Lifshitz-van Der Waals Component Research Articles

Surface and Electrokinetic Properties of Clays and Other Mineral Particles, Untreated and Treated with Organic or Inorganic Cations

Abstract The apolar (Lifshitz van der Waals)component (yLW) and the polar [electron-acceptor (y ) and electron-donor (y ) ] parameters of the surface tension of more than sixty different clay and other mineral particles or surfaces have been measured, as well as their -potentials. It is essentially the y parameter that determines the hydrophobic (target;⩾y28 mJ/m1)or hydrophilicy ( y target;⩾28 mJ/mJ) character of the mineral surface. The surface properties were measured for twelve ion exchanged smectites, as a funclion of substitution with various alkali and alkalin earth cations. The hydrophobizing influence of exchanged organic cations on the surface properties of a number of clay particles is also determined. Finally, the hydrophobizing influence of plurivalent cations is demonstrated with Ca2+and La 3+for three different negatively charged mineral particles.

The Relationship between the Interfacial Free Energy and the Free Energy of Micellization of Triton X-100 and Sodium Dodecyl Sulfonate

The contact angles for water and Triton X-100 on Teflon; for water, glycerol, formamide, and diiodomethane on Teflon covered with a Triton X-100 film and a sodium dodecyl sulfonate film and glass covered with a sodium dodecyl sulfonate film; and for water, glycerol, and diiodomethane on glass were measured. Also, the surface tension of Triton X-100 and the interfacial tensions of Triton X-100–n-dodecane and Triton X-100–diiodomethane were measured. From the results of these measurements, the Lifshitz–van der Waals component and the electron-acceptor and electron-donor parameters of the acid–base component of the apolar and polar moieties of Triton X-100 and sodium dodecyl sulfonate were determined. Next, taking into account the molecular dimensions of these surfactants, the free energy of interfacial interaction through water was calculated for the apolar and polar parts of Triton X-100 and sodium dodecyl sulfonate. Also, the electrostatic free energy of interactions between DSs−ions was evaluated. Good agreement between the free energy of micellization obtained from the cmc data and the free energy of interaction between molecules of surfactant through water was found.

The Effect of Surface Activation in Polymer Matrix-Carbon Fiber Interactions

Various carbon fibers (CF) were surface modified by chemical and electrochemical treatments for the purpose of establishing organic functional groups on the fiber surface. A series of fibers, surface oxidized for various periods of time, was prepared. The amounts of surface functionalities formed were assessed by means of contact angle measurements on single fibers. A suitable set of probe liquids was used to determine the LW (Lifshitz-van der Waals) and acid-base components of carbon fiber surfaces. Similar tests were made on commercial, sized carbon fibers, polystyrene (PS) and polymethyl methacrylate (PMMA), and their surface energies determined in terms of LW, surface acidity and surface basicity components. Work of adhesion values were calculated of all combinations of CF and polymer matrix couples by using these surface energies of both constituents. The calculated work of adhesion values were correlated to the ILSS values obtained from single fiber pull out tests with PS and PMMA as matrices.

Lifshitz-van der Waals Energy of Spherical Particles in Cylindrical Pores

The Lifshitz-van der Waals component of the interaction energy between a spherical particle and the wall of a cylindrical pore is obtained in Hamaker's microscopic approach. In contrast to the earlier numerical studies, the present scheme results in a much simpler semianalytical result for the energy of interaction. Asymptotic analytical results are derived for particles close to the pore wall and for particles close to the pore centerline. For all feasible combinations of particle size, radial position, and pore size, the maximum deviation of analytical results from the numerical solutions is less than 20% and the mean deviation is about 5%. The energy at contact is usually several orders of magnitude larger than the energy near the centerline, and the discrepancy increases with decreasing particle size and increasing pore size. A commonly used simple model of a sphere interacting with a semi-infinite flat plate is found to be reasonable only for very small particles close to the wall, but in all other cases, it seriously underestimates the energy. Calculations of the energy for semi-infinite and finite pores show that the entry length is limited to about twice the pore radius.

Concept of surface interaction energy densities: basis for emulsifying properties of organic solvents immiscible with water

The surface-energy basis of the optimal or required hydrophile-lipophile balance (HLBO) concept is founded on the fact that emulsifying properties are mainly determined by the Lifshitz-van der Waals components of the free surface energy density, which are experimentally accessible and, thus, need not be estimated. A linear correlation has been found between the Lifshitz-van der Waals component of the free surface energy of the solvents and their emulsifying properties expressed by the HLBO value. The interaction energy density, defined as the geometric mean of the surface energy density of the Lifshitz-van der Waals component of both emulsion components, has been used to represent theoretically the HLBO value. According to the definition of the HLB value required (HLBO) it is conclusive that the respective emulsifier compensates the molecular cohesion between the hydrophobic parts of the emulsion components. Good agreement has been obtained with HLBO values calculated from the free surface energies of the solvents according to Becher, in K.L. Mittal (Ed.), surfactant in solutions, Vol. 3, 1984, p. 1925.

Surface free energy components of monodisperse zinc sulfide

Apolar, Lifshitz-van der Waals ( γ LW ) and polar, acid-base (Lewis) ( γ AB ) surface free energy components, of monosized, spherical ZnS colloidal particles were experimentally determined using the thin-layer wicking technique. The results were compared with those obtained on a pure, commercial sample of zinc sulfide. The fact that the synthetized sample showed a very high electron-donor ( γ s −) component suggested that some species, related in principle to surface oxidation of ZnS during the synthesis reaction, could be formed on the surface of the particles. To check for this possibility, the surface free energy components of pure and oxidized ZnS, and of zinc oxide and sulfate, were determined by both the contact angle and thin-layer wicking methods. The similarity between γ s components obtained with both methods for pure ZnS lead to the conclusion that both techniques give reliable results. The high γ s − value determined for synthetic ZnS particles cannot be explained simply by surface oxidation of the colloidal particles, since partially oxidized ZnS, or even zinc oxide or sulfate, gave very similar γ s −, always lower than that found for synthetic spherical ZnS. The fact that the Lifshitz-van der Waals ( γ s LW ) component of the surface free energy is somewhat higher for the latter material is believed to be related to elemental sulfur present on the surface of the particles. The general compatibility of the results obtained by both methods suggests that the thin-layer wicking technique is useful to further characterize these or other systems, particularly if the examined material is sufficiently monodisperse.

Surface Thermodynamics of Ozone-Induced Particle Destabilization

The phenomenon of ozone-induced particle destabilization was studied employing a colloidal suspension of 150 mg/L sodium montmorillonite (Na-M) suspended in river water containing 3.1 mg/L natural organic matter (NOM). The suspension was treated with high ( 106 pM) and low ( 10 pM) ozone doses. Extended DLVO theory was utilized to investigate the surface thermodynamics of unozor?ated and ozonated Na-M coated with NOM (cNa-M). Ozonation decreased the surface charge and the Lewis base parameter, and increased the Lewis acid parameter and Lifshitz-van der Waals component of the surface energy. The overall result of these changes was a decrease in the change in the total free energy of interaction and hence a decrease in the stability of cNa-M with increasing ozonation. Modification in the surface thermodynamics responsible for destabilization could possibly be attributed to partial dealuminization of Na-M and wociated NOM transformations, increasing the autophilicity of the colloids.

The influence of oleate adsorption at the fluorite/water interface on fluorite surface free energy

Contact-angle measurements for water, glycerol, formamide, di-iodomethane and bromoform on fluorite plates covered with a film of oleate are made. Using the contact-angle values, the Lifshitz-van der Waals component and the electron-acceptor parameter of the surface free energy of the fluorite/oleate film are calculated. On the basis of the contact-angle measurements and the calculations done, it is found that at low equilibrium oleate concentration the surface free energy of the fluorite/oleate film comes close to the value for paraffin, however at high oleate concentration, the surface of the fluorite/oleate film can interact with the adherent phase not only by Lifshitz-van der Waals forces but also by acid-base forces. It results from a hydration process which takes place at the highest sodium oleate concentrations. It is stated that the considerable decrease of the fluorite/oleate- film-water interfacial free energy at oleate species concentration higher than 87.1 mg/ dm 3 can also result from electrostatic interactions across the interface.

A Study of Poly(α-hydroxy acid)s Monolayers Spread at the Air/Water Interface: Influence of the D,L-Lactic Acid/Glycolic Acid Ratio

The interfacial behavior of poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) acid monolayers spreading at the air/water interface was studied by using a film balance and by measuring contact angles on LB films. The homopolymer of lactic acid gave a more rigid film, with higher surface pressure than the copolymer which contained glycolic units. On compression, it appeared that orientation of the lactic acid units was probably the cause of a well characterized first-order transition for the polymers with high lactic group contents. A less oriented monolayer was observed when the glycolic content increased. For small areas, the high surface pressure was attributed to the strong interactions occuring between lactic groups with the formation of microdomains. We concluded that the glycolic segments were expulsed from the copolymer monolayers but facilitated the respreading of the copolymer by disrupting interactions between lactic groups. In condensed states, the major contribution to the surface free energy, deduced from contact angle measurements, was nonpolar; a small polar component (due to oxygen atoms) was measured. So, we assumed that the lactic groups and particularly the methyl substituents are oriented toward the air phase. This explains the Lifshitz-Van der Waals component of the surface free energy increasing with the lactic unit content.

The surface energies of cation substituted Laponite

AbstractLaponite RD forms stable, coherent films which adhere strongly to glass slides. Such films are capable of supporting liquid drops allowing the direct measurement of contact angles for five liquids of which, two were apolar (0:-bromonaphthalene and diiodomethane) and three were polar (water, formamide, glycerol); surface tension components and parameters (γLw, γ⊕ and γ⊖) were determined by solving the Young equation. These determinations were made for homoionic samples saturated with Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba and NH4 as well as the natural material. Whereas the values of γLw (the apolar Lifshitz-van der Waals component) varied only within narrow limits (41-44 mJ/m2), the Lewis base parameter varied comparatively widely (24-41 mJ/m2). The Lewis acid parameter was small and relatively constant (1·3-3·0 mJ/m2). The variation of γ⊖ as a function of the exchangeable cation suggests that the divalent cations are shielded from the silicate surface by the water molecules of their sphere of hydration, whereas the monovalent cations are in direct contact with the oxygen atoms of the silicate surface. Furthermore, the divalent cations may screen the Lewis base sites to a greater degree than do the monovalent cations. Lithium behaves anomalously and this may indicate that it physically enters into the ditrigonal hole in the silicate layer.

Components of surface free energy of cholesterol in the presence of bile salts

Measurements of the contact angle for water and diiodomethane on cholesterol discs covered with films of the bile salts sodium cholate, sodium deoxycholate and sodium chenodeoxycholate, were made. Using these values of contact angles, the total surface free energy of a cholesterol/bile salt film and its components resulting from different kinds of intermolecular interactions were calculated. For this purpose both the geometric mean approach and the approach of van Oss et al. to solid—liquid interfacial free energy were used. Next, using the Lifshitz—van der Waals component, and the electron-acceptor and electron-donor parameters of the surface free energy of cholesterol covered with bile salt films, the free energy of interaction in the system cholesterol/bile salt film—water—cholesterol/bile salt film was calculated. On the basis of the contact angle measurements and calculations with the two theoretical approaches, it was found that the cholesterol surface free energy strongly changed when the concentration of bile salt in solution reached a fairly narrow concentration range, defining an operational critical micellar concentration of the bile salt. At this concentration, a change of sign of the free energy of interaction between two particles of cholesterol in water from negative to positive occurs, which indicates the existence of repulsive forces under these conditions.

The forces involved in bioadhesion to flat surfaces and particles — Their determination and relative roles

The non‐covalent forces involved in bioadhesion involving flat surfaces, small particles, cells and bio‐polymers are: Lifshitz‐van der Waals (LW), polar (electron‐acceptor‐electron‐donor) or Lewis acid‐base (AB) and electrostatic (EL) forces. LW and AB forces are determined by: (a) direct contact angle measurement with at least three liquids on flat surfaces, or (b) wicking, by capillary rise measurements of at least three liquids along glass plates coated with a thin layer of small particles. This approach yields the LW and AB components of the surface tension, as well as the electron‐acceptor and the electron donor parameters of its AB‐component. Together, these yield the total apolar + polar interfacial energies involved in bioadhesion. EL interaction energies must be obtained separately, by electrokinetic methods. In bioadhesion, the importance of these forces usually is: AB > > LW > EL. The electron‐donor properties of cells and biopolymers are dominant; their electron‐acceptor parameters are negligi...

The surface free energies of talc and pyrophyllite

The components of the interfacial surface tension of talc and pyrophyllite were determined by measuring the rate of the capillary rise of a number of liquids through thin, sedimented deposits of the powdered minerals. The rate of capillary rise of a liquid in a powder is related to the contact angle between the liquid and the solid by the Washburn equation. The contact angles thus derived were used to determine the apolar (Lifshitzvan der Waals) component, γ LW , and the polar, electronacceptor and electron-donor parameters, γ ⊕ and γ ⊖ respectively, of the Lewis acid/base component of the total interfacial surface energy using the Young equation. The values of γ LW for talc and pyrophyllite (31.5 and 34.4 mJ/m2) are slightly smaller than for smectite clay minerals (e.g., the value for hectorite is 39.9 mJ/m2), the electron donor parameter values are roughly comparable for talc and pyrophyllite (γ ⊕ = 2.4 and 1.7 mJ/m2) as are the values of the electron acceptor parameter (γ ⊖ = 2.7 and 3.2 mJ/m2). The well-known hydrophobicity of these two minerals is due to the remarkably small value (for silicate minerals) of γ ⊖(γ⊕ is normally small or zero for silicates and many other oxides). The small values of both γ ⊕ and γ ⊖ mean that the Lewis acid/base interactions between talc or pyrophyllite and highly polar water molecules are very weak. In contrast, low-charge smectites, the minerals most similar chemically and structurally to talc and pyrophyllite, have much greater values of γ ⊖ (≥ 30 mJ/m2) and are hydrophyllic.

Estimation of casein micelles' surface energy by means of contact angle measurements

SummaryThe surface energies of highly hydrated casein micelle layers isolated from variously pretreated skim milks have been determined by means of contact angle measurements. The long range Lifshitz-Van der Waals (LW) and the short range hydrogen bonding (SR) components of surface energy were determined using α-bromonaphthalene and water for contact angle measurements. Casein micelles isolated from untreated and heat treated milks showed similar surface energy values of about 63·5 mJ.m-2 with an LW component of 19·2 mJ.m-2 and an SR component of 44·3 mJ.m-2. The calculated attraction potential energy was − 0·7 mJ.m-2. Casein micelles isolated from renneted milk showed a surface energy of 33·0 mJ.m-2 with an LW component of 30·7 mJ.m-2 and an SR component of 2·3 mJ.m-2. The attraction potential energy of renneted micelles was nearly two orders of magnitude higher than those of micelles from other milks ( − 63·3 mJ.m-2). The SR component of interfacial energy accounted for 98% of this attraction potential. The importance of attractive forces in relation to casein micelle stability is discussed.