Oxygen and carbon dioxide dual gas-responsive and switchable microgels prepared from emulsion copolymerization of fluoro- and amino-containing monomers

Development and Applications of CO2-Responsive Gels in CO2 Flooding and Geological Storage

Gel systems are widely used as plugging materials in the oil and gas industry. Gas channeling can be mitigated by reducing the heterogeneity of the formation and the mobility ratio of CO2 to crude oil. Cracks and other CO2 leaking pathways can be plugged during the geological storage of CO2 to increase the storage stability. By adding CO2-responsive groups to the classic polymer gel's molecular chain, CO2 responsive gel is able to seal and recognize CO2 in the formation while maintaining the superior performance of traditional polymer gel. The application of CO2 responsive gels in oil and gas production is still in the stage of laboratory testing on the whole. To actually achieve the commercial application of CO2 responsive gels in the oil and gas industry, it is imperative to thoroughly understand the CO2 responsive mechanisms of the various types of CO2 responsive gels, as well as the advantages and drawbacks of the gels and the direction of future development prospects. This work provides an overview of the research progress and response mechanisms of various types of CO2 responsive groups and CO2 responsive gels. Studies of the CO2 responsive gel development, injectivity, and plugging performance are comprehensively reviewed and summarized. The shortcomings of the existing CO2 responsive gels system are discussed and the paths for future CO2 responsive gel development are suggested.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Dual Gas-responsive Fluorescent Diblock Copolymer Synthesized via RAFT Polymerization

Stimulus-responsive polymers with luminescence properties have a wide range of applications in the fields of controlled drug release, fluorescent probes, and biological stents. In this paper, carbon dioxide (CO₂)/oxygen (O₂) dual-responsive fluorescent diblock copolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization method with two fluorescent monomers synthesized as its luminescence source, DEAEMA (CO₂ responsive monomer) and tFMA (O₂ responsive monomer). An experimental study demonstrated that the synthesized stimulus-responsive fluorescent polymer had a high sensitivity to CO₂; the double-responsive fluorescent diblock copolymer could form and achieve the reversal of polymer micelles in the aqueous solution when it was sequentially subjected to the introduction of CO₂ and O₂.

Morphology transformation of pillararene-based supramolecular nanostructures

In this feature article, the construction methods and the factors that influence the morphological transformation of pillararene-based supramolecular nanostructures are reviewed.

Carbon Dioxide and Nitrogen-Modulated Shape Transformation of Chitosan-Based Composite Nanogels

Chitosan/poly[N-(3-(dimethylamino)propyl)methacrylamide]/poly(acrylic acid) (CS/PDMAPMA/PAA) composite nanogels (CPACNGs) were fabricated in the solution of chitosan by surfactant-free emulsion polymerization. N-(3-(Dimethylamino)propyl)methacrylamide (DMAPMA) and acrylic acid (AA) were initiated by 2,2'-azobis-2-methyl-propanimidamide to graft from the backbone of chitosan. Nanogels were formed by noncovalent forces, including of hydrogen bonds, hydrophobic, and electrostatic interaction. Nanogels were characterized by transmission electron microscopy, scanning electron microscope dynamic light scattering, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer spectra, and 1H NMR. Spherical nanoparticles were observed in the latex system. Nanogels exhibited an excellent CO2 responsivity and CO2/N2 reversible response and switchability and had a faster response rate. The morphological shape transformation of nanogels was modulated by bubbling with CO2 and N2. The responsive mechanism was explored by determining the pH and electrical conductivity. In addition, nanogels were successfully emulsified by bubbling with CO2, and then a phase transition was achieved by bubbling with N2 in the organic solvent/water mixture.

CO2 switchable hollow nanospheres

HYPOTHESIS

Hollow nanospheres, characterized by a cavity inside a solid shell, have potential applications due to their unique structure, but the unchangeable morphology and permeability of the shell restrain their further practical utilization. While several smart hollow nanospheres that can respond to pH, ion strength, and temperature have been developed, they are inclined to suffer from problems associated with high energy consumption or the difficult removal of residual stimulants. Thus, it is desirable to develop a novel and free-of-residual trigger stimulating mode.

EXPERIMENTS

In this work, CO₂ is used to fabricate smart hollow nanospheres composed of crosslinked poly(diethylamino-ethyl methacrylate) (PDEAEMA) network from polystyrene (PS)/PDEAEMA core-shell nanospheres by a template-removal technique. The morphology evolution of the resultant nanospheres during the fabrication process was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TGA) and dynamic light scattering (DLS) and was visualized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

FINDINGS

Hollow nanospheres can be generated by experiencing a morphology change from a core nanosphere, core-shell, yolk-shell to a final hollow structure. The increase in shell-stiffness can restrain the collapse of hollow spheres. It is demonstrated that CO₂ is easy to introduce and remove (via N₂ input) without stimulation residues in this system. In addition, mild CO₂/N₂ purging can only reversibly change the swelling/collapse of hollow particles; violent CO₂/N₂ bubbling can reversibly regulate both the size and aggregation/re-dispersion state of the hollow nanospheres, which can be intuitively observed by atomic force microscopy (AFM).

Synthesis and characterization of CO2-sensitive temperature-responsive catalytic poly(ionic liquid) microgels

A class of poly(ionic liquid) microgels exhibiting CO₂-switchable temperature-responsive volume phase transition behavior have been synthesized and used for CO₂ fixation.

Thermoresponse and self-assembly of an ABC star quarterpolymer with O2 and redox dual-responsive Y junctions

The stimuli-tunable LCST-type phase transition and self-assembly behaviors of a multi-responsive 3-miktoarm star bearing O₂/redox-sensitive and H-bond-switchable Y junctions were revealed.

CO2-Switchable Membranes Prepared by Immobilization of CO2-Breathing Microgels

Herein, we report the development of a novel CO₂-responsive membrane system through immobilization of CO₂-responsive microgels into commercially available microfiltration membranes using a method of dynamic adsorption. The microgels, prepared from soap-free emulsion polymerization of CO₂-responsive monomer 2-(diethylamino)ethyl methacrylate (DEA), can be reversibly expanded and shrunken upon CO₂/N₂ alternation. When incorporated into the membranes, this switching behavior was preserved and further led to transformation between microfiltration and ultrafiltration membranes, as indicated from the dramatic changes on water flux and BSA rejection results. This CO₂-regulated performance switching of membranes was caused by the changes of water transportation channel, as revealed from the dynamic water contact angle tests and SEM observation. This work represents a simple yet versatile strategy for making CO₂-responsive membranes.

Highly Porous Poly(high internal phase emulsion) Membranes with "Open-Cell" Structure and CO2-Switchable Wettability Used for Controlled Oil/Water Separation

Polymer membranes with switchable wettability have promising applications in smart separation. Hereby, we report highly porous poly(styrene-co-N,N-(diethylamino)ethyl methacrylate) (i.e., poly(St-co-DEA)) membranes with "open-cell" structure and CO₂-switchable wettability prepared from water-in-oil (W/O) high internal phase emulsion (HIPE) templates. The open-cell porous structure facilitates fluid penetration through the membranes. The combination of CO₂-switchable functionality and porous microstructure enable the membrane with CO₂-switchable wettability from hydrophobic or superoleophilic to hydrophilic or superoleophobic through CO₂ treatment in an aqueous system. This type of membrane can be used for gravity-driven CO₂-controlled oil/water separation, in which oil selectively penetrates through the membrane and separates from water. After being treated with CO₂ switching wettability of the membrane, a reversed separation of water and oil can be achieved. Such a wettability switch is fully reversible, and the membrane could be regenerated through simple removal of CO₂ and oil residual through drying. This facile and cost-effective approach represents the development of the first CO₂-switchable polyHIPE system, which is promising for smart separation in a large volume.

Breathable Microgel Colloidosome: Gas-Switchable Microcapsules with O2 and CO2 Tunable Shell Permeability for Hierarchical Size-Selective Control Release

Microcapsules enabling precise delivery and controlled release are highly desirable. However, it is still challenging to control the release profile by regulating the microcapsule shell permeability. In this work, gas-switchable microgel colloidosome (MGC) with oxygen (O₂) and carbon dioxide (CO₂) dual gas-tunable shell permeability has been developed and tested for control release of water-soluble cargo molecules, based on the size exclusion mechanism. The O₂ and CO₂ dual gas-switchable poly(2-(diethylamino)ethyl methacrylate-co-2,3,4,5,6-pentafluorostyrene), P(DEA-co-FS), microgels having surface modified with amino group (-NH₂) were synthesized and used to stabilize oil-in-water (O/W) Pickering emulsions. The oil-soluble poly(propylene glycol) diglycidyl ether (PPGDGE) was added as an intermicrogel cross-linker. The cross-linking between adjacent microgel particles at the water-oil interface was achieved through the amine-epoxy reaction of PPGDGE with the amine groups at the particle surface. Fluorescent-labeled dextran model cargo molecules of 10 kDa (D₁) and 2000 kDa (D₂) were uploaded under CO₂ treatment and locked inside the MGC with N₂ treatment. The O₂ and CO₂ dual-gas switchable properties offered the MGC with tunable shell permeability, which allowed the hierarchical release of D₁ and D₂ based on size exclusive mechanism. This work provides a robust method for preparation of gas-switchable microcapsules with tunable permeability and size-exclusive hierarchical release profile, promising for multiple ingredient controllable release, separation, and reaction.

Gas-Responsive Polymers

Gas-responsive polymers have inspired much interest over the past ten years. Gas triggers can interact with functionalities on polymer chains and, thus, modulate their chain structures, architectures, and aggregation states. This review summarizes the latest research progresses in the theme of developing different gas triggers for fine control over some critical properties of polymers, as well as their potential applications in various areas. We focus on the interactions/reactions between gases and gas-responsive functionalities of polymers and highlight some state-of-art developments, which provided good insight and understanding of each particular gas-responsive polymer. We also offer a perspective point of view on future research directions on gas-responsive polymers, both in fundamental studies and in potential application developments.

CO2-Responsive fluorescent hyperbranched poly(ether amine)s

Hyperbranched polymers bearing a fluorophore display gas-controlled fluorescence switching as a result of reversible protonation/deprotonation of amino groups in their structure.

Oxygen and carbon dioxide dual gas-responsive homopolymers and diblock copolymers synthesized via RAFT polymerization

This article reports a new strategy to prepare homopolymers with CO₂ and O₂ responsiveness via the installation of CO₂- and O₂-responsive functionalities in the same repeated unit.

Post-synthetic modification of polyvinyl alcohol with a series of N-alkyl-substituted carbamates towards thermo and CO2-responsive polymers

Intensive efforts have been devoted to the synthesis of thermoresponsive polymers with terminal N-alkyl-substituted groups.

CO2-Responsive polymer materials

This paper reviews the chemical fundamentals of CO₂-responsive polymers as well as the latest reported “smart” material systems switched by CO₂.

CO2-Responsive graft copolymers: synthesis and characterization

The synthesis and self-assembly study of CO₂-responsive graft copolymers fabricated from a “graft-to” strategy based on pentafluorophenyl esters as grafting sites.

CO2-Responsive polymer membranes with gas-tunable pore size

A novel type of CO₂-responsive polymer membrane shows gas-tunable pore size that can be used for size exclusion-based filtration of gold nanoparticles.

Oxygen and Carbon Dioxide Dual Gas-Switchable Thermoresponsive Homopolymers

Herein, we report the first oxygen (O₂) and carbon dioxide (CO₂) dual gas-switchable thermoresponsive polymers based on a newly synthesized monomer N-(2-fluoroethyl amide)-N-(2-(diethylamino)ethyl) acrylamide, that is, AM(F1EA-DEAE), which bears both O₂-switchable fluorinated ethyl amide (F1EA) and CO₂-switchable N,N-diethylamino ethyl (DEAE) moieties on its side chain. PolyAM(F1EA-DEAE) samples prepared from reversible addition-fragmentation chain transfer (RAFT) polymerization exhibited good temperature-responsive properties. Their inherent low critical solution temperature (LCST) could be reversibly tuned to different levels by respectively purging O₂ or CO₂ into its aqueous solution. The O₂-treatment shifted LCST to a higher temperature, while the CO₂-treatment made the polymer fully water-soluble. The polymer could be readily recovered to its initial state by washing off the trigger gas with an inert gas such as nitrogen. This work provides an effective monomer design approach for the preparation of O₂ and CO₂ dual gas-responsive polymers.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

CO2 is an ideal trigger for switchable or stimuli-responsive materials because it is benign, inexpensive, green, abundant, and does not accumulate in the system. Many different CO2-responsive materials including polymers, latexes, solvents, solutes, gels, surfactants, and catalysts have been prepared. This review focuses on the preparation, self-assembly, and functional applications of CO2-responsive polymers. Detailed discussion is provided on the synthesis of CO2-responsive polymers, in particular using reversible deactivation radical polymerization (RDRP), formerly known as controlled/living radical polymerization (CLRP), a powerful technique for the preparation of well-defined (co)polymers with precise control over molecular weight distribution, chain-end functional groups, and polymer architectural design. Self-assembly in aqueous dispersed media is highlighted as well as emerging potential applications.

CO2-switchable fluorescence of a dendritic polymer and its applications

The synthesis and properties of CO2 responsive and fluorescent dendritic polymers, poly(amido amine)/Pluronic F127 (PAMAM/F127), are reported in this paper. The morphologies and sizes of PAMAM/F127 dendritic polymers were investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). PAMAM/F127 dendritic polymers showed unimolecular micelle morphologies at low concentrations, and changed to multimolecular micelles at higher concentrations. Additionally, fluorescence spectra and confocal laser scanning microscopy images showed that PAMAM/F127 dendritic polymers exhibited a fluorescent enhancement response to the presence of CO2. Apart from that, the release behavior of PAMAM/F127 gels under simulated body fluids was investigated by choosing curcumin as the hydrophobic drug. The results indicated that PAMAM/F127 dendritic polymers can be used to improve the solubility of curcumin, and the drug released faster in the presence of CO2. Such CO2 responsive fluorescent dendritic polymers are potentially applicable in cellular imaging or drug controlled release.

Oxygen-switchable thermo-responsive random copolymers

In this paper, we report the synthesis of oxygen (O₂)-switchable thermo-responsive random copolymers based on fluorinated acrylamide monomer homologues: N-(2-fluoroethyl)acrylamide (F1EA), N-(2,2-difluoroethyl)acrylamide (F2EA), and N-(2,2,2-trifluoroethyl)acrylamide (F3EA).