Nonlinear optical evidences of aggregation in asphaltene-toluene solutions

Evidences of asphaltene aggregation are presented through the application o f the Z-scan technique to study the nonlinear optical response of solutions of asphaltenes in toluene. Strong dependence of the two photon absorption coefficients (beta) with the input intensity was observed for concentrated solutions, as opposed to the observed behavior at low concentration. The re sults suggest that a change in (beta) occurs as a consequence of aggregatio n. The results are of importance for the study of dark samples like those r elevant for crude oils. (C) 2001 Elsevier Science Ltd. All rights reserved.