Interfacial energy of heavy naphthenic bitumen in aqueous medium

The impact of the interfacial properties of naphthenic bitumen is very relevant for road paving. In this work, we propose an approach for predicting the interfacial energy of bitumen in aqueous media based on contact angle hysteresis measurements. We measured the surface tension of naphthenic bitumen at high temperature with the pendant drop method. We estimated the surface energy of bitumen as the value of surface tension extrapolated to room temperature. The acid–base properties of naphthenic bitumen films were investigated by contact angle titration with buffered water. Due to the occurrence of contact angle hysteresis, we performed advancing–receding contact angle measurements on bitumen films at different values of pH with the low-rate dynamic contact angle technique. We observed that the receding angle was dependent on pH. Instead, advancing contact angle just reflected the nature of bitumen in dry conditions. We chose the average contact angle of advancing and receding contact angles as an estimate of the thermodynamically meaningful contact angle. Finally, the bitumen-water interfacial energy at room temperature was calculated using the Young equation. The low interfacial energy of bitumen at high pH confirmed the existence of native surfactants.