Study On Magnetic CO₂ Responsive Worm-like Micelles

In recent years,responsive and functional worm-like micelles(WLMs)have attracted widespread attention in the academic world due to their special functionality and reversible&controllable viscoelasticity.Their unique microstructure and response mechanism have been studied by many scholars.Among them,the CO2-responsive WLMs are green,biocompatible,clean and renewable,while magnetic WLMs are reported less,but they can be manipulated over the migration property by an external magnetic field makes them promising as a new type of fracturing fluid for oil and gas field development.Therefore,based on magnetic surfactants and magnetic particles,three CO2-responsive WLMs with magnitism were prepared,their CO2-response behavior and magnetic characteristics were studied in detail.Firstly,a CO2-responsive WLM system with weak magnetism was prepared by compounding magnetic surfactant(CTAFe),sodium salicylate(NaSal)and N,N-dimethylcycyclohexylamine(DMCHA).The CO2-response mechanism and magnetic characteristics were systematically studied using a rheometer,a conductivity meter,a pH meter,a vibrating sample magnetometer(VSM),a cryo-transmission electron microscope(Cryo-TEM)and other instruments,Studies have shown that CTAFe and NaSal can form purple viscoelastic WLMs due to self-assembly,and DMCHA will enter the hydrophobic core of WLMs,which will break the WLM structure and transform into a low-viscosity water-like solution with a viscosity of only 0.327 Pa s.With the introduction of CO2,the pH of the system gradually decreases.DMCHA is protonated into DMCHA�H+and escapes from the inside of WLMs.The self-assembly between CTAFe and NaSal molecules is regained,and the WLMs with viscoelasticity is restored,the viscosity increased by two orders of magnitude,that is 53.22 Pa s.In the WLMs state,after passing through N2 and heating to discharge CO2,the ststem becomes a low-viscosity water-like solution,all of this showing of CO2-responsiveness.The WLMs also have weak magnetic properties by VSM test and macro magnet attraction.Secondly,Fe3O4 magnetic particles coated with polyethylene glycol-6000(PEGylated Fe3O4)were used as magnetic components,CTAB and NaSal were used as the main component of the micelles,by introducing the CO2-responsive tertiary DMCHA and N,N-dimethylbenzylamine(BDMA),two kinds of CO2-responsive WLM systems with strong magnetism were prepared.The effects of concentration on the viscosity and stability,the rheological properties,the CO2-responsive mechanism and magnetic properties were studied in detail.The results showed that the viscosity of the system decreased with the increase of the concentration of the responsive tertiary amine until phase separation occurrs.Before the introduction of CO2,the PEGylated Fe3O4-CTAB-NaSal-DMCHA and PEGylated Fe3O4-CTAB-NaSal-BDMA systems are water-like solutions with low viscosity,the zero-shear viscosity(?0)of them are only 0.11 Pa s and 0.36 Pa s respectively.After bubbling CO2 for a period of time,both systems become black-brown worm-like micellar fluids and exhibit shear thinning phenomenon,the ?0 increases into 89.12 Pa�and 96.35 Pa s respectively.When CO2 was removed,both systems turn into the initial water-like solutions with low viscosity again,which confirmed that the two systems have excellent CO2-response cycle.The VSM test proved that the two WLMs also have strong ferromagnetism due to the presence of PEGylated Fe3O4,which can be magnetic migration under an external magnetic field.