Elastic properties of crude oil/water interface in presence of polymeric emulsion breakers

Emulsions are formed during oil exploitation due to the presence of natural surfactants, such as asphaltenes and resins. These molecules strongly stabilise the water/oil interface and prevent coalescence of water droplets. As water/oil phase separation is necessary before oil refining, surfactants are used to break water-in-oil emulsions. Formulations based on non-toxic silicone copolymers are found to be effective in promoting emulsion breaking. Moreover, those polysiloxane copolymers can destabilise any kind of crude oil whatever its nature and origin. Thus, the understanding of their molecular action has become essential in order to develop their use in oil exploitation. In present study we use three linear copolymers with very different demulsification efficiency. Two of them are PEO–PDMS–PEO block copolymers, while the third one is a PPO–PDMS–PPO block copolymer. The kinetics of emulsion destabilisation has been followed by turbidimetric measurements. The PEO–PDMS–PEO copolymers gave better results. In order to characterize their elasticity, oscillations of the copolymer monolayers at the water/air interface have been performed. The measured values correspond to two-dimensional condensed film. The liquid/liquid Langmuir balance allowed the determination of the elastic modulus in presence and in absence of copolymer at the water/crude oil interface. The results obtained contribute to a better understanding of the molecular interactions leading to the demulsification process.