E.I. Vargha-Butler

SURFACE TENSION EFFECTS IN THE SEDIMENTATION OF POLYMER PARTICLES IN VARIOUS LIQUID MIXTURES

ABSTRACT The sedimentation volume, V sed of polymer particles in mixtures of pairs of nonpoiar as well as polar liquid combinations was determined at 20°C The liquid combinations were chosen such that the interfacial tension, γSV, of the polymer particles fell between the surface tensions of the two liquids. Constant: amounts of a given polymer powder were suspended in constant volumes of liquid mixtures of different concentrations It was found that the sedimentation volume changed with the composition and hence the surface tension of the liquid mixtures. A maximum or a minimum occurred in V sed when the surface tension of the suspending liquid was equal to that of the particles, i.e., when γLV = γSV Maxima occurred in the polar and minima in the nonpoiar and slightly polar liquid mixtures The results are discussed in terms of van der Waals interactions and mechanisms of particle aggregation.

SURFACE TENSION EFFECTS IN THE SEDIMENTATION OF COAL PARTICLES IN VARIOUS LIQUID MIXTURES

The sedimentation volume, V sed, of coal particles in mixtures of pairs of non-polar and more polar organic liquid combinations as well as in aqueous solutions was determined at 20°C. The liquid combinations were chosen such that the surface tension, γSV, of the coal particles fell between the surface tensions, γLV, of the two liquids. A constant mass of a given coal sample was suspended in constant volumes of liquid mixtures of different concentrations. It was found that the sedimentation volume changed with varying composition of the liquid mixtures, as did the surface tension. A maximum or a minimum occurred in V sed when the surface tension of the suspending liquid was equal to that of the coal particles, i.e. when γLV = γSV. Maxima occurred in more polar and minima in the non-polar or less polar liquid mixtures. The position of the extrema, and hence the surface tension, γsv, of the particles, was found to change with particle size, in agreement with findings from other independent techniques. It was...

Sedimentation behaviour of low surface energy powders in different non-polar liquid systems

Abstract The sedimentation volume, V sed , of four different powders in non-polar single component liquids as well as in non-polar binary liquid mixtures was determined at 20°C. The liquids were chosen such that they span a range of surface tensions, γ LV , that includes the surface tension, γ SV , of the powders. Samples of each powder were suspended in liquids of different surface tension. It was found that the sedimentation volume changed with varying surface tension, γ LV , of the liquids. A minimum occurred in V sed at a surface tension which corresponds to γ LV = γ SV . The sedimentation volumes obtained using binary non-polar liquid mixtures as the suspending medium yielded essentially the same particle surface tension, γ SV , as when experiments were performed using single component liquids.

Determination of specific heats of coal powders by differential scanning calorimetry

Abstract Specific heats ( C p ) of bituminous and subbituminous coals were investigated in the temperature range 300–360K by differential scanning calorimetry (DSC). To establish the validity of the procedure, specific heats of glass beads and graphites in powdered and bulk form were determined. Good agreement was obtained with the values for the specific heats of glass and graphites in the literature, and it was established that the specific heats were not dependent on the degree of diminution of these materials. Specific heats of coal samples were found to depend upon mesh size, temperature, rank, moisture content and whether the coal powder was wet- or dry-screened. However, there were only minor differences in C p between bituminous and subbituminous coals.

Surface-tension effects in the sedimentation of coal particles in n-propanol/water mixtures

Abstract Sedimentation-volume experiments with Pittsburgh coal No. 8 in binary mixtures of n-propanol and water are reported. Two maxima in the plot of sedimentation volume versus surface tension of the binary mixtures are observed. They occur near 35 and 70 mJ m −2 , respectively. From thermodynamic considerations, we expect such extrema under circumstances when the effective surface tension, γ SV , of the solid particles is equal to the surface tension, γ LV , of the suspending liquid. The emerging fact that this specific coal has different effective surface tensions depending on the surface tension of the liquid media is in agreement with the results of studies of other coal samples by two different techniques: the solidification-front technique and the adhesion technique.

Surface properties of coal particles in aqueous media II. Adhesion of coal particles to polymeric substrates

Abstract The adhesion technique for the determination of the surface tension of small particles was used to characterize the surface properties of three types of coal particles. It was found that in aqueous media with relatively high surface tensions the coal particles were very hydrophilic with surface tension values in the 65–70 mJ m−2 range. These findings are in good agreement with data obtained from other techniques. Exploratory measurements at low surface tensions give an indication of the hydrophobic nature of coal, which normally manifests itself when suspended in organic media.

ADSORPTION AND WETTING PROPERTIES OF PLURONIC BLOCK COPOLYMERS ON HYDROPHOBIC SURFACES STUDIED BY OPTICAL WAVEGUIDE LIGHTMODE SPECTROSCOPY AND DYNAMIC TENSIOMETRIC METHOD

Adsorption of four different poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymers (Pluronics®) onto the hydrophobized surface of the sensor was measured by the optical waveguide lightmode spectroscopy (OWLS). Adsorbed amounts of Pluronic PE10300, PE10500, PE6400, and PE6800 determined in the concentration range of 10−2−10 gdm−3 were found to follow the order of the hydrophobicity of the Pluronic compounds characterized by their hydrophil–lipophil balance (HLB) values. Wettability of two hydrophobic surfaces, the poly(lactide-co-glycolide), PLGA70/30 copolymer (used as drug carrier in pharmaceutical applications) and silylated glass, in aqueous solutions of the above Pluronics were studied by a dynamic tensiometric method. The significant increase in the wetting tension observed after the adsorption of the surfactants, and hence the decrease of the apparent contact angle as the indication of the wetting effect on both the biopolymer and the hydrophobic glass, was correlated to the poly(ethylene oxide) (PEO) content of the adsorbed layer obtained on the hydrophobized sensor surface by the OWLS method.

WETTABILITY MEASUREMENTS ON COAL PARTICLES BY MEANS OF THE SOLIDIFICATION FRONT TECHNIQUE

Abstract Reliable methods for the characterization of the surface properties and the wettability of small particles have not been available in the past. A novel technique, based on the behaviour of the lest particles at the solidification front of certain well defined solidifying melts (matrix materials) has been developed recently in our laboratory. This method was used to determine contact angles and surface tensions of coal particles in the range of 20-250 μm. Two types of bituminous and one type of subbituminous coal were tested using thymol, biphenyl, napthalene, salol and 2-phenyl phenol as matrix materials. The results show that contact angles on small particles can be determined to within ± 2°, i.e. to the same degree of accuracy that is typically reported for extended smooth surface by means of conventional techniques. The measurements also show that within one and the same coal sample the larger particles are somewhat more hydrophilic than the smaller ones. Surface tensions and contact angles of...

Surface properties of coal particles in aqueous media. I: Solidification front measurements

Abstract The particle/vapour interfacial tension of three types of powdered coal was determined by means of the solidification front technique in organic as well as in aqueous media. The results obtained from experiments performed in organic media show that the three types of coal have an intermediate hydrophobicity in the surface tension range of 30–40 mJ m −2 at 20°C. However, in the presence of water the coal is markedly more hydrophilic with a surface tension near that of water. This striking difference suggests that one and the same coal sample may have two effective surface tensions or even a range of surface tensions, depending on the suspending liquid. It appears that, in water, the coal particles acquire a thick hydration layer so that they are perceived by other phases present as “black water particles”.

Direct contact angle measurements on polished sections of coal

The wettability of three bituminous Canadian coals was determined by direct contact angle measurements. Advancing contact angles of water, glycerol and ethylene glycol were measured at room temperature on segments of coal with five different surface finishes. It was found that the contact angles measured with water varied only moderately, but randomly, with the roughness of the coal surface; contact angles of organic liquids increased with decreasing surface roughness. These findings are at variance with results normally obtained with more homogeneous solids, such as Teflon, under similar experimental conditions. The irregular behaviour of coal is interpreted on the basis of both the chemical and mechanical heterogeneity of coal. The solid/vapour surface tensions, γsv, of the coal samples, calculated from the contact angles, were compared with surface tensions obtained from other techniques using powders of the same coals. This comparison suggests that the information obtained from the contact angles is l...