H. Balard

Comparison of the surface properties of graphite, carbon black and fullerene samples, measured by inverse gas chromatography

Three types of carbon were examined by inverse gas chromatography (IGC), at infinite and finite concentration conditions: graphite, carbon black and fullerene (C60) samples. Those samples differ by their structure and also by their surface properties (existence of defects, of polar surface groups...): surface free energy characteristics and surface energetic heterogeneity. IGC allows to determine in part these properties and evidences strong differences amongst the 3 carbons.

Inverse gas chromatography: A valuable method for the surface characterization of fillers for polymers (glass fibres and silicas)

Abstract Inverse gas chromatography (IGC) is most useful for the study of the surface characteristics of powders, such as silicas and glass fibres, which can hardly be examined otherwise. Examples are provided to illustrate the potential of IGC measurements either at finite concentration or at infinite dilution chromatographic conditions. It is shown that the interpretation of the results is facilitated when studying solid surfaces modified in a controlled way.

London component of the surface energy of heat-treated silicas

Abstract The surface properties of silicas of various origins were measured by inverse gas chromatography. Thus, after thermal treatment of silicas, the variation in the dispersive components (γSD) of their surface energies was determined. Different but typical behaviors either for amorphous or for crystalline silicas were observed. In comparison with other studies, a correlation is suggested between the variation in γSD and the modification of chemical and physical properties of silica surfaces after heat treatment.

Inverse gas chromatography investigation of the surface properties of cellulose

Cellulose samples differing in origin and crystallinity were examined by inverse gas chromatography (IGC). Surface energy characteristics such as the apparent dispersive component of the surface energy and acid-base properties, and also nanomorphology indices of the different cellulose samples, were assessed. The influence of humidity on these properties was demonstrated. A decrease of 10-20% of the interaction potential was detected. Crystalline cellulose is the most sensitive to the presence of adsorbed water, which possibly disorders its surface structure. IGC appears to be an appropriate method for the evaluation of the surface characteristics of cellulose. However, care has to be taken when trying to understand differences in surface properties between various cellulose samples, since IGC is very sensitive to minor variations in surface characteristics.

Chemical nature and water/oil emulsifying properties of asphaltenes

Abstract Asphaltenes which differ in their abilities to form water/oil emulsions were analysed by acidimetry, infrared and nuclear magnetic resonance spectroscopies. Asphaltenes which easily form such emulsions are loosely packed molecules and exhibit a marked acid/base imbalance.

Surface characteristics of commercial carbon fibres determined by inverse gas chromatography

Abstract The surface characteristics of carbonized and stabilized carbon fibres have been studied using inverse gas chromatography. First, the dispersive component of the surface energy of both types of fibres was determined. Secondly, using polar probes of known properties, acid-base surface characteristics of the fibres were obtained. It has been shown that the carbonized fibres exhibit an electron donating (base) character, whereas stabilized fibres are more amphoteric.

Surface energy and adsorption energy distribution measurements on some carbon blacks

Abstract The dispersive component of the surface energy (γsd) of various carbon blacks and of nitric acid or heat-treated samples has been measured by inverse gas chromatography (IGC). It is shown that IGC, at infinite dilution, applies poorly to carbon blacks and provides only apparent and excessively high values of γsd (a few hundreds of mJ/m2). IGC, at finite concentration, readily allows the obtention of n-alkanes, benzene and chloroform adsorption isotherms from which various thermodynamic values are computed (spreading pressure π, isosteric enthalpy of adsorption, surface energy characteristics). The γsd values calculated from πe are in the 80–120 mJ/m2 range (i.e. values which are in fair agreement with published data on graphite or graphitized carbons). Further, the specific interaction potential of polar probes is in relation, as expected, with the oxygen content of the carbons. Finally, from the adsorption isotherms, the adsorption energy distribution function is computed, supposing a patchwise distribution of adsorption sites. The results confirm the high surface heterogeneity of carbon blacks and the influence of surface treatments, but indicate also major differences between carbon blacks from different preparation processes.

The preparation of a ferrofluid by decomposition of dicobalt octacarbonyl: I. Experimental Parameters

Abstract The experimental parameters which lead to the formation of a stable suspension of metallic cobalt particles in an organic solvent (ferrofluid) were evidenced. The cobalt particles originate from the thermolysis of dicobalt octacarbonyl solution in the presence of a chosen surface active agent. The kinetics of the CO evolution depend on the reaction temperature, the nature of the solvent and of the surfactant, the weight ratio of carbonyl and surfactant, and the initial concentration of the cobalt carbonyl solution. Spherical particles, of a remarkable narrow size distribution, are obtained when the decomposition of Co2(CO)8 is carried out, in an aromatic solvent, above 110°C, in the presence of a surfactant possessing a long hydrocarbon chain and a strong ionic group (sulfonate). The decomposition in toluene, in which ethyl (2 hexyl) sodium sulfo-succinate is dissolved, leads to particles of about 70 A in diameter. The kinetics of the CO evolution are rather complex, but when a ferrofluid is being formed, several sequences are always recorded: an initial and rapid evolution of CO corresponding to the formation of Co4(CO)12. Part of this compound is insoluble in the reaction medium and appears to be a regulating intermediate. After this short initial stage the rate of decomposition of Co4(CO)12 slows down and becomes practically constant. Later the CO formation is accelerated again and finally it decreases as the reaction goes to completion. This S-shaped curve which describes the decomposition of Co2(CO)8 is always observed when a ferrofluid is in progress of formation.

Organization of the layers of polyethylene oxide grafted with different densities on silica

Abstract EPR spectroscopy of labeled grafted polyethylene oxide chains has been used to estimate the ratio of the population of free end segments in solution to that of adsorbed segments on a silica surface as a function of temperature. The configurations of the chains have been studied in the case of certain extreme coverages. Grafted molecules of mol wt 2000 with grafting ratios of 0.045, 0.057, 0.126, and 0.42 molecules/nm 2 were in contact with benzene. DSC thermograms are also shown. At low grafting ratios the chains lie very flat, whereas at higher grafting ratios the layer is more organized.

The preparation of a ferrofluid by decomposition of dicobalt octacarbonyl: II. Nucleation and growth of particles

Abstract The formation of a ferrofluid by thermal decomposition of a toluene solution of dicobalt octacarbonyl , in the presence of ethyl (2 hexyl) sodium sulfosuccinate, has been studied. The carbon monoxide evolution, the diameters of the particles, and the number of growing particles have been measured using also small-angle X-ray scattering and magnetic methods. The different sequences of CO evolution are explained. At least two factors are responsible for the formation of particles of very narrow size distribution: the presence of microreactors in the reaction medium and a diffusion controlled growth mechanism.