Critical Solution Temperature Of Poly Research Articles

A temperature‐responsive dual network hydrogel for reversible smart actuator

AbstractNowadays, soft actuators have received extensive attention in many application fields, among which hydrogels have become an important choice for constructing soft actuators due to their unique properties. However, the actuating behaviors of hydrogel‐based actuators are usually monotonous due to their unchangeable shapes and structures. Herein, we report a temperature‐responsive hydrogel actuator with a bilayer structure. Based on the dual network structure (polyvinyl alcohol/poly acrylamide and polyvinyl alcohol/poly (N‐isopropylacrylamide), the actuators can realize the reinforcement compared with the single network. Because of the intrinsic lower critical solution temperature of poly (N‐isopropylacrylamide, both sides of actuators have different swelling rates, enabling them to achieve the thermal‐responsive actuation and shape programming. Therefore, this work is promising to provide a new strategy for designing temperature switches and thermally driven soft robots.

The Influence of pH/Salt Concentrations on Tuning Lower Critical Solution Temperature of Poly(NIPAAm-co-DMAA-co-DTBAVA) Multi-Environmentally Terpolymer

New series of thermo-pH multi-responsive terpolymers were fabricated. Cationic acrylate monomer was synthesized and named by [2-((ditert-butylamino)methyl)-4-formyl-6-methoxyphenyl acrylate] and abbreviated as (DTBAVA). 1H NMR and 13C NMR investigated the new compounds and FT IR. The new terpolymers were fabricated by the free radical polymerization of N-isopropylacrylamide NIPAAm, 10 mol% N, N-dimethylacrylamide and 5, 10, and 20 mol% DTBAVA. The investigation process involved the chemical method such as 1H NMR and FT IR; physical methods for the solid terpolymers as glass temperature by DSC, polymer degradation by TGA, and polymer crystallinity via XRD. GPC was performed for molecular weights and dispersity; contact angles for identifying the hydrophilic or hydrophobic terpolymers solutions. The lower critical solution temperatures Tc,s, and cloud points Cp,s of terpolymers were recorded considering the impact of pH solutions and the concentrations of different sodium salts of (SO4−2, Cl−1, and SCN−1) in the Hofmeister series; turbidity measurements were used via UV/vis spectroscopy and micro-DSC. In a new optimization study, we will use these terpolymers in the post-polymerization with biomolecules such as chitosan, protein, and amino acids via Schiff base.

Effect of concentration and ionic strength on the lower critical solution temperature of poly(N-isopropylacrylamide) investigated by small-angle X-ray scattering

ABSTRACT Thermoresponsive polymers, with special emphasis on poly(N-isopropylacrylamide) (PNIPAAM) have been the focus of several investigations due to its potential applications in many fields of physical and polymer chemistry. PNIPAAM has a “lower critical solution temperature” at 32°C. The LCST can be finely tuned by copolymerization with hydrophobic or hydrophilic comonomers, and with a change of physical chemical parameters, such as ionic strength of the solution. We investigated the effect of polymer concentration on the LCST in two different solution environment, in pure water and in 50 mM NaCl solution with small-angle X-ray scattering (SAXS) of relatively low molecular mass polymers. We showed that the radius of gyration of the pNIPAAM chains increases with the addition of NaCl to the system due to the low level of specific adsorption of chloride ions on the polymer, whilst increasing the temperature causes a shrinkage of the polymer chains. Furthermore, by increasing the temperature the attractive interaction between the individual polymer chains is enhanced which turns into aggregation at the LCST.

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.

Prediction of the lower critical solution temperature of poly(N-isopropylacrylamide-co-methoxy triethyleneglycol acrylate) in aqueous salt solutions using support vector regression

This study investigates the lower critical solution temperature (LCST) behavior of a novel thermosensitive NIPA-co-MTGA polymer comprising N-isopropylacrylamide (NIPA) and methoxy triethyleneglycol acrylate (MTGA) by inducing hydrophilic/hydrophobic transitions in an aqueous salt solution. The LCST of the NIPA-co-MTGA polymer was in between that of the NIPA and MTGA homopolymers, and depended on the polymer composition. The LCST of all the polymers decreased with increasing salt concentration. The extent of decrease depended on the type of salt, with the order qualitatively corresponding to the Hofmeister series of anions. The LCSTs of the polymers in aqueous salt solutions were modeled and successfully predicted using support vector regression (SVR), a machine learning methodology. This is the first study to predict the LCST of thermosensitive polymers in aqueous salt solutions using SVR.

Temperature Responsive Poly(N-isopropylacrylamide-block-styrene) Block Copolymer Coatings with Tunable Hydrophilicity

Responsive polymers have been explored for both fundamental and applied studies due to their ability to undergo conformational and chemical changes upon receiving an external stimulus. In this work, we report the wetting behavior of thermoresponsive poly(N-isopropylacrylamide-block-styrene) diblock copolymer films, below and above the lower critical solution temperature of poly(N-isopropylacrylamide) studied using contact angle measurements. The water contact angle determined for the 2 wt% films at 27°C is found to be 24° and 57° at 40°C. Though the water contact angle showed a systematic increase with increasing temperature, it never crossed to the hydrophobic domain. This infers that the PNIPAM chains lie in the corona of the poly(N-isopropylacrylamide-block-styrene) micelles. Here, we show that a temperature tunable surface can be obtained by coating a surface with poly(N-isopropylacrylamide-block-styrene) block copolymer; however, the response lies within the limits of hydrophilicity.

Hemozoin-catalyzed precipitation polymerization as an assay for malaria diagnosis

Methods to diagnose malaria are of paramount interest to eradicate the disease. Current methods have severe limitations, as they are either costly or not sensitive enough to detect low levels of parasitemia. Here we report an ultrasensitive, yet low-resource chemical assay for the detection and quantification of hemozoin, a biomarker of all Plasmodium species. Solubilized hemozoin catalyzes the atom transfer radical polymerization of N-isopropylacrylamide above the lower critical solution temperature of poly(N-isopropylacrylamide). The solution becomes turbid, which can be observed by naked eye and quantified by UV-visible spectroscopy. The rate of turbidity increase is proportional to the concentration of hemozoin, with a detection limit of 0.85 ng mL−1. Malaria parasites in human blood can be detected down to 10 infected red blood cells μL−1. The assay could potentially be applied as a point-of-care test. The signal-amplification of an analyte by biocatalytic precipitation polymerization represents a powerful approach in biosensing.

Stimuli-Responsive Zwitterionic Microgels with Covalent and Ionic Cross-Links

We describe a facile method for the synthesis of microgels with covalent and noncovalent ionic cross-links. Microgels were synthesized by copolymerization of various N-vinyllactams with zwitterionic monomer (methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide in the presence of a cross-linking agent (bis(acrylamide)) in water-in-oil emulsion. Monodisperse colloidally stable microgels with a high amount (>30 mol %) of zwitterionic groups were synthesized. High contents of zwitterionic groups in microgels led to the formation of reversible ionic cross-links along with permanent covalent cross-links generated by bis(acrylamide). The obtained microgels exhibit interesting temperature-triggered swelling/deswelling behavior in aqueous solution. With an increase of the temperature above 10 °C, the microgels swell due to the destruction of the zwitterionic cross-links. Above the lower critical solution temperature of poly(N-vinyllactam) chains at T > 32 °C, the microgels shrink due to the destruction...

Thermoreversible Surface Polymer Patches: A Cryogenic Transmission Electron Microscopy Investigation.

Hybrid core-shell type nanoparticles from gold nanoparticle cores and poly( N-isopropylacrylamide) shells were investigated with regard to their structural plasticity. Reversible addition-fragmentation chain transfer polymerization was used to synthesize well-defined polymers that can be readily anchored onto the gold nanoparticle surface. The polymer shell morphologies were directly visualized in their native solution state at high resolution by cryogenic transmission electron microscopy, and the microscopic results were further corroborated by dynamic light scattering. Different environmental conditions and brush architectures are covered by our experiments, which leads to distinct thermally induced responses. These responses include constrained dewetting of the nanoparticle surface at temperatures above the lower critical solution temperature of poly( N-isopropylacrylamide), leading to surface polymer patches. This effect provides a novel approach toward breaking the symmetry of nanoparticle interactions, and we showfirst evidence for its impact on the formation of colloidal superstructures.

Thermoresponsive Antibacterial Surfaces Switching from Bacterial Adhesion to Bacterial Repulsion

AbstractHerein, ene‐functionalized dopamine is first coated onto a polyether sulfone membrane surface to introduce double bonds as anchoring sites for hydrogel film. Then, a hydrogel film is synthesized and simultaneously attached onto the membrane via photoinduced crosslinking copolymerization of N‐isopropylacrylamide (NIPAAm) and methacryloxyethyltrimethyl ammonium chloride. The thickness of the hydrogel film can be well‐controlled ranging from the nanometer to micrometer scales, which can retain the permeability of the membrane. Water contact angle and swelling tests demonstrate that the modified membrane shows thermoresponsive surface wettability. The quaternary ammonium salts in the hydrogel film can kill the attached bacteria efficiently and the dead bacteria can be detached by reducing the temperature below the lower critical solution temperature of poly(NIPAAm). The modified membrane also shows improved hemocompatibility, confirmed by prolonged clotting time and low hemolysis ratio. Hence, the designed thermoresponsive antibacterial hydrogel film with enhanced hemocompatibility has great potential to be applied in biomedical areas.

Hydrogen bonding reinforcement as a strategy to improve upper critical solution temperature of poly(N-acryloylglycinamide-co-methacrylic acid)

HB-type copolymers with suitably tunable UCST and corresponding core–shell nanogels showing UCST–LCST type behavior.

Synthesis and Thermothickening Behavior of Graft Copolymers Based on poly(N,N-Diethylacrylamide-co-N,N-Dismethylacrylamide) Side Chains

ABSTRACTA new type of thermothickening graft copolymer was synthesized through free radical copolymerization and grafting onto technique in aqueous solution. Their molecular structure combines a hydrophilic backbone based on poly(acrylicacid-co-2-acrylamido-2-methylpropane sulfonic acid and thermosensitive side chains based on N,N-diethylacrylamide and N,N-dimethylacrylamide (DMAA). The lower critical solution temperature of poly(N,N-diethylacrylamide) was increased easily by copolymerizing with hydrophilic monomers DMAA. The results demonstrate that the polymers in aqueous solution exhibit a significant increase in viscosity with the temperature rising and their thermothickening behavior is related to various physicochemical parameters such as the concentration of the polymer, shear rate, chemical composition of side chains, salt concentration, and pH value.

Tunable Upper Critical Solution Temperature of Poly(N-isopropylacrylamide) in Ionic Liquids for Sequential and Reversible Self-Folding.

We demonstrate sequential folding of micropatterned polymer actuators by tuning the upper critical solution temperature (UCST) of poly(N-isopropylacrylamide) (PNIPAM) copolymers in the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl) imide. Incorporation of comonomers having different hydrogen-bonding capacities, acrylic acid and methyl acrylate, is shown to shift the UCST of PNIPAM to higher and lower temperatures, respectively. Relying on the ability to tune the transition temperature through copolymerization along with the wide thermal range afforded by the IL as a solvent, we fabricated a photopatterned self-folding device which shows reversible and sequential bending of three sets of hinges. Such sequential and reversible bending of microactuators offers potential for the design of complex self-folding origami and soft robots.

Fully Reversible Quantitative Phase Transfer of Gold Nanoparticles Using Bifunctional PNIPAM Ligands.

Ligand exchange with end-functionalized polymers is often applied to render nanoparticles with enhanced colloidal stability, to change the solubility in various environments, and/or to introduce new functionalities. Here we show that exchange of citrate molecules with α-trithiocarbonate-ω-carboxyl-terminated poly(N-isopropylacrylamide) can successfully stabilize spherical gold particles of different diameters ranging from 15 to 53 nm. This is verified by transmission electron microscopy, dynamic light scattering, and extinction spectroscopy. We show that the polymer-decorated nanoparticles respond to temperature and pH allowing access to control interparticle interactions. In a range of pH slightly below the pKa of the terminal carboxyl groups, phase transfer of the particles from water to chloroform can be mediated by increasing the dispersion temperature above the lower critical solution temperature of poly(N-isopropylacrylamide). Upon cooling, fully reversible phase transfer to the water phase is observed. Extinction spectroscopy reveals phase transfer efficiencies close to 100% for every system under investigation.

Entropic Mechanism for the Lower Critical Solution Temperature of Poly(ethylene oxide) in a Room Temperature Ionic Liquid.

Polymers exhibit interesting phase behavior in room temperature ionic liquids. For example poly(ethylene oxide) (PEO) displays a lower critical solution temperature (LCST) in [BMIM][BF4] with a critical temperature and concentration that are only weakly dependent on molecular weight, contrary to the behavior of polymers in other solvents. To shed light on the mechanism of the LCST, we study the phase behavior of PEO in [BMIM][BF4] using molecular dynamics (MD) simulations. The simulations show the signature of a phase transition as the temperature is increased. At low temperatures, interactions similar to a hydrogen bond are found between the imidazolium hydrogen and the PEO oxygen (HI-O H-bond) and the imidazolium hydrogen and the anion fluorines (HI-F H-bond). These interactions stabilize the mixed phase. A potential of mean force (PMF) analysis shows an entropic cost associated with the HI-O H-bond, which makes the bond formation unfavorable at higher temperatures, while the HI-F H-bond does not show a significant temperature dependence: This suggests that LCST phase separation is driven by the entropic penalty of the polymer for a PEO-cation hydrogen bond. We test the effect of scaling the charges on the [BMIM][BF4]. Interestingly, the scaled charge force-field does not predict a phase separation at any temperature, thus, emphasizing the pitfalls of charge scaling for mixtures.

Adjusting the low critical solution temperature of poly(N-isopropyl acrylamide) solutions by salts, ionic surfactants and solvents: A rheological study

The control over the Low Critical Solution Temperature (LCST) and thickening of thermosensitive polymers is of crucial interest for applications such as drug delivery systems and temperature sensors. Commonly the design of a new drug delivery system of a temperature sensor requires the synthesis of new thermosensitive polymers that respond to a desired target temperature. In this study we follow the LCST by rheology and report examples of how the onset of LCST can be adjusted by chemical species that are able to change polymer solubility, such as salts, organic solvents or surfactants.For this purpose we used the thermo-responsive polymer, poly(N-isopropyl acrylamide) or PNIPAM, and surfactants, salts and ethanol as additives. The LCST was investigated by means of rotational rheology, as it has been shown a good correlation between the LCST and the onset of the temperature-induced thickening. From this study we observe that salts can both increase or decrease the temperature at which the LCST occurs. This is attributed to the affinity of the different salts with the polymer. More hydrophobic salts such as KSCN shifted the LCST of PNIPAM to higher temperature values while the opposite scenario is observed in the case of more hydrophilic salts such as KCl. When surfactants are added to the system, it is observed that, in both cases (SDS and CTAB) and at the concentrations employed, the LCST was shifted to higher temperatures. Surfactants interact with the polymeric chains, converting the macromolecule into a polyelectrolyte and retarding the occurrence of clouding or phase separation. Major effects were also observed by changing the polarity of the bulk: the presence of 10% ethanol shifted the LCST of PNIPAM solution to lower temperatures, forming a co-non-solvent pair with water. No phase transition was observed when PNIPAM was dissolved in absolute ethanol. These observations highlight the role of hydrophobic associations and the entropy of counterions.

Synthesis and characteristics of poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive semi‐hollow latex particles and their application to drug carriers

ABSTRACTIn this work, the poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite semi‐hollow latex particles was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate‐co‐methacrylic acid) (poly (MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second process was to polymerize methacrylic acid (MAA), N‐isopropylacrylamide (NIPAAm), and crosslinking agent, N,N′‐methylenebisacrylamide, in the presence of poly(MMA‐MAA) latex particles to form the linear poly(methyl methacrylate‐co‐methacrylic acid)/crosslinking poly(methacrylic acid‐co‐N‐isopropylacrylamide) (poly(MMA‐MAA)/poly(MAA‐NIPAAm)) core–shell latex particles with solid structure. In the third process, part of the linear poly(MMA‐MAA) core of core–shell latex particles was dissolved by ammonia to form the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles. The morphologies of the semi‐hollow latex particles show that there is a hollow zone between the linear poly(MMA‐MAA) core and the crosslinked poly(MAA‐NIPAAm) shell. The crosslinking agent and shell composition significantly influenced the lower critical solution temperature of poly(MMA‐MAA)/poly(MAA‐NIPAAm) semi‐hollow latex particles. Besides, the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles were used as carriers to load with the model drug, caffeine. The processes of caffeine loaded into the semi‐hollow latex particles appeared four situations, which was different from that of solid latex particles. In addition, the phenomenon of caffeine released from the semi‐hollow latex particles was obviously different from that of solid latex particles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3441–3451

Synthesis and characteristics of poly(methacrylic acid-co -N -isopropylacrylamide) thermosensitive composite hollow latex particles and their application as drug carriers

In this work, the poly(methacrylic acid-co-N-isopropylacrylamide) thermosensitive composite hollow latex particles was synthesized by a three-step reaction. The first step was to synthesize the poly(methyl methacrylate-co-methacrylic acid) (poly(MMA-MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second step was to polymerize methacrylic acid (MAA), N-isopropylacrylamide (NIPAAm), and N,N′-methylenebisacrylamide in the presence of poly(MMA-MAA) latex particles to form the linear poly(methyl methacrylate-co-methacrylic acid)/crosslinking poly(methacrylic acid-co-N-isopropylacrylamide) (poly(MMA-MAA)/poly(MAA-NIPAAm)) core–shell latex particles. In the third step, the core–shell latex particles were heated in the presence of ammonia solution to form the crosslinking poly(MAA-NIPAAm) thermosensitive hollow latex particles. The morphologies of poly(MMA-MAA)/poly(MAA-NIPAAm) core–shell latex particles and poly(MAA-NIPAAm) hollow latex particles were observed. The influences of crosslinking agent and shell composition on the lower critical solution temperature of poly(MMA-MAA)/poly(MAA-NIPAAm) core–shell latex particles and poly(MAA-NIPAAm) hollow latex particles were, respectively, studied. Besides, the poly(MAA-NIPAAm) thermosensitive hollow latex particles were used as carriers to load with the model drug, caffeine. The effect of various variables on the amount of caffeine loading and the efficiency of caffeine release was investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5203–5214

Wetting behaviour and direct observation of thermally responsive polystyrene-block -poly(N -isopropylacrylamide)-block -polystyrene electrospun fibres in aqueous environment

Electrospun fibres of thermally responsive triblock copolymer polystyrene-block-poly(N-isopropylacrylamide)-block-polystyrene were prepared. Fibre morphology and swelling were studied below and above the lower critical solution temperature of poly(N-isopropylacrylamide) (PNIPAM) using cryo-electron microscopy. Cryo-transmission electron microscopy showed that the fibre diameter increased up to 150% after immersion in water at 20 °C. In contrast, at 45 °C the fibre diameter increased considerably less. The sessile drop technique was used to characterize temperature-dependent wetting of fibre mats. Contact angle (θCA) measurements revealed that a block copolymer fibre mat changed from hydrophobic (θCA > 90°) to hydrophilic (θCA < 90°) state within seconds after applying a water droplet on it at 20 °C. At 40 °C the initial contact angle was measured to be higher (135°) and it decreased much less than at 20 °C during the first minute of measurement. We observed using scanning electron microscopy that the electrospun fibres of the block copolymer having 77 wt% of PNIPAM lost their cylindrical shape and changed from fibres to thin sheets at both 20 and 40 °C within seconds after applying water on the fibres. Fibres having 55 wt% of PNIPAM were observed to be stable in water at both 20 and 40 °C, which resulted, surprisingly, in fibre mats with the strongest effects on thermally sensitive wetting. We discuss the surprising results and the implications that the evolution of fibre surface roughness has on the long-term wetting behaviour, demonstrating a self-adaptable hydrophilicity/hydrophobicity nature of the fibre mats. © 2013 Society of Chemical Industry

Influence of poly(n‐isopropylacrylamide)–CNT–polyaniline three‐dimensional electrospun microfabric scaffolds on cell growth and viability

This study investigates the effect on: (1) the bulk surface and (2) the three-dimensional non-woven microfabric scaffolds of poly(N-isopropylacrylamide)-CNT-polyaniline on growth and viability of cells. The poly(N-isopropylacrylamide)-CNT-polyaniline was prepared using coupling chemistry and electrospinning was then used for the fabrication of responsive, non-woven microfabric scaffolds. The electrospun microfabrics were assembled in regular three-dimensional scaffolds with OD: 400-500 μm; L: 6-20 cm. Mice fibroblast cells L929 were seeded on the both poly(N-isopropylacrylamide)-CNT-polyaniline bulk surface as well as non-woven microfabric scaffolds. Excellent cell proliferation and viability was observed on poly(N-isopropylacrylamide)-CNT-polyaniline non-woven microfabric matrices in compare to poly(N-isopropylacrylamide)-CNT-polyaniline bulk and commercially available Matrigel™ even with a range of cell lines up to 168 h. Temperature dependent cells detachment behavior was observed on the poly(N-isopropylacrylamide)-CNT-polyaniline scaffolds by varying incubation at below lower critical solution temperature of poly(N-isopropylacrylamide). The results suggest that poly(N-isopropylacrylamide)-CNT-polyaniline non-woven microfabrics could be used as a smart matrices for applications in tissue engineering.