R.F. Giese

Determination of contact angles and pore sizes of porous media by column and thin layer wicking

A simple method is described for the determination of contact angles (0) on powdered materials such as clay particles. This is done by depositing the particles from a liquid suspension onto glass slides, by sedimentation, followed by drying. The dried thin-layer plates are then subjected to wicking in a number of liquids using the Washhurn equation to determine cos . However, one other unknown in the Washburn equation, i.e. the average interstitial pore radius R, must first be determined. This is done by wicking with low-energy spreading liquids, such as alkanes. It could be shown with spherical monosized polymer particles, as well as with clay particles, that spreading liquids pre-wet the surfaces of the particles over which they subsequently spread. Thus, it can be demonstrated that spreading coefficients, in the sense of Harkins, play no role in this type of spreading and cos 0 equals unity in the Washburn equation for all values of γ1, for all spreading liquids (L). Results were obtained by thin layer...

Colloid And Surface Properties Of Clays And Related Minerals

Applications of clays and clay minerals clay minerals other mineral colloids theory of colloids measurement of surface thermodynamic properties electrokinetic methods interactions between colloids surface thermodynamic properties of minerals biological interactions with mineral particles.

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, γLW, 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 γLW 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.

Linkage between ζ-potential and electron donicity of charged polar surfaces 1. Implications for the mechanism of flocculation of particle suspensions with plurivalent counterions

Abstract Studies were carried out on the surface properties of montmorillonite (SWy-1), glass and calcite particles by means of parallel measurements of electrophoretic mobilities and contact angles, as a function of the concentration of La 3+ or Ca 2+ ions. The investigations indicated that with a decrease in ζ-potential a concomitant strong increase in hydrophobicity takes place, for example, in aqueous NaCl solutions (ionic strengthΓ/2 = 0.015, pH 7.5), SWy-1 has a ζ-potential of −66 mV, an electron-acceptor surface tension parameter γ ⊕ = 0.2 mJ m −2 and an electron-donor surface tension parameter γ ⊖ = 34 mJ m −2 , which is higher than that of water. This causes these particles to be very hydrophilic and to form an extremely stable suspension in water, owing to an electrostatic energy (15%) and to a net Lewis acid-base (polar) repulsion energy (85%). However, in the presence of 1.6 mM LaCl 3 (Γ/2 = 0.024, pH 7.5), ζ = −13 mV, γ ⊕ = 0.15 mJ m −2 and γ ⊖ = 5.51 mJ m −2 , which makes the particles very hydrophobic and causes them to flocculate: the energies of attraction in this case are caused by hydrophobic interactions (87%) and van der Waals forces (13%).

Influence of the water–air interface on the apparent surface tension of aqueous solutions of hydrophilic solutes

Abstract It is well known that sugars such as sucrose and glucose, when dissolved in water, cause an increase in its measured surface tension. We determined however that polymers of sucrose and glucose, i.e. ficoll and dextran, both cause a decrease in the measured surface tension of their aqueous solutions. From the surface tension properties of solid layers of dried sucrose and glucose, and from the aqueous solubilities of these two sugars, their surface tension components and parameters in the dissolved state could be determined. From these it follows that the surface tension of these sugars in the dissolved state is about twice as high as that of water. From the surface tension data of both sugars it also follows, however, that their molecules are repelled by the water–air interface, which leaves a thin zone inside the water–air interface that is depleted of sugar molecules, thus giving rise to an apparent measured surface tension for these aqueous sugar solutions that is only a few mJ/m2 higher than that of water. The cause of the high polar components of the surface tensions of sugars in the dissolved state lies in the elevated free energy of cohesion between the electron-acceptor and electron-donor sites of molecularly dissolved sugar molecules, as manifested by a very elevated Lewis acid-base (AB) surface tension component, γAB, of about double that of water. In polymers of these sugars the strong electron-acceptor/electron-donor interactions between sugar monomers is no longer possible, or much attenuated, which lends ficoll and dextran a γAB value of only above 40% of that of water. These polymer molecules are also repelled by the water–air interface, so that the decrease in surface tension they cause in aqueous solution, is relatively modest. Hydrophilic solutes are repelled by the water–air interface and although they homogeneously pervade almost the whole volume of the aqueous solvent at very low to very high concentrations, they are absent from the depletion layer, which, for relatively low molecular weight solutes, typically is slightly thinner than 1.0 nm, closest to the air interface. Partly hydrophilic/partly hydrophobic solutes orient their hydrophobic sites to the water–air interface. The bulk solution has a (usually rather dilute) concentration of solute, not surpassing its solubility, however the solute concentration at the water–air interface can be much more concentrated than the solubility limit, e.g. by having the amphipathic solute molecules form micelle-like structures, with their hydrophilic sites directed to the water-phase, and their hydrophobic moieties protruding into the air, usually with loss of water of hydration. This causes a drastic apparent decrease in the measured surface tension of the aqueous solvent, generally already noticeable at fairly low to very low solute concentrations. Thus, whether solutes are repelled by the water–air interface (e.g. sugars and their polymers, and salts), or attracted to that interface, the measured apparent surface tension of all such aqueous solutions is not proportional to the free energy of cohesion of the bulk liquid. In general, therefore, contact angle measurements using non-homogeneous liquids, such as solutions or mixtures of liquids, are best avoided.

Change in surface properties of solids caused by grinding

Abstract The surface properties (i.e. the values of the Lifshitz-van der Waals ( γ LW ) components and Lewis acid ( γ + ) and base ( γ − ) parameters) of talc, calcite, dolomite, silica and zirconia, untreated and as ground powders, were determined by contact angle measurements (directly on flat surfaces and by thin layer wicking for powders). The values of γ LW , γ + and γ − for these solids tend to change after grinding; γ LW and γ − decreased for all these solids and γ + often increased, depending on the material.

Stability versus flocculation of particle suspensions in water—correlation with the extended DLVO approach for aqueous systems, compared with classical DLVO theory

Abstract Stability versus flocculation is studied for aqueous suspensions of a variety of mineral particles (e.g. clay, asbestos, glass), via the extended DLVO (XDLVO) approach (which includes Lewis acid–base interactions in addition to van der Waals and electrostatic interactions), as well as via classical DLVO theory, as a function of absence or presence of plurivalent counterions. Also discussed are XDLVO and DLVO analyses of polymers, biopolymers, cells and phospholipids, in aqueous media, under similar conditions. It is concluded that, in aqueous media, XDLVO analysis practically always describes the interactions of immersed or dissolved particles, cells, vesicles, polymers, biopolymers or phospholipids more accurately than classical DLVO theory.

Mechanisms of adjuvancy: I—metal oxides as adjuvants

The exact mechanism of how immune adjuvants function still remains largely unknown, despite their long history of use. This work reports the properties of alum and the related compounds Al(OH)3 or Al2O3. Experiments were performed in rats to determine the relative adjuvancy of silica, talc, ground glass, Al2O3, SnO2, ZrO2, hematite and magnetite. Antibody response and cell-mediated immunity (CMI) to ovalbumin (OVA) were determined and were found to be significantly enhanced by silica and talc. Antibody response to OVA was moderately enhanced by Al2O3, hematite, and magnetite, while CMI to OVA was not affected, SnO2, ZrO2, and ground glass only gave a slight adjuvant effect. The magnitude of adjuvancy appeared to correlate with the magnitude of the inflammatory response produced by each metal oxide and also correlated with their surface area. No correlation could be drawn between the hydrophilicity or hydrophobicity of the metal oxides and the magnitude of their adjuvancy.

Interaction between proteins and inorganic oxides — Adsorption of albumin and its desorption with a complexing agent

Abstract Human serum albumin (HSA) absorbs to SiO 2 , talc, SnO 2 and ZrO 2 particles (in increasing order of strength of adsorption), and can be totally desorbed by a complexing agent such as EDTA. The surface properties of the SiO 2 , talc, SnO 2 and ZrO 2 particles used have been measured by wicking: SiO 2 is hydrophilic, whereas talc and ZrO 2 are quite hydrophobic. The mechanism of protein binding to these surfaces is discussed.

Surface tension parameters of ice obtained from contact angle data and from positive and negative particle adhesion to advancing freezing fronts

From contact angle data obtained on flat ice surfaces with a number of liquids, combined with data on particle and macromolecule adhesion or non-adhesion to advancing freezing fronts, the apolar (Lifshitz-van der Waals or LW) and polar (Lewis acid-base or AB) surface tension (γ) components and parameters have been determined. At 0°C these are γLW iee = 26.9 and γAB ice = 39.6 mJ/m2. The latter consists of an electron-acceptor (γ⊕) and an electron-donor (γ⊖) parameter: γ⊕ = 14 and γ⊖ = 28 mJ/m2.