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

Development of an orbital shaker-assisted fatty acid-based switchable solvent microextraction procedure for rapid and green extraction of amoxicillin from complex matrices: Central composite design

In this study, a cheap, fast and simple orbital shaker-assisted fatty acid-based switchable solvent microextraction (OS-FASS-ME) procedure was developed for the extraction of amoxicillin (AMOX) in dairy products, pharmaceutical samples and wastewater prior to its spectrophotometric analysis. Fatty acid-based switchable solvents were investigated for extracting AMOX. The key factors of the OS-FASS-ME procedure were optimized using a central composite design. The linearity of OS-FASS-ME procedure was in the range 5-600 ng mL-1 with a correlation coefficient of 0.991. In five replicate experiments for 20 ng mL-1 of AMOX solution, the recovery and relative standard deviation were 95.8% and 2.2%, respectively. Limits of detection and quantification were found 1.5 ng mL-1 and 5 ng mL-1, respectively. The accuracy, precision, robustness and selectivity of the OS-FASS-ME procedure were investigated in detail under optimum conditions. The OS-FASS-ME procedure was applied to milk, cheese, wastewater, syrups and tablets. A comparison of the results obtained from the reference method and the OS-FASS-ME method showed that the OS-FASS-ME procedure can be successfully applied to complex matrices.

Review of ionic liquid and ionogel-based biomaterials for advanced drug delivery

Ionic liquids (ILs) play a crucial role in the design of novel materials. The ionic nature of ILs provides numerous advantages in drug delivery, acting as a green solvent or active ingredient to enhance the solubility, permeability, and binding efficiency of drugs. They could also function as a structuring agent in the development of nano/micro particles for drug delivery, including micelles, vesicles, gels, emulsion, and more. This review summarize the ILs and IL-based gel structures with their advanced drug delivery applications. The first part of review focuses on the role of ILs in drug formulation and the applications of ILs in drug delivery. The second part of review offers a comprehensive overview of recent drug delivery applications of IL-based gel. It aims to offer new perspectives and attract more attention to open up new avenues in the biomedical applications of ILs and IL-based gels.

Gas-Responsive and Gas-Releasing Polymer Assemblies

In order to explore the unique physiological roles of gas signaling molecules and gasotransmitters in vivo, chemists have engineered a variety of gas-responsive polymers that can monitor their changes in cellular milieu, and gas-releasing polymers that can orchestrate the release of gases. These have advanced their potential applications in the field of bio-imaging, nanodelivery, and theranostics. Since these polymers are of different chain structures and properties, the morphology of their assemblies will manifest distinct transitions after responding to gas or releasing gas. In this review, we summarize the fundamental design rationale of gas-responsive and gas-releasing polymers in structure and their controlled transition in self-assembled morphology and function, as well as present some perspectives in this prosperous field. Emerging challenges faced for the future research are also discussed.

Engineering Dual CO2- and Photothermal-Responsive Membranes for Switchable Double Emulsion Separation

Stimulus-responsive membranes demonstrate promising applications in switchable oil/water emulsion separations. However, they are unsuitable for the treatment of double emulsions like oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) emulsions. For efficient separation of these complicated emulsions, fine control over the wettability, response time, and aperture structure of the membrane is required. Herein, dual-coated fibers consisting of primary photothermal-responsive and secondary CO2-responsive coatings are prepared by two steps. Automated weaving of these fibers produces membranes with photothermal- and CO2-responsive characteristics and narrow pore size distributions. These membranes exhibit fast switching wettability between superhydrophilicity (under CO2 stimulation) and high hydrophobicity (under near-infrared stimulation), achieving on-demand separation of various O/W/O and W/O/W emulsions with separation efficiencies exceeding 99.6%. Two-dimensional low-field nuclear magnetic resonance and correlated spectra technique are used to clarify the underlying mechanism of switchable double emulsion separation. The approach can effectively address the challenges associated with the use of stimulus-responsive membranes for double emulsion separation and facilitate the industrial application of these membranes.

pH-Controllable Redox Responsive Amphiphilic Viologens for Switchable Emulsions

A pH and redox dual responsive amphiphilic viologen is synthesized, which can be reversibly transformed among the zwitterionic (SVa), monovalent anionic (SV+), and divalent anionic (SVH2+) forms upon pH variation, exhibiting pH-controllable redox responsive properties. Switchable Pickering emulsions with different droplet size and viscosity are prepared by the mixture of hydrophilic silica nanoparticles and the viologens (SV+ or SVH2+) at acidic conditions, while such combination yielded an oil-in-dispersion emulsion at neutral pH value. Not only can rapid reversible demulsification/stabilization of the Pickering emulsions be achieved by redox reactions, but the rate of redox-demulsification can also be controlled by pH trigger. The dual-responsive amphiphilic viologens have potential applications in developing intelligent colloid materials and molecular logic systems.

Simultaneous switching of two different CO2-switchable amines in the same solution

Most CO2-responsive systems operate by using a base in water that is expected to be mostly deprotonated when under an atmosphere of air and mostly protonated under an atmosphere of CO2. This concept has led to the development of many different CO2-responsive materials such as solvents, polymers, surfactants, and solutes. As CO2-responsive materials research continues, more complex systems may be developed, including systems containing two different bases with different basicities. Understanding the influence each base has on the protonation equilibrium of the other base is important for designing systems in which effective deprotonation and protonation occur. This article presents a model that can predict the solution pH and the % protonation of two different bases at various concentrations under air and CO2. Experimental data was collected to demonstrate the successful simultaneous switching of two amines and to evaluate the accuracy of the predictive model. The simultaneous switching of two different CO2-switchable amines in the same solution was determined to be possible but only if the amine concentrations and basicities are within certain ranges, and only if the pKaH values of the two bases differ by no more than 3 units.

CO2-Responsive Water-Soluble Conjugated Polymers as a Multifunctional Fluorescent Probe for Bioimaging Applications

We describe important progress in the synthesis and development of gas-responsive water-soluble conjugated polymers (WSCPs) with potential as multifunctional fluorescent materials for biomedical imaging and probes. A water-soluble WSCP (I-PT) composed of a hydrophobic fluorescent polythiophene backbone and a hydrophilic imidazole side chain was successfully prepared through a facile and efficient two-step synthetic route. Owing to the repulsive force between the hydrophilic and hydrophobic segments and the highly sensitive carbon dioxide (CO2)- and nitrogen (N2)-responsive imidazole groups in its structure, I-PT can spontaneously self-assemble into spherical-like nanoparticles in an aqueous environment, and thus exhibits unique light absorption and fluorescence properties as well as rapid responsiveness to CO2 and N2. In addition, its structure, optical absorption/fluorescence behavior, and surface potential can be quickly turned on and off through alternating cycles of CO2 and N2 bubbling and exhibit controllable cyclic switching stability, thereby allowing effective manipulation of its hierarchical structure and chemical-physical characteristics. More importantly, a series of in vitro cell experiments confirmed that, compared to the significant cytotoxicity of pristine and N2-treated I-PT nanoparticles, CO2-treated I-PT nanoparticles exhibit extremely low cytotoxicity in normal and cancer cells and undergo greatly accelerated cellular uptake, resulting in a significant increase in the intensity and stability of their fluorescence signal in the intracellular environment. Overall, this newly discovered CO2/N2-responsive system provides new insights to effectively enhance the biocompatibility, cellular internalization, and intracellular fluorescence characteristics of WSCPs and holds great potential for biomedical imaging/sensing applications.

A review of stimuli-responsive polymer-based gating membranes

The formation and properties of smart (stimuli-responsive) membranes are reviewed, with a special focus on temperature and pH triggering of gating to water, ions, polymers, nanoparticles, or other molecules of interest. The review is organized in two parts, starting with all-smart membranes based on intrinsically smart materials, in particular of the poly(N-isopropylacrylamide) family and similar polymers. The key steps of membrane fabrication are discussed, namely the deposition into thin films, functionalization of pores, and the secondary crosslinking of pre-existing microgel particles into membranes. The latter may be free-standing and do not necessitate the presence of a porous support layer. The temperature-dependent swelling properties of polymers provide a means of controlling the size of pores, and thus size-sensitive gating. Throughout the review, we highlight "positive" (gates open) or "negative" (closed) gating effects with respect to increasing temperature. In the second part, the functionalization of porous organic or inorganic membranes of various origins by either microgel particles or linear polymer brushes is discussed. In this case, the key steps are the adsorption or grafting mechanisms. Finally, whenever provided by the authors, the suitability of smart gating membranes for specific applications is highlighted.

Computational Insights into a CO2-Responsive Emulsion Prepared Using the Superamphiphile Assembled by Electrostatic Interactions

The superamphiphiles exhibit broad prospects for fabricating stimuli-responsive emulsions. Because the superamphiphiles are assembled via noncovalent interactions, they have the advantage of fast response and high efficiency. Recently, a series of switchable emulsions using CO2-responsive superamphiphiles have been developed, which extends the applications of CO2-responsive materials in widespread field. However, there is still a lack of fundamental understanding on the switching mechanism related to the assembled structure of superamphiphiles at the oil-water interface. We employed molecular dynamics (MD) simulations to investigate the reversible emulsification/demulsification process of a responsive emulsion system stabilized by a recently developed responsive superamphiphile (BTOA), which consists of oleic acid (OA) and cationic amine (named 1,3-bis(aminopropyl)tetramethyldisiloxane, BT). The simulation results present the morphologies in both the emulsion and demulsification states. It is found that the ionized OA- and the protonated BT+ together form an adsorption layer at the oil-water interface. The hydrophobic parts of BT+ are inserted into the adsorption layer, and the two amine groups contact the water phase. This adsorption layer reduces the interfacial tension and stabilizes the emulsion. After the bubbling of CO2, the surfactants were fully protonated to OA and BT2+. Because of the changes in the molecular polarity, OA and BT2+ entered the oil and water phases, respectively, resulting in demulsification. The structural and dynamical properties were analyzed to reveal the different intermolecular interactions that were responsible for the reversible reversibility of the emulsion. The observations are considered to be complementary to experimental studies and are expected to provide deeper insights into studies on developing responsive materials via supramolecular assemblies.

Chitosan modified multi-walled carbon nanotubes and arginine aerogel for enhanced carbon capture

Global warming is emerging as a significant issue because of increasing CO2 levels in the atmosphere due to urbanization, industrialization, and fossil-fuel usage. Therefore, reducing atmospheric CO2 levels using new materials with high carbon capture capacity and efficient CO2 capture technologies is essential. Herein, we propose a hybrid chitosan (CS) aerogel containing multi-walled carbon nanotubes (MWCNTs) and an arginine (Arg) aerogel (CSCNTArg aerogel) for efficient carbon capture. This aerogel was successfully synthesized using a cross-linker reagent via step-freeze drying method. Fourier-transform infrared spectroscopy and X-ray diffraction analyses confirmed the successful grafting of CS, MWCNTs, and Arg onto the CSCNTArg aerogel. The thermogravimetric analysis (TGA) confirmed good thermal stability up to 500 °C of the as-developed aerogel. Field-emission scanning electron microscopy showed that the surface morphology of the CSCNTArg aerogel differed from that of CS, Arg, and MWCNTs with pores on their surfaces. N2 and CO2 adsorption-desorption studies on the CSCNTArg aerogel were performed using the Brunauer-Emmett-Teller method and TGA, respectively. The CSCNTArg aerogel showed a high adsorption capacity of approximately 5.00 mmol g-1 at 35 °C. Therefore, this new material may be useful for facilitating high-efficiency CO2 adsorption to reduce atmospheric carbon footprint.

Flexible nanofibrous membranes of dual metallic metal-organic framework with enhanced Lewis basic sites and high loading mass for efficient CO2 capture

Excessive CO2 emissions and the resultant global warming present significant environmental challenges, posing threats to human health and public safety. Metal-organic frameworks (MOFs), known for their high specific area and large porosity, hold the promise for CO2 capture. However, a major obstacle is the low loading mass of MOFs and the limited interface affinity and compatibility between MOFs and substrates. In this study, we present an electrospinning-assisted in-situ synthesis dual metallic framework strategy for preparing flexible Zn/Co-ZIF nanofibrous membranes (NFMs). This method achieves the high loading mass of MOFs and introduces abundant Lewis basic sites, thereby enhancing the CO2 adsorption. The dual metallic Zn/Co-ZIF NFMs exhibit remarkable features, including high MOF loading mass (70.23 wt%), high specific surface area (379.63 m2g-1), large porosity (92.34 %), high CO2 adsorption capacity (4.43 mmol/g), high CO2/N2 adsorption selectivity (37), and high CO2/CH4 adsorption selectivity (31). Moreover, the dual metallic Zn/Co-ZIF NFMs demonstrate robust structural stability and durability attributed to the excellent interface affinity between MOFs and NFMs, retaining 96.56 % of their initial capacity after 10 adsorption-desorption cycles. This work presents a prospective direction for developing flexible dual metallic MOF NFMs for the efficient capture of CO2.

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-Switchable colloids

The development and design of CO2-switchable colloidal particles is described. A presentation of the principles of CO2 switching, especially as they apply to colloids, is followed by recent progress in the preparation of several types of colloidal particles (polymer nanoparticles, metal-organic frameworks (MOFs), quantum dots, graphene, cellulose nanocrystals, carbon nanotubes) for various applications (Pickering stabilizers, catalysts, latexes), and our perspective on future opportunities.

Facile one-pot multicomponent synthesis of peptoid based gelators as novel scaffolds for drug incorporation and pH-sensitive release

Infections caused by bacteria are the primary cause of illness and death globally, and antibiotics are the most commonly used medications to treat them. However, there are certain inherent problems in administering these drugs without any changes to their effectiveness. In order to sustain the targeted dosage over time, the use of a biocompatible local drug delivery system using low molecular mass gelators is preferred as a potential approach to reduce its side effects. Low molecular weight organic gelators (LMWOGs) have drawn a lot of attention due to their numerous and varied applications in multiple fields. But nowadays its quite a challenging task to synthesize new types of LMWOGs that can fill the significant gap towards potential applications. In this work, we have explored a multicomponent pathway for the synthesis of a small repertoire of peptoids from simple building blocks by a one-pot Ugi reaction. A variety of novel effective low molecular weight organic gelators have been synthesized, leading to the formation of stable self-assembled aggregates in various solvents such as DMSO, aqueous DMSO, and methanol. Consequently, these aggregates give rise to the creation of organogels and organo/hydrogels. The gels have a minimum gelation concentration (MGC) of 1-2% w/v with high thermal stability. Furthermore, successful encapsulation and release of metronidazole (MZ) were achieved within the gel matrix under physiological pH conditions at 37 °C, ensuring the preservation of its structural and functional properties. The results demonstrated that the release rate of MZ from the organo/hydrogels is contingent on pH, exhibiting a gradual and regulated release in mild alkaline environments. Moreover, the devised system displayed noteworthy antimicrobial efficacy against E. coli, underscoring the potential of these novel low molecular weight organic gels (LMWOGs) as effective drug delivery systems in the pharmaceutical industry. The gel formulations exhibit biocompatibility and negligible cytotoxicity, as evidenced by cell viability studies conducted using the MTT assay.

Biomimetic materials in oil/water separation: Focusing on switchable wettabilities and applications

Clean water resources are crucial for human society, as the leakage and discharge of oily wastewater not only harm the economy but also disrupt our living environment. Therefore, there is an urgent need for efficient oil-water separation technology. Surfaces with switchable superwetting behavior have garnered significant attention due to their importance in both fundamental research and practical applications. This review introduces the fundamental principles of wettability in the oil-water separation process, the basic theory of switchable wettability, and the mechanisms involved in oil-water separation. Subsequently, the review discusses the research progress, challenges, and issues associated with three conventional types of special wettability materials: superhydrophobic/superoleophilic materials, superhydrophilic/superoleophobic materials, and superhydrophilic/underwater superoleophobic materials. Most importantly, it provides a detailed exploration of recent advancements in switchable wettability smart materials, which combine elements of traditional special wettability materials. These include stimulus-responsive smart materials, pre-wetting-induced materials, and Janus materials. The discussion covers key response factors, detailed examples of representative works, design concepts, and fabrication strategies. Finally, the review offers a comprehensive summary of switchable superwetting smart materials, encompassing their advantages and disadvantages, persistent challenges, and future prospects.

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).

Supramolecular design of CO2-responsive lipid nanomaterials

HYPOTHESIS

Stimuli-responsive materials can innovate in various fields, including food and pharmaceutical sciences. Their response to a specific stimulus can be utilized to release loaded bioactive molecules or sense their presence. The biocompatibility and abundance of CO₂ in the environment make it an exciting stimulus for such applications. We hypothesize the formation of CO₂-responsive self-assemblies of oleyl-amidine in water. Their integration into glycerol-monooleate-based (GMO) dispersions is further thought to form CO₂-switchable liquid crystalline nanoparticles. The switch from an non-charged acetamidine surfactant to its cationic amidinium form triggers curvature changes that ultimately induces phase transitions.

EXPERIMENTS

The CO₂-switchable lipid (E)-N,N-dimethyl-N-((Z)-octadec-9-en1-yl)acetimidamide (OAm) is synthesized and formulated into emulsions and dispersed liquid crystals with GMO. The supramolecular structure and its response to CO₂ are characterized using small angle X-ray scattering, dynamic light scattering, ζ-potential measurements and cryogenic transmission electron microscopy.

FINDINGS

Depending on the composition, OAm is discovered to self-assemble into a variety of CO₂-responsive lyotropic liquid crystalline structures that can be dispersed in excess water. CO₂-triggered colloidal transformations from unstructured OAm-in-water emulsions to direct micelles; dispersed inverse hexagonal phase to direct rod-like micelles, and sponge phase to vesicles are discovered. These structural changes are driven by the reaction of OAm's amidine headgroup with CO₂. The results provide a fundamental understanding of CO₂-triggered functional nanomaterials and may guide their future design into delivery platforms and biosensors.

In Vitro Release and In Vivo Pharmacokinetics of Praziquantel Loaded in Different Polymer Particles

Approximately 1 billion people are affected by neglected diseases around the world. Among these diseases, schistosomiasis constitutes one of the most important public health problems, being caused by Schistosoma mansoni and treated through the oral administration of praziquantel (PZQ). Despite being a common disease in children, the medication is delivered in the form of large, bitter-tasting tablets, which makes it difficult for patients to comply with the treatment. In order to mask the taste of the drug, allow more appropriate doses for children, and enhance the absorption by the body, different polymer matrices based on poly(methyl methacrylate) (PMMA) were developed and used to encapsulate PZQ. Polymer matrices included PMMA nano- and microparticles, PMMA-co-DEAEMA (2-(diethylamino)ethyl methacrylate), and PMMA-co-DMAEMA (2-(dimethylamino)ethyl methacrylate) microparticles. The performances of the drug-loaded particles were characterized in vitro through dissolution tests and in vivo through pharmacokinetic analyses in rats for the first time. The in vitro dissolution studies were carried out in accordance with the Brazilian Pharmacopeia and revealed a good PZQ release profile in an acidic medium for the PMMA-DEAEMA copolymer, reaching values close to 100 % in less than 3 h. The in vivo pharmacokinetic analyses were conducted using free PZQ as the control group that was compared with the investigated matrices. The drug was administered orally at doses of 60 mg/kg, and the PMMA-co-DEAEMA copolymer microparticles were found to be the most efficient release system among the investigated ones, reaching a C_max value of 1007 ± 83 ng/mL, even higher than that observed for free PZQ, which displayed a C_max value of 432 ± 98 ng/mL.

Application of Recently used Green Solvents in Sample Preparation Techniques: A Comprehensive Review of Existing Trends, Challenges, and Future Opportunities

Green solvents (GSs) has gained significant attention in recent years due to their potential as safer and more sustainable alternatives to traditional organic solvents. Solvents are used in a wide range of applications, from industrial processes to everyday products. Solvent emissions and losses can have a significant impact on the environment and human health, which is why many initiatives are being undertaken to get rid of or switch to eco-friendly alternatives. A key area of green chemistry that led to the concept of "green" solvents is the development of alternative solvents that are less toxic and more environmentally friendly than traditional organic solvents. The advantages of using green solvents over conventional ones are their environmental friendliness, biocompatibility, biodegradability, and simplicity of preparation. Different sample preparation techniques have successfully utilized green solvents to offer a sustainable separation media for the extraction of a variety of inorganic and organic compounds which are crucial for research in environmental samples. Recent developments in green analytical chemistry (GAC) have focused on how to prepare and use samples using environmentally sustainable solvents. The current study covers the advance and currently used green solvents with an emphasis on environmentally friendly sample preparation methods. This review aims to briefly summarize the current state of knowledge about the use of green solvents particularly ionic liquids, deep eutectic solvents and switchable solvents (SSs) with the perspective of GAC in sample preparation methods.

Scalable and switchable CO2-responsive membranes with high wettability for separation of various oil/water systems

Smart membranes with responsive wettability show promise for controllably separating oil/water mixtures, including immiscible oil-water mixtures and surfactant-stabilized oil/water emulsions. However, the membranes are challenged by unsatisfactory external stimuli, inadequate wettability responsiveness, difficulty in scalability and poor self-cleaning performance. Here, we develop a capillary force-driven confinement self-assembling strategy to construct a scalable and stable CO₂-responsive membrane for the smart separation of various oil/water systems. In this process, the CO₂-responsive copolymer can homogeneously adhere to the membrane surface by manipulating the capillary force, generating a membrane with a large area up to 3600 cm² and excellent switching wettability between high hydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity under CO₂/N₂ stimulation. The membrane can be applied to various oil/water systems, including immiscible mixtures, surfactant-stabilized emulsions, multiphase emulsions and pollutant-containing emulsions, demonstrating high separation efficiency (>99.9%), recyclability, and self-cleaning performance. Due to robust separation properties coupled with the excellent scalability, the membrane shows great implications for smart liquid separation.

A CO2-Responsive Imidazole-Functionalized Fluorescent Material Mediates Cancer Chemotherapy

We present a breakthrough in the synthesis and development of functional gas-responsive materials as highly potent anticancer agents suitable for applications in cancer treatment. Herein, we successfully synthesised a stimuli-responsive multifunctional material (I-R6G) consisting of a carbon dioxide (CO₂)-sensitive imidazole moiety and spirolactam-containing conjugated rhodamine 6G (R6G) molecule. The resulting I-R6G is highly hydrophobic and non- or weakly fluorescent. Simple CO₂ bubbling treatment induces hydrophobic I-R6G to completely dissolve in water and subsequently form self-assembled nanoparticles, which exhibit unique optical absorption and fluorescence behaviours in water and extremely low haemolytic ability against sheep red blood cells. Reversibility testing indicated that I-R6G undergoes reversible CO₂/nitrogen (N₂)-dependent stimulation in water, as its structural and physical properties can be reversibly and stably switched by alternating cycles of CO₂ and N₂ bubbling. Importantly, in vitro cellular assays clearly demonstrated that the CO₂-protonated imidazole moiety promotes rapid internalisation of CO₂-treated I-R6G into cancer cells, which subsequently induces massive levels of necrotic cell death. In contrast, CO₂-treated I-R6G was not internalised and did not affect the viability of normal cells. Therefore, this newly created system may provide an innovative and efficient route to remarkably improve the selectivity, safety and efficacy of cancer treatment.

Advanced Formulations Based on Poly(ionic liquid) Materials for Additive Manufacturing

Innovation in materials specially formulated for additive manufacturing is of great interest and can generate new opportunities for designing cost-effective smart materials for next-generation devices and engineering applications. Nevertheless, advanced molecular and nanostructured systems are frequently not possible to integrate into 3D printable materials, thus limiting their technological transferability. In some cases, this challenge can be overcome using polymeric macromolecules of ionic nature, such as polymeric ionic liquids (PILs). Due to their tuneability, wide variety in molecular composition, and macromolecular architecture, they show a remarkable ability to stabilize molecular and nanostructured materials. The technology resulting from 3D-printable PIL-based formulations represents an untapped array of potential applications, including optoelectronic, antimicrobial, catalysis, photoactive, conductive, and redox applications.

In-situ Spontaneous Fabrication of Tough and Stretchable Polyurethane-Polyethyleneimine Hydrogels Selectively Triggered by CO2

We develop CO₂ -triggered in-situ hydrogels from waterborne poly(ε-caprolactone)-based polyurethane (PU) dispersion and aqueous polyethyleneimine (PEI) solution without any other chemicals and apparatus (e.g., UV light). In our approach, non-toxic CO₂ in air is used as a selective trigger for the hydrogel formation. CO₂ adsorption onto PEI results in the formation of ammonium cations in PEI and the subsequent multiple ionic crosslinking between PU and PEI chains. Besides the amount of CO₂ in air, the rate of hydrogel formation can be controlled by NaHCO₃ in the PU-PEI mixture, which serves as a CO₂ supplier. The PU hydrogels exhibit tough and stretchable properties with high tensile strength (2.05 MPa) and elongation at break (438.24%), as well as biocompatibility and biodegradability. In addition, the PU hydrogels exhibit high adhesion strength on skin and injectability due to the in-situ formation. We believe that these PU hydrogels have the ideal features for various future applications, such as tissue adhesion barriers, wound dressing, artificial skin, and injectable fillers. This article is protected by copyright. All rights reserved.

Effects of cyclic and acyclic amidine side-chains on the properties of polysiloxane ionomers constructed in situ from three uncharged components

Ionomers, polysiloxanes with imidazolinium dithiocarbamate side chains, have been synthesized in situ from three uncharged components-a polysiloxane with imidazole side chains, CS₂, and hexylamine or octadecylamine. Their structural and dynamic properties are compared over a temperature range of 0-50 °C with those of the analogous ionomers in which the polysiloxanes have amidinium side chains. The results, primarily from differential scanning calorimetry, powder X-ray diffraction measurements, and rheology show that the small structural (and smaller electronic) differences between the cyclic 5-membered ring imidazolinium and acyclic amidinium groups have marked effects on the bulk properties of the ionomers. These include their shear strengths and the manner in which the microcrystalline portions of the ionomers with dithiooctadecylcarbamate anions are packed. Thus, it is possible to finely tune the natures of the ionomers from one polysiloxane by changing temperature, the chain length of the alkylamine, and the nature of the base attached to the polysiloxane chain. Why these changes occur to the various properties is discussed.

Electrical Response of Poly(N-[3-(dimethylamino)Propyl] Methacrylamide) to CO2 at a Long Exposure Period

Amine-functionalized polymers (AFPs) are able to react with carbon dioxide (CO₂) and are therefore useful in CO₂ capture and sensing. To develop AFP-based CO₂ sensors, it is critical to examine their electrical responses to CO₂ over long periods of time, so that the device can be used consistently for measuring CO₂ concentration. To this end, we synthesized poly(N-[3-(dimethylamino)propyl] methacrylamide) (pDMAPMAm) by free radical polymerization and tested its ability to behave as a CO₂-responsive polymer in a transducer. The electrical response of this polymer to CO₂ upon long exposure times was measured in both the aqueous and solid phases. Direct current resistance measurement tests on pDMAPMAm films printed along with the silver electrodes in the presence of CO₂ at various concentrations reveal a two-region electrical response. Upon continuous exposure to different CO₂ flow rates (at a constant pressure of 0.2 MPa), the resistance first decreased over time, reaching a minimum, followed by a gradual increase with further exposure to CO₂. A similar trend is observed when CO₂ is introduced to an aqueous solution of pDMAPMAm. The in situ monitoring of pH suggests that the change in resistance of pDMAPMAm can be attributed to the protonation of tertiary amine groups in the presence of CO₂. This two-region response of pDMAPMAm is based on a proton-hopping mechanism and a change in the number of free amines when pDMAPMAm is exposed to various levels of CO₂.

Solvent-assisted self-assembly of block copolymer thin films

Solvent-assisted block copolymer self-assembly is a compelling method for processing and advancing practical applications of these materials due to the exceptional level of the control of BCP morphology and significant acceleration of ordering kinetics. Despite substantial experimental and theoretical efforts devoted to understanding of solvent-assisted BCP film ordering, the development of a universal BCP patterning protocol remains elusive; possibly due to a multitude of factors which dictate the self-assembly scenario. The aim of this review is to aggregate both seminal reports and the latest progress in solvent-assisted directed self-assembly and to provide the reader with theoretical background, including the outline of BCP ordering thermodynamics and kinetics phenomena. We also indicate significant BCP research areas and emerging high-tech applications where solvent-assisted processing might play a dominant role.

Switched Proton Conduction in Metal-Organic Frameworks

Stimuli-responsive materials can respond to external effects, and proton transport is widespread and plays a key role in living systems, making stimuli-responsive proton transport in artificial materials of particular interest to researchers due to its desirable application prospects. On the basis of the rapid growth of proton-conducting porous metal-organic frameworks (MOFs), switched proton-conducting MOFs have also begun to attract attention. MOFs have advantages in crystallinity, porosity, functionalization, and structural designability, and they can facilitate the fabrication of novel switchable proton conductors and promote an understanding of the comprehensive mechanisms. In this Perspective, we highlight the current progress in the rational design and fabrication of stimuli-responsive proton-conducting MOFs and their applications. The dynamic structural change of proton transfer pathways and the role of trigger molecules are discussed to elucidate the stimuli-responsive mechanisms. Subsequently, we also discuss the challenges and propose new research opportunities for further development.

Tuning the High‐Pressure Phase Behaviour of Highly Compressible Zeolitic Imidazolate Frameworks: From Discontinuous to Continuous Pore Closure by Linker Substitution

The high‐pressure behaviour of flexible zeolitic imidazolate frameworks (ZIFs) of the ZIF‐62 family with the chemical composition M(im)_2−x(bim)_x is presented (M²⁺=Zn²⁺, Co²⁺; im⁻=imidazolate; bim⁻=benzimidazolate, 0.02≤x≤0.37). High‐pressure powder X‐ray diffraction shows that the materials contract reversibly from an open pore (op) to a closed pore (cp) phase under a hydrostatic pressure of up to 4000 bar. Sequentially increasing the bim⁻ fraction (x) reinforces the framework, leading to an increased threshold pressure for the op‐to‐cp phase transition, while the total volume contraction across the transition decreases. Most importantly, the typical discontinuous op‐to‐cp transition (first order) changes to an unusual continuous transition (second order) for x≥0.35. This allows finetuning of the void volume and the pore size of the material continuously by adjusting the pressure, thus opening new possibilities for MOFs in pressure‐switchable devices, membranes, and actuators.

Stimuli-Responsive Pickering Emulsions Regulated via Polymerization-Induced Self-Assembly Nanoparticles

With the development of reversible deactivated radical polymerization techniques, polymerization-induced self-assembly (PISA) is emerging as a facile method to prepare block copolymer nanoparticles in situ with high concentrations, providing wide potential applications in different fields, including nanomedicine, coatings, nanomanufacture, and Pickering emulsions. Polymeric emulsifiers synthesized by PISA have many advantages comparing with conventional nanoparticle emulsifiers. The morphologies, size, and amphiphilicity can be readily regulated via the synthetic process, post-modification, and external stimuli. By introducing stimulus responsiveness into PISA nanoparticles, Pickering emulsions stabilized with these nanoparticles can be endowed with "smart" behaviors. The emulsions can be regulated in reversible emulsification and demulsification. In this review, the authors focus on recent progress on Pickering emulsions stabilized by PISA nanoparticles with stimuli-responsiveness. The factors affecting the stability of emulsions during emulsification and demulsification are discussed in details. Furthermore, some viewpoints for preparing stimuli-responsive emulsions and their applications in antibacterial agents, diphase reaction platforms, and multi-emulsions are discussed as well. Finally, the future developments and applications of stimuli-responsive Pickering emulsions stabilized by PISA nanoparticles are highlighted.

Water treatment using stimuli-responsive polymers

Stimuli-responsive polymers are a new category of smart materials used in water treatment via a stimuli-induced purification process and subsequent regeneration processes.