Tunable Lower Critical Solution Temperature Research Articles

HPC-PAA-PAM semi-solid hydrogel with interpenetrating network for energy-saving smart windows

Hydrogels demonstrate significant potential as materials for fabricating energy-saving smart windows. Nevertheless, their liquid nature poses challenges and renders them susceptible to leakage during operation. In this study, we developed an HPC-PAA-PAM semi-solid hydrogel through a two-step polymerization process at 80 °C, with acrylamide serving as the curing agent. The resulting hydrogel exhibited a precisely tunable lower critical solution temperature (LCST) spanning from 31.5 °C to 36.2 °C. Additionally, we constructed double-layered glass-encapsulated HPC-PAA-PAM semi-solid hydrogel smart windows, which demonstrated remarkable optical transmittance (Tlum = 88.3 %), excellent solar energy modulation (ΔTsol = 47.9 %), and remained stability through 100 heating and cooling cycles. Thermal regulation tests conducted in model houses revealed outstanding heat-shielding performance of these hydrogel smart windows, surpassing conventional double-glazed windows and double-glass encapsulated water windows. Notably, after 90 days of outdoor exposure, the HPC-PAA-PAM semi-solid hydrogel smart window experienced only a minimal reduction in solar modulation, underlining its exceptional weather durability in practical applications. Consequently, the HPC-PAA-PAM semi-solid hydrogel presents substantial promise for the production of smart windows, particularly suited for energy-efficient buildings in tropical and subtropical regions, where it can effectively prevent the intense summer sun's heat from penetrating indoors, fostering a more pleasant indoor temperature.

A Coordinating Small Organic Molecule with Tunable Lower Critical Solution Temperature for Efficient Management of Solar Radiation.

Structurally well-defined small molecules with lower critical solution temperature (LCST) behavior offer enormous prospects for fine-tuning their phase transition properties to be "on-demand" applied in the specific scene but are still underexplored. Herein, a novel amphiphilic small LCST molecule is rationally designed and synthesized. The molecule, namely TG, features a conjugation of multiple short ethylene glycol (EG) chains with the functional coordinating terpyridine (Tpy) moiety. The molecule TG demonstrates excellent LCST behavior down to 0.05× 10-3 m in a water solution. And a cloud point Tcp = 30.9°C with a very short thermal hysteresis ΔT = 0.2°C and good reversibility can be achieved when c = 0.1× 10-3 m. The excellent LCST properties of TG have enabled its successful performance as the smart window for solar radiation management with the ∆Tlum, ∆TIR, and ∆Tsol being 83.6%, 49.1%, and 67.2%, respectively. Moreover, the presence of Tpy moiety in TG enables its coordination with Ru3+ and the resulting complex also exhibits modulated LCST behavior with different concentration-dependent Tcp. These studies would provide novel small-molecule-based scaffolds for constructing better solar radiation management systems as well as other thermal-responsive smart materials.

Thermally Responsive Hydrogels for Passive Temperature Regulation under Direct Sunlight

By spontaneously emitting midinfrared radiation to outer space through the atmospheric window and reflecting sunlight, daytime radiative coolers achieve notable passive cooling performance. However, existing daytime radiative cooling systems generally lack the ability to adaptively switch between heating and cooling states based on ambient conditions. Herein a passive thermal regulation system that features a temperature‐dependent switchable solar reflectance from 0.05 (low temperature) to 0.8 (high temperature) is presented. This, along with a ≈0.95 midinfrared emittance, it enables automatic switching between radiative cooling and solar heating. Switchablity is enabled using a poly(N‐isopropylacrylamide) (PNIPAM) hydrogel which exhibits high solar scattering above its tunable lower critical solution temperature (LCST) and transparency below its LCST. The lower part of the hydrogel is loaded with graphite to absorb solar energy in the heating state. In testing under sunny and partly cloudy outside conditions, this system maintains a temperature close to the set LCST.

Thermoresponsive magnetic ionic liquids as forward osmosis draw solutes for seawater desalination

Thermoresponsive magnetic ionic liquids (TMILs) showing lower critical solution temperature (LCST)-behavior were fabricated and utilized as forward osmosis (FO) draw solutes for seawater desalination. The MILs, 8-alkyl-1,8-diazabicyclo[5.4.0]undec‑7-ene bromotrichloroferrate (DBU-R[FeBrCl3], or d-R-FeX4) with different alkyl chain lengths (R = C4H9, C6H13, C7H15, or C8H17), exhibited tunable LCSTs from 30 to 65 °C by varying the chain length and the solution concentration. Upon heating above their LCSTs, more than 43% of the TMILs could be magnetically extracted via phase separation, demonstrating a facile magnet-assisted draw solution regeneration approach. In addition, an aqueous solution containing 25 wt% D-Bu-FeX4 was able to achieve a water flux as high as 4.5 L m−2h−1 (LMH) in desalinating seawater. Their ionic nature, together with unique thermo- and magnetic-responsive behaviors, make them promising candidates as ideal FO draw solutes for desalination and wastewater reclamation.

Fluorescent Nanoassemblies in Water Exhibiting Tunable LCST Behavior and Responsive Light Harvesting Ability.

Responsive fluorescent nanomaterials have been received considerable attention in recent years. In this work, a bola-type amphiphilic molecule, CSO, was synthesized which contains a hydrophobic cyanostilbene core and hydrophilic oligo(ethylene glycol) (OEG) coils at both sides. The cyanostilbene group is aggregation-induced emission (AIE) active, while the OEG coils are thermo-responsive. As a result, the CSO molecules can self-assemble into blue-fluorescent nanoassemblies with lower critical solution temperature (LCST) behavior in aqueous media. It is noteworthy that the LCST behavior can be reversibly regulated with changes in concentration and the introduction of K+ . Intriguingly, fluorescence of CSO assembly shows a blue-shift upon heating. Finally, by employing CSO as a light capturing antenna and energy donor, an artificial light harvesting system with tunable emission and thermo-responsive characteristics was fabricated. This study not only demonstrates an integrated approach to create responsive fluorescent nanomaterials, but also shows great potential for producing luminescent materials and mimicking photosynthesis in nature.

Amphiphile regulated ionic-liquid-based aqueous biphasic systems with tunable LCST and extraction behavior

Ionic liquid (IL)/H2O mixtures with tunable lower critical solution temperature (LCST) behavior exhibit tantalizing prospect in the field of liquid-liquid phase separation and purification. Herein, different types of amphiphiles were evaluated for the facile regulation of IL ([P4444][DMBS]) based aqueous biphasic systems (ABSs). Interestingly, the addition of zwitterionic 3-(1-dodecyl-3-imidazolio) propanesulfonate (DIPS) remarkably increases the phase separation temperature of IL aqueous solution, while the addition of anionic sodium dodecyl benzene sulfonate (SDBS) and dodecyl-benzenesulphonic acid (DBSA) results in decreasing of the phase separation temperature. The tunable phase separation temperature ranges from 10 to 90 °C, which almost cover the full usable temperature range of ABSs. The regulation mechanism of amphiphile additives on the LCST behavior of IL/H2O mixtures was investigated through isothermal titration calorimetry, 1H NMR spectroscopy and molecular dynamics simulations. Briefly, the addition of zwitterionic DIPS increased LCST through electrostatic shielding effect, while the addition of anionic SDBS and DBSA decreased LCST through ion exchange effect. As a proof of concept, the amphiphile regulated ABSs were demonstrated to selectively separate aliphatic and aromatic amino acids.

Self-assembled Fluorescent Nanoparticles with Tunable LCST Behavior in Water.

The development of stimuli-responsive fluorescent materials in water based on organic molecule has drawn significant interest. Herein, we designed and synthesized an amphiphilic molecule M containing a fixed tetraphenylethylene moiety (FTPE) as hydrophobic part and tri(ethylene glycol) (TEG) chains as hydrophilic part. Notably, the FTPE moiety is aggregation-induced emission (AIE) active, while the TEG chains are thermo-responsive. M can self-assemble into fluorescent nanoparticles (NPs) in water, which showed lower critical solution temperature (LCST) behavior. Moreover, its clouding point can be reversibly tuned upon the concentration variation. Interestingly, the NPs can be acted as a fluorescence thermometer in aqueous media owing to their unique AIE and LCST behaviors. Our work herein not only provides an integration strategy to construct stimuli-responsive fluorescent materials but also shows great potential in biological applications including bioimaging and biosensors.

An amphiphilic water-soluble biphen[3]arene with a tunable lower critical solution temperature behavior

The first amphiphilic water-soluble thermoresponsive biphen[3]arene with a tunable lower critical solution temperature behavior is reported.

Allyl group-containing polyvinylphosphonates as a flexible platform for the selective introduction of functional groups via polymer-analogous transformations.

Polyvinylphosphonates are highly promising candidates for (bio)medical applications as they exhibit a tunable lower critical solution temperature, high biocompatibility of homo- and copolymers, and a broad foundation for post-synthetic modifications. In this work we explored polymer-analogous transformations with statistical polyvinylphosphonates comprising diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). The C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C double bonds were used as a starting point for a cascade of organic transformations. Initially, the reactive moieties were successfully introduced via bromination, epoxidations with OXONE and mCPBA, or thiol–ene click chemistry with methyl thioglycolate (6). The obtained substrates were then employed in a variety of consecutive reactions depending on the introduced functional motif: (1) the brominated substrates were converted with sodium azide to enable the copper-mediated alkyne–azide coupling with phenylacetylene (1). (2) The epoxides were reacted with sodium azide for an alkyne–azide click coupling with 1 as well as small nucleophilic compounds (phenol (2), benzylamine (3), and 4-amino-2,1,3-benzothiadiazol (4)). Afterwards the non-converted allyl groups were reacted with thiochloesterol (5) to form complex polymer conjugates. (3) An acid-labile hydrazone-linked conjugate was formed in a two-step approach. The polymeric substrates were characterized by NMR, FTIR, and UV/Vis spectroscopy as well as elemental analysis and gel permeation chromatography to monitor the structural changes of the polymeric substrates and to prove the success of these modification approaches.

Self-adaptive chip cooling with template-fabricated nanocomposite P(MEO2MA-co-OEGMA) hydrogel

Conventional microchannels provide effective chip cooling with constant flow rate and this comes at the cost of high pumping power consumption. Considering the dynamic heat load in reality, a self-adaptive microchannel cooling is desired for regulating the flow rate to diminish the operational cost while preserving the inherent cooling effectiveness. Taking the advantages of easy synthesis, well tunable lower critical solution temperature (LCST) and remarkable mechanical strength, this paper reports the self-adaptive microchannel cooling with the thermal-sensitive nanocomposite (NC) P(MEO2MA-co-OEGMA) hydrogel. A novel route is developed to integrate the hydrogel with the chip using template-aided imprint molding and in situ polymerization. Circular hydrogel is elaborately designed and anchored firmly in the channel. The cooling performance is tested with a custom test vehicle under different operating conditions. The hydrogel acts as a smart valve and tailors the flow rate from 0.14 mL/s to 0.46 mL/s based on heat load variation. Compared with conventional channels, heat flux of 100 W/cm2 can be extracted with similar temperature rise while the coefficient of performance (COP) is improved by an order of magnitude. The transient characteristics and repeatability are also validated. The self-adaptive scheme offers both effective and economical liquid cooling for modern electronic devices.

Tunable Lower Critical Solution Temperature of Poly(butyl acrylate) in Ionic Liquid Blends

We describe the lower critical solution temperature (LCST)-type phase behavior of poly(butyl acrylate) (PBA) dissolved in hydrophobic 1-alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide ionic liquids (ILs). The temperature-composition phase diagrams of these PBA/ILs systems are strongly asymmetric with the critical composition shifted to low concentrations of PBA. As the molecular weight increases from 5.0×103 to 2.0×104, the critical temperature decreases by about 67 °C, and the critical composition shifts to a lower concentration. Furthermore, the LCST of PBA/ILs system increases as increasing the alkyl side chain length in the imidazolium cation. Using IL blends as solvents, the LCST of PBA can be tuned almost linearly over a wide range by varying the mixing ratio of two ionic liquids without modifying the chemical structure of the polymers.

Facile Synthesis of Novel Thermo‐Responsive Polyvalerolactones with Tunable LCSTs

AbstractThermoresponsive polymers have emerged as promising candidates for biomedical applications. Seven novel oligoethylene glycol (OEG) functionalized polyvalerolactones P1–P7 are synthesized from poly(α‐allyl‐δ‐valerolactone) via thiol‐ene addition post‐polymerization modification. All seven polymers exhibit thermoresponsive behavior with lower critical solution temperatures (LCSTs) ranging from 13.8 to 92.2 °C. Polymers P5–P7 are synthesized via thiol‐ene addition reaction using two thiol mixtures at three different ratios. LCSTs of P5–P7 fall in between those of P1 and P2, and exhibit a linear relationship, indicating a tunable thermoresponsive system. This newly developed system offers great control for a desired thermoresponsive biocompatible, biodegradable polymeric system with desired LCSTs.

Organocatalytic Ring-Opening Polymerization Toward Poly(γ-amide-ε-caprolactone)s with Tunable Lower Critical Solution Temperatures

γ-Amide-e-caprolactones including 7-oxo-N-propyloxepane-4-carboxamide (NNCL), N-isopropyl-7-oxooxepane-4-carboxamide (NICL), N,N-diethyl-7-oxooxepane-4-carboxamide (DECL), and 5-(pyrrolidine-1-carb...

Multiple Stimuli-Responsive Cellulose Hydrogels with Tunable LCST and UCST as Smart Windows

It has been a significant challenge to prepare multiple-response hydrogels with both lower critical solution temperature (LCST) and upper critical solution temperature (UCST). This work reports the...

Functional cellulose nanocrystals containing cationic and thermo-responsive polymer brushes

Cationic and thermo-responsive polymer brushes were grafted from the surface of cellulose nanocrystals. Di(ethylene glycol) methyl ether methacrylate (MEO2MA) and poly(oligoethylene glycol) methyl ether acrylate (OEGMA300) and (2-methacryloyloxyethyl) trimethylammonium chloride (DMC) were grafted from cellulose nanocrystals (CNCs) via free radical polymerization. The CNC-g-POEGMA (CP) possessed a tunable lower critical solution temperature (LCST) of about 50 °C, and cloud point measurements confirmed that the LCST of the nanoparticles could be manipulated within the range of 40−47 °C by adjusting the DMC content. The salt effect was also investigated, and the results revealed a typical salting-out effect for the CNC-g-POEGMA after the introduction of KCl. On the other hand, the CNC-g-POEGMA-g-DMC (CPD) copolymers displayed two salt-responsive characteristics; polyelectrolyte effect at lower salt concentrations, followed by the salting-out effect at higher salt concentrations, which is dependent on the DMC content.

100th Anniversary of Macromolecular Science Viewpoint: Poly(N-isopropylacrylamide)-Based Thermally Responsive Micelles.

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermally responsive micelles are of great importance as smart materials for a number of applications such as drug delivery and biosensing, owing to their tunable lower critical solution temperature (LCST). Their design and synthesis in the nanoscale size range have been widely studied, and research interest in their structural and physic-chemical properties is continually growing. In this Viewpoint, representative research on the construction of PNIPAAm-based thermally responsive micelles as well as their applications are highlighted and discussed, which would serve as a good start for newcomers in this field and a positive guide for future research.

Design of low temperature-responsive hydrogels used as a temperature indicator

Development of highly thermo-sensitive hydrogels, particularly at a low-temperature range, has promising applications in diverse fields. Herein we designed, synthesized, and characterized tri-copolymer poly(N-tert-butyl acrylamide-co-N-isopropyl acrylamide-co-acrylamide) p(NTBAM-co-NIPAM-co-AM) hydrogels using a facile one-pot method. The copolymerization of two thermo-responsive monomers of NTBAM and NIPAM with hydrophilic AM monomers aimed to tune the temperature range of lower critical solution temperature (LCST) between 8°C and 10 °C by varying the concentrations and molar ratios of NTBAM, NIPAM, and AM. At optimal conditions, p(NTBAM-co-NIPAM-co-AM) hydrogels showed a rapid and large deswelling by reducing their original sizes by 21% in 2 min as temperature was slightly changed from 8 °C to 10 °C. Such low-temperature-triggered de-swelling behavior and tunable LCST property are likely attributed to delicate interplay between different network components and their interactions with water. Due to high temperature sensitivity (∼2 °C), large volume deswelling ratio (90%), and low temperature-responsive range (8–10 °C), we further demonstrated a prototype hydrogel ball actuator as temperature indicator to monitor minor temperature-induced size changes. The design strategy for this p(NTBAM-co-NIPAM-co-AM) hydrogel could be generally applicable to other thermo-responsive hydrogels with different shapes and temperature-responsive ranges, which could be used as low-temperature indicator for many applications including vaccine storage and transportation.

Functional Brush Poly(2-ethyl-2-oxazine)s: Synthesis by CROP and RAFT, Thermoresponsiveness and Grafting onto Iron Oxide Nanoparticles.

Brush polymers are highly functional polymeric materials combining the properties of different polymer classes and have found numerous applications, for example, in nanomedicine. Here, the synthesis of functional phosphonate-ester-bearing brush polymers based on poly(2-oxazine)s is reported through a combination of cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazine and reversible addition-fragmentation chain transfer (RAFT) polymerization. In this way, a small library of well-defined (Đ ≤ 1.17) poly(oligo(2-ethyl-2-oxazine) methacrylate) P(OEtOzMA)n brushes with tunable lower critical solution temperature (LCST) behavior and negligible cell toxicity is prepared. Upon deprotection, the phosphonic acid end-group of the P(OEtOzMA)n brush enables the successful grafting-onto iron oxide nanoparticles (IONPs). Colloidal stability of the particle suspension in combination with suitable magnetic resonance imaging (MRI) relaxivities demonstrates the potential of these particles for future applications as negative MRI contrast agents.

Thermoresponsive DNA by Intercalation of dsDNA with Oligoethylene-Glycol-Functionalized Small-Molecule Intercalators.

Thermoresponsive polymeric materials are important building blocks for smart materials. In this work, the transformation of dsDNA into a thermoresponsive polymer is reported by intercalation of short, oligoethylene-glycol-modified proflavine intercalators. The thermoresponsiveness of the dsDNA-intercalator complex originates from the heating-induced dehydration of the ethylene glycol side chains, which leads to aggregation of the intercalated dsDNA. This work demonstrates the possibility of designing small-molecule intercalators to prepare thermoresponsive dsDNA complexes with tunable lower critical solution temperature behavior.

Synthesis of water soluble and multi-responsive selenopolypeptides via ring-opening polymerization of N-carboxyanhydrides.

We report here the synthesis of water soluble selenopolypeptides via the ring-opening polymerization of N-carboxyanhydrides. The oligoethylene glycol-bearing selenopolypeptides are thermally responsive in aqueous solutions with tunable lower critical solution temperatures. The polymers can also undergo rapid and reversible helix-coil transitions upon responding to the added redox cycle.