Temperature-responsive Behavior Research Articles

Molecular dynamics simulation on temperature and stain rate-dependent tensile response and failure behavior of Ni-coated CNT/Mg composites

This paper focuses on the molecular dynamics (MD) simulation of the tensile response of Ni-coated CNT-reinforced magnesium matrix composites (Ni-CNT/Mg) subjected to uniaxial tension at different temperatures and strain rates. The results show that Ni-CNTs can improve the mechanical properties of the composites effectively. The maximum stress of Ni-(6,6)CNT/Mg is, respectively, increased by 25.66 and 11.13%, while the elastic modulus is increased by 23.69 and 14.43% compared with those of the single-crystal Mg and uncoated (6,6)CNT/Mg at 300 K and 1 × 109 s−1. In addition, the calculated elastic modulus of the Ni-(6,6)CNT/Mg composite is consistent with the prediction based on the rule-of-mixture. The Ni-CNT/Mg composites still have better mechanical properties at 500 K but exhibit a significant temperature softening effect in the temperature range 100–500 K and a strong positive strain-rate sensitivity at a strain rate greater than 1 × 109 s−1. The various failure modes of the composite at the nano-scale are mainly determined by the combined effects of the different factors such as the atomic disordering, the void and dislocation nucleation, structural phase transformations in Mg nanocrystals near the interface, and the subsequent fracture of the Ni-coated CNT close to the voids.

A starch-based stimuli-responsive magnetite nanohydrogel as de novo drug delivery system

A novel starch-based stimuli-responsive magnetite nanohydrogel (MNHG), namely Fe3O4-g-[poly(N-isopropylacrylamide-co-maleic anhydride)]@strach; Fe3O4-g-(PNIPAAm-co-PMA)@starch, was successfully developed for targeted delivery of doxorubicin (DOX) as an anticancer drug. First, magnetite nanoparticles (MNPs) was modified using chloroacetyl chloride moiety followed by grafting of NIPAAm and MA monomers through ATRP technique. The resultant Fe3O4-g-(PNIPAAm-co-PMA) nanocomposite was crosslinked through the reaction between the anhydride group of MA and hydroxyl groups of starch to afford a Fe3O4-g-(PNIPAAm-co-PMA)@starch MNHG. The chemical structure of the synthesized materials were confirmed using Fourier transform infrared (FTIR) spectroscopy. Furthermore, morphology, size, thermal property, and magnetic properties of the synthesized MNHG were studied. This MNHG was loaded with DOX, and drug loading and encapsulation efficiencies as well as pH- and temperature-responsive drug release behavior of the fabricated MNHG were also evaluated. As results, we envision that the developed MNHG has potential as de novo drug delivery system (DDS) due to its smart physicochemical features.

Temperature-Responsive Hydrogel-Coated Gold Nanoshells.

Gold nanoshells (~160 nm in diameter) were encapsulated within a shell of temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) using a surface-bound rationally-designed free radical initiator in water for the development of a photothermally-induced drug-delivery system. The morphologies of the resultant hydrogel-coated nanoshells were analyzed by scanning electron microscopy (SEM), while the temperature-responsive behavior of the nanoparticles was characterized by dynamic light scattering (DLS). The diameter of the P(NIPAM-co-AA) encapsulated nanoshells decreased as the solution temperature was increased, indicating a collapse of the hydrogel layer with increasing temperatures. In addition, the optical properties of the composite nanoshells were studied by UV-visible spectroscopy. The surface plasmon resonance (SPR) peak of the hydrogel-coated nanoshells appeared at ~800 nm, which lies within the tissue-transparent range that is important for biomedical applications. Furthermore, the periphery of the particles was conjugated with the model protein avidin to modify the hydrogel-coated nanoshells with a fluorescent-tagged biotin, biotin-4-fluorescein (biotin-4-FITC), for colorimetric imaging/monitoring.

Effects of nonionic surfactant and salts on the interactions between oppositely charged star-shaped copolymer and ionic surfactant in aqueous solutions

The interaction between star-shaped copolymer poly(2-(dimethylamino)ethyl methacrylate-b-2-(2-methoxyethoxy)ethyl methacrylate) (CDPDPM) and anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solutions are investigated by using fluorescence and dynamic light scattering (DLS) techniques. The effects of nonionic surfactant dodecyl β-D-maltopyranoside (C12G2) and salts including inorganic salt ammonium bromide (NH4Br) and organic salt tetra-n-butylammonium bromide (Bu4NBr) on the interaction between CDPDPM and SDS have been explored systematically. The results have suggested that SDS molecules can bind on CDPDPM by electrostatic interaction between the positively charged CDPDPM and negatively charged SDS and thus weaken the binding ability of CDPDPM to water molecules. CDPDPM exhibits temperature-responsive aggregation behavior in aqueous solution gradually with the increase of SDS concentration and the lower critical solution temperature (LCST) decreases correspondingly. The introduction of nonionic surfactant C12G2 changes the interaction between CDPDPM and SDS significantly by participate the formation of complexes and the stability of the CDPDPM/SDS complexes declines leading to the chance of forming larger complexes is deprived at higher temperature. The addition of NH4Br to the CDPDPM/SDS system can retard the binding of SDS on the polymer chains because of electrostatic shielding. Correspondingly, LCST is higher and the formed aggregates are smaller. For CDPDPM/Bu4NBr/SDS system, the phenomenon is similar to that of the CDPDPM/C12G2/SDS system. This should be attributed to the nature of Bu4N+, possesses not only positive charges but also certain hydrophobicity, and thus Bu4N+ has the ability to participate and facilitate the formation of SDS micelles. Obviously, the LCST of the mixed system can be tailored by adjusting the system composition on purpose.

Rationally designed hyperbranched azopolymer with temperature, photo and pH responsive behavior

A novel hyperbranched azopolymer, HPAzoAMAM-star-EG3, was synthesized and it could self-assemble into uniform large compound micelles with multi-stimuli responsive behavior.

Experimental and Numerical Study on the Behavior of Energy Piles Subjected to Thermal Cycles

A laboratory‐scale model test is conducted to improve the understanding of the effects of thermal cycles on the mechanical behavior of energy piles. The model pile is composed of cement mortar and dry sand with a relative density of 30% is used for the model ground. After applying the working load to the pile head, the pile is subjected to three thermal cycles with a magnitude of 15°C. The measured temperature response and mechanical behavior are analyzed and used to validate the proposed numerical approach. In the numerical analysis, the temperature variation due to thermal cycles is calculated using uncoupled heat transfer analysis. Then, the computed temperature field is used as the boundary condition in the sequence stress analysis. A series of numerical sensitivity analyses are carried out using the sequentially coupled method to investigate the long‐term performance of energy piles under different soil and pile head restraint conditions. The numerical results suggest that the restraint condition at the pile head plays an important role in the mechanical response of energy piles. The ultimate pile resistance after thermal cycles does not decrease significantly. The accumulation of settlement of the free head pile and the reduction in the axial force of the restrained head pile should be considered in the design.

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

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

Synthesis and Characterization of Thermoresponsive Hydrogels Based on N-Isopropylacrylamide Crosslinked with 4,4'-Dihydroxybiphenyl Diacrylate.

A novel crosslinker [4,4′-dihydroxybiphenyl diacrylate (44BDA)] was developed, and a series of temperature-responsive hydrogels were synthesized through free radical polymerization of N-isopropylacrylamide (NIPAAm) with 44BDA. The temperature-responsive behavior of the resulting gels was characterized by swelling studies, and the lower critical solution temperature (LCST) of the hydrogels was characterized through differential scanning calorimetry. Increased content of 44BDA led to a decreased swelling ratio and shifted the LCST to lower temperatures. These novel hydrogels also displayed resiliency through multiple swelling–deswelling cycles, and their temperature responsiveness was reversible. The successful synthesis of NIPAAm-based hydrogels crosslinked with 44BDA has led to a new class of temperature-responsive hydrogel systems with a variety of potential applications.

Thermally Induced Bending of ReS2 Nanowalls.

Among the variety of stimuli-responsive materials, temperature-responsive materials (TRMs) can adapt to the surrounding environment in the presence of a thermal stimulus, and they have attracted considerable attention in sensors, actuators, and surface engineering. However, polymers, as the most representative TRMs, are far from ideal with respect to long-term reliability and durability. Here, for the first time, an inorganic material, ReS2 , is analyzed, which possesses an unexpected temperature-responsive behavior that is triggered by stable and reversible thermally induced bending (TIB). Due to thermal fluctuations in the ReS2 layers, intrinsic ripples tend to aggravate rapidly with rising temperature. Then, the weak interlayer interaction of ReS2 is further weakened, thus resulting in interlayer sliding. Due to a decrease in bending rigidity with increasing temperature, out-of-plane bending spontaneously occurs in the ReS2 layers. Interestingly, this TIB of ReS2 can recover to its initial configuration when the temperature drops, which is further confirmed by the reversible wetting measurement. Above all, the TIB behavior of ReS2 exhibits great potential in smart applications, such as smart windows and microfluidic devices, and fills the significant gaps of inorganic TRMs.

Catalytically Initiated Gel-in-Gel Printing of Composite Hydrogels.

Herein, we describe a method to 3D print robust hydrogels and hydrogel composites via gel-in-gel 3D printing with catalytically activated polymerization to induce cross-linking. A polymerizable shear-thinning hydrogel ink with tetramethylethylenediamine as catalyst was directly extruded into a shear-thinning hydrogel support bath with ammonium persulfate as initiator in a pattern-wise manner. When the two gels came into contact, the free radicals generated by the catalyst initiated the free-radical polymerization of the hydrogel ink. Unlike photocuring, a catalyst-initiated polymerization is suitable for printing hydrogel composites of varying opacity, since it does not depend upon light penetration through the sample. The hydrogel support bath also exhibited a temperature-responsive behavior in which the gel "melted" upon cooling below 16 °C. Therefore, the printed object was easily removed by cooling the gel to a liquid state. Hydrogel composites with graphene oxide and multiwalled carbon nanotubes (MWCNTs) were successfully printed. The printed composites with MWCNTs afforded photothermally active objects, which have utility as stimuli-responsive actuators.

Development of Novel N-isopropylacrylamide (NIPAAm) Based Hydrogels with Varying Content of Chrysin Multiacrylate.

A series of novel temperature responsive hydrogels were synthesized by free radical polymerization with varying content of chrysin multiacrylate (ChryMA). The goal was to study the impact of this novel polyphenolic-based multiacrylate on the properties of N-isopropylacrylamide (NIPAAm) hydrogels. The temperature responsive behavior of the copolymerized gels was characterized by swelling studies, and their lower critical solution temperature (LCST) was characterized through differential scanning calorimetry (DSC). It was shown that the incorporation of ChryMA decreased the swelling ratios of the hydrogels and shifted their LCSTs to a lower temperature. Gels with different ChryMA content showed different levels of response to temperature change. Higher content gels had a broader phase transition and smaller temperature response, which could be attributed to the increased hydrophobicity being introduced by the ChryMA.

SYNTHESIS AND TEMPERATURE-RESPONSIVE BEHAVIOR OF N-VINYLCAPROLACTAM-GRAFTED NR

ABSTRACT Temperature-responsive polymers are smart materials that respond to changes in temperature, making them suitable for a range of applications. We report the synthesis and temperature-responsive behavior of N-vinylcaprolactam-grafted natural rubber. The grafting reaction was carried out using deproteinized natural rubber (DPNR) latex, with 2,2′-azoisobutyronitrile (AIBN) as the free radical initiator. The temperature responsiveness of the graft copolymers was investigated using water swelling and contact angle measurement and compared with that of pure DPNR. The graft copolymer was found to be temperature responsive in the range 32–34 °C, whereas the DPNR was not responsive to temperature. Since the temperature responsiveness of graft copolymer is near the human body temperature, it can be used to fabricate biomedical and sensing materials. Dye adsorption studies revealed the Langmuir isotherm, indicating monolayer coverage. The novel temperature-responsive natural rubber demonstrated in this study has potential uses in a wide range of applications.

Structure-Performance Relationships of Temperature-Responsive PLGA-PEG-PLGA Gels for Sustained Release of Bone Morphogenetic Protein-2

PLGA (poly(lactic-co-glycolic) acid)-PEG (polyethylene glycol)-PLGA synthesis conditions have an impact on the physicochemical features of the copolymer and its usefulness as biomaterial. This study reports on an analysis of the composition and structural properties of PLGA-PEG-PLGA copolymers applying a variety of analytical techniques. Viscoelastic properties and particularly the temperature-responsive behavior of PLGA-PEG-PLGA showed a marked dependence on copolymer structural features. Physicochemical and biological properties, such as bioadhesion, biocompatibility and cell viability, of the raw copolymers and their gels were also evaluated. The most promising copolymer was chosen to formulate the osteoinductive protein bone morphogenetic protein-2 (125I-BMP-2), and the ability of its gels to sustain the release both in vitro and in vivo was monitored in situ using a gamma counter. In vitro diffusion studies were carried out using a bioinspired set-up that included a biorelevant receptor medium. In vivo release tests after implantation in a critical-size calvarial defect model showed an important burst, but then the release fitted well to the square-root kinetics. Importantly, the release rate constants recorded in vitro and in vivo matched each other suggesting close in vitro–in vivo correlation. Overall, the information gathered opens new perspectives in the biomedical application of these temperature-sensitive materials.

Thermoresponsive Copolymer Poly(N-Vinylcaprolactam) Grafted Cellulose Nanocrystals: Synthesis, Structure, and Properties

A novel thermoresponsive copolymer poly(N-vinylcaprolactam) grafted cellulose nanocrystals (PVCL-g-CNCs) was synthesized using surface-initiated atom transfer radical polymerization, and its temperature responsive behavior was studied in this work. The chemical structure characterization by Fourier transform infrared spectroscopy, solid-state CP/MAS 13C NMR spectroscopy, and X-ray photoelectron spectroscopy confirmed the presence of covalently grafting PVCL chains on the CNC surface. The crystalline structure and nanorod-shaped morphology of CNCs were well preserved after polymerization. Transmission electron microscope results indicated that the surface of CNCs was covered with grafted PVCL brushes. The viscoelastic properties of PVCL-g-CNC aqueous suspensions (1.0 wt %) by dynamic rheology measurements confirmed the thermally induced phase transition behavior. The work presented herein paves the way to design CNC-based advanced functional materials benefiting both from the intrinsic characteristics of C...

Functionalization of Carbon Particles by Atom Transfer Radical Polymerization

ABSTRACTSpherical carbon particles (CPs) with controllable size and surface functionalities were prepared via hydrothermal treatment using sucrose as a precursor and then post modification methods. The CPs were prepared in two steps; firstly, dewatering of sucrose molecules at relatively low temperatures and secondly, carbonization at high temperatures. The micro/nano-sized CPs were functionalized by 2-Acrylamido-2-methylpropane sulfonic acid (AMPS), (3-Acrylamidopropyl)-trimethylammonium chloride (APTMACI), and N-isopropylacrylamide (NIPAM) in order to have the corresponding polymers on the surface of CPs. The monomers were polymerized via atom transfer radical polymerization (ATRP) by means of grafted initiator onto the CPs surface. Additionally, copolymer of these monomers was synthesized to introduce additional properties. The stability of the functionalized CPs in different solutions, and pH, temperature responsive behaviors of the newly prepared CP-polymers composite were evaluated.

Composites Formed from Thermoresponsive Polymers and Conductive Nanowires for Transient Electronic Systems.

The disintegration of transient electronic systems after a preprogrammed time or a particular stimulus (e.g., water, light, or temperature) is fundamentally linked to the properties and behavior of the materials used for their construction. Herein, we demonstrate that polymers exhibiting lower critical solution temperature (LCST) behavior can work as thermoresponsive substrates for circuitry and that these materials can be coupled with conductive nanowires to form a transient electronics platform with unique, irreversible temperature-responsive behavior. The transient systems formed from composites of LCST polymers and conductive nanowires exhibit stable electrical performance in solution (Tsolution > LCST) for over 24 h until a cooling stimulus triggers a rapid (within 5 min) and gigantic (3-4 orders of magnitude) transition in electrical conductance due to polymer dissolution. Using a parylene mask, we are able to fabricate thermoresponsive electrical components, such as conductive traces and parallel-plate capacitors, demonstrating the versatility of this material and patterning technique. With this unique stimulus-responsive transient system and polymers with LCSTs above room temperature (e.g., poly(N-isopropylacrylamide), methyl cellulose), we have developed a platform in which a circuit requires a source of heat to remain viable and is destroyed and vanishes once this heat source is lost.

Temperature-responsive N-isopropylacrylamide-grafted natural rubber

Temperature-responsive polymers are smart materials that respond to changes in temperature and have a wide range of applications, ranging from sensing to biomedical fields. In this work, we investigated the synthesis and temperature-responsive behavior of responsive elastomer based on N-isopropylacrylamide-grafted natural rubber. The grafting reaction was carried out using deproteinized natural rubber (DPNR) latex and potassium persulfate as free radical initiator. The temperature responsiveness of the graft copolymers was investigated using water swelling and contact angle measurements, and compared with that of pure DPNR. The lower critical solution temperature of the graft copolymer was found to be in the range 30–34 °C, whereas the DPNR was not responsive to temperature. Furthermore, the graft copolymer exhibited temperature responsiveness in a solid state. As the temperature responsiveness of the graft copolymer is close to the human body temperature, it can be used in biomedical applications. Dye adsorption studies revealed the Langmuir isotherm, indicating monolayer coverage. The technique proposed in this study produces a temperature-responsive natural rubber, with potential applications as a responsive material for use in sensing and biomedical products.

Robust Stimuli‐Responsive Membranes Prepared from a Blend of Polysulfone and a Graft Copolymer Bearing Binary Side Chains with Thermo‐ and pH‐Responsive Switching Behavior

A stimuli-responsive membrane exhibiting independent pH- and temperature-responsive behavior was fabricated from a blend of commercial polysulfone with a functional amphiphilic binary graft copolymer, namely, polysulfone-graft-(poly(isopropylacrylamide-co-acrylic acid)-random-poly(methyl acrylate)), denoted PSf-g-(P(NIPAAm-co-AA)-r-PMMA). Two graft copolymers with different lengths of P(NIPAAm-co-AA) side chains were designed and enriched on the membrane surface to serve as thermo- and pH-responsive on/off switches. The differences between the dual-responsive behaviors of the two kinds of polymer-blend membranes were studied by water-flux and contact-angle measurements. The PMMA side chains served to securely anchor the graft copolymers to the membrane substrate, and the blended membrane prepared from binary graft copolymer was more stable and exhibited more robust stimuli-responsive behavior than that prepared from mono-graft copolymer PSf-g-P(NIPAAm-co-AA).

Self-supporting pH- and temperature-responsive ethyl cellulose-g-PDMAEMA microporous membranes through non–solvent-induced phase separation process

ABSTRACTFirst, ethyl cellulose-g-poly(2-(dimethylamino) ethyl methacrylate) (EC-g-PDMAEMA) was synthesized through atom transfer radical polymerization. Second, the polymer was used to prepare self-supporting microporous membranes through nonsolvent-induced phase separation process. The chemical structures of EC0.2-g-PDMAEMA15 was confirmed by 1H NMR and FTIR. And the copolymer micelles were characterized by UV, laser particle-size analysis, and TEM. The results indicated that the copolymer had pH- and temperature-responsive behaviors. Furthermore, the morphology study of microporous membranes indicated that the pores became smaller and more uniform with the increase of tetrahydrofuran (THF) content and “open time”, and the most optimal preparation conditions were using 75% THF/25% DMF (v/v) as solvents with the “open time” 30 s. What’s more, the membranes were responsive to pH and temperature stimulus in terms of water flux.

Control of pH- and temperature-responsive behavior of mPEG-b-PDMAEMA copolymers through polymer composition

ABSTRACTA series of poly(ethylene glycol) monomethyl ether-block-poly(2-(dimethylamino)ethyl methacrylate) (mPEG-b-PDMAEMA) diblock copolymers were synthesized using atom transfer radical polymerization to achieve controlled polymer molecular weight and narrow molecular weight distribution. The thermoresponsive properties of the mPEG-b-PDMAEMA diblock copolymers in aqueous buffered solutions were determined using UV-Visible spectroscopy and dynamic light scattering. The cloud point, a soluble-to-insoluble transition, was observed for all mPEG-b-PDMAEMA diblock copolymer solutions. Increasing either the mPEG or PDMAEMA molecular weight resulted in a decrease in observed cloud points as a function of pH and polymer concentration. Changing the mPEG molecular weight determined whether a second, higher temperature, thermal transition was observed as a function of pH and polymer concentration. Controlling the thermoresponsive properties of mPEG-b-PDMAEMA diblock copolymers through polymer composition, concentration, and pH enables the tailoring of these copolymers for applications ranging from non-viral gene delivery to use as a strengthening agent in paper.