Crosslinking Polymerization Of Acrylamide Research Articles

In situ polymerization of acrylamide on magnetic SnFe2O4/CeO2 nanocomposite: A novel adsorbent for removing various dyes

Environmental conservation requires effective, secure, and economical treatment options for dye-contaminated wastewater. The current study comprises a novel fabrication of tin ferrite/ceria/polyacrylamide magnetic and porous ternary nanocomposite. This occurs through crosslinking polymerization of acrylamide on the SnFe2O4/CeO2 binary nanocomposite. The SnFe2O4/CeO2/PAM nanocomposite was comprehensively characterized using FTIR, TGA, XRD, TEM, VSM, EDX, SEM and N2 adsorption-desorption isotherms. The ternary nanocomposite's efficiency as a novel adsorbent for anionic (direct violet 4, DV4) and cationic (bismarck brown r, BBR) azo dyes was investigated. A range of variables were studied to optimize the effectiveness of eliminating both dyes. In an acidic medium, DV4 removal was more efficient, whereas BBR removal was higher in an alkaline environment. Non-linear regression was employed to analyze adsorption kinetics and isotherm models, using three statistical error functions to determine the best-fit models. Adsorption data for both dyes demonstrated a good conformity with pseudo-second-order and Freundlich isotherm models. The dyes' adsorption was both endothermic and spontaneous. The nanocomposite displayed notable performance throughout five reuses. Moreover, the nanocomposite shows good adsorption efficiency for various dyes (congo red, acid blue 40, methyl green, and crystal violet) as well as DV4 and BBR. Therefore, it emerges as a promising adsorbent for wastewater purification.

Magneto-Induced Janus Adhesive-Tough Hydrogels for Wearable Human Motion Sensing and Enhanced Low-Grade Heat Harvesting.

Janus hydrogels with different properties on the two surfaces have considerable potential in the field of material engineering applications. Various Janus hydrogels have been developed, but there are still some problems, such as stress mismatch caused by the double-layer structure and Janus failure caused by material diffusion in the gradient structure. Here, we report a Janus adhesive-tough hydrogel with polydopamine-decorated Fe3O4 nanoparticles (Fe3O4@PDA) at one side induced by magnetic field to avoid uncontrollable material diffusion in the cross-linking polymerization of acrylamide with alginate-calcium. The magneto-induced Janus (MIJ) hydrogel has an adhesive surface and a tough bulk without an obvious interface to avoid stress mismatch. Due to the intrinsic dissipative matrix and the abundant catechol groups on the adhesive surface, it shows strong adhesion onto various substrates. The MIJ hydrogel has high sensitivity (GF = 0.842) in detecting tiny human motion. Owing to the synergy of Fe3O4@PDA-enhanced interfacial adhesion and heat transfer, it is possible to quickly generate effective temperature differences when adhering to human skin. The MIJ hydrogel achieves a Seebeck coefficient of 13.01 mV·K-1 and an output power of 462.02 mW·m-2 at a 20 K temperature difference. This work proposes a novel strategy to construct Janus hydrogels for flexible wearable devices in human motion sensing and low-grade heat harvesting.

Polyacrylamide/EDTA-modified chitosan/graphene oxide hydrogels as an adsorbent and supercapacitor for sustainable applications

Due to high security and versatility, hydrogels have attracted great interest in sustainable applications such as wastewater treatment and energy storage. However, the poor adsorption capacity as an adsorbent and the low conductivity as an electrolyte seriously restrict the sustainable application of hydrogels. Here, we prepare nanocomposite hydrogels (PAAm/CS-EDTA/GO) by mixing ethylene diamine tetraacetic acid (EDTA)-modified chitosan (CS) and graphene oxide (GO) in crosslinking polymerization of acrylamide (AAm). Nanocomposite gives PAAm/CS-EDTA/GO hydrogel excellent mechanical properties (e.g., fracture energy of ∼1208 kJ∙m−3). EDTA, CS and GO support rich and special adsorption sites for the removal of metal ions and dyes. The addition of lithium chloride (LiCl) makes PAAm/CS-EDTA/GO/Li hydrogel have anti-freezing and anti-dehydration properties. Interestingly, the synergy of CS-EDTA and GO increases the conductivity of the hydrogel. The supercapacitor assembled by PAAm/CS-EDTA/GO/Li hydrogel electrolyte shows high capacitance and temperature tolerance. Our work provides a route for the rational development of adsorption materials and energy storage devices for sustainable applications.

Bioinspired cellulose nanofibrils and NaCl composited polyacrylamide hydrogels with improved toughness, resilience, and strain‐sensitive conductivity

AbstractHydrogels are regarded as excellent substrates for flexible materials owing to their porous structure, softness, and flexibility. However, the requirement of enhancement and functionalization for a hydrogel is still an important issue. Cellulose nanomaterials present promising reinforcing potentials for hydrogels thanks to their high strength, good compatibility, and environmental friendliness. Inspired by the composition of the dermis, we use carboxymethyl cellulose nanofibrils (CMCNFs) and NaCl as additives to participate in the crosslinking polymerization of acrylamide (AM), fabricating PAM/CMCNFs/NaCl composite hydrogels with excellent mechanical properties, good resilience, and strain‐sensitive conductivity. The interactions between CMCNFs and PAM chains contribute to mechanical improvement of composite hydrogels; 0.5 M NaCl in precursor solutions imparts further synergistic reinforcement and ionic conductivity. The compressive stress, tensile strength and elongation at break values of PAM‐based hydrogels are increased with the incorporation of CMCNFs, and the optimal CMCNFs dosage is found at 4 wt% of AM. The resilience of composite hydrogels can be maintained at approximately or over 90% after five compression or stretching cycles. Moreover, the strain‐sensitive conductivity of a composite hydrogel demonstrates their potential application in flexible sensors. In brief, this work provides a facile one‐step approach to fabricate composite hydrogels suitable for application as flexible sensors.

Superabsorbent polymer nanocomposites with surfactant- or acid-modified Ca-montmorillonite: synthesis and water absorbency

A series of clay polymer nanocomposites (CPN) were synthesized via the crosslinking polymerization of acrylamide and itaconic acid in the presence of calcium montmorillonite (Ca-Mt) clay mineral or modified Ca-Mt to form a superabsorbent polymer with improved swollen gel strength. Ca-Mt was modified by either organification with cetyltrimethylammonium bromide (CTAB) or hexadecanoic acid at surfactant levels of 0.25–4 times the cationic exchange capacity (CEC) of the Ca-Mt, or by acid-treatment with either hydrochloric acid or sulfuric acid at concentrations from 0.25 to 4 M. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the successful modification of the Ca-Mt structure. The effects of Ca-Mt modification and its content on the equilibrium water absorbency and absorbency with or without an applied load, of the prepared CPN were characterized. The CPN with 1 % Ca-Mt modified with CTAB at 4 times the CEC (CPN/1%Ca-Mt-4CTAB) without load exhibited the highest water absorbency of 805 ± 6 g g-1 in deionized water, 78 ± 3 g g-1 in artificial reference urine (ARU) and 52 ± 2 g g-1 in normal saline solution. Furthermore, it also exhibited the highest absorbency under load at 22.6 ± 0.4 and 19.7 ± 0.2 g g-1 in ARU under a load of 1.93 and 4.83 kPa, respectively. The improved absorbency and absorbency under load could have resulted from the 1.52-fold increased basal layer spacing (d001-value) of the CPN/1%Ca-Mt-4CTAB (2.41 nm) over that of CPN/1%Ca-Mt (1.59 nm), and the fine intercalated-dispersion of the Ca-Mt-CTAB within the CPN matrix, respectively.

Multiresponsive macroporous semi-IPN composite hydrogels based on native or anionically modified potato starch

Macroporous semi-interpenetrating polymer networks (semi-IPN) composite hydrogels were synthesized by cross-linking polymerization of acrylamide (AAm) with N,N’-methylenebisacrylamide (BAAm) in the presence of potato starch (PS) or an anionic polyelectrolyte derived from PS (PA), below the freezing point of the reaction solution (−18°C). The composite cryogels have been further modified by the partial hydrolysis of the amide groups in poly(acrylamide) (PAAm) matrix, under alkaline conditions. The influence of the entrapped polymer on the properties of the composite gels, both before and after the hydrolysis, has been evaluated by the swelling kinetics, FT-IR spectroscopy, scanning electron microscopy, and external stimuli responsiveness. The potential of the anionic composite cryogels as intelligent hydrogels has been evaluated by the investigation of the deswelling/reswelling kinetics as a function of solvent nature, ionic strength, and environment pH. Cryogels with fast responsivity at variation of the external stimuli, which withstood repeated deswelling/reswelling cycles, have been obtained at a low cross-linker ratio (one mole BAAm for 80 moles of AAm) and a monomer concentration around 3wt%.

Macroporous composite IPN hydrogels based on poly(acrylamide) and chitosan with tuned swelling and sorption of cationic dyes

The synthesis of macroporous ionic composite cryogels consisting of two independently cross-linked and oppositely charged networks is reported in the paper. Semi-interpenetrating network cryogels were prepared first by cross-linking polymerization of acrylamide (AAm) with N,N′-methylenebisacrylamide (BAAm) in the presence of chitosan (CS), under freezing conditions, the main parameters varied being cross-linker ratio (X), pH of the CS solution, and CS molar mass. The fraction of CS trapped in the semi-IPN cryogels increased with the increase of both X and pH of CS solution. The CS chains trapped in the semi-IPN cryogels have been cross-linked with epichlorohydrin under alkaline conditions, to generate the second network, when a partial hydrolysis of the amide groups in the PAAm matrix simultaneously occurred. Examination of scanning electron microscope images showed inter-connected macropores, in both semi-IPN and full-IPN cryogels. The generation of an anionic matrix during the formation of the second network led to a high sorption capacity of a model cationic dye, methylene blue (MB), by the full-IPN cryogel, around 750mg dye/g gel, at 25°C. The benefits of the full-IPN cryogels consist of their high reusability and in the high selectivity in separation of MB from the mixture with methyl orange.

Preparation of Homogeneous Hydrogels by Controlling the Crosslinker Reactivity and Availability

Network microstructures of polyacrylamide (PAAm) hydrogels were investigated by static light scattering measurements. The gels were prepared by free‐radical crosslinking polymerization of acrylamide (AAm). To suppress the degree of gel inhomogeneity, the crosslinker reactivity during gelation was controlled by decreasing its availability in the reaction system. Our first approach was the addition of the crosslinker N,N′‐methylenebis(acrylamide) (BAAm) in one or three portions during the course of the gelation reactions. As a second approach, a slightly water soluble crosslinker, namely ethylene glycol dimethacrylate (EGDM) was used as a crosslinker in AAm polymerization. Due to the low water solubility of EGDM, EGDM phase in the gelation system act as a reservoir of crosslinker so that the crosslinker can be supplied continuously to the aqueous reaction zone during the course of gelation. It was found that the delayed crosslinker addition technique further increases the degree of inhomogeneity of PAAm hydrogels. The results were explained with increasing viscosity of the reaction solution at the time of the crosslinker addition so that the crosslinking reactions are limited to local regions in the reaction system. The second approach, namely use of the slightly water soluble crosslinker EGDM significantly increases the degree of structural homogeneity of PAAm hydrogels.

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We have studied the effect of polarity, current density, current duration, crosslinking density, swelling ratio, and permeation enhancers on the transdermal flux of ketoprofen from acrylamide hydrogel. Hydrogel was prepared by free radical crosslinking polymerization of acrylamide. Drug loading was made just before transport experiment by soaking the hydrogel in solution containing drug. In vitro flux study using hairless mouse skin was performed at using side-by-side diffusion cell, and the drug was analysed using HPLC/UV system. The result showed that, compared to passive flux, the total amount of drug transported increased about 18 folds by the application of cathodal current. Anodal delivery with same current density also increased the total amount of drug transported about 13 folds. It seemed that the increase in flux was due to the electrorepulsion and the increase in passive permeability of the skin by the current application. Flux increased as current density, the duration of current application and loading amount (swelling duration) increased. As the cross linking density of the hydrogel increased, flux clearly decreased. The effect of hydrophilic enhancers (urea, N-methyl pyrrolidone, Tween 20) and some hydrophobic enhancers (propylene glycol monolaurate and isopropyl myristate) was minimal. However, about 3 folds increase in flux was observed when 5% oleic acid was used. Overall, these results provide some useful information on the design of an optimized iontophoretic delivery system of ketoprofen.

Pectin and polyacrylamide composite hydrogels: Effect of pectin on structural and dynamic mechanical properties

AbstractComposite hydrogels of pectin and polyacrylamide were synthesized and evaluated by scanning electron microscopy, atomic force microscopy, light microscopy, and dynamic mechanical analysis. The crosslinking polymerization of acrylamide in pectin solution resulted in a composite having a macroporous pectin domain with an interstitial polyacrylamide domain. This composite had improved mechanical properties compared to those of either polymer alone, and it absorbed and retained more water than crosslinked polyacrylamide alone. Furthermore, crosslinking polymerization of acrylamide in an existing pectinate scaffold resulted in a double‐network architecture, where filamentous polyacrylamide networks penetrated through pores of the pectin scaffold. It was found that pectins dictated the features of microstructure in the composites through regulating the coordination of phase separation of the two components and water partition between the two phases. Results from this study highlight potential new uses of pectins in protecting the physical structure of environmentally sensitive polymers from mechanical damage related to freezing, lyophilization, and other conditions experienced during their use in biomedical and industrial products. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1893–1901, 2004

In situ photon transmission technique for monitoring phase separation in real time during gelation

In situ, real time photon transmission technique was used to monitor the formation of heterogeneities during the free-radical crosslinking polymerization of acrylamide in the presence of N,N'-methylenebis(acrylamide) (BAAm) as a crosslinker. Two different gelation experiments were performed with various BAAm and water contents separately at room temperature. It was observed that the transmitted photon intensity, I tr decreases dramatically at a certain time, in both type of experiments during the gel formation process from interconnected microgels. Decrease in I tr was interpreted in terms of phase separation during gelation. The extent of phase separation was measured depending on the crosslinker content and on the degree of monomer dilution during the gel formation process.

Phase separation during the formation of poly(acrylamide) hydrogels

The crosslinking polymerization of acrylamide (AAm) was investigated at a monomer concentration of 5 w/v% in water with N, N′-methylenebis(acrylamide) (BAAm) as the crosslinker. The crosslinker ratio (mole ratio of BAAm to AAm) was set to 1/82. The fractional monomer conversion x, the weight fraction of gel W g, and the equilibrium weight swelling ratio q w of the hydrogels were measured as a function of the reaction time. Experimental results indicate that the first gel molecule in the reaction system appears after a reaction time t c =4±1 min or after a monomer conversion of x c=0.07±0.02. At this critical point the homogeneous reaction system turned into a heterogeneous one consisting of gel and separated solution phases. The network formation process took place in this heterogeneous system within the first 60 min of the reaction time. Experimental x, W g, and q w data indicate that, during the gel growth process, the growing hydrogel molecule cannot occupy the entire polymerization system, which is responsible for the observed phase separation. It was shown that the volume of the separated liquid phase decreases as the polymerization and crosslinking reactions proceed and finally, the reaction system becomes homogeneous again due to the decreasing dilution degree of the hydrogel.

Biodegradable Hydrogel for Controlled Release of Biologically Active Macromolecules

The preparation, swelling and mechanical behavior and in vitro biodegradation of a novel hydrogel suitable for controlled release of biologically active macromolecules were investigated. The hydrogel was based on the biode gradable polypeptide, poly[ N5-(2-hydroxyethyl)-L-glutamide] with methacryl oylated side chains (mole fraction 0.02-0.10). These were used as a "macro monomer crosslinker" in the crosslinking polymerization of acrylamide. The polymerization can be carried out under conditions that avoid loss of the biolog ical activity of proteins. The network density of the gels was controlled by the number of methacryloylated side chains in the macromonomers and by the amount of diluent during gel formation. It was found that the network density decreases with increasing dilution and decreasing concentration of the double bonds in the macromonomer. The enzymatic degradation of the hydrogels by papain increased with decreasing network density. The release of a model pro tein entrapped in the gel was also influenced by the network density of the gel. All the gels can be fully degraded to soluble products.

Polyacrylamide networks. Kinetic and structural studies by high field 1H-NMR with polymerization in situ

The crosslinking polymerization of acrylamide (AA) and N, N′-methylene-bis-acrylamide (BA) in aqueous solution at 22°C has been studied by H.R. 1H-NMR spectroscopy. The initial comonomer mixture was placed inside the NMR spectrometer probe head and the polymerization was followed for 10 hr. This procedure allows measurement of the instant composition of the residual comonomer mixture even during and after gelation and therefore to calculate the composition of the formed copolymer or network. When the reaction was finished, the structure of the most mobile part of the network was also analyzed.