Jean-Baptiste Donnet

Surface properties of high-energy solids: I. Determination of the dispersive component of the surface free energy of mica and its energy of adhesion to water and n-alkanes

Abstract A method for measuring the dispersive part of the surface free energy γsD of a high-energy solid, and its interaction energy with water and n-alkanes, WSL, has been developed. It is based on the measurement of the contact angle of water on the solid under n-alkanes. Muscovite mica was chosen as a model high surface energy solid. The results obtained for γsD and WSL of mica are in good agreement with the results obtained by other techniques. The present method can be considered to be applicable for other solids.

Surface properties of high-energy solids: II. Determination of the nondispersive component of the surface free energy of mica and its energy of adhesion to polar liquids

Abstract A method of determining the polar term of the adhesion energy of several liquids to a high-energy solid, I SL P , has been developed, based on the measurement of the contact angle of water on a solid in a liquid medium. The I SL P values for mica are found to be a linear function of the square root of the polar term of the surface free energy of liquids. This finding agrees with the suggestion that the polar term of the energy of adhesion may be represented by the geometric mean of the polar term of the surface free energy of a solid and a liquid. The slope of the straight line provides the value of γ S P = 90 ergs/cm 2 for the polar term of the surface free energy of mica. The results were compared with those obtained by a cleavage method and also discussed in terms of each component of the surface free energy of mica. The present method is useful for the determination of the polar part of the energy of adhesion of a high-energy solid to liquids, and its surface free energy.

Structure and reactivity of carbons: From carbon black to carbon composites☆

Abstract The reactivity and the surface properties of carbons are closely related to their crystalline structure. Dealing with various types of carbonaceous materials carbon blacks, graphites and carbon fibres, it is shown that the chemical reactivity of carbons toward oxidation reagents depends primarily on their degree of crystalline organization. Several types of carbon surface groups can be evidenced on carbons. Their properties are illustrated. Grafting surface reactions and their mechanism are discussed. The surface energy of carbon materials of different structures or surface treatment are finally discussed.

Effects of alkylation of silica filler on rubber reinforcement

Abstract Rubber reinforcement of silicas with different surface alkylation have been evaluated by studies of NH3-modified swelling, swelling volume fraction, stress-strain tests, and scanning electron microscopy. Effects of silica alkylation on filler dispersion has been explained on the basis of surface energy and acid-base interactions. Bound rubber reductions have been explained according to acid-base interactions and/or physical entanglements. Hysteresis losses have been interpreted based on the reductions of polymer-filler and filler-filler interactions. The results show that the extent of reinforcement in NR and SBR vulcanizates is reduced when the silicas are alkylated, especially in the case of the hexadecyl group. However, in NBR vulcanizates the alkylation seems to have less influence on the reinforcement characteristics of the silica.

Effects of alkylation of silicas on interfacial interaction and molecular motions between silicas and rubbers

The interactions between rubbers and silicas were studied by means of bound rubber determination, vulcanizate swelling procedure, and tensile retraction measurement. The mobilities of rubber chain segments in mixture with silicas were investigated by thermomechanical and dynamic mechanical analyzers. The results show that when the untreated silica was incorporated into rubbers, the strong interaction of rubber with the silica apparently constrains the segmental motions of the rubber molecules, resulting in the decrease in the dynamic loss peak and the thermal expansion coefficient, and the increase in the glass transition temperature. The alkylations on silica surfaces weaken the interfacial interaction between rubbers and silicas, and the mobilities of the rubber molecules become less restricted. Furthermore, proton spin–spin relaxation time (T2) measurements by the pulsed NMR on the insoluble bound rubber, indicate that there are two relaxing regions: an immobile (or a tight) region and a relatively free (or a loose) one. The types of the rubbers and the activities of the silica surfaces have influences on the relaxation process of the two bound rubber components.

Observation of plasma-treated carbon black surfaces by scanning tunnelling microscopy

Abstract The graphitized carbon black N550G was treated in different atmospheric plasmas, such as air, ammonia, argon, and hydrogen. The plasma-treated surfaces were investigated by scanning tunnelling microscopy (STM) until atomic resolution. The surface chemical properties of these carbon blacks were characterized by electron spectroscopy (ESCA). It was found that air, ammonia, and argon plasmas result in a destruction of graphitic structure of graphitized carbon black surfaces. Chemical modification of the surface also takes place in air and ammonia plasma treatment. The hydrogen plasma, however, has only a little effect on the black surface. The surface energy of carbon blacks, measured by inverse gas chromatography, shows a good correlation with the defects of graphitic basal planes.

Electroinitiated polymerization of 2-ethylhexylacrylate on carbon fibers

Abstract The electroinitiated polymerization of 2-ethylhexylacrylate in dimethylformamide in the presence of tetrabutylammoniumiodide was investigated at 288–314 K, with graphitized monofibers being used as a cathode. Electron microscopy showed that the surface of a carbon fiber is characterized by considerable microheterogeneity. The fiber interaction with the propagating polymer chain was supposed to be different due to the energetic microheterogeneity of the fiber surface. This has been proved by micrographs of carbon fiber samples after electrolysis. The local excrescences of poly (2-ethylhexylacrylate) could not be separated after prolonged acetone extraction of the samples. They were conventionally referred to as a grafted polymer. It is inferred that the energetic surface microheterogeneities have a considerable effect on the grafting process regardless of the nature of the reactive centers. The use of carbon monofibers as a cathode does not substantially affect the mechanism of the 2-ethylhexylacrylate electroinitiated bulk polymerization. It is shown that the solution polymerization of 2-ethylhexylacrylate in dimethylformamide occurs according to an anionic mechanism and leads to oligomer formation. The experimental rate constants of the electroinitiated polymerization of 2-ethylhexyl-acrylate, depending on current density and temperature, as well as the total activation energy were determined.