Introduction Asphaltenes are defined by solubility characteristics: they are insoluble in light alkanes such as n-heptane and are soluble in toluene [1]. They are generally composed of polyaromatic nuclei carrying aliphatic chains and rings and a number of heteroatoms, including sulphur, oxygen, nitrogen and metals such as vanadium, nickel and iron. These heteroelements account for a variety of polar groups, such as aldehyde, carbonyl, carboxylic acid, amine and amide [2, 3, 4]. As one of the primary components of crude oil, asphaltenes are known to cause a number of problems in connection with production, transport and processing of crude oils [5, 6, 7, 8]. The state of the asphaltenes is dependent upon pressure and temperature as well as the composition of the crude oil [9, 10, 11, 12, 13, 14]. It is probable that they will pre- cipitate and cause plugging of reservoirs or production equipment if they are exposed to large changes in these parameters. The general view is that at high pressures, the asphaltenes are in a condition of monomeric entities dissolved in the crude oil. At lower pressures, the as- phaltenes exists as aggregates (micelles) [15, 16] of enti- ties with an altogether elliptical form [17]. These aggregates are kept dispersed in the solution by resins [18, 19, 20, 21, 22], which are molecules similar to the asphaltenes containing various polar groups as the as- phaltenes do, yet are soluble in light alkanes and insol- uble in toluene. Gonzalez and Middea [23] studied the peptization of asphaltenes in aliphatic solvents by various oil-soluble amphiphiles. They showed that the effectiveness of amphiphiles on asphaltene stabilization was influenced by the interactions between the polar headgroups of the amphiphiles and polar groups on the asphaltene mole- cules; however, their results also indicated that other interactions could be of importance, for instance, the p electrons of the aromatic portions of the asphaltenes may act as electron donors for hydrogen bonds with hydroxyl groups of the amphiphiles. In 1994, Chang and Fogler [24, 25] discussed the stabilization of as- phaltenes in aliphatic solvents using alkylbenzene-de- rived amphiphiles. The results supported earlier suggestions of a hydrogen-bonding effect or possible acid–base interactions between the amphiphile head- groups and polar groups on the asphaltenes, and also showed that the length of the amphiphiles alkyl tail was of significance. ORIGINAL CONTRIBUTION Colloid Polym Sci (2002) 280: 695–700 DOI 10.1007/s00396-002-0660-9 Inge Harald Auflem Trond Erik Havre Johan Sjo¨blom Near-IR study on the dispersive effects of amphiphiles and naphthenic acids on asphaltenes in model heptane-toluene mixtures Received: 11 May 2001 Accepted: 8 January 2002 Published online: 23 May 2002 Ó Springer-Verlag 2002 I.H. Auflem (&) ® T.E. Havre ® J. Sjo¨blom Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway E-mail: inha@statoil.com J. Sjo¨blom Statoil ASA, R & D Centre, 7005 Trondheim, Norway Abstract Near-IR spectroscopy is used to follow the disintegration of asphaltene aggregates at 1,600 nm. It is shown that the technique is applicable to determine the efficiency of various additives as disaggrega- tion chemicals. Keywords Asphaltenes ® Naphthenic acids ® Near-IR spectroscopy ® Inhibitors