Asphalt Association colloids

Rheological investigations of asphalts by Traxler and associates (123,124), Lee et al. (51), Pfeiffer and Van Doormaal (94), Thelen (117), Mack (60), and others show the following to be characteristic colloidal properties. 

Mack (58, 59) points out that asphaltenes from different sources in the same petro-lenes give mixtures of approximately the same rheological type, but sols of the same asphaltenes in different petrolenes differ in flow behavior. Those in aromatic petrolenes show viscous behavior and presumably approach true solution. Those in paraffinic media show complex flow and are considered to be true colloidal systems. Pfeiffer and associates (91) consider that degree of peptization of asphaltene micelles determines the flow behavior. Thus, a low concentration of asphaltenes well peptized by aromatic petrolenes leads to purely viscous flow. High concentrations of asphaltenes and petrolenes of low aromatic content result in gel-type asphalts. All shades of flow behavior between these extremes are observed. 

Asphalt is a lyophilic colloid in which asphaltene interacts with the dispersion medium through the peptizing agent. Because of the hydrogen bonding and dipole-dipole interaction, the asphaltene particles form micelles and even associations/clusters in the asphalt system. 

Crude oil has been characterized as a colloid (1,2) in which high molecular weight, asphaltic particles are dispersed. Such particulates—known as asphaltenes—are held in solution via peptization by lower molecular weight components—classified as resins. This association forms a micellar type structure (3-5). Classification of the asphaltic constituents in crude oil is based primarily upon each component s solubility in various solvents (e.g., the pentane soluble, propane insoluble resin or maltene fraction and the benzene soluble, pentane insoluble asphaltene fraction) (6,7). 

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