Volume Phase Transition Temperature Research Articles

Real and In Silico Microgels Show Comparable Bulk Moduli Below and Above the Volume Phase Transition.

The compressibility of soft colloids influences their phase behavior and flow properties, especially in concentrated suspensions. Particle compressibility, which is proportional to the reciprocal of the bulk modulus K, is a key parameter for soft polymer-based particles that can be compressed in crowded environments. Here, microgels with different degrees of cross-linking, i.e.,softness, are investigated below and above their volume phase transition temperature (VPTT). By combining molecular dynamics simulations with small-angle neutron scattering with contrast variation, a change in the particle bulk moduli of two orders of magnitude is observed. The degree of cross-linking has a significant impact on the bulk modulus of the swollen microgel, while above the VPTT the values of K are almost independent of the cross-linking density. The excellent agreement between experimental results and simulations also highlight that the model microgels from computer simulationspossess both the internal architecture and the elastic properties of real polymeric networks. This paves the way to a systematic use of simulations to investigate the behavior of dense microgelsuspensions below and above their VPTT.

Super soft poly(N-isopropylacrylamide) microgels using functionalized starch nanoparticles as crosslinker

A set of poly(N-isopropylacrylamide) p(NIPAM) microgels was successfully prepared through precipitation polymerization (PP) using acryloyl starch nanoparticles (ASNPs) as crosslinkers. Functionalized starch nanoparticles used in microgel preparation, with a degree of substitution (DS) of 0.78 (ASNP12) or 1.37 (ASNP24) were found to have different properties. Dynamic light scattering (DLS) revealed that microgels prepared with ASNP12 exhibit a higher swelling capacity compared to the microgels designed with ASNP24, which was also observed by atomic force microscopy (AFM), showing super soft microgels flattened into disk shape on the substrate. This may be related to softer and surface smoothed microgels. Turbidity analysis revealed a slight shift of the so-called volume phase transition temperature (VPTT) towards higher values for microgels synthesized with ASNP24, indicating its contribution as a hydrophilic comonomer. Considering their high swelling capacity, these bio-based crosslinked microgels are potential materials for adsorptive processes. They can also be considered as candidates for biomedical applications due to the presence of a biopolymer in their structure.

New Approach for Preparation of Porous Polymers with Reversible Pore Structures for a Highly Safe Smart Supercapacitor.

Porous polymers have many industrial applications, but their pore structures (open or closed) are usually fixed during polymerization. In this study, polymers with reversible and controllable pore structures, namely, thermosensitive porous hydrogels with regulated volume phase transition temperature, were prepared using a Pickering high-internal-phase emulsion as the template. Upon heating, the hydrogels transformed not only in their wettability (between hydrophilicity and hydrophobicity with water contact angles of 21.8 and 100.9°) but also their pore structure (between open through-holes and closed holes with pore throat sizes of 15.58 and 0 μm, respectively) in a short time (<10 s). When the hydrogel was used as a separator in smart supercapacitors (SCs), this behavior effectively limited the path of electrolyte migration, reducing the chance of conflagration accidents. Moreover, by utilizing the highly reversible pore structures and wettability of the porous hydrogel, reversible charging and discharging were restored after the system cooled down. This work not only provides great guidance for preparing porous polymers with reversible pore structures but also paves the way for designing smart SCs with enhanced safety.

The Influence of Initiators, Particle Size and Composition on the Electrokinetic Potential of N-(Isopropyl)acrylamide Derivatives.

The aim of this study was to characterize and compare the zeta potential of particles sensitive to external thermal stimuli. Poly N-(isopropyl) acrylamide (PNIPA) was selected as the thermosensitive polymer with a volume phase transition temperature (VPTT) between 32 and 33 °C. The hydrodynamic diameter (DH) of the nanoparticles was measured by dynamic light scattering. Zeta potential (ZP) measurements were performed with the same instrument used for DH measurements. ZP measurements allow the prediction of the stability of colloidal systems in aqueous solutions. These measurements were combined with a pH study before and after the purification process of the particles. The ZP was measured to determine the electrostatic interactions between the particles, which can lead to particle aggregation and decrease their colloidal stability. The effect of the composition of the synthesized particles on the ZP was assessed. One of the most important factors influencing ZP is pH, especially in aqueous solutions. The initiator did not significantly affect the DH of the particles, but it did significantly affect the ZP. The synthesized particles were subjected to a visible radiation absorption study in the selected temperature range to determine the VPTT.

Tuning the bulk behavior and 2D interfacial self-assembly of microgels by keggin-type polyoxometalate ionic specificity

Finding new ways to tune the behavior of thermoresponsive microgels in bulk and confined at 2D liquid interfaces is key to achieve a deeper understanding and control of these smart materials. We studied the interaction of positively and negatively charged pNIPAM microgels with the Keggin-type polyoxometalates Na3PW12O40 (POM3−) and H4SiW12O40 (POM4−). In bulk, we observed charge inversions of the positively charged microgels below and above the volume phase transition temperature (VPTT) at significantly low POM concentrations as 5⋅10−5 M. In the presence of POM, both microgels exhibited a deswelling-swelling-deswelling behavior below the VPTT, and a two-step further deswelling above the VPTT for the positively charged microgels. When the later were confined at 2D water/air interfaces, adding 10−5 M of POM3− below the VPTT was equivalent to heating above the VPTT and compressing the monolayer from 5 to 20mN m−1. Above the VPTT, the diameter at the interface did not change while the portion immersed in the subphase further deswelled, in agreement with the behavior in bulk. Adding more POM3− did not change the diameter at the interface nor the height of the microgels, showing a saturation effect in 2D. The restructuring of the pNIPAM polymeric network by the POM3− was characterized by EDS mapping and XPS. The microgel monolayers with POM3− improved their resistance to plasma etching, which could be useful for soft colloidal lithography.

Cell harvesting on robust smart thermosensitive pseudo-double networks prepared by one-step procedure

In this work, pseudo-double networks (pseudo-DN) based on N-vinyl caprolactam (VCL, major component, precursor of thermosensitive chains) and hexyl methacrylate (HMA, minor component, hydrophobic) have been prepared by using single step approach. The adjective pseudo refers to the fact that through the simultaneous copolymerization of VCL and HMA with different relative reaction kinetics, in the presence of an appropriate mixture of crosslinkers, networks with complex structures that tend towards DN-type structures are obtained. Hydrogels have been prepared with HMA/VCL molar ratios from 0 to 23.2 mol %. The series of hydrogels prepared show a composition-dependent behaviour in terms of thermosensitivity, swelling at temperatures below the Volume Phase Transition Temperature (VPTT) value, mechanical properties and performance during the cell culture experiments. More precisely, hydrogels with low percentages of HMA show elastic moduli under compression tests slightly lower than 1 MPa and presented a high thermal response (high swelling below the VPTT) allowing in addition the non-aggressive detachment of cell monolayer by controlled decrease of temperature. As the percentage of HMA increases, the elastic modulus increases, obtaining improved mechanical properties (reaching values in the range 1–3 MPa), thermosensitivity decreases (low swelling below VPTT) and a progressive delay in cell proliferation is also observed, being still cytocompatible. In this sense, hydrogels with low percentages of HMA (up 2.7 mol %) allow cell proliferation and transplantation similar to the control sample.

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions.

Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PW12O403- (PW) and SiW12O404- (SiW) on the aqueous swelling and internal structure of nonionic poly(N-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and small-angle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations. The microgels thus become charged and swell at low POM concentration, surprisingly without strongly increasing the volume phase transition temperature, and deswell at higher POM concentration. The swelling arises because of the osmotic pressure of dissociated counterions of the POMs, while the deswelling is due to POMs acting as physical cross-links in the microgels under screened electrostatics in NaCl or excess POM solution. This swelling/deswelling transition is sharper for PW than for SiW related to the lower charge density, weaker hydration, and stronger binding of PW. The POMs elicit qualitatively and quantitatively different swelling effects from ionic surfactants and classical salts. Moreover, the network softness and topology govern the swelling response upon POM binding. The softer the microgel, the stronger is the swelling response, while, inside the microgel, regions of high polymer density swell/contract more upon electric charging/cross-linking than regions with low polymer density. POM binding thus enables fine-tuning of microgel properties and highlights the role of network topology in microgel swelling. Because POMs decompose at an alkaline pH, these POM/microgel systems also exhibit pH-responsive swelling in addition to the typical temperature responsiveness of pNiPAM microgels.

Development and characterization of colloidal pNIPAM-methylcellulose microgels with potential application for drug delivery in dentoalveolar tissue engineering strategies

Incorporation of growth factors, signaling molecules and drugs can be vital for the success of tissue engineering in complex structures such as the dentoalveolar region. This has led to the development of a variety of drug release systems. This study aimed to develop pNIPAM-methylcellulose microgels with different synthesis parameters based on a 23 full factorial design of experiments for this application. Microgel properties, including volume phase transition temperature (VPTT), hydrodynamic size, drug loading and release, and cytocompatibility were systematically evaluated. The results demonstrated successful copolymerization and development of the microgels, a hydrodynamic size ranging from ∼200 to ∼500 nm, and VPTT in the range of 34–39 °C. Furthermore, loading of genipin, capable of inducing odontoblastic differentiation, and its sustained release over a week was shown in all formulations. Together, this can serve as a solid basis for the development of tunable drug-delivering pNIPAM-methylcellulose microgels for specific tissue engineering applications.

Impact of Protein Corona Formation on the Thermoresponsive Behavior of Acrylamide-Based Nanogels.

The ability to fine-tune the volume phase transition temperature (VPTT) of thermoresponsive nanoparticles is essential to their successful application in drug delivery. The rational design of these materials is limited by our understanding of the impact that nanoparticle-protein interactions have on their thermoresponsive behavior. In this work, we demonstrate how the formation of protein corona impacts the transition temperature values of acrylamide-based nanogels and their reversibility characteristics, in the presence of lysozyme, given its relevance for the ocular and intranasal administration route. Nanogels were synthesized with N-isopropylacrylamide or N-n-propylacrylamide as backbone monomers, methylenebis(acrylamide) (2.5-20 molar %) as a cross-linker, and functionalized with negatively charged monomers 2-acrylamido-2-methylpropanesulfonic acid, N-acryloyl-l-proline, or acrylic acid; characterization showed comparable particle diameter (c.a.10 nm), but formulation-dependent thermoresponsive properties, in the range 28-54 °C. Lysozyme was shown to form a complex with the negatively charged nanogels, lowering their VPTT values; the hydrophilic nature of the charged comonomer controlled the drop in VPTT upon complex formation, while matrix rigidity only had a small, yet significant effect. The cross-linker content was found to play a major role in determining the reversibility of the temperature-dependent transition of the complexes, with only 20 molar % cross-linked-nanogels displaying a fully reversible transition. These results demonstrate the importance of evaluating protein corona formation in the development of drug delivery systems based on thermoresponsive nanoparticles.

1H-NMR studies on the volume phase transition of DNA-modified pNipmam microgels.

DNA functionalized pNipmam microgels, which have recently been introduced, are examined at different concentrations of sodium chloride and in PBS solutions via temperature dependent 1H-NMR measurements and are compared to pure pNipmam microgels. We show that the DNA modification shifts the volume phase transition temperature towards lower temperatures and the addition of salt and PBS further supports this effect in both materials. Thermodynamic values, i.e. enthalpy, entropy and Gibbs free energy, are determined via a non-linear fit which can be applied directly to the measurement data without further linearization.

Phase Transition Behaviors of Poly(N-isopropylacrylamide) Nanogels with Different Compositions Induced by (−)-Epigallocatechin-3-gallate and Ethyl Gallate

Phase transition behaviors of poly(N-isopropylacrylamide) nanogels with different compositions induced by (−)-epigallocatechin-3-gallate (EGCG) and ethyl gallate (EG) has been investigated systematically. Monodisperse poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) (P(NIPAM-co-NMAM)) and poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-co-HEMA)) nanogels with different feeding monomer ratios were prepared by emulsion polymerization. P(NIPAM-co-NMAM) nanogels exhibit rapid isothermal phase transition behavior in EGCG solutions with low concentration (10−3 mol/L) in less than 10 minutes. The thermosensitive phase transition behaviors of nanogels are affected not only by the copolymerized monomers but also by the concentrations of EGCG and EG in aqueous solutions. Nanogels remain in a shrunken state and do not exhibit thermosensitive phase transition behaviors in EGCG solutions (≥5 mmol/L), whereas they display thermo-responsive phase transition behaviors in EG solutions. The volume phase transition temperature (VPTT) shifts to lower temperatures with increasing EG concentration. The diameters of P(NIPAM-co-NMAM) nanogels decrease with increasing EG concentration at temperatures between 29 and 33 °C. In contrast, the diameters of P(NIPAM-co-HEMA) nanogels increase with increasing EGCG concentration at temperatures between 37 and 45 °C. The results demonstrate the potential of nanogels for simple detection of EG and EGCG concentrations in aqueous solutions over a wide temperature range, and EGCG can serve as a signal for the burst-release of drugs from the P(NIPAM-co-NMAM)-based carriers at physiological temperature.

4D Printing Nanocomposite Hydrogel Based on PNIPAM and Prussian Blue Nanoparticles Using Stereolithography

AbstractThe potential of photoactive Prussian blue nanoparticles dispersed in thermo‐responsive PNIPAM hydrogels in 4D printing using a stereolithography is investigated with digital light processing. The proportion of Prussian blue nanoparticles used in the resin is chosen to deliver a significant photothermal effect providing a heating above the volume phase transition temperature of the final nanocomposite hydrogels; while, giving only a limited effect on light scattering during the 3D printing process. Four formulations with various amounts of Prussian blue nanoparticles are used to print 3D structures with different shapes, such as Aztec pyramids, cylinders, gyroid porous cubes, and porous films. The shrinkage effect triggered by light irradiation at 808 nm on the as‐obtained nanocomposite hydrogels is demonstrated through the delivery of a representative molecule fluorescein and a triggered 4D shape‐morphing effect.

A Phase Field Study of the Influence of External Loading on the Dynamics of Martensitic Phase Transformation

An elastoplastic phase field model was employed for simulations to investigate the influence of external loading on the martensitic phase transformation kinetics in steel. The phase field model incorporates external loading and plastic deformation. During the simulation process, the authenticity of the phase field model is ensured by introducing the relevant physical parameters and comparing them with experimental data. During the calculations, loads of various magnitudes and loading conditions were considered. An analysis and discussion were conducted concerning the volume fraction and phase transition temperature during the phase transformation process. The simulation results prominently illustrate the preferential orientation of variants under different loading conditions. This model can be applied to the qualitative phase transition evolution of Fe-Ni alloys, and the crystallographic parameters adhere to the volume expansion effect. It is concluded that uniaxial loading promotes martensitic phase transformation, while triaxial compressive loading inhibits it. From a dynamic perspective, it is demonstrated that external uniaxial loading accelerates the kinetics of martensitic phase transformation, with uniaxial compression being more effective in accelerating the phase transformation process than uniaxial tension. When compared to experimental data, the simulation results provide evidence that under the influence of external loading, the martensitic phase transformation is significantly influenced by the applied load, with the impact of external loading being more significant than that of plastic effects.

LuMA-Functionalized Thermosensitive Hydrogel: A Versatile and Robust Dopamine-Triggered Platform for Diverse Biomolecules Sensing.

It is of great significance for the analysis of multiple biomarkers because a single biomarker is difficult to accurately achieve early diagnosis, disease course monitoring, and prognosis evaluation. Herein, a luminescence thermosensitive hydrogel was synthesized by radical polymerization using a methacrylic acid derivative monomer of luminol (LuMA) as luminescent, N-isopropylacrylamide (NIPAM) as thermosensitive monomer, and acrydite-oligonucleotides [dopamine (DA) aptamer, DNA C1, and DNA C2] as recognition elements. The combined DA based on the affinity interaction between the DA and the aptamer on the hydrogel polymer chain was electrochemically oxidized to dopamine quinone during the electrochemiluminescence (ECL) scanning, which effectively quenched the ECL signal of LuMA due to the resonance energy transfer (RET). In addition, the thermosensitive hydrogel showed swelling-collapse characteristics when the temperature was below and above the volume phase transition temperature. Undergoing the collapse process initiated by the temperature, the RET efficiency was further enhanced due to the shortened distance between the energy donor and acceptor, showing a 1.4 times signal amplification and achieving sensitive detection of DA with a limit of detection (LOD) of 1.7 × 10-10 M. For a proof of concept application, coupled with the target-induced release of DA from the DNA-magnetic beads bioconjugations based on duplex-specific nuclease (DSN)-assisted target recycling amplification strategy and DNAzyme cleavage reaction, this ECL-RET approach was successfully used to evaluate multiple targets including miRNA-141 and MUC1 with the LOD of 2.5 aM and 1.6 fg/mL, respectively. The excellent performances of the versatile and robust ECL-RET hydrogel in multiple target sensing showed potential applications in clinical diagnosis and disease therapeutic assay.

Multi-responsive P(DMAEMA-co-COU) hydrogel for temperature sensor and information encryption

Multi-responsive hydrogels for temperature sensor and information encryption were developed through the synergistic application of light, temperature and pH response of the hydrogel. The multi-responsive hydrogels were prepared by copolymerization of dimethylaminoethyl methacrylate (DMAEMA) and 7-(2-methacryloyloxyethoxy)-4-methylcoumarin (CoumMAc). Through incorporating coumarin groups into the hydrogels, the crosslinking degree of hydrogels could be increased by photo-crosslinking of polymer chains based on the photodimerization of coumarin groups. After the hydrogel was irradiated by a photomask under UV light (365 nm), the irradiated and unirradiated region in the hydrogel showed different crosslinking degrees, leading to different volume phase transition temperature (VPTT) in the two region of the hydrogel. The pattern in the hydrogel appeared only within a specific temperature range, and the temperature of the environment can be monitored by the prepared hydrogel sensor. After soaking the patterned hydrogel in the acidic solution, no pattern information was displayed at all temperatures, and the pattern information can only emerge by dual decryption (base and temperature). In addition, the information can be erased by UV light (254 nm), which further ensures information security. This work provide a new way for low-cost unpowered temperature sensors and information encryption with more security.

Photoinduced Mechanical Cloaking of Diarylethene-Crosslinked Microgels.

The serial connection of multiple stimuli-responses in polymer architectures enables the logically conjunctive gating of functional material processes on demand. Here, a photoswitchable diarylethene (DAE) acts as a crosslinker in poly(N-vinylcaprolactam) microgels and allows the light-induced shift of the volume phase-transition temperature (VPTT). While swollen microgels below the VPTT are susceptible to force and undergo breakage-aggregation processes, collapsed microgels above the VPTT stay intact in mechanical fields induced by ultrasonication. Within a VPTT shift regime, photoswitching of the DAE transfers microgels from the swollen to the collapsed state and thereby gates their response to force as demonstrated by the light-gated activation of an embedded fluorogenic mechanophore. This photoinduced mechanical cloaking system operates on the polymer topology level and is thereby principally universally applicable.

Dynamic Behavior of Heavy Water Inside and Outside of Poly (N-Isopropylacrylamide) (PNIPAM) Microgel Using Broadband Dielectric Spectroscopy

One pot free radical precipitation polymerization was used to synthesize an aqueous suspension of non-ionic poly ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -isopropylacrylamide) [PNIPAM] microgel particles. For dielectric measurements in the frequency range of 100 MHz to 50 GHz and temperature range of 288 K to 323 K, 10 wt. % of freeze-dried PNIPAM microgels dispersed in heavy water were used. The relaxation process was seen at around 15 GHz, which corresponds to the entire rotational motion of the heavy water, both within and outside the microgel. Furthermore, in the high frequency relaxation spectrum, heavy water outside the microgel (h1-process with a relaxation time of h1, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h1</sub> , fixed as that of pure heavy water) and confined heavy water within the microgel (h2-process with a relaxation time of h2, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> ) were evaluated in view of the two-water model’s assumption and contribution. Under volume phase transition temperature (VPTT), τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> is about 4 to 5 times larger than τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h1</sub> , and it does not change much even though the temperature is raised. However, τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h2</sub> rapidly increases above VPTT from 7 to 14, which reveals that the dynamics of heavy water are severely constrained inside the shrunken state of the PNIPAM microgel. The obtained results are compared to the dynamics of pure water in PNIPAM microgels aqueous suspension to better understand the effect of deuterium substitution for hydrogen on the dynamics of heavy water inside and outside of PNIPAM microgels.

Modified Sulfanilamide Release from Intelligent Poly(N-isopropylacrylamide) Hydrogels.

The aim of this study was to examine homopolymeric poly(N-isopropylacrylamide), p(NIPAM), hydrogels cross-linked with ethylene glycol dimethacrylate as carriers for sulfanilamide. Using FTIR, XRD and SEM methods, structural characterization of synthesized hydrogels before and after sulfanilamide incorporation was performed. The residual reactants content was analyzed using the HPLC method. The swelling behavior of p(NIPAM) hydrogels of different crosslinking degrees was monitored in relation to the temperature and pH values of the surrounding medium. The effect of temperature, pH, and crosslinker content on the sulfanilamide release from hydrogels was also examined. The results of the FTIR, XRD, and SEM analysis showed that sulfanilamide is incorporated into the p(NIPAM) hydrogels. The swelling of p(NIPAM) hydrogels depended on the temperature and crosslinker content while pH had no significant effect. The sulfanilamide loading efficiency increased with increasing hydrogel crosslinking degree, ranging from 87.36% to 95.29%. The sulfanilamide release from hydrogels was consistent with the swelling results-the increase of crosslinker content reduced the amount of released sulfanilamide. After 24 h, 73.3-93.5% of incorporated sulfanilamide was released from the hydrogels. Considering the thermosensitivity of hydrogels, volume phase transition temperature close to the physiological temperature, and the satisfactory results achieved for sulfanilamide incorporation and release, it can be concluded that p(NIPAM) based hydrogels are promising carriers for sulfanilamide.

Synthesis of thermoresponsive PNIPAm nanogel adsorbent by microwave-assisted polymerization for wastewater treatment application

This research demonstrated the fast synthesis technique using microwave-assisted polymerization for the preparation of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) nanogel which was to be used for paraquat pesticide adsorption. PNIPAm nanogel was synthesized by free-radical polymerization in an aqueous solution using water-soluble ammonium peroxodisulfate (APS) and N,Ń-methylenebisacrylamide (BIS) as initiators and cross-linker, respectively. Microwave irradiation was used as an alternative heating technique and its efficiency was compared to that of the conventional heating method. The results showed that reaction time could be greatly shortened from several hours to only 20 min with the yield of PNIPAm nanogel of approximately 65 % using microwave heating method. The FTIR analysis confirmed that microwave irradiation did not alter the chemical structure of PNIPAm nanogel. The cross-linker concentrations and the sequence of cross-linker addition affected the hydrodynamic diameter of PNIPAm nanogel. The hydrodynamic diameter of swollen PNIPAm nanogels at 25 °C decreased as increasing the cross-linker concentrations and then further decreased when the cross-linker was added after 10 min of the irradiation time. Besides, all PNIPAm nanogel showed well thermoresponsive reversibility over 5 cycles, across the volume phase transition temperature (VPTT) at around 32 °C. The adsorption and release mechanisms of the paraquat took advantage of the phase transition change (swelling-collapse) in response to temperature stimuli, respectively. The PNIPAm nanogel synthesized from the microwave heating method had a profound effect on paraquat adsorption, having 60 – 70 % adsorption with a paraquat release of around 35 – 45 %. These results demonstrated that PNIPAm nanogels could be used as an alternative adsorbent material for industrial wastewater treatment.

PH Modulated Formation of Complexes with Various Stoichiometry between Polymer Network and Fe(III) in Thermosensitive Gels Modified with Gallic Acid.

Thermoresponsive gels based on N-isopropylacrylamide functionalized with amino groups were modified with gallic acid, with gallate (3,4,5-trihydroxybenzoic) groups being introduced into the polymer network. We investigated how the properties of these gels were affected at varying pH, by the formation of complexes between the polymer network of the gels and Fe3+ ions (which form stable complexes with gallic acid, exhibiting 1:1, 1:2, or 1:3 stoichiometry, depending on pH). The formation of complexes with varying stoichiometry within the gel was confirmed using UV-Vis spectroscopy, and the influence of such complexes on swelling behavior and volume phase transition temperature were investigated. In the appropriate temperature range, complex stoichiometry was found to strongly affect the swelling state. Changes in the pore structure and mechanical properties of the gel caused by the formation of complexes with varying stoichiometry were investigated using scanning electron microscopy and rheological measurements, respectively. The volume changes exhibited by p(NIPA-5%APMA)-Gal-Fe gel were found to be greatest at close to human body temperature (~38 °C). Modification of thermoresponsive pNIPA gel with gallic acid opens new opportunities for the development of pH- and thermosensitive gel materials.