Critical Solution Temperature Research Articles

Preparation and performance evaluation of intelligent plugging agent for thermo‐sensitive water‐based drilling fluid

AbstractIn the process of unconventional oil and gas exploitation, the invasion of a large amount of drilling fluid into the formation is one of the most critical reasons leading to wellbore instability. A temperature‐sensitive polymer (AOS) was synthesized from acrylamide, oligo (ethylene glycol) methyl ether methacrylate (OEGMA), and sodium p‐styrene sulfonate by emulsion polymerization. The material is a solid‐free fluid with good fluidity at room temperature, after injection into the formation, the fluid is gradually transformed into hard gel above the lower critical solution temperature (LCST) (90°C), thus blocking micro‐fractures and improving wellbore stability. Infrared and NMR characterization confirmed the successful preparation of the target product. The transmittance of AOS with ambient temperature was measured by UV–vis spectrophotometer, and the LCST behavior of AOS was verified by rheological and viscoelastic measurements. The interaction mechanism between AOS and sodium bentonite was evaluated according to the American Petroleum Institute standard. The results show that after aging at 180°C, the filtration loss is reduced by 93%, and the medium permeability (100, 200 mD) formation is effectively plugged, with a plugging efficiency is as high as 74.7%.

Synthesis of novel stimuli-responsive hydrogels based on polyurethane

This article describes the study of a thermo-responsive hybrid systems based on polyurethane (PU) modified with sensitive acrylamide derivates. The hybrid systems were synthesized using PU and two acrylamide derivatives (N-isopropylacrylamide (NIPA) and N-isopropylmethacrylamide (NIPMA)) in different proportions. The systems were characterized using infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic light scattering (DLS). Water-uptake capacity and sedimentation rate were also determined. The results showed that the hybrids with 30% acrylamide derivate (AD) showed a T50 of approximately 360 °C indicating that thermal degradation decreased with the addition of NIPA and NIPMA. Additionally, the incorporation of AD increases the glass transition temperature from −34 to −22 °C when 30% AD was used. The hybrids with 30% AD showed a variation in the diameters (above 60%) when the temperature was decreased from 50 to 22 °C. These changes were attributed to the hydrophilic → hydrophobic transition that occurs when measuring below and above the low critical solution temperature (LCST) of the polymer. Furthermore, the extra methyl group in the structure of NIPMA makes the collapse less pronounced than in NIPA, decreasing the relative diameter change by 10%. Sedimentation tests showed that the addition of the hybrid hydrogels in the sand increased the time of decantation by 60%. So, the combination of two thermo-responsive polymers to alter the hydrophilic/hydrophobic balance allows these polymers to modify their conformation at a specific temperature and could be potentially useful as self-suspending support agents or drug delivery systems.

Ion‐Mediated Gelation of Thermo‐Responsive Cellulose Nanofibril/Poly(N‐isopropylacrylamide) Hybrid Hydrogels with Tunable De‐Swelling Kinetics

AbstractThe tunability of the lower critical solution temperature (LCST) of poly(N‐isopropylacrylamide) (PNIPAM) to lower or higher temperatures, as well as the ease of modulation of the LCST phase transition kinetics broadens the scope of application of PNIPAM‐based materials in biomedical fields. This work reports a facile approach to formulate a smart, injectable cellulose nanofibril (CNF)/PNIPAM hybrid gel. Hofmeister salts are used to induce ion‐mediated gelation of the nanofibrils and PNIPAM chains, resulting in an interpenetrating network (IPN) structure. From rheological measurements, the hybrid material displays excellent structural integrity at room temperature and tunable thermo‐stiffening around body temperature. De‐swelling kinetics can be modulated by varying the nature and concentration of the Hofmeister ion used. The successful realization of the IPN hybrid gel structure is dependent on the molecular weight of PNIPAM used. Moreover, the hybrid gels show good thermo‐reversibility during thermal cycling, as well as excellent injectability and remarkable self‐healing post‐injection, owing to shear‐thinning and thixotropic characters. Since rheology is a crucial technique in the analysis of soft matter and flow behavior is fundamental for the design and synthesis of application‐specific viscoelastic materials, the work reported herein provides a rheological basis for careful design and synthesis of smart gels.

Lipidation alters the phase-separation of resilin-like polypeptides.

Biology exploits biomacromolecular phase separation to form condensates, known as membraneless organelles. Despite significant advancements in deciphering sequence determinants for phase separation, modulating these features in vivo remains challenging. A promising approach inspired by biology is to use post-translational modifications (PTMs)-to modulate the amino acid physicochemistry instead of altering protein sequences-to control the formation and characteristics of condensates. However, despite the identification of more than 300 types of PTMs, the detailed understanding of how they influence the formation and material properties of protein condensates remains incomplete. In this study, we investigated how modification with myristoyl lipid alters the formation and characteristics of the resilin-like polypeptide (RLP) condensates, a prototypical disordered protein with upper critical solution temperature (UCST) phase behaviour. Using turbidimetry, dynamic light scattering, confocal and electron microscopy, we demonstrated that lipidation-in synergy with the sequence of the lipidation site-significantly influences RLPs' thermodynamic propensity for phase separation and their condensate properties. Molecular simulations suggested these effects result from an expanded hydrophobic region created by the interaction between the lipid and lipidation site rather than changes in peptide rigidity. These findings emphasize the role of "sequence context" in modifying the properties of PTMs, suggesting that variations in lipidation sequences could be strategically used to fine-tune the effect of these motifs. Our study advances understanding of lipidation's impact on UCST phase behaviour, relevant to proteins critical in biological processes and diseases, and opens avenues for designing lipidated resilins for biomedical applications like heat-mediated drug elution.

Cartilage-Inspired, High-Strength, and Heat-Tolerant Lubricating Hydrogels by Macrophase Separation.

Hydrogels are considered as a potential cartilage replacement material based on their structure being similar to natural cartilage, which are of great significance in repairing cartilage defects. However, it is difficult for the existing hydrogels to combine the high load bearing and low friction properties (37 °C) of cartilage through sample methods. Herein, we report a facile and new fabrication strategy to construct the PNIPAm/EYL hydrogel by using the macrophase separation of supersaturated N-isopropylacrylamide (NIPAm) monomer solution to promote the formation of liposomes from egg yolk lecithin (EYL) and asymmetric template method. The PNIPAm/EYL hydrogels possess a relatively high compressive strength (more than 12 MPa), fracture energy (9820 J/m2), good fatigue resistance, lubricating properties, and excellent biocompatibility. Compared with the PNIPAm hydrogel, the friction coefficient (COF 0.046) of PNIPAm/EYL hydrogel is reduced by 50%. More importantly, the COF (0.056) of PNIPAm/EYL hydrogel above lower critical solution temperature (LCST) does not increase significantly, exhibiting heat-tolerant lubricity. The finite element analysis further proves that PNIPAm/EYL hydrogel can effectively disperse the applied stress and dissipate energy under load conditions. This work not only provides new insights for the design of high-strength lubricating hydrogels but also lays a foundation for the treatment of cartilage injury as a substitute material.

Influence of PEG-PPG-PEG Block Copolymer Concentration and Coagulation Bath Temperature on the Structure Formation of Polyphenylsulfone Membranes

The effect of amphiphilic block copolymer polyethylene glycol (PEG)-polypropylene glycol (PPG)-PEG concentration in the polyphenylsulfone (PPSU) casting solution and coagulation bath temperature (CBT) on the structure, separation, and antifouling performance of PPSU ultrafiltration membranes was studied for the first time. According to the phase diagram obtained, PPSU/PEG-PPG-PEG/N-methyl-2-pyrrolidone (NMP) systems are characterized by a narrow miscibility gap. It was found that 20 wt.% PPSU solutions in NMP with the addition of 5–15 wt.% of PEG-PPG-PEG block copolymer feature upper critical solution temperature, gel point, and lower critical solution temperature. Membrane composition and structure were studied by Fourier-transform infrared spectroscopy, scanning electron and atomic force microscopies, and water contact angle measurements. The addition of PEG-PPG-PPG to the PPSU casting solution was found to increase the hydrophilicity of the membrane surface (water contact angle decreased from 78° for the reference PPSU membrane down to 50° for 20 wt.%PPSU/15 wt.% PEG-PPG-PEG membrane). It was revealed that the pure water flux increased with the rise of CBT from 18–20 L·m−2·h−1 for the reference PPSU membrane up to 38–140 L·m−2·h−1 for 20 wt.% PPSU/10–15 wt.% PEG-PPG-PEG membranes. However, the opposite trend was observed for 20 wt.% PPSU/5–7 wt.% PEG-PPG-PEG membranes: pure water flux decreased with an increase in CBT. This is due to the differences in the mechanism of phase separation (non-solvent-induced phase separation (NIPS) or a combination of NIPS and temperature-induced phase separation (TIPS)). It was shown that 20 wt.% PPSU/10 wt.% PEG-PPG-PEG membranes were characterized by significantly higher antifouling performance (FRR—81–89%, DRr—26–32%, DRir—10–20%, DT—33–45%) during the ultrafiltration of bovine serum albumin solutions compared to the reference PPSU membrane prepared at different CBTs (FRR—29–38%, DRr—6–14%, DRir—74–89%, DT—88–94%).

Poly(N-isopropylacrylamide)-based hydrogel carrier containing Prussian blue for thermally controlled release

A hydrogel consisted of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAm-co-AA) and Prussian blue (PB) was synthesized for a cargo carrier by controlling the release of organic dye under near infrared (NIR) light. The AA moiety of the hydrogel provided chemical bonding with Fe (III) ions for further PB formation. Biocompatible, NIR-responsive PB generated heat and the heat was transferred to the hydrogel. The NIPAAm moiety in the hydrogel was shrunken because of the low critical solution temperature behavior of the hydrogel, and the hydrogel released the loaded dye with 62%. These results suggest dye-loaded hydrogel as a prospective platform for light-triggered carriers.

Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the “grafting to” technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25–45 °C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

Bi-layered hydrogel conduit integrating microneedles for enhanced neural recording and stimulation therapy in peripheral nerve injury repair

Nerve conduit is an alternative strategy in peripheral nerve injuries (PNI) treatment both for neural signals recording and therapeutic electrical stimulation (ES). Most conventional conduits suffer from surgical suturing and lacking real-time insights of nerve recovery, as well as failing in integrating therapy strategies. Herein, we introduce a bi-layered hydrogel conduit with microneedles (BHCM), in which poly (N-isopropylacrylamide) (PNIPAm)-incorporated polyethyleneimine (PEI) forms the outer layer for conductivity and electro-driven drug loading and release, whereas PNIPAm/alginate/tannic acid hydrogel (PNIPAm/SA/TA) forms the inner layer to ensure biocompatible mechanics and strong tissue adhesion. Meanwhile, the differences in doping manipulated different critical solution temperature (LCST) and swelling between the double layers determine the self-curling performance. Therefore, the BHCM responds to temperature and self-curls into conduit to wrap and bind to sciatic nerve, avoiding the complicated suturing and enhancing the interfacial electrical transmission. By puncturing the epineurium, the microneedles strongly enhance the electrochemical performance, and synergistically facilitate controllable drug delivery as well as electrical stimulation and recording efficiency. Further, BHCM is demonstrated to regulate macrophage polarization from M1 to M2 through electrically stimulated Rhein release, thereby reducing inflammation and facilitating diabetic PNI repair. The present design aims to improve biosafety, surgical simplicity to realize overall recovery of injured nerves, making it a promising candidate for advanced peripheral nerve repair strategies.

Isolation of nucleic acids using liquid–liquid phase separation of pH-sensitive elastin-like polypeptides

Extraction of nucleic acids (NAs) is critical for many methods in molecular biology and bioanalytical chemistry. NA extraction has been extensively studied and optimized for a wide range of applications and its importance to society has significantly increased. The COVID-19 pandemic highlighted the importance of early and efficient NA testing, for which NA extraction is a critical analytical step prior to the detection by methods like polymerase chain reaction. This study explores simple, new approaches to extraction using engineered smart nanomaterials, namely NA-binding, intrinsically disordered proteins (IDPs), that undergo triggered liquid–liquid phase separation (LLPS). Two types of NA-binding IDPs are studied, both based on genetically engineered elastin-like polypeptides (ELPs), model IDPs that exhibit a lower critical solution temperature in water and can be designed to exhibit LLPS at desired temperatures in a variety of biological solutions. We show that ELP fusion proteins with natural NA-binding domains can be used to extract DNA and RNA from physiologically relevant solutions. We further show that LLPS of pH responsive ELPs that incorporate histidine in their sequences can be used for both binding, extraction and release of NAs from biological solutions, and can be used to detect SARS-CoV-2 RNA in samples from COVID-positive patients.

Thermo-thickening/amphoteric polymer nanocomposite incorporating vinyl-functionalized nano-silica as a viscosifier for high-salt and ultra-high temperature water-based drilling fluids

In the relentless extraction of oil and gas from deeper reservoirs, the harsh geological conditions pose significant rheological challenges for conventional polymer viscosifiers. Hence, the spotlight has turned to the unique potential of thermo-thickening polymers to enhance drilling fluid performance. In this study, a novel polymer nanocomposite (VMS-ATA) was designed to associate thermo-thickening responses, amphoteric characteristics, and vinyl-functionalized nano-silica (VMS) as nanofillers for the formation of a thermally stable polymer nanocomposite-bentonite hybrid system. VMS-ATA was prepared via in-situ polymerization under optimal synthetic conditions, and the unique chemical structure was analyzed using various techniques such as Fourier transform spectroscopy, proton nuclear magnetic resonance, elemental analysis, thermogravimetric analysis, X-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The study systematically investigated the enhancement of in-situ covalent bonding characteristics of VMS on the thermo-thickening behavior of VMS-ATA, while comparing it with amine-nano-silica (AMS) incorporated in a polymer composite (AMS-CGBA). TGA analysis revealed that VMS-ATA exhibits excellent thermal stability compared to AMS-CGBA, attributed to the thermally stable VMS (370 °C) compared to AMS (355 °C). Interestingly, VMS-ATA displayed relatively stable and prolonged thermo-thickening responses (100–200 °C) owed to high thermal-induced activation responses above the lower critical solution temperature (LCST) in both salt-free and saturated salt contamination. The rheological results of VMS-ATA viscosity retention at 220 °C and 20 wt% NaCl, exceeded 60 %, which is twice that of AMS-CGBA-containing fluids. As demonstrated, VMS-ATA and AMS-CGBA exhibited similar macro-interactions with rigid imidazole and caprolactam rings, but significantly differed in their micro-interactions owed to in-situ covalent binding induced by VMS compared to hydrogen bonding in AMS. This breakthrough exhibited the potential of VMS nanofillers to effectively maintain thickening response by facilitating efficient heat distribution to minimize rapid viscosity decay and revolutionize the landscape of high-salt and high-temperature (HSHT) drilling applications.

Preparation and Performance Study of HTPB-g-(PNIPAM/PEG) Thermoresponsive Polymer Brush.

In recent years, a great deal of work has been devoted to the development of thermoresponsive polymers that can be made into new types of smart materials. In this paper, a branched polymer, HTPB-g-(PNIPAM/PEG), with polyolefin chain segments as the backbone and having polyethylene glycol (PEG) and poly(N-isopropylacrylamide) (PNIPAM) as side chains was synthesized by ATRP and click reactions using N3-HTPB-Br as the macroinitiator. This initiator was designed and synthesized using hydroxyl-terminated polybutadiene (HTPB) as the substrate. The temperature-responsive behavior of the branched polymer was investigated. The lower critical solution temperature (LCST) of the branched polymer was determined by ultraviolet and visible spectrophotometry (UV-vis) and was found to be 35.2 °C. The relationship between the diameter size of micelles and temperature was determined by dynamic light scattering (DLS). It was found that the diameter size changed at 36 °C, which was nearly consistent with the result obtained by UV-vis. The results of the study indicate that HTPB-g-(PNIPAM/PEG) is a temperature-responsive polymer. At room temperature, the polymer can self-assemble into composite micelles, with the main chain as the core and the branched chain as the shell. When the temperature was increased beyond LCST, the polyolefin main chain along with the PNIPAM branched chain assembled to form the nucleus, and the PEG branched chain constituted the shell.

Unraveling the Role of Deep Eutectic Solvents with Varying Hydrogen-Bond Acceptors on the Thermoresponsive Polymer Poly(N-isopropylacrylamide).

Deep eutectic solvents (DESs) have emerged as promising tools for crafting polymeric materials across diverse domains. This study delves into the impact of a series of DESs on the phase behavior of poly(N-isopropylacrylamide) (PNIPAM) in aqueous environments, presenting compelling insights into their performance. Specifically, we explore the conformational phase behavior of PNIPAM in the presence of four distinct lactic acid (LA)-based DESs: LA-betaine (LA-BET), LA-proline (LA-PRO), LA-choline chloride (LA-CC), and LA-urea (LA-U). By maintaining a consistent hydrogen-bond donor (HBD) while varying the hydrogen-bond acceptor (HBA), we unravel how different DES compositions modulate the phase transition behavior of PNIPAM. Our findings underscore the profound influence of DESs comprising LA as the HBD and diverse HBAs-BET, PRO, CC, and U on the thermoresponsive behavior of PNIPAM. Employing spectroscopic techniques such as ultraviolet-visible (UV-vis) spectroscopy, steady-state fluorescence, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), ζ-potential, and transmission electron microscopy (TEM), we elucidate the preferential interactions between the HBA groups within DESs and the hydration layer of PNIPAM. Notably, temperature-dependent DLS analyses reveal a discernible decrease in the lower critical solution temperature (LCST) of PNIPAM with increasing DES concentration, ultimately disrupting the hydrogen-bond interactions and resulting in early hydrophobic collapse of the polymer, which can be clearly seen in the TEM micrographs. Furthermore, the formation of polymer composites within the mixed system leads to notable alterations in the physiochemical properties of PNIPAM, as evidenced by shifts in its LCST value in the presence of DESs. This perturbation disrupts hydrogen-bond interactions, inducing hydrophobic collapse of the polymers, a phenomenon vividly captured in TEM micrographs. In essence, our study sheds new light on the pivotal role of varying HBA groups within DESs in modulating the conformational transitions of PNIPAM. These insights not only enrich our fundamental understanding but also hold immense promise for the development of smart polymeric systems with multifaceted applications spanning bioimaging, biomedical science, polymer science, and beyond.

Photo‐Responsive TiO2‐Gold Nanoparticle‐Polymer Nanohybrid Exhibits Photothermal, Thermo‐Release, and Photocatalytic Effects

The development of multi‐responsive nanohybrid systems that combine photothermia, thermo‐responsive effects and photocatalysis is a challenging topic in the research of multifunctional materials with a large field of applications. Here, we report the first example of a three‐components light‐responsive nanosystem consisting of titania, gold nanoparticles and poly‐N‐isopropylacrylamide (TiO2‐Au‐PNM). The hybrid nanostructure exhibited photothermal conversion effect upon green‐light excitation and capacity to entrap methylene blue and curcumin selected as cargo models. The formation of the nanohybrid―cargo adducts, the photothermal‐controlled cargo release triggered by green‐light irradiation (532 nm) and mediated by lower critical solution temperature (LCST), as well as the photocatalytic effect prompted by UV‐light excitation (300 nm) were demonstrated by spectroscopic techniques. The mechanism involved in the interaction of the polymeric component with the cargos was investigated by molecular modelling calculations.

Biomimicking TRPM8: A Conversely Temperature-Dependent Nonionic Retrorse Nanochannel for Ion Flow Control.

Ion channels play a crucial role in the transmembrane transport and signal transmission of substances. In animals, transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential melastatin 8 (TRPM8) serve as temperature-sensing units in sensory nerve endings. TRPV1 allows cells to sense heat, while TRPM8 enables them to detect cold, both serving to protect living organisms from harmful substances and environments. However, almost all studies on artificial nanochannels have mainly focused on TRPV1-like "forward nanochannels" thus far, which are incapable of "backward" responding to heat. So, we constructed an innovational TRPM8-inspired "retrorse nanochannel" through internal modification of poly(acrylamide-co-acrylonitrile) [P(AAm-co-AN)] with an upper critical solution temperature (UCST). Our results demonstrated that the internally modified nanochannels exhibited rapid, stable, and reversible heat-closing capability and converse temperature dependence within the typical temperature range of 25-40 °C. The biomimetic ion channel can effectively function as a facile, precise, and reversible thermal gate for controlling the transport of ions and substances. It also offers a promising microscopic technology for managing thermal effects on the substance, fluid, energy, and even signal delivery.

PNIPAM/PEDOT:PSS Hydrogels for Multifunctional Organic Electrochemical Transistors

AbstractThe development of multifunctional organic materials represents a vibrant area of research, with applications spanning from biosensing to drug delivery. This study shows the development of a multifunctional bioelectronic device suitable for prolonged temperature monitoring and drug delivery applications. The device relies on a conducting and thermo‐responsive hydrogel made of poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) and poly(N‐isopropylacrylamide) (PNIPAM). This multifunctional hydrogel is 4D printable by Digital Light Processing (DLP) method and exhibits optimal biocompatibility. The hydrogel features a low critical solution temperature (LCST) ≈35 °C, above which its resistance changes dramatically due to the shrinkage it undergoes with temperature. The integration of PNIPAM/PEDOT hydrogel into an organic electrochemical transistor (OECT) as the gate electrode allows to generate a miniaturized bioelectronic device with a reversible response to temperature variations between 25 to 45 °C, along with high sensitivity of 0.05 °C−1. Furthermore, the PNIPAM/PEDOT hydrogel demonstrates its utility in drug delivery, achieving an Insulin‐FITC release rate of 82 ± 4% at 37 °C, mimicking human body conditions. The hydrogel's functionality to store and release the insulin does not compromise its thermo‐responsivity and the overall performance of the OECT. This multifunctional OECT opens new avenues for the development of customizable and personalized sensing and drug‐delivery systems.

Smart antibiofouling composite coatings based on photothermally-active polyaniline and thermo-responsive poly(N-isopropylacrylamide)

Marine biofouling profoundly affects the economic viability of the marine sector. With a view towards addressing this issue, this work reported the successful development of smart photo-responsive and thermo-responsive antibiofouling coatings by combining photothermally-active polyaniline (PANI) with temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM). Under light irradiation, the PNIPAM/PANI coating could be photothermally heated to temperatures as high as 89.3 ± 1.6 °C, delivering a maximum antibacterial rate of 99.99 %. Impressively, light-induced temperature changes in the PNIPAM/PANI coating caused dynamic changes in film morphology and wettability. Upon lowering the temperature to below the lower critical solution temperature (LCST) of PNIPAM, the water contact angle of the PNIPAM/PANI coating decreased from 81° to 35° and the coating surface roughened appreciably, resulting in a 99.99 % release rate for both E.coli and S. aureus, thus achieving a dynamic self-cleaning effect. Furthermore, the developed PNIPAM/PANI coating demonstrated excellent resistance against protein and algae adhesion. These findings showcase the broad application potential of PNIPAM/PANI antifouling coatings in the marine sector.

UCST-Type Thermoresponsive Sol–Gel Transition Triblock Copolymer Containing Zwitterionic Polymer Blocks

Thermoresponsive sol–gel transition polymers are of significant interest because of their fascinating biomedical applications, including as drug reservoirs for drug delivery systems and scaffolds for tissue engineering. Although extensive research has been conducted on lower critical solution temperature (LCST)-type sol–gel transition polymers, there have been few reports on upper critical solution temperature (UCST)-type sol–gel transition polymers. In this study, we designed an ABA-type triblock copolymer composed of a poly(ethylene glycol) (PEG) block and zwitterionic polymer blocks that exhibit UCST-type thermoresponsive phase transitions. A sulfobetaine (SB) monomer with both ammonium and sulfonate (–SO3) groups in its side chain or a sulfabetaine (SaB) monomer with both ammonium and sulfate (–OSO3) groups in its side chain was polymerized from both ends of the PEG block via reversible addition–fragmentation chain-transfer (RAFT) polymerization to obtain PSB-PEG-PSB and PSaB-PEG-PSaB triblock copolymers, respectively. Although an aqueous solution containing the PSB-PEG-PSB triblock copolymer showed an increase in viscosity upon cooling, it did not undergo a sol-to-gel transition. In contrast, a sol-to-gel transition was observed when a phosphate-buffered saline containing PSaB-PEG-PSaB was cooled from 80 °C to 25 °C. The PSaB blocks with –OSO3 groups exhibited a stronger dipole–dipole interaction than conventional SB with –SO3 groups, leading to intermolecular association and the formation of a gel network composed of PSaB assemblies bridged with PEG. The fascinating UCST-type thermoresponsive sol–gel transition properties of the PSaB-PEG-PSaB triblock copolymer suggest that it can provide a useful platform for designing smart biomaterials, such as drug delivery reservoirs and cell culture scaffolds.

Flexible and thermoresponsive AEMR-pNIPAM/Cs0.33WO3 composite hydrogel film with NIR shielding potential for smart windows and smart curtains

Thermoresponsive flexible smart windows and smart curtains having high near-infrared (NIR) shielding and tuned visible light transmittance are essential for improving the energy efficiency of the buildings. The lower critical solution temperature (LCST) of the cross-linked poly(N-isopropylacrylamide) (pNIPAM) hydrogel film was precisely modified to a desired LCST value at 27.4 °C through the free radical copolymerization with 10 wt% of acrylated epoxidized methyl ricinoleate (AEMR). Cs0.33WO3 as NIR shielding nanoparticles (particle size < 200 nm) were synthesized via high energy ball milling method with AEMR as a surfactant for high NIR shielding efficiency and dispersion—the composite flexible hydrogel films with different wt% (0.3, 0.5,0.7, and 0.9 wt%) of Cs0.33WO3 nanoparticles were fabricated to analyze the NIR shielding efficiency and thermal insulation performance. The copolymeric hydrogel film with 0.7 wt% of Cs0.33WO3 nanoparticles (0.7-CWO) demonstrates a significant reduction in the NIR transmittance (15.0 % to 2.3 %) and variation in visible light transmittance from 73.6 % to 15.7 % while undergoing temperature-induced phase transition. The smart window fabricated with composite hydrogel film exhibits good integral luminous transmittance (Tlum, 380–780 nm, 68.7 %, below LCST) and justifiable solar modulation ability (ΔTsol, 300–2500 nm, 53.6 %). A model house was designed to monitor the indoor temperature difference, and a noticeable variation of 7 °C was observed in the house with and without 0.7-CWO film. Further, the developed composite material showed improvement in flexibility, water resistance, and thermal stability, confirming its usage for energy-saving smart windows or smart curtains.

Peculiarities of Emulsions Stabilized by Stimuli-Responsive Interpenetrating Polymeric Network Microgels.

Emulsions have become a crucial product form in various industries in modern times. Expanding the class of substances used to stabilize emulsions can improve their stability or introduce new properties. Particularly, the use of stimuli-responsive microgels makes it possible to create "smart" emulsions whose stability can be controlled by changing any of the specified stimuli. Thus, finding new ways to stabilize emulsions may broaden their application. In this work, for the first time, we applied microgels based on interpenetrating polymeric networks (IPNs) of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) as stabilizing agents for "oil-in-water" emulsions. We have demonstrated that emulsions stabilized by such soft particles can remain colloidally stable for an extended period, even after being heated up to 40 °C, which is above the lower critical solution temperature (LCST) of PNIPAM. On the contrary, the emulsions stabilized by PNIPAM homopolymer microgels were broken upon heating. To understand the stabilization mechanism of the emulsions, mesoscopic computer simulations were performed to study the IPN microgels at the liquid-liquid interface. The simulations demonstrated that when the first subnetwork (PNIPAM) collapses, the particle adopts a flattened core-shell morphology with a highly swollen PAA-rich shell and a collapsed PNIPAM-rich core. Unlike its PNIPAM homopolymer counterpart, the IPN microgel maintains its three-dimensional shape, which provides stability to the microgel-based emulsions over a wide range of temperatures. Our combined findings could be useful in developing new approaches to emulsions' storage, biphasic catalysis, and lubrication of mechanisms in various operating and climatic conditions.