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The study was extended to analysis of mass, size and conformation of micelles formed in aqueous solutions of ethoxylated nonyl phenols. The results obtained by ultracentrifugal technique between 293 and 323 K have proved that the slightly ethoxylated nonyl phenols form micelles with high molecular mass and larger size at constant temperature, while the increasing length of the ethylene oxide chain favours formation of micelles of smaller molecular mass and size. The transformation of conformation from oblate to spherical shapes ensues with increasing temperature at constant ethoxy number or with ethoxylation at constant temperature. The second virial coefficient decreases with increasing temperature and decreasing ethoxy number. In accordance with the earlier conclucions, the change of the second virial coefficient relates to enhanced variation of monomer solubility, stabilization of micelle structure and increased deviation from ideal behaviour of a given micellar system.

List of symbolsmole fraction the partial molar enthalpy the relative partial molar enthalpy (eqs 2, 6 and 9) the relative enthalpy of solution (eq. 3) the relative molar enthalpy of solution (eqs. 3 and 4) the relative molar enthalpy of mixing polynomial of the fourth degree parabola directional vector directional vector directional derivative Subscripts 1 = H20 = water 2 = NaC 8 = sodium n-octanoate = sodium caprylate 3 = C10OH = n-decanol k = constant molar ratio of water to sodium octanoate

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper gives an overview on the application of Nonionic surfactants in hydrocarbon industry, particularly oil production. Advantages and disadvantages are critically analyzed in field of recovery and well treatment methods, drilling and well completion, surface technology and pipe line transportation. On the basis of the literature survey it is concluded that the practice oriented R&Ds performed during the past half century were not sufficiently supported by fundamental physico chemical and colloid chemical research. In the second part of the paper the authors give a concise summary of their studies aimed at forming a theoretical basis of wide range applications of ethoxylated nonyl-phenols in oilfield chemistry. The research program comprised the thermodynamic characterization of micellization, determination of micelle and solution structure, effect of different additives, interfacial properties in gas−water and oil−water systems and the effect of tensides on interfacial rheological properties. The microscopic approach and molecular interpretation of the observed phenomena allowed the authors to recommend more precisely where, when and which of the tensides have the highest potential in different oilfield applications.

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