Thickening Supercritical CO2 with π-Stacked Co-Polymers: Molecular Insights into the Role of Intermolecular Interaction

Abstract

Vinyl Benzoate/Heptadecafluorodecyl acrylate (VBe/HFDA) co-polymers were synthesized and characterized as thickening agents for supercritical carbon dioxide (SC-CO2). The solubility and thickening capability of the co-polymer samples in SC-CO2 were evaluated by measuring cloud point pressure and relative viscosity. The molecular dynamics (MD) simulation for all atoms was employed to simulate the microscopic molecular behavior and the intermolecular interaction of co-polymer–CO2 systems. We found that the introduction of VBe group decreased the polymer–CO2 interaction and increased the polymer–polymer interaction, leading to a reduction in solubility of the co-polymers in SC-CO2. However, the co-polymer could generate more effective inter-chain interaction and generate more viscosity enhancement compared to the Poly(Heptadecafluorodecyl) (PHFDA) homopolymer due to the driving force provided by π-π stacking of the VBe groups. The optimum molar ratio value for VBe in co-polymers for the viscosity enhancement of SC-CO2 was found to be 0.33 in this work. The P(HFDA0.67-co-VBe0.33) was able to enhance the viscosity of SC-CO2 by 438 times at 5 wt. %. Less VBe content would result in a lack of intermolecular interaction, although excessive VBe content would generate more intramolecular π-π stacking and less intermolecular π-π stacking. Both conditions reduce the thickening capability of the P(HFDA-co-VBe) co-polymer. This work presented the relationship between structure and performance of the co-polymers in SC-CO2 by combining experiment and molecular simulations.

Effective viscosification of supercritical carbon dioxide by oligomers of 1-decene

“…(2011) See-through, windowed cell 329 21 Not mentioned Capillary Shi et al. (2015) Fixed volume view chamber with two sapphire windows on opposite walls 318–343 21 Installed stirrer, maximum speed of 1,200 rpm N/A Sun et al. (2018) Variable volume cell, windows made of quartz glass 308 15–30 Magnetic stirrer Falling ball Al-Hinai et al.…”

CO2 Viscosification by Functional Molecules from Mesoscale Simulations

“…The styrene beads, shown in red in Figure 3c, are the key ingredient that keeps the HFDA agglomerates stable over time, through π-stacking interactions. 26 We have found 20 that in the HFDA composition we have modeled, the intermolecular π-stacking interaction is predominant over the intramolecular π-stackings, leading to aggregation. These contrasting structuring mechanisms under flow are in agreement with the results from equilibrium DPD simulations 20 and reveal the origin of the viscosification differences, as seen in Figure 4.…”

Evaluation of CO2‐philicity and thickening capability of multichain poly(ether‐carbonate) with assistance of molecular simulations

“…The structure and the testing method of the viscometer are very simple. The relative viscosity is calculated as below, 39 where η mix is the viscosity of polymer and CO 2 mixture, η CO 2 is the viscosity of pure CO 2 .…”

“…To be considered as a good carbon dioxide thickener, in addition to the solvation capability, the thickening ability is a very important characteristic. Many researchers 21,19,39 have reported that tuning the intermolecular force can be used for thickening, such as “π–π” stacking in phenyl groups can promote the thickening degree.…”