokinetic phenomena driven by strong forcing-fields, dissociation-association processes involving ionogenic solutes may be significant in apolar liquids.

Repacking protein interiors

Several goals of protein engineering may be achieved through redesign and repacking of protein interiors. The effects of interior apolar substitutions on protein stability depend strongly on the site of the substitution. One reason for this is that protein interiors have properties both of apolar liquids and of crystalline solids. Substitutions at interior sites affect the stability of a protein by changing the hydrophobicity, but each site in a protein has a characteristic energy associated with introducing packing changes, and the net stability depends on both of these factors.

Influence of Polar and Apolar Liquids on the Stability of the Pyrite-Air Bubble Aggregate

Abstract Measurements of the detachment force of an air bubble from “dry” and “wetted” (by water) pyrite surfaces pre-coated with apolar or polar liquid film were carried out. The following liquids were tested: n-hexane, n-undecane, n-hexadecane (apolar liquids) and Alifal C, terpineol, diacetone alcohol (polar liquids). The detachment force of an air bubble from pyrite surface in the polar liquid aqueous solutions was also measured. On the basis of the results obtained it was concluded that both apolar and polar liquid film influence the stability of pyrite particle-air bubble aggregates. The stability depends on the kind, thickness and structure of the liquid films. The stability of the aggregates also depends upon the properties of the hydration layer present on pyrite surface.

Influence of Polar and Apolar Liquids on the Stability of the Pyrite-Air Bubble Aggregate

Measurements of the detachment force of an air bubble from “dry” and “wetted” (by water) pyrite surfaces pre-coated with apolar or polar liquid film were carried out. The following liquids were tested: n-hexane, n-undecane, n-hexadecane (apolar liquids) and Alifal C, terpineol, diacetone alcohol (polar liquids). The detachment force of an air bubble from pyrite surface in the polar liquid aqueous solutions was also measured. On the basis of the results obtained it was concluded that both apolar and polar liquid film influence the stability of pyrite particle-air bubble aggregates. The stability depends on the kind, thickness and structure of the liquid films. The stability of the aggregates also depends upon the properties of the hydration layer present on pyrite surface.

Differences in the structures of highly polar and hydrogen-bonded liquids

For apolar liquids the molar energy of vaporization per unit volume at 25°C appears to be proportional to the square of the polarizability per unit volume, and is found to be equal to 3.97 kJ cm −3 ( n 2 D−1) 2/( n 2 D+2) 2, where n D is the refractive index. The standard deviation is of the order of 3.5 kJ mol −1. With this expression n D can be used to estimate the contribution of the dispersion forces to the molar energy of vaporization of other liquids, either highly polar or hydrogen bonded. The remainder is the share of dipole—dipole interactions or hydrogen bonds. For the normal nitriles (μ⋍3.5 D) this contribution decreases when progressing through the homologous series. In contrast, for the normal alcohols upto hexanol, the part of the vaporization energy which is not due to dispersion forces remains practically constant (25–29 kJ mol −1). This demonstrates that for most of the time the OH groups in these pure alcohols are involved in hydrogen bonds and exhibit highly preferential contacts with the oxygen atoms of the neighbouring molecules at the expense of the other groups. Such a situation provokes a decrease in the entropy of the pure alcohols and this decrease becomes still larger when inert substances are dissolved in the liquid. This phenomenon is at the origin of the hydrophobic effect.

Adhesion of quartz particles on glass and properties of their suspensions in the presence of a cationic surfactant

Angle of detachment, sediment volume and relative viscosity of monodisperse quartz fractions were examined in media of varying polarity. The particles were made hydrophobic by adsorption of a cationic surfactant. A critical value of surface excess n σ(ν) was found, at which the angle of detachment had a maximum value in water and a minimum in apolar liquids. Change in the sediment volume and the viscosity of the suspensions may be directly correlated with change in the adhesion. Sediment volume and viscosity of the partially hydrophobized quartz particles in media with different polarity depend on the surface coverage and the particle size of the fraction. The changes in adhesion could be explained by the changes in surface coverage and the lyophilicity in the different liquids.

Molecular conformational equilibria in liquids

The extended RISM integral equation theory is employed to study molecular conformational equilibria in liquids. Solvent induced torsional free energy surfaces are computed for the solutes n-butane and 1, 2-dichloroethane at infinite dilution in apolar and polar model liquids, CCl4 and water. In addition, the intramolecular distribution of conformers for the neat molecular liquids n-butane and 1, 2-dichloroethane are determined. The qualitative features of these free energies agree well with available simulation results. Quantitatively, the absolute solvent effects are consistently overestimated; however, the differences between polar and apolar systems are accurately predicted. The thermodynamic components of the solvent induced free energies for the dilute solutions are analyzed. For the systems examined here, the internal energy dominates the torsional free energies. In particular, for n-butane in water, the increase in gauche conformers is in accord with the notion of a hydrophobic interaction. However, the thermodynamic behavior found here opposes the usual belief that such association is an entropy driven process.

Polyimide capillary column for gas-liquid chromatography

A new principle and method have been developed for producing a high-efficiency WCOT column by forming a polyimide capillary tube of 1–5 μm wall thickness inside a supporting glass capillary (tube-in-tube system). This polyimide layer is chemically resistant, heat-proof (up to 450°C) and mechanically stable. Adsorption on the silica surface can be virtually eliminated using this polyimide column. The preparation of the column is simpler than usual because it is not necessary to use pre-treatment or deactivation procedures. The polyimide tube can be coated easily with polar and apolar stationary liquids by dynamic or static coating methods. The wettability, thermal stability, character of interactions between Carbowaxes and the polymer surface and the adsorption effect of the polyimide tube were investigated. The performance of some polyimide capillary columns is demonstrated with different examples.