Critical Solution Temperature Research Articles

Antidehydration and Stable Mechanical Properties during the Phase Transition of the PNIPAM-Based Hydrogel for Body-Temperature-Monitoring Sensors.

Poly(N-isopropylacrylamide) (PNIPAM) enhances the reversibility and responsiveness of wearable temperature-sensitive devices. However, an open question is whether and how the hydrogel design can prevent adhesive performance loss caused by phase-transition-induced dehydration and unstable mechanical properties between devices and human skin and reduce interfacial failure. Herein, a gelatin-mesh scaffold-based hydrogel (NAGP-Gel) is constructed to inhibit dehydration and volume change, leading to stable mechanical properties, superior adhesiveness, and thermal sensing sensitivity during the phase transition. NAGP-Gel enhances the polymer chains-water interaction and weakens the degree of aggregation of polymer chains-chains, improving antidehydration properties under 45 °C conditions that are higher than the lower critical solution temperature (LCST; i.e., ∼32 °C). The mesh scaffold greatly restricts the phase-transition-induced polymer chain movement and maintains the mechanical performance. In a 60 °C environment, the maximum water loss and volume retention ratio of NAGP-Gel are only 3.58% and 97.3%, respectively. Additionally, NAGP-Gel serves as a temperature sensor, producing a stable thermal-electrical signal within the LCST range. It also can be assembled into an electronic device enabling the transmission of information and recognition of sign language via Morse code. This work broadens the application of PNIPAM in constructing intelligent hydrogels and opens the door to exploring emerging hydrogels for temperature-monitoring applications.

Surface-induced nano-generator utilizing a thermo-responsive smart window based on ionic liquid aqueous solution that exhibits lower critical solution temperature type phase separation

We demonstrate a surface-induced nano-generator utilizing a thermo-responsive smart window based on ionic liquid aqueous solution that exhibits lower critical solution temperature (LCST) type phase separation. This smart window was fabricated by filling an aqueous solution of [nBu4P][CF3COO] between the glass substrates coated with two different polymers: a polyimide with an alkyl side chain and an amorphous fluoropolymer. Below the LCST, the transmittance of the smart window was 87 %, nearly identical to that of a glass substrate. In contrast, when heated above the LCST, the [nBu4P][CF3COO] aqueous solution undergoes phase separation, causing the [nBu4P] cations and [CF3COO] anions to adsorb onto the polyimide with the alkyl side chain and the amorphous fluoropolymer facilitated by the surface pinning effect. This adsorption process results in the smart window generating electricity while transitioning to an opaque state. Therefore, the proposed smart window functions as an electricity-generating thermo-responsive device that can switch between transparent and opaque states in response to temperature changes.

Tuning the properties of peptide imprinted nanoparticles for protein immunoprecipitation using magnetic streptavidin beads

Maximizing the binding properties of thermoresponsive molecularly imprinted nanoparticles (MIN) was aimed to explore their feasibility as antibody substitutes in protein immunoprecipitation (IPP) with magnetic streptavidin beads (MSB). Thermoresponsive MIN targeting the cannabinoid CB1 receptor were produced by epitope imprinting through solid-phase synthesis. It was intended to determine how different variables influenced physicochemical features, binding behaviour and immunoprecipitation of the target recombinant glutathione S-transferase tagged fusion protein (GST-CTer). Such variables included the cross-linking degree of MIN, and variables like pH, temperature or the use of Tween-20 for binding and IPP experiments. The cross-linker (CL) amount influenced the coil-to-globule transition of thermoresponsive MIN, making the lower critical solution temperature (LCST) decrease from 37.2 °C using 5% of CL, to 29.0 °C using 25%, also suggesting higher plasticity on the former. Temperature influence on size was corroborated by dynamic light scattering, observing size reductions from 250–450 nm (RT) to 70–100 nm (> LCST) for MIN produced with 5–15% of CL. However, binding behaviour did not clearly improve for more than 10% CL. Further experiments revealed that temperature and pH control were critical for efficient binding and release, selecting 40 °C and pH 5 as appropriate. Following binding experiments, the GST-CTer-MIN complex was successfully immunoprecipitated using MSB, achieving an IPP efficiency of 11.48% over the initial input protein concentration, which was calculated after SDS-PAGE separation and Western blot analysis. The methodology may be exploited for selective protein extraction and quantification from complex tissue homogenates.Graphical

Synthesis of poly (N-isopropylacrylamide)-poly(ε-caprolactone) for temperature-controlled wettability of poly(L-lactic acid)

Abstract In the work, poly(N-isopropylacrylamide)-poly(ε-caprolactone) (PNIPAm-PCL) with the low critical solution temperature (LCST) was synthesized by a combination of chain transfer and ring-opening method to endow poly (lactic acid) (PLLA) with the temperature-controlled wettability. The effects of PNIPAm-PCL on the thermal properties, mechanical properties, and temperature-controlled wettability were studied. At 20 wt% of PNIPAm-PCL/PLLA, the tensile strength of the material reduces slightly, but its elongation at break is enhanced significantly, which reaches 135.1%. PNIPAm-PCL/PLLA exhibits good temperature-controlled wettability. With the temperature rising from 0 to 45oC, the water contact angle increases from 29.8 ° to 80.1 °; conversely, it goes down, and there is a hysteresis. The material still has good stability and degradability. This work provides an example for the development of intelligent tissue engineering materials.

Construction and Performance Study of an Injectable Dual-Network Hydrogel Dressing with Inherent Drainage Function.

With the widespread utilization of moist wound dressings, the extended healing time and increased risk of wound infection caused by excessively moist environments have garnered significant attention. The development of hydrogel dressings that can effectively control the wound moisture level and promote healing is very important. Inspired by the pore-opening perspiration effect of the skin, this study constructed an injectable dual-network hydrogel, CMCS-OSA/AG/MXene, by the composition of a dynamic covalent network of carboxymethyl chitosan and oxidized sodium alginate based on the Schiff base and hydrogen bond network of the thermosensitive low-melting-point agar with the advantage of the upper critical solution temperature (UCST) effect. Under near-infrared (NIR) light stimulation, the CMCS-OSA/AG/MXene hydrogel shows characteristics conducive to rapid removal of wound exudate while maintaining an appropriate moist environment for the wound and excellent antibacterial effects with its photothermal responses. The excellent conductivity of the hydrogel can also promote cell proliferation under external electrical stimulation (ES). Further validation through animal experiments on a full-thickness skin defect model demonstrates the excellent capability of CMCS-OSA/AG/MXene in accelerating wound healing. This work provides an innovative approach to the development of injectable hydrogel dressing materials with inherent drainage functionality and shows a new avenue to wound moisture control and wound healing promotion.

Robust, Switchable and Printable Underwater Adhesives Based on a Temperature‐Deactivated Design

AbstractConventional adhesives generally suffer from diminished adhesion in aqueous environments, posing significant challenges for their application in wet and submerged conditions. While extensive research efforts are directed toward enhancing the interfacial bonding, cohesive strength, and durability of adhesives in such environments, most existing underwater adhesives remain static and irreversible. This limitation hinders their reusability and often results in undesirable residues. Addressing the challenge of achieving strong underwater adhesion with on‐demand detachment remains crucial. This study introduces the development of temperature‐responsive underwater adhesives that demonstrate outstanding bonding strength, reversibility, and durability. Through the strategic integration of interfacial bonding, reinforced cross‐linking networks, dynamic hydrogen bonds, and upper critical solution temperature (UCST)‐driven phase transitions, one of the few temperature‐deactivated adhesives is created. The optimized adhesive is distinguished by its performance to achieve underwater adhesion strengths exceeding 1.4 MPa, nearly 100% switching efficiency and residue‐free adherend under mild thermal cycling. Beyond the template‐assisted fabrication of adhesive patches, 3D printable adhesives are achieved with programmable architectures via direct ink‐writing. This work highlights the development of temperature‐deactivated underwater adhesives activated by UCST‐type phase transitions, not only boosting adhesion strengths and switching efficiencies across various water conditions but also broadening their applicability with user‐defined and application‐specific functions.

Mussel-inspired thermo-switchable underwater adhesive based on a Janus hydrogel

On-demand underwater adhesives with excellent adhesive and gentle detachment properties enable stable connections to various biomedical devices and biointerfaces and avoid the risk of harmful tissue damage upon detachment. Herein, we present a Janus hydrogel adhesive that can reversibly switch its adhesion strength, which is controlled by temperature, using a thermoresponsive polymer and mussel-inspired molecules. This thermoswitchable adhesive (TSA) hydrogel displays both strong adhesion and gentle detachment with an over 1000-fold gap in underwater adhesion strength onto glass, titanium, aluminum, and Teflon substrates when exposed to temperatures above and below the lower critical solution temperature (LCST). The adhesion switch is possibly caused by the change in toughness of the TSA hydrogels with temperature because the Janus hydrogel possesses gradient crosslinked structures. Moreover, the lowermost surface is sufficiently soft to gently detach from the substrate below the LCST. The electrode-integrated hydrogel remains on human skin, and electrical signals are continuous over 10 min above the LCST. In contrast, commercially available hydrogel electrodes quickly swell and detach from the skin. The thermoswitchability of the TSA hydrogel, with its robust adhesion and gentle detachment, offers significant potential for biomedical applications characterized by minimally invasive procedures.

Slow release of surfactant by smart thermosensitive polymer-functionalized mesoporous silica for enhanced oil recovery: Synthesis and characterization

The efficiency of surfactant flooding can be improved through slow-release technology, which enables stimuli-sensitive and gradual release of surfactant. In this study, we synthesized a novel nanocomposite capsule composed of mesoporous silica functionalized with thermosensitive poly N-vinyl caprolactam (PNVCL). Well-optimized nanocarriers were synthesized by conducting sensitivity analyses on key synthesis parameters such as pH, reaction duration, and hydrophobic phase, resulting in hydrodynamic diameters ranging from 47 to 109 nm. Characterization of the nanocarrier structure was performed using dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) analysis, and field emission scanning electron microscopy (FESEM), while Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDS) were employed to analyze the nanocarrier composition. Poly N-vinyl caprolactam (NVCL)-functionalized mesoporous silica exhibited high surfactant loading (approximately 52 % w/w) and a large specific surface area (542.88 m2/g), featuring ink-bottle pores. Additionally, it demonstrated thermosensitive behavior, with the lower critical solution temperature of 39 °C. Gradual release of cetyltrimethylammonium bromide (CTAB) was observed in both deionized water and formation brine, with release rates increasing with temperature. Overall, the synthesized nanocomposite carrier holds significant potential as an ideal candidate for effectively controlling the release of surfactants in reservoirs subjected to high-temperature and high-salinity conditions.

Exploring LCST- and UCST-like Behavior of Branched Molecules Bearing Repeat Units of Elastin-like Peptides as Side Components.

Elastin-like peptides (ELPs) exhibit lower critical solution temperature (LCST)-type behavior, being soluble at low temperatures and insoluble at high temperatures. While the properties of linear, long-chain ELPs are well-studied, short-chain ELPs, especially those with branched architectures, have been less explored. Herein, to obtain further insights into multimeric short ELPs, we investigated the temperature-responsive properties of branched molecules composed of a repeating pentapeptide unit of short ELPs, Phe-Pro-Gly-Val-Gly, as side components and oligo(Glu) as a backbone structure. In turbidimetry experiments, the branched ELPs showed LCST-like behavior similar to conventional ELPs and upper critical solution temperature (UCST)-like behavior, which are rarely observed in ELPs. In addition, the morphological aspects and mechanisms underlying the temperature-responsiveness were investigated. We observed that spherical aggregates formed, and the branched ELPs underwent structural changes through the self-assembly process. This study demonstrates the unique temperature-responsiveness of branched short ELPs, providing new insights into the future development and use of ELPs with tailored properties.

Bidirectional Temperature‐Responsive Thermochromic Hydrogels With Adjustable Light Transmission Interval for Smart Windows

AbstractThermochromic smart windows have been widely developed for solar regulation to save building energy. However, most current smart windows still exhibit a single responsiveness to a specific temperature, which is not conducive to daytime energy saving or nighttime privacy protection. Herein, a low‐temperature response is achieved by pre‐initiation of the monomer acrylamide (AAm) and acrylic acid (AA) in the synthesis of P(AAm‐co‐AA). Then, N‐isopropyl acrylamide and AAm are introduced into P(AAm‐co‐AA) to form a pre‐polymerized precursor solution. The liquid precursor solution can be encapsulated within two quartz glasses and synthesized in situ to prepare smart windows, which exhibit a high visible light transmittance of 84.4%, excellent solar modulation of 69.5%, and bidirectional temperature responsiveness (cold and hot). In addition, the upper critical solution temperature and the lower critical solution temperature of the hydrogel and the light transmission interval between the two temperatures can be flexibly adjusted to adapt to different climates and individual user needs. The designed smart window maintains a high light transmission within the human body's comfort temperature range. The bidirectional temperature response window achieves the dual functions of energy saving and privacy protection, making it an ideal smart window candidate with good prospects for practical applications.

Phase-changing NIPAM-AM/ATO hydrogels for thermochromic smart windows with highly adaptive solar modulation

Improving the solar regulation and reducing the response temperature of thermochromic smart windows are pivotal importance for energy-saving buildings. However, these two strategies are challenging to be integrated into one window. Herein, a novel composite hydrogel based on N-isopropylacrylamide (NIPAM) doped with antimony-doped tin oxide (ATO) nanoparticles and acrylamide (AM) was developed for producing a high-performance smart window, which successfully achieved enhanced solar energy regulation and reduced response temperature. This smart window was fabricated by combining a reversible thermoresponsive hydrogel (TAH) that acted as a thermochromic material with a ATO multilayer film that performed as a transparent heater. The as-prepared smart window could modulate solar light over a range from ultraviolet (UV) to infrared (IR) radiation and achieved active responses to high-temperature weather. The smart window showed high luminous transmittance (Tlum, 82.92 %) together with an excellent solar modulation performance (ΔTlum = 73.31 %, ΔTIR = 38.26 %, and ΔTsol = 60.74 %), and a lower critical solution temperature of 32 °C. Even after 120 high- and low-temperature cyclic durability tests, the smart windows still exhibited a high solar modulation capability. In outdoor demonstrations, the as-prepared smart window exhibited a promising temperature regulation ability under strong solar irradiation. Therefore, the present universal modification framework provided some insights for the future design of energy-saving windows.

Phase behavior of aqueous two-phase systems formed with cholinium-based magnetic ionic liquids: Experimental insights and theoretical correlations

In this work, three cholinium-based MILs were synthesized, characterized and successfully applied to construct the magnetically responsive aqueous two-phase system (ATPs). This ATPs combined the advantages of ILs and magnetic responsiveness, and showed great potential in the field of extraction and separation. Phase behavior for the magnetic ionic liquid aqueous two-phase systems (MIL-ATPSs) containing [N 1 1n 2OH] [TEMPO-OSO3] + salts + water was investigated experimentally at different temperatures. Merchuk equation was adopted to fit the experimental binodal data with satisfactory correlation performances. The effects of the structure of MILs, temperature and types of salts on the phase behavior were evaluated. Investigation on the phase separation mechanism showed that the phase formation was affected by the structure and viscosity of MILs. The salting-out effect is recognized as the major force for phase separation, which is closely related to the Gibbs free energy of hydration (ΔhydG) and entropy of hydration (ΔhydS) of salts. In addition, a larger biphasic area was obtained by increasing the temperature, indicating the phase separation process was endothermic and entropically driven. The binodal curve at different temperature confirms that this MIL-ATPs has low critical solution temperature (LCST) phase transition behavior. All these experimentally measured data and the theoretical correlations can provide meaningful and valuable information that may promote further research and application.

Experimental setup for comprehensive study of non-stationary heat transfer in complex liquid media.

This paper presents a setup for studying non-stationary heat exchange in liquid media on a scale of small times and sizes at high heat flux densities created using a high-speed precision power controller. A platinum wire with a diameter of 20μm and a length from 0.5 to 1cm is used as a probe. The heating time ranged from 1 to 300ms, and the heat flux densities from 1 to 20 MW/m2 were achieved in the experiments. Strictly specified conditions for heat release in the probe are confirmed by maintaining a constant power in a series of pulses with an accuracy of 0.05%. Acquiring a primary electrical signal of thermograms is synchronized with high-speed video recording, allowing an accurate relationship between the applied thermal load and the mechanics of processes in the studied liquid. The setup capabilities were shown by comparing the boiling patterns of a simple substance, such as ethanol, and a solution with a lower critical solution temperature, a 30 vol.% solution of polypropylene glycol-425 in water, which have similar thermograms. As a result, a qualitative difference between the heating and boiling patterns observed using high-speed video and the presented setup fitting its purpose has been shown.

Impregnation, dehydration and crosslinking of responsive organoboron polymer to generate smart gating membrane for multimolecular gradient separation

Responsive materials have garnered increasing attention in the membrane separation field. However, fabricating smart gating membranes with tunable pore sizes to separate complex systems remains challenging. Herein, gating membranes with boroxine skeleton and temperature-tunable pores were successfully fabricated by fixing lower critical solution temperature (LCST)-type organoboron polymers (poly(N-isopropylacrylamide-co-glycidyl methacrylate/3-aminophenylboronic acid), PNG-APBA) onto the membrane surface via "impregnation-dehydration-crosslinking" strategy. The conformational behavior of the NIPAM-containing polymer chains (shrinking above LCST-stretching below LCST) serves as a functional gate, enabling the membranes to achieve reversibly tunable pore sizes and surface properties. The modified membranes exhibit gradient separation capabilities for small/medium/large molecules in complex polymer systems through temperature-tunable channels. The tunable pores also provided a potential tool for the high-selectivity separation of mixed proteins, such as lysozyme (LZM) and hemoglobin (Hb). Notably, the conformational behavior of the polymer chains endowed the membranes with excellent self-cleaning ability (FRR> 99.5%), while the boroxine network enhanced the grafting stability of the polymer chains, ensuring effective reversibility and repeatability of membranes.

A structural underpinning of the lower critical solution temperature (LCST) behavior behind temperature-switchable liquids

A structural underpinning of the lower critical solution temperature (LCST) behavior behind temperature-switchable liquids

Temperature-dependent behavior of poly(N-isopropylacrylamide) brushes via neutron reflectometry

Poly(N-isopropylacrylamide) (PNIPAAm)-modified interfaces are promising for various biomedical applications, however, the PNIPAAm brush structure must be investigated at various temperatures to enable the design of functional PNIPAAm interfaces. In this study, PNIPAAm brush structures with various densities and chain lengths are prepared via atom-transfer radical polymerization and analyzed using neutron reflectometry. The volume fraction of PNIPAAm exhibits temperature-dependent shrinkage; slight PNIPAAm shrinkage is observed below the lower critical solution temperature (LCST) of PNIPAAm, whereas large shrinkage occurs across the LCST of PNIPAAm. The volume of water in the PNIPAAm brush is 40% even when it is dehydrated at 37 °C and is slightly extended relative to its dry state. The dense PNIPAAm brush is thicker than the diluted PNIPAAm brush because the densely packed PNIPAAm chain tends to form an extended structure. A higher volume fraction of D2O is observed in the diluted PNIPAAm brush than in the dense PNIPAAm brush because the former can accommodate a larger volume of D2O. These results indicate that neutron reflectometry can provide essential information on the PNIPAAm brush configurations with various chain lengths and densities at different temperatures. These findings are applicable to the design of further functional PNIPAAm brush interfaces for biomedical applications.

An orthogonal analytical platform for determining critical material attributes for in situ formation of thermosensitive hyaluronic acid-poly(N-isopropylacrylamide) copolymers

The developability assessment of the in situ formation of thermosensitive injectables requires the unequivocal determination of their lower critical solution temperatures (LCSTs). Herein, we established a standardized threshold for LCST detection by harmonizing and cross-validating the orthogonal methods using techniques such as nuclear magnetic resonance spectroscopy, light scattering, turbidimetry, backgrounded membrane imaging, and rheology. The selected techniques were in agreement and promptly disclosed unique features and instrumental biases of otherwise difficult interpretations in the characterization of thermosensitive polymers. Thus, various hyaluronic acid–poly(N-isopropylacrylamide) copolymers were synthesized via strain-promoted azide–alkyne cycloaddition to understand their critical material attributes. Structure–function relationships and behaviors of the copolymers were tested under in vitro-simulated in vivo conditions.

Microalgae aggregation induced by thermoresponsive polymers

Algal biomass harvesting is one of key technical hurdles impeding the commercialization of algae-based biorefinery. The goal of this work is to develop an innovative technology for algae cell harvesting. Thermoresponsive polymers (TRPs) such as poly(N-isopropylacrylamide) (PNIPAM) and its derivatives were studied on their properties and potential applications for microalgae harvesting. Various PNIPAM was synthesized, and the effects of charge, molecular weight (MW), amine content, and polymer concentration on the polymer phase transition temperature, the degree of phase separation, and the harvesting of microalgae (Chlorella vulgaris) were investigated. The lower critical solution temperature (LCST) of PNIPAM decreased with the increase of polymer concentration, while the decline rate reduced under high MW. The amine content didn’t significantly affect the LCST of TRPs. Approx. 92 % of algae cells were harvested by PNIPAM-300 kDa. Modified TRPs showed few benefits in enhancing algae harvesting. TRPs are a promising class of polymers for microalgae harvesting.

Innovative temperature-responsive membrane with an elastic interface for biofouling mitigation in industrial circulating cooling water treatment

To address the issues of scaling caused by heat and water evaporation in regard to circulating cooling water (CCW), TFC membrane filtration systems have been increasingly considered for terminal treatment processes because of their excellent separation performance. However, membrane biofouling phenomenon significantly hinders the widespread utilization of TFC membranes. In this study, to harness the thermal phenomenon of CCW and establish a stable and durable multifunctional antibiofouling layer, temperature-responsive Pnipam and the spectral antibacterial agent Ag were organically incorporated into commercially available TFC membranes. Biological experimental findings demonstrated that above the lower critical solution temperature (LCST), the contraction of Pnipam molecular chains facilitated the inactivation of bacteria by the antibacterial agent, resulting in an impressive sterilization efficiency of up to 99 %. XDLVO analysis revealed that below the LCST, the establishment of a hydration layer on the functional interface resulted in the creation of elevated energy barriers, effectively impeding bacterial adhesion to the membrane surface. Consequently, a high bacterial release rate of 98.4 % was achieved on the low-temperature surface. The alterations in the functional membrane surface conformation induced by temperature variations further amplified the separation between the pollutants and the membrane, creating an enhanced "elastic interface." This efficient and straightforward cleaning procedure mitigated the formation of irreversible fouling without compromising the integrity of the membrane surface. This study presents a deliberately engineered thermoresponsive antibiofouling membrane interface to address the issue of membrane fouling in membrane-based CCW treatment systems while shedding new light on the mechanisms of "inactivation" and "defense."

Thermoresponsive nanofiber yarns for water harvesting enhanced by harp system

The escalating global water crisis necessitates innovative approaches to developing sustainable water resources. Fog water collectors with variable surface wettability offer controlled fog harvesting in water-scarce regions. This study develops thermoresponsive fog collecting materials by electrospinning poly(N-isopropylacrylamide)-polyvinylidene fluoride (PNIPAm-PVDF) into yarns that are transformed into harp-like structures for enhanced water harvesting rate. Both meshes and harps using electrospun membranes exhibit the remarkable ability to transition between hydrophilic and hydrophobic wetting states at temperatures below the lower critical solution temperature (LCST). Hydrophilic and hydrophobic surfaces play distinct roles in fog water collection. Hydrophilic surfaces have a high affinity for water and enables droplet capture. Hydrophobic surfaces help the removal of aggregated water droplet and fog water collection. The highest water collection rate obtained with the electrospun PNIPAm-PVDF harp was 1415 ± 7.0 mg·cm−2 h−1. The water harvesting system based on the electrospun PNIPAm-PVDF harps exhibits a 485 % increase in water collection compared to the standard meshes made from the same material, emphasizing their potential for significantly improving the overall rate in fog water harvesting applications.