  Systems of Cooee bitumen and water up to 4 mass % are studied by molecular
dynamics simula- tions. The cohesive energy density of the system is shown to
decrease with an increasing water content. This decrease is due mainly to an
increase in potential energy which is not high enough to counterbalance the
increase in volume due to the addition of water. It is not due to a decrease of
potential energy between the slightly polar asphaltene molecules. The water
molecules tend to form a droplet in bitumen. The size and the distribution of
sizes of the droplets are quantified, with multiple droplets being more stable
at the highest temperature simulated. The droplet is mainly located close to
the saturates molecules in Cooee bitumen. Finally, it is shown that the water
dynamics is much slower in bitumen than in pure water because it is governed by
the diffusion of the droplet and not of the single molecules.
