Molecular simulation aided design of copolymer thickeners for supercritical CO2 as non-aqueous fracturing fluid

摘要

Molecular modeling of CO2-polymer system was established to study the molecular behaviors and intermolecular interaction of copolymers in supercritical carbon dioxide (SC-CO2) by all-atom molecular dynamics (MD) simulation. According to the simulation results, the correlations of the intermolecular interaction with the molecular structure and composition were explored. The effects of intermolecular interactions on the copolymer properties in SC-CO2 were identified. A series of copolymers were synthesized with CO2-philic monomer 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl acrylate (HFDA) and CO2-phobic monomer vinyl nOctanoate (VOc), vinyl acetate (VAc), vinyl pivalate (VPi), respectively. The solubility and viscosification of the copolymers in SC-CO2 were evaluated by cloud point pressure and relative viscosity measurements. It was found that P(HFDA(0.49-co)-VAc0.51), which is the most effective thickener among the copolymers, could enhance the viscosity of SC-CO2 by 62 times at 5 wt%. It was suggested that the thickening capability of the copolymers in SCCO2 may originate from intermolecular cross-links generated by associative groups. Combining the molecular simulation and experiment results, the structure-activity relationships of the copolymers in SC-CO2 were revealed. It is believed that the molecular simulation aided design method for the SC-CO2 copolymer thickener is reliable.