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Une famille de phosphobétaïnes neutres (I) à caractères structuraux variés - chaînes lipophiles R = C12H25 et C18H37; distances intercharges définies par un nombre de groupe méthylène n entre têtes polaires (2 < n < 6); substituants R3 = éthoxy et phényle sur l'atome de phosphore - ont été étudiés comme agents tensioactifs associés au pentanol dans la formation de micro émulsions. Des diagrammes pseudo-ternaires ont été dressés qui indiquent la formation des différentes phases Wl, II, III et monophasique. Des évolutions sensibles sont observées en fonction des divers paramètres moléculaires. L'effet de distance intercharge se traduit par l'augmentation de la surface par tête polaire augmentant régulièrement les surfaces Wl et WIII tandis que le facteur HLB suggère la présence de structures différemment ordonnées. L'hydrophilie des phosphobétaïnes peut être contrôlée par la nature du substituant R2 placé sur l'atome de phosphore. Un remarquable maintien des propriétés est obtenu dans les différentes conditions de salinité et de température. Sur la base de ces résultats, il est possible de définir les paramètres moléculaires utiles à ces tensioactifs pour leur utilisation comme agent dopant des produits de la récupération assistée du pétrole. A family of neutral amphiphilic phosphobetaines (I), with R = C12H25 or C18H37, with 2 < n < 6, and with R3 -ethoxy and phenyl, was investigated in pseudo-ternary-phase diagrams as new surfactants. In all cases, microemulsions are depicted with the occurrence of Winsor type systems, WI, WII and WIll. Remarkable variations in the diagrams are observed with molecular structural changes of zwitterionic amphiphiles. Interionic distances effects are obtained in the WI and WIll phases, suggesting a polar head surface change, while the HLB factor implies the appearance of differently ordered structures. The nature of the substituent covalently bonded on phosphorus can be used as a molecular probe to check the hydrophilicity of amphionics. Analyses of phases behaviors under various salinity and temperature conditions are also described, and attempts are made to rationalize these variations through the molecular parameters of the surfactants. On the basis of these results, an analysis can be made to optimize the structural parameters of surfactants for use as additives in tertiary oil-recovery processes.

The crystallization of paraffins from their solution at low temperature was investigated in the presence of ethylene-vinyl acetate (EVA) copolymers that allow the control of the size of the crystals. Depending on the type of solvent and distribution of the paraffin lengths, the mechanisms of crystal formation and growth are different. Precipitation of the EVA prior to the paraffins leads to the nucleation of a large number of crystals, whereas the adsorption of EVA on the surface of the growing crystals slows down the crystal growth. EVA can act either as a nucleating agent or as a growth inhibitor. These two mechanisms were identified from the analysis of the temperature of crystallization (cloud point), the chemical composition of the crystals, and the observations of the crystal habit. The EVA was able to co-crystallize with the paraffins in crystals of an orthorhombic structure and the melting enthalpies of the crystalline paraffin did not depend significantly on their neighborhood. The energies of interaction between the different paraffinlike components are close to each other, so that minor changes of the experimental conditions may lead to dramatic effects. This is the basic rationale for the large behavioral diversity observed in these systems.

The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by means of a new experimental approach. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax antisettling additives used for preventing wax crystal sedimentation adsorb at the surfaces of wax particles and provide them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals. The reported methodology makes it possible to investigate the fundamental mechanisms, but also to evaluate structure-activity relationships of the various additives used in the petroleum industry.