Lower Critical Solution Temperature Values Research Articles

Tunable thermoresponsive and stretchable hydrogel sensor based on hydroxypropyl cellulose for human motion/health detection, visual signal transmission and information encryption

Thermoresponsive hydrogels can be used as smart flexible sensors. However, the design and facile preparation of multifunctional thermoresponsive hydrogel sensors still face great challenges. Herein, a tunable thermoresponsive, thermochromic and stretchable poly(2-hydroxypropyl acrylate-co-acrylamide) (P(HPA-co-AM))/hydroxypropyl cellulose (HPC)/lithium chloride (LiCl) hydrogel with the networks constructed from non-covalent interaction was fabricated by photopolymerization. PHPA exhibits excellent thermoresponsiveness. HPC endows the hydrogel with outstanding mechanical performance and enhanced temperature-sensitivity. LiCl not only provides good conductivity, but also regulates the lower critical solution temperature (LCST) of the hydrogel. The hydrogel shows tensile strength up to 300 kPa and maximum strain up to 790 %. The LCST value of the hydrogel can be adjusted from 38 to 75 °C. Therefore, the thermoresponsive conductive hydrogel can realize the information encryption, and be used as sensor through strain and temperature changes in the external environment to realize the motion and health detection, and visual signal transmission. This work is expected to provide ideas for the next generation of smart multifunctional electronic skin and information encryption device.

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.

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.

Influence of ionic liquid modified gold nanoparticles on conformational transition of poly(N-isopropylacrylamide)-b-poly(acryloylmorpholine) block copolymer

Utilizing stimuli-responsive polymers for surface modification of nanoparticle allows the adjustment of properties for individual system; however, limited research explores the impact of ionic liquid-modified gold nanoparticles (AuNPs) on the conformational phase transition of block copolymers. Herein, we synthesized poly(N-isopropylacrylamide)-b-poly(acryloylmorpholine) (PNIPAM-b-PACMO) copolymers by reversible addition − fragmentation chain-transfer polymerization and investigated the effect of ionic-liquid modified AuNPs (IL-AuNPs) on the aggregation behavior of the copolymer. Copolymerization of PNIPAM with PACMO shifted the lower critical solution temperature (LCST) towards higher temperature in comparison to LCST value of PNIPAM. Addition of IL-AuNPs further raises the transition temperature in concentration dependent manner. A more significant alteration in the transition temperature was observed in the presence of IL-AuNPs with a higher alkyl chain length. The variation in transition temperature of the copolymer by different IL-AuNPs yields benefits in the temperature responsive properties which can helpful for various applications.

Investigation of nanocomposite PNIPAm‐g‐graphene with pre‐lower critical solution temperature rapid thermal response function for chip adaptive cooling: A molecular dynamics and computational fluid dynamics simulations

AbstractTemperature‐sensitive hydrogels have been widely used for rapid adaptive cooling in electronic device thermal management with promising applications. However, existing temperature‐sensitive hydrogels can only regulate the flow in the chip cooling system after the ambient temperature reaches their lower critical solution temperature (LCST). Before reaching LCST, effective rapid heat dissipation for electronic chips is not achievable. This study aims to develop a temperature‐sensitive hydrogel that can provide assisted adaptive cooling for electronic chips before reaching its LCST. This requires the hydrogel to have a thermal conductivity far surpassing existing hydrogel materials. Using the temperature‐sensitive hydrogel PNIPAm and graphene molecules as base materials, this research utilized molecular dynamics simulations to graft graphene molecules onto PNIPAm molecules in different ways, resulting in the temperature‐sensitive hydrogel material PNIPAm‐g‐graphene. Non‐equilibrium molecular dynamics (NEMD) was employed to calculate the thermal conductivity of this material under different temperature conditions. The results indicate that the thermal conductivity of PNIPAm‐g‐graphene can reach up to 1.95474 W/m K (graphene grafted at CH3 functional group, temperature at 280 K). Compared to the thermal conductivity of PNIPAm under the same conditions (0.45 W/m K), the increase in thermal conductivity is significant, demonstrating excellent thermal conductivity compared to PNIPAm. Subsequently, this study analyzed the underlying mechanisms of different thermal conductivities in materials obtained by grafting graphene molecules at different points using the method of overlap in Phonon Density of States Curves (PDOS) from the perspective of interfacial thermal conduction. Finally, through computational fluid dynamics (CFD) simulations, this study investigates the chip's adaptive cooling performance with PNIPAm‐g‐graphene material. The results show that, compared to traditional temperature‐sensitive hydrogels, PNIPAm‐g‐graphene can achieve efficient adaptive cooling of chip hotspots before the cooling fluid temperature reaches its LCST value. This finding is significant for the field of chip cooling. The study proposes a new method for rapid, adaptive cooling of chip hotspots and explores its feasibility from the perspectives of molecular dynamics and CFD simulation. It holds importance in the thermal management of electronic devices and the rapid adaptive cooling of electronic chips.

Characterization of a conjugate between poly(N-vinyl caprolactam) and a triazine-based covalent organic framework as a potential biomaterial.

Thermoresponsive polymers (TRPs) have been explored over decades for biomedical applications, and poly(N-vinylcaprolactam) (PVCL) TRP is extensively investigated due to its low toxicity and lower critical solution temperature (LCST), close to physiological temperatures. Besides this, the utilization of covalent organic frameworks (COFs), which belong to a class of porous polymers, in bio-based applications is of great interest due to their remarkable properties. Thus, the integration of PVCL and covalent organic frameworks (COFs) as conjugate materials can lead to advanced bio-based applications; however, the need is to understand the influence of the COF on the PVCL conformation. Herein, a triazine-based COF, CC-TAPT-COF, has been synthesized and completely characterized. Later, the effect of CC-TAPT-COF on the PVCL polymer conformation was studied using various techniques. In fluorescence spectroscopy, a fluorescence quenching for PVCL in the presence of CC-TAPT-COF was observed, which indicated conformational changes. Later, results from thermal fluorescence studies and dynamic light scattering as a function of temperature showed a slight decrease in LCST value for PVCL after the addition of CC-TAPT-COF concentrations. These results showed a slight effect of CC-TAPT-COF on the PVCL conformation. Likewise, a slight decrease in the transmittance value for specific bands in infrared spectra showed a slight effect of CC-TAPT-COF on the PVCL conformation. Further, results from electron microscopy and atomic force microscopy revealed a conjugate formation between PVCL and CC-TAPT-COF due to the presence of binding interactions between them. Overall, the results from several studies showed a slight effect of CC-TAPT-COF on the PVCL during conjugate formation between PVCL and CC-TAPT-COF. This study will be beneficial for the development of COF-thermoresponsive polymer conjugates with a mixture of their unique features as advanced biomaterials.

Development and Characterization of Thermoresponsive Smart Self-Adaptive Chitosan-Based Polymer for Wellbore Plugging.

To meet the escalating demand for oil and gas exploration in microporous reservoirs, it has become increasingly crucial to develop high-performance plugging materials. Through free radical grafting polymerization technology, a carboxymethyl chitosan grafted poly (oligoethylene glycol) methyl ether methyl methacrylate acrylic acid copolymer (CCMMA) was successfully synthesized. The resulting CCMMA exhibited thermoresponsive self-assembling behavior. When the temperature was above its lower critical solution temperature (LCST), the nanomicelles began to aggregate, forming mesoporous aggregated structures. Additionally, the electrostatic repulsion of AA chains increased the value of LCST. By precisely adjusting the content of AA, the LCST of CCMMA could be raised from 84.7 to 122.9 °C. The rheology and filtration experiments revealed that when the temperature surpassed the switching point, CCMMA exhibited a noteworthy plugging effect on low-permeability cores. Furthermore, it could be partially released as the temperature decreased, exhibiting temperature-switchable and self-adaptive plugging properties. Meanwhile, CCMMA aggregates retained their reversibility, along with thermal thickening behavior in the pores. However, more detailed experiments and analysis are needed to validate these claims, such as a comprehensive study of the CCMMA copolymer's physical properties, its interaction with the reservoir environment, and its performance under various conditions. Additionally, further studies are required to optimize its synthesis process and improve its efficiency as a plugging material for oil and gas recovery in microporous reservoirs.

Temperature-sensitive polymer based nano-SiO2 composite multi-component synergistic improvement of shale stability in water-based drilling fluids

Shale instability caused by the development of nano-micron-scale fractures, pores, and bedding is always a challenge for drilling complex formations. In this work, two additives (Temperature-sensitive polymer based nano-SiO2 composite (SNAS) and poly (NVP-TAAC-AMPS) (NTA)) were synthesized. The lower critical solution temperature (LCST) value of SNAS could be controlled by adjusting the monomer ratio. As temperature-sensitive nanocomposites, SNAS has the rheological control of drilling fluid. The effects of SNAS and NTA on shale stability were tested based on analytical approaches, including shale wettability, microporous membrane fluid loss, pressure transmission rate, shale specific surface area, shale pore volume, shale strength, linear swelling percentage and shale cuttings recovery. When the temperature is higher than the LCST value, due to the transition from hydrophilicity to hydrophobicity of SNAS, it not only changes the wetting angle of shale, but also enhances the plugging effect of SNAS. The composite system could form tight plugging layer and hydrophobic region compared with single SNAS, which was more conducive to improve plugging performance of shale. Finally, the synergistic improvement mechanism of shale stability combined with SNAS and NTA were further proposed.

Synthesis and characterization of chitosan-based graft copolymers with temperature-switchable and self-adaptive plugging performance for drilling in microporous formation

The increasing oil–gas explorations in microporous formations and the intensified environmental requirements necessitate the development of high-performance, environmentally friendly and sustainable plugging materials to maintain wellbore stability in drilling engineering. In this work, a series of graft copolymers of carboxymethyl chitosan-g-poly(oligo(ethylene glycol) methyl ether methacrylate-co-acrylic acid) (GCOA) is synthesized through free-radical graft-from polymerization. The oligo(ethylene glycol) methyl ether methacrylate (OEGMA) and acrylic acid (AA) can be well copolymerized in the grafts as confirmed by structural characterizations, and the incorporation of AA improves the grafting ratio and grafting efficiency. All obtained GCOAs possess the temperature-responsive aggregation behavior, which causes the formation of aggregated meso-assemblies from original nano-micelles when heating above their lower critical solution temperature (LCST), accompanied by the phase separation. Meanwhile, the presence of AA segments increases the LCST due to the resistance of enhanced polymer–polymer electrostatic repulsion to the hydrophobic attraction. By the delicate control of AA molar ratio from 0 to 50 mol%, the LCST values of GCOAs can be adjusted from 90 °C to 110 °C. Furthermore, the GCOAs are formulated as smart plugging fluids and the intelligent plugging evaluation method is established based on core flow test with continuous temperature control. The results indicate that the GCOAs can form effective plugging in both low- and median-permeability cores when temperature reaches above a switching point and the formed plugging can be partially removed after cooling, showing the temperature-switchable and self-adaptive plugging capacity as a consequence of reversible retention of GCOA aggregates and thermo-thickening behavior in pore-throat spaces. These features enable the implementation and removal of in-situ plugging in the specific temperature sections during drilling, and provide a new insight into the design of novel smart plugging materials with sustainable and recycling values.

Thermo‐responsive macroporous p(NIPAM) cryogel affords enhanced thermal stability and activity for ɑ‐glucosidase enzyme by entrapping in situ

AbstractThe concept of using a macroporous thermo‐responsive poly(N‐isopropylacrylamide) (p(NIPAM)) polymer matrix for enzyme immobilization having lower critical solution temperature (LCST) is rationalized by the availability of the many compartments (pores) to entrap enzymes to operate within pores of three‐dimensional matrix providing special environmental conditions. Therefore, the ɑ‐glucosidase (ɑ‐G) immobilization within p(NIPAM) cryogel (ɑ‐G@p(NIPAM)) was carried out under the storage conditions of enzymes, generally ~ −20°C to afford the unnecessary loss of enzyme functionality in comparison to the other enzyme entrapment methods. The LCST value for the prepared p(NIPAM)‐based cryogels was determined as 34.8 ± 1.4°C. The immobilization yield, immobilization efficiency, and activity recovery% values were calculated as 89.4 ± 3.1, 66.2 ± 3.3, and 74.0% ± 3.3%, respectively, at pH 6.8 and 37°C for ɑ‐G@p(NIPAM) cryogel system. Interestingly, the optimum working conditions were attained as 25°C and pH 6.8 with higher activity, 98.4% ± 0.2% for the prepared ɑ‐G@p(NIPAM) cryogel system. The reuse and storage stability studies revealed that the prepared ɑ‐G@p(NIPAM) cryogel system is more effective than the native ɑ‐G enzyme; for example, it showed at least 80% activity after the fifth usage and provided higher activity up to a 10‐day room temperature storage time. Moreover, the kinetic parameters such as Km and Vmax of native ɑ‐G enzyme and ɑ‐G@p(NIPAM) cryogel system were calculated by non‐linear Lineweaver–Burk plot equations.

Investigation of Temperature-Responsive Tocosomal Nanocarriers as the Efficient and Robust Drug Delivery System for Sunitinib Malate Anti-Cancer Drug: Effects of MW and Chain Length of PNIPAAm on LCST and Dissolution Rate

In this study, for the first time, the coated tocosome by blend of chitosan, CS, and poly(N-isopropylacrylamide), PNIPAAm, was developed as the efficient and robust drug delivery system with improved drug encapsulation efficiency, extended stability, proper particle size and industrial upscaling for Sunitinib malate anti-cancer drug. Tocosome was synthesized by using Mozafari method as a scalable and robust method and without the need for organic solvents. The effects of tocosome composition and drug concentration on the stability, particle size of tocosome, zeta potential, encapsulation efficacy and loading of drug into it were investigated by Taguchi method, and optimum composition was selected for combining with the polymeric blend. Homopolymer of PNIPAAm was synthesized by two different polymerization methods, including free radical and reversible addition–fragmentation chain transfer (RAFT). Effects of molecular weight (MW) and chain length of the polymers on lower critical solution temperature (LCST) were examined. The developed nanocarrier in this research, CS-Raft-PNIPAAm-tocosome, indicated LCST value beyond 37°C (about 45°C) and this is suitable for hyperthermia and spatio-temporal release of drug particles.

Temperature Dependence of the Rayleigh Ratio for Toluene: Thermoresponsive Polymers Characterization

AbstractBenzene and toluene are commonly used reference substances for static light scattering (SLS) measurements. However, due to the appearance and wide availability of solid‐state lasers with various wavelengths, there is a need for data on the Rayleigh ratios for references at various wavelengths. Thermoresponsive polymers, which are widely researched now, can have lower critical solution temperature (LCST) values very close to the human body temperature (30–36 °C). Such polymers can be used to develop efficient means for targeted drug delivery. In this paper, we report how to accurately determine the absolute molecular weights of thermoresponsive polymers by the SLS method. This is especially important when the LCST value of a polymer is close to the room temperature (at which SLS measurements are usually taken), which can lead to overestimated results due to the aggregation of macromolecules. So, it is necessary to carefully select the measurement temperature and, accordingly, data are needed on the temperature dependence of the Rayleigh ratios for a reference sample. The Rayleigh ratios and depolarization factors, ρu and ρv, were first determined for toluene within a wide temperature range (10–50 °C). The temperature dependencies of these parameters were shown to be linear in the whole range investigated. Temperature coefficients for the calculation of the Rayleigh ratios at different scattering geometries were obtained. The particular importance of choosing the optimal measurement temperature when determining the molecular weights of thermoresponsive polymers with low values of LCST using the static light scattering method was demonstrated.

Effect of the Hydrophilic/Hydrophobic Pendants on Physicochemical Properties: Applications Based on Cyclotriphosphazene Core

AbstractThis study focused on investigating the effect of hydrophilic and hydrophobic substituents on the physicochemical properties for medical applications. In this study, to understand the effect of hydrophilic and hydrophobic substituents on physicochemical parameters such as lipophilicity and thermosensitivity, a series of cis‐tris nongeminal [N3P3(R1‐4)3(Ra‐f)3] cyclotriphosphazenes [R1‐4=diethylene glycol monomethyl ether (DEGME), triethylene glycol monomethyl ether (TEGME), methoxypolyethylene glycol (mPEG350), methoxypolyethylene glycol‐550 (mPEG550); (2–5) respectively; Ra‐f=pyrazole, 3,5‐dimethylpyrazole, imidazole, 2‐methyl imidazole, benzimidazole, 5,6‐dimethyl benzimidazole, [2(a–f), 3(a–f), 4(a–f), 5(a–f)] respectively] were synthesized and fully characterized by mass, 31P and 1H NMR spectroscopies. Solubility and thermosensitivity based on substituent dependent LCST (lower critical solution temperature) behaviour of all synthesized molecules are investigated. Each compound analysed by HPLC to determine the lipophilicity values (logPo/w) between n‐octanol and water. A good correlation (r=0.9975 and R2=0.9948) was observed between the experimentally determined logPo/w and estimated milogP values. The results showed that LCST values of the reported compounds were linearly correlated with their lipophilicity values.

Intelligent micro-vehicles for drug transport and controlled release to cancer cells

The idea that pH decreases significantly in tumors is widespread, however recent progress in the measurement of pH in cancer tissues has revealed that the intracellular pH of cancer cells is neutral or even mildly alkaline compared to normal tissues [Hao et al., 2018]. However, in both cancer and normal cells the pH drops from 6.0–5.5 in endosomes to 5.0 in lysosomes after particle internalization by EPR effect. Here, the design of “intelligent” delivery systems able to exploit these pH variations is reported.Poly(N-isopropylacrylamide-co-4-vinylpyridine) (poly(NIPAAm-co-4-VP)) was synthesized and characterized as an exciting pH/temperature sensitive copolymer with a pKa value of 5.05. The lower critical solution temperature (LCST) of the copolymer was determined at physiological conditions (phosphate buffer (PB) at pH = 7.4 and 36 °C), and at acidic pH values similarly to those of cell compartments. Values of LCST of the copolymer with the co-monomer molar ratio of 86:14 (NIPAAm:4-VP) are 22.1 and 36.8 °C in PB at pH = 7.4 and pH = 5.0, respectively. Therefore, the drug loaded microspheres synthesized from this copolymer are insoluble at physiological conditions and keep the drug inside, but quickly solubilize at lysosomal conditions (pH = 5.0) releasing the cargo.

Dual stimuli-responsive silver nanoparticles decorated SBA‒15 hybrid catalyst for selective oxidation of alcohols under ‘mild’ conditions

Herein, we develop an efficient and novel catalytic system, i.e. silver nanoparticles (AgNPs) incorporated mesoporous silica SBA‒15/copolymer hybrid material, for selective oxidation of different alcohols to aldehydes or ketones under ‘mild’ conditions. The copolymer of N,-N -dimethylaminoethyl methacrylate and 2-hydroxyethyl acrylate (p(DMAEMA- co -HEA)) was used to graft the surface-modified SBA‒15 (MS) using free radical polymerization method. Then AgNPs were decorated on the polymer grafted SBA‒15. The dual (thermal and pH) responsive behaviors of the AgNPs/p(DMAEMA- co -HEA)/MS catalyst were investigated using the dynamic light scattering technique. The lower critical solution temperature (LCST) of the copolymer was found to be approximately 30–35 °C. The catalytic activity of AgNPs/p(DMAEMA- co -HEA)/MS was investigated for the selective oxidation of different alcohols to aldehydes or ketones. The conversion of catalytic products and selectivity were calculated using gas chromatographic techniques, whereas the molecular structure of products was determined using 1 H and 13 C nuclear magnetic resonance spectroscopy. The catalyst showed improved catalytic activity toward the oxidation of alcohols to aldehydes in aqueous medium below LCST and pKa value (7–7.5) of the copolymer. The selectivity toward the corresponding aldehyde was found to be significantly high (99%). The main advantages of the hybrid catalyst as compared to existing catalysts include outstanding alcohol conversion (up to 99%), short reaction time (1 h), small necessary amount of catalyst (6 mg), and performing the catalytic conversion at room temperature using water as a solvent, which are highly beneficial for organic conversion under mild reaction conditions. • A catalytic system for selective oxidation of alcohols under ‘mild’ conditions was developed. • The catalyst consists of a temperature and pH-responsive copolymer, SBA-15, and Ag nanoparticles. • The catalyst showed outstanding alcohol conversion (up to 99%) within a short reaction time (1 h). • The catalyst performed the catalytic conversion at room temperature using water as a solvent.

Monitoring phase transition behavior of Poly(N-vinylcaprolactam) via nanostructure-based functionalized carbon nanotubes

The ubiquitous behavior of thermoresponsive polymers (TRPs) in terms of their amphiphilicity and reversible behavior towards temperature make them to exhibit wide applications in biomedical science, biosensors and biotechnological fields. The electrical and surface properties of multiwalled carbon nanotubes (MWCNTs) have received immense attention due to their high flexibility to take any shape (tube, circles) to bind with different macromolecular moieties. Nonetheless, TRPs-MWCNTs interactions with variation in temperature are rarely explored. However, the low solubility of carbon nanotubes (CNTs) in molecular solvents limits their utility in biological process. Therefore, functionalization of CNTs was performed to enhance the dispersibility of CNTs in aqueous medium. In this present study, effect of functionalized carbon nanotubes (fCNTs) on the coil to globular conformation of poly (N-vinylcaprolactam) (PVCL) is explored. PVCL exhibits coil to globular transition due to its biocompatible nature with several additive in permissible range of temperature values. To investigate the lower critical solution temperature (LCST) of PVCL in presence of fCNTs, various biophysical techniques such as fluorescence spectroscopy, dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were employed. Furthermore, for better understanding of morphological changes of PVCL in fCNTs, Transmission electron microscopy (TEM) was assessed. The DSC and DLS results confirmed that LCST value of PVCL (32.0 °C) has dropped by 2 °C in presence of fCNTs due to hydrophobic interactions of polymer and fCNTs. This exclusive modification in LCST of PVCL will be sensitive in biological applications. We have studied the first time effect of fCNTs on the phase transition behavior of PVCL which will lead to its widespread applications in the field of biomedical sciences such as drug delivery systems.

Nanocomposite smart hydrogel based on sepiolite nanochannels/N-isopropyl acrylamide/itaconic acid/acrylamide for invertase immobilization

ABSTRACT Novel nanocomposite smart hydrogel (NSH) and smart hydrogel (SH) are prepared to be used as a support for invertase. Spectrophotometric and thermal analysis methods were used for the characterization. Lower critical solution temperature values of SH and NSH were found as 32.68°C and 30.44°C, respectively. From the pH-responsive swellings performed at three different temperatures, the inflection point values of NSH were found at higher pHs compared to SH. Invertase was immobilized onto SH and NSH (SH−I and NSH−I). The optimum pH and temperature values were found. Michaelis constant and maximum reaction rate were calculated. NSH−I showed excellent thermal, operational and pH stability.

Hofmeister Effect on Thermo-responsive Poly(N-isopropylacrylamide) Hydrogels Grafted on Macroporous Poly(vinyl alcohol) Formaldehyde Sponges

In this work, the Hofmeister effects of nine kinds of anions at different concentrations on the lower critical solution temperature (LCST) of the macroporous thermo-responsive poly(N-isopropylacrylamide) grafted poly(vinyl alcohol) formaldehyde (PVF-g-PNIPAM) hydrogels are investigated with differential scanning calorimetry (DSC). Four kinds of anions with strong hydration, including CO32–, SO42–, S2O32–, and F–, and four kinds of anions with weak hydration, including Br–, NO3–, I–, and ClO4–, and Cl– as a medium anion are systematically studied and found to demonstrate the effects of the residual hydroxyl groups and network structure of PVF on the LCST values of PVF-g-PNIPAM hydrogels in comparison with that of neat PNIPAM. On the one hand, the existence of hydroxyl groups on PVF backbone promotes the solubility of grafted PNIPAM due to their hydrophilicity and hydrogen-bond interactions with water. On the other hand, the network structure of as-prepared samples restricts free movements of grafted PNIPAM chains, which results in the increase of LCST values. In addition, the difference of grafting percentage also influences the variation of LCST values of PVF-g-PNIPAM hydrogels under salt concentration.

Comonomer effect: Switching the lower critical solution temperature to upper critical solution temperature in thermo‐pH sensitive binary graft copolymers

ABSTRACTHydrophilic biocompatible surfaces can be obtained by grafting stimuli‐sensitive polymers onto commercially available medical devices. Thermo and pH‐responsive polymers are two of the most studied materials due to their potential application as drug delivery systems. Poly(N‐vinylcaprolactam) has a lower critical solution temperature (LCST) near to physiological temperature. However, when it is grafted with pH‐sensitive moieties its LCST it is affected undergoing remarkable displacements. We studied the effect of acrylic acid (AAc), 4‐vinylpyridine (4VP), and 1‐vinylimidazole (Vim) on the LCST of N‐vinylcaprolactam (NVCL) grafted onto silicone rubber (SR), and SR‐g‐NVCL (32.5 °C). The binary graft copolymers were obtained by ionizing grafting radiation using the simultaneous technique; the samples were characterized by Fourier transform infrared attenuated total reflectance (FTIR‐ATR), cross‐polarization magic angle spinning nuclear magnetic resonance (CP/MAS 13C‐NMR), and thermogravimetrical analysis (TGA). LCST value was dramatically affected by the comonomer content; even it was observed the switching from LCST to upper critical solution temperature (UCST) for (SR‐g‐NVCL)‐g‐AAc and (SR‐g‐NVCL)‐g‐4VP samples. The observed behavior is rarely reported for binary graft copolymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48170.

Synthesis and self‐assembly of thermoresponsive poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) double hydrophilic block copolymers

ABSTRACTWe report on the synthesis of novel poly(N‐isopropylacrylamide)‐b‐poly(oligo ethylene glycol methyl ether acrylate) (PNIPAM‐b‐POEGA) thermoresponsive block copolymers using reversible addition–fragmentation chain transfer polymerization methodologies. The synthesized block copolymers are characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared (FTIR) techniques in terms of molecular weight and composition. Their thermoresponsive self‐assembly in aqueous media is investigated using dynamic and static light scattering. The PNIPAM‐b‐POEGA thermoresponsive block copolymers formed aggregates in water by increasing the temperature above the lower critical solution temperature value of PNIPAM block. Solution pH seems to affect the self‐assembly behavior in some cases due to the presence of COOH end groups. Therefore, the copolymers were utilized as “smart” nanocarries for the hydrophobic drug indomethacin, implementing a novel encapsulation protocol taking advantage of the thermoresponsive character of the PNIPAM block. The empty and loaded self‐assembled nanocarriers systems were studied by light scattering techniques, ultraviolet–visible, and FTIR spectroscopy, which gave information on the size and structure of the nanocarriers, the drug loading content and the interactions between the drug and the components of the block copolymers. Drug loaded nanostructures show stability at room temperature, due to active drug/block copolymer interactions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1467–1477