Langmuir and Langmuir−Blodgett Films of Mixed Asphaltene and a Demulsifier

Abstract

Asphaltene was extracted from Athabasca oil sands bitumen with n-heptane. The extracted maltene-free asphaltene was characterized for physicochemical properties through molecular weight, chemical composition, and functional group analysis. Monolayer characteristics of mixtures of asphaltene and a polymeric demulsifier were studied using a Langmuir interfacial trough at air−water and heptol−water interfaces through measurements of pressure−area and relaxation isotherms (“heptol” refers to a solvent mixture of heptane and toluene). Single-layer Langmuir−Blodgett (LB) films from monolayers of mixed asphaltene and demulsifier were deposited on silicon wafers at air−water and heptol−water interfaces. The deposited LB films were characterized by atomic force microscopy (AFM) imaging and contact angle measurements. Asphaltene forms nanoaggregates at both air−water and heptol−water interfaces. Asphaltene monolayers at a heptol−water interface are more compressible than those at an air−water interface and show little hysteresis. The presence of a demulsifier in a mixed monolayer renders the monolayer more compressible at both air−water and heptol−water interfaces. The asphaltene and demulsifier aggregates follow ideal mixing behavior at both air−water and heptol−water interfaces. AFM images of deposited monolayers reveal the presence of nanosize aggregates. The presence of demulsifier in an asphaltene monolayer can reduce the mechanical strength of the asphaltene monolayer as indicated by reduced rigidity with increasing demulsifier content in the compressibility plot.