Bending of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel in electric fields

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.     

Electrical sensitivity behavior of a hydrogel composed of polymethacrylic acid/poly(vinyl alcohol)

An interpenetrating polymer network (IPN) composed of polymethacrylic acid (PMAA) and poly(vinyl alcohol) (PVA) was prepared and exhibited electrical sensitivity behavior. The swelling behavior of the PMAA/PVA IPN hydrogel was studied by immersion of the gel in aqueous NaCl solutions at various concentrations and pH values. The stimuli response of the PMAA/PVA IPN hydrogel in electric fields was also investigated. When swollen IPN hydrogel was placed between a pair of electrodes, the PMAA/PVA IPN hydrogel exhibited bending behavior upon the application of an electric field. The PMAA/PVA IPN hydrogel also showed stepwise bending behavior depending on the electric stimulus. Also, for biomedical applications, the bending behavior of PMAA/PVA IPN hydrogel in Hank's solution at pH 7.4 was studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3613–3617, 2004     

Adsorption and adhesion of poly(vinyl alcohol) and poly(ammonium acrylate) as organic additives for wet mold processing of Al2O3

Adsorption and adhesion of polyvinyl alcohol (PVA) molecules on Al₂O₃ surfaces in pH 3–10 or 0–0.1 mass% poly(ammonium acrylate) (PAA) aqueous solution was examined using the AFM colloidal probe method. The PVA behavior on the solid surface was estimated using force curve measurements obtained using colloidal probe AFM. Extensions originating from the bridging of PVA between the solid surfaces were observed primarily at less than approximately 200 nm in the pH 3 aqueous solution. The extensions, which were observed at more than approximately 600 nm for pH 6 and 10 aqueous solutions, resulted from different conformations of the PVA molecules. In the PVA–PAA system, the number of extensions decreased by increasing the PAA content. This was not observed in a PAA aqueous solution of greater than 0.1 mass%, which indicates that PAA was adsorbed selectively onto the solid surface. The force curve showed that PAA was more effective than PVA.     

Electric stimuli responses to poly(vinyl alcohol)/chitosan interpenetrating polymer network hydrogel in NaCl solutions

An interpenetrating polymer network (IPN) hydrogel composed of poly(vinyl alcohol) (PVA) and chitosan exhibited electric‐sensitive behavior. The PVA/chitosan IPN hydrogel was synthesized by an ultraviolet (UV) irradiation method that is used in several biomedical and industrial fields. The swelling behavior of the PVA/chitosan IPN hydrogel was studied by immersion of the gel in NaCl aqueous solutions at various concentrations. The swelling ratio decreased with increasing concentration of NaCl solution. The stimuli response of the IPN hydrogel in electric fields was also investigated. When a swollen PVA/chitosan IPN was placed between a pair of electrodes, the IPN exhibited bending behavior in response to the applied electric field. The bending angle and the bending speed of the PVA/chitosan IPN increased with increasing applied voltage and concentration of NaCl aqueous solution. The PVA/chitosan IPN also showed stepwise bending behavior depending on the electric stimulus. In addition, thermal properties of PVA/chitosan IPN were investigated by differential scanning calorimetry (DSC) and dielectric analysis (DEA). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2285–2289, 2002     

Properties of electroresponsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) exhibited electrical-sensitive behavior. PAAc as an initial network was prepared inside a PVA solution using UV irradiation; then, PVA networks as a secondary network were formed by a repetitive freeze–thawing process. Their mechanical properties were influenced by the swelling ratio, crosslinking by UV radiation and a freeze–thawing process, and intermolecular force by hydrogen bonding. When a swollen PVA/PAAc IPN was placed between a pair of electrodes, the IPN exhibited bending behavior upon the applied electric field. The equilibrium bending angle (EBA) and the bending speed of the PVA/PAAc IPN increased with the applied voltage and the content of the PAAc network having negatively charged ionic groups within the IPN. The electroresponsive behavior of the present IPN was also affected by the electrolyte concentration of the external solution. Particularly, IPN37 showed a maximum EBA when the critical ionic strength was 0.1. Anisotropic deswelling of the IPN was observed in a direct contact with a pair of electrodes under aerobic conditions. The PVA/PAAc IPN also showed stepwise bending behavior depending on the electric stimulus. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1675–1683, 1999     

Bending behaviour of electroresponsive poly(vinyl alcohol)/poly(acrylic acid) semi‐interpenetrating network hydrogel fibres under an electric stimulus

Poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) composite fibres were prepared via solution spinning and subsequently, semi‐interpenetrating networks (SIPN) were obtained by crosslinking the fibres with glutaraldehyde. The hydrogel fibres exhibited bending behaviour under DC electric stimulation. The effects of a number of factors have been systematically studied, including the PAA content within the network, electric voltage imposed across the fibre, the fibre diameter, concentration of the crosslinking agent, pH and ionic strength of the bath solution. Our experimental results show a stable reversibility of bending behaviour under the applied electric field. The degree of bending at equilibrium and the bending speed of the hydrogel fibre increased with the intensity of the applied electric voltage and the PAA content having negatively charged ionic groups within the SIPN. The electroresponsive behaviour of the present SIPN hydrogel fibre was also affected by the aforementioned extrinsic factors. These observations are interpreted in terms of fibre stiffness, fixed charge density and swelling pressure, which depend on the hydrogel equilibrium states in different pH and ionic environments together with the electrochemical reactions under DC electric field. © 2002 Society of Chemical Industry     

Preparation and characteristic of electric stimuli responsive hydrogel composed of polyvinyl alcohol/poly (sodium maleate‐co‐sodium acrylate)

Maleic anhydride was used to preparare polyvinyl alcohol/poly (sodium maleate‐co‐sodium acrylate) hydrogels (PVA/poly(SMA‐SAA)) by a repeated frost‐defrost process because of its higher charge density and potential electric stimuli sensitivity. The bending angle was measured in a noncontact electric field using carbon as plate electrodes. It was found that the bending angle was dependent on various factors, including composition of hydrogel, concentration of NaCl solution, types of electrolyte solution, and electric voltage. It exhibited that the bending angle increased when the concentration of NaCl solutions and the electric voltages increased. An abnormal bending direction was observed, and it was affected not only by the kinds of hydrogels, but also by the exterior variations. The hydrogel showed good reversibility in on‐off electric field and could be a candidate for practical application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pervaporation separation of binary organic-aqueous liquid mixtures using crosslinked poly(vinyl alcohol) membranes. IV. Methanol–water mixtures

The pervaporation separation of methanol–water (M/W) mixtures was carried out using crosslinked poly(vinyl alcohol) (PVA) membranes with the low molecular weight of poly(acrylic acid) (PAA) as the crossinking agent. The PVA/PAA ratio in the crosslinked membrane was 90/10, 85/15, and 80/20 by weight. The operating temperatures were 50, 60, and 70°C, and the compositions of methanol–water mixtures to be separated were 70/30, 80/20, 90/10, and 95/5 (M/W) solutions. In all cases, the PVA/PAA = 80/20 membrane showed the best results. For M/W = 90/10 solution, the separation factor, α_w/m = 465, and the permeation rate, 0.109 kg/m²h, at 70°C were obtained using the PVA/PAA = 80/20 menbrane. The permeation rate and the separation factor for M/W = 95/5 solution showed 0.033 kg/m²h and α_w/m = 2650, respectively, when PVA/PAA = 80/20 membrane was used. © 1996 John Wiley & Sons, Inc.     

Electrochemical behavior of an interpenetrating polymer network hydrogel composed of poly(propylene glycol) and poly(acrylic acid)

An interpenetrating polymer network (IPN) hydrogel based on poly(propylene glycol) and poly(acrylic acid) was prepared by UV irradiation. The swelling behavior of the IPN hydrogel was studied by the immersion of the gel in aqueous NaCl solutions of various concentrations. The swelling ratio decreased with an increase in the NaCl concentration. The electrically sensitive behavior of the IPN hydrogel in electric fields was also investigated. The IPN hydrogel also showed a stepwise bending behavior that depended on the electric stimulus. The bending angle and bending speed of the IPN hydrogel were greatest in 0.6 wt % aqueous NaCl and increased with an increase in the applied voltage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2301–2305, 2003     

Stimuli‐sensitive behaviour of novel betaine‐type polyampholytes

Novel linear and crosslinked polyampholytes of betaine structure based on acrylic acid and ethyl 3‐aminocrotonate (ethyl ester of 3‐amino‐2‐butenoic acid) have been synthesized by Michael addition reaction followed by radical copolymerization. The mechanism of formation of monomer and polymer betaines is discussed. The linear polyampholyte has been characterized by potentiometric titration, IR, NMR and GPC. Crosslinked polymeric betaines were synthesized in the presence of N,N′‐methylenebisacrylamide. The stimuli‐sensitive properties of amphoteric gels have been studied as a function of pH, ionic strength, water–organic mixture composition, electric, and combined electric and magnetic fields. The isoelectric points of linear and crosslinked polymeric betaines correspond to pH 2.0–2.1. The effect of ionic strength on the solution and gel properties of polybetaine has been interpreted on the basis of destruction of inter‐chain, intra‐chain and intra‐group salt bonds. Water–acetone, water–ethanol or water–DMF mixtures cause the shrinking of amphoteric gel due to change of the dielectric constant of the medium and decrease of the osmotic pressure. Electrocollapse is observed under the action of DC electric field. Simultaneously cross action of electric and magnetic fields enhances the collapsing rate. Appearance of pH gradient within the volume of polyampholyte gel under the externally imposed DC electric field has been observed. Copyright © 2003 Society of Chemical Industry     

Electroactive characteristics of interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(N‐isopropylacrylamide)

An interpenetrating polymer network (IPN) composed of poly(vinyl alcohol) (PVA) and poly(N‐isopropylacrylamide) (PNIPAAm) was prepared by the sequential IPN method. The equilibrium swelling ratio and bending behavior under electric fields of the IPN hydrogel were measured in an aqueous NaCl solution. The IPN exhibited a high equilibrium swelling ratio, in the range 280–380%. When the IPN in aqueous NaCl solution was subjected to an electric field, the IPN showed significant and quick bending toward the cathode. The IPN hydrogel also showed stepwise bending behavior, depending on the electric stimulus. In addition, the ionic conductivity of the IPN hydrogel was measured using dielectric analysis, and its conductive behavior followed the Arrhenius equation. The conductivity of the IPN hydrogel and the activation energy for the form of the IPN were 1.68 × 10^?5 S/cm at 36°C and 61.0 kJ/mol, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 890–894, 2003     

Safe and flexible chitosan-based polymer gel as an electrolyte for use in zinc-alkaline based chemistries

A novel flexible, high performing chitosan-based gel electrolyte with poly (vinyl alcohol) (PVA) and potassium hydroxide (KOH) additives is prepared, using an optimized energy and time efficient method. Incorporation of a gel-based electrolyte in batteries aims to eliminate safety hazards present within conventional liquid-based electrolyte constructions. The ionic conductivity values obtained at room temperature are in the range of 5.32–105 mS/cm depending on composition. Optical, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectra studies are conducted to understand morphological and structural changes in the films with additives. Thermogravimetric analysis, manual bending and tensile tests, linear scan and cyclic voltammetry analysis are also conducted to study the physical and electrochemical stability of the films. Also, the prepared electrolytes are incorporated to form Zn-MnO₂ batteries and tested. Results reveal no physical damage of the films under continuous bending over 250 cycles. Mechanical properties for CPK0.3 suggest a strong and ductile material well suited for the intended application. Additionally, the novel electrolyte exhibits excellent physical stability up to 50^οC, electrochemical stability until 2 V for zinc electrodes and prove to successfully accommodate redox reactions involved in the Zn-MnO₂ alkaline system.     

Release of diclofenac through gluteraldehyde crosslinked poly(vinyl alcohol)/poly(acrylic acid) alloy membranes

A controlled‐release preparation of diclofenac sodium for transdermal administration has been developed. Poly(vinyl alcohol) (PVA) and PVA/poly(acrylic acid) (PAA) alloy membranes were prepared from a solvent‐casting technique using different PVA/PAA (v/v) ratios. The release of the drug from the membrane was evaluated under in vitro conditions at pH 7.4. The delivery system provided linear release without time lag, burst effect, and boundary layer resistance. Effects of variables such as film thickness and PVA/PAA ratio on the permeation behavior of the polymeric membranes were discussed. The optimal PVA/PAA was determined as 50/50. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 72–77, 2004     

Preparation of PAA‐g‐PEG/PANI polymer gel electrolyte and its application in quasi solid state dye‐sensitized solar cells

A microporous hybrid polymer of poly(acrylic acid)‐g‐poly(ethylene glycol)/polyaniline (PAA‐g‐PEG/PANI) is synthesized by a two‐step solution polymerization method. The influence of aniline concentration on the conductivity of PAA‐g‐PEG/PANI gel electrolyte is discussed, when the concentration of aniline is 0.66 wt%, the conductivity of PAA‐g‐PEG/PANI gel electrolyte is 11.50 mS cm^?1. Using this gel electrolyte as host, a quasi solid state dye‐sensitized solar cell (QS‐DSSC) is assembled. The QS‐DSSC based on this gel electrolyte achieves a power conversion efficiency of 6.38% under a simulated solar illumination of 100 mW cm^?2 (AM 1.5). POLYM. ENG. SCI., 55:322–326, 2015. © 2014 Society of Plastics Engineers     

Binary blends based on poly(N‐isopropylacrylamide): Miscibility studies with PVA,PVP, and PAA

Blends of poly(vinyl alcohol) (PVA), poly(acrylic acid), (PAA), and poly(vinyl pyrrolidone) (PVP), with poly(N‐isopropylacrylamide) (PNIPAM), were prepared by casting from aqueous solutions. Mechanical properties of PNIPAM/PVA blends were analyzed by stress–strain tests. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to analyze the miscibility between the polymeric pairs. The results revealed that PNIPAM is not miscible with PVA and PVP in the whole range of composition. On the other hand, PNIPAM interacts strongly with PAA forming interpolymer complex due to the formation of cooperative hydrogen bonds. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 743–748, 2004     

Crosslinking reaction of poly(vinyl alcohol) with poly(acrylic acid) (PAA) by heat treatment: Effect of neutralization of PAA

The crosslinking reaction of poly(vinyl alcohol) (PVA) by esterification using poly(acrylic acid) (PAA) as a crosslinking reagent was investigated to obtain highly insoluble PVA materials. Blend films of PVA and PAA (PVA/PAA = 8/2) were prepared to examine the effect of degree of neutralization (DN) in PAA and heat‐treatment conditions on the degree of crosslinking reaction. The degree of crosslinking reaction varied significantly when the DN of PAA changed. The optimum DN for the crosslinking reaction was in the range of 5 to 10 mol %. In the case of unneutralized PAA, the degree of crosslinking reaction was at most 15 mol % by heat treatment for 20 min at 200°C. Applying partially neutralized PAA (DN = 10 mol %) raised the degree to about 40 mol % under the same heat‐treatment conditions. FTIR analysis revealed that the hydroxyl group of PVA in the film blended with unneutralized PAA was degraded to a greater degree than that with partially neutralized PAA as a result of heat treatment. It was found that heat treatment at a low pH condition enhances the degradation of the hydroxyl group of PVA, resulting in a decrease of the number of crosslinking sites by esterification. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2420–2427, 2003     

Effects of composition on the properties of dual physically cross-linked hydrogel composed of polyvinyl alcohol and poly (acrylamide-co-acrylic acid)

In previous work, we have developed a dual physically cross-linked hydrogel composed of poly (acrylamide-co-acrylic acid) (PAM-co-PAA) and polyvinyl alcohol (PVA), named as PVA/CP DN gel, by facile copolymerization and freezing/thawing. The PVA/CP DN gel is featuring both excellent mechanical properties and self-healing ability. Additionally, we have preliminarily found that the comonomer ratio for PVA/CP DN gel have great influence on the self-healing efficiency. In this research article, we will further discuss the mechanical and self-healing properties of the PVA/CP DN gel by varying the comonomer ratio of PAM-co-PAA. The results proved that the structure of DN will be loosen when the number of PAA segments exceed that of PAM. More PAA segments in copolymer make the PVA/CP DN gel have better elongation at break but weak in tensile strength and young’s modulus because of less PVA crystalline domains formed in the gel. The energy dissipation value for the double-network hydrogel decrease with the addition of PAA segments, whereas self-healing efficiency of PVA/CP DN gel increased. Anyway, this work provides more information to further understand the effects of composition on the properties of dual physically cross-linked PVA/CP DN hydrogel.     

PH-induced structure change of poly(vinyl alcohol) hydrogel crosslinked with poly(acrylic acid)

The structure of the hydrogel of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) was investigated by small angle X-ray scattering (SAXS) of synchrotron radiation. A physically crosslinked blend gel, which was prepared by repetitive freezing and thawing of an aqueous solution of PVA and PAA, could be chemically crosslinked by esterfication of PVA with PAA even in the hydrogel state. The chemical crosslinking induced the destruction of physical crosslinks into a folded structure, indicating that the chemical crosslinking proceeds at the sites around the physical crosslinks that contain PVA and PAA in much higher concentration than other portion of the gel. The pH-induced structure changes of the PVA hydrogels, chemically crosslinked with poly(acrylic acid) (PAA) were investigated by SAXS on the samples of various chemical crosslinking time. The gels were shrunk at pH4, and swollen at pH8. The results of SAXS showed, that the Porod slope changed with chemical crosslinking time from -3.5 to ?2.9 at pH4, and from ?2.9 to ?2.4 at pH8. The results suggest that a folded structure as a structural domain, which is characterized by fractally rough interface, tends to change into the structure that corresponds to percolation cluster, particularly at pH8. The gels immersed in pH8 showed a remarkable structure change accompanying swelling. The results revealed that a conformational change of PAA chains, induced by the pH change, can be explained by the presence of a structural domain in the gel network, where both PVA chains and PAA chains get entangled and partially form a interpenetrating polymer network(IPN).     

Electrical behavior of chitosan and poly(hydroxyethyl methacrylate) hydrogel in the contact system

Semi‐interpenetrating polymer networks (semi‐IPNs), as polymer hydrogels composed of chitosan and poly(hydroxyethyl methacrylate) (PHEMA), exhibiting electrical‐sensitive behavior, were prepared. The swelling behavior of the chitosan/PHEMA hydrogels was studied by immersing the gels in various concentrations of aqueous NaCl solution. The electrical responses of the semi‐IPN hydrogel, in applied electric fields, were also investigated. When the semi‐IPN hydrogels were swollen, where one electrode was placed in contact with the gel and the other fixed 30 mm apart from one, they exhibited bending behavior on the application of an electric field on a contact system. The electroresponsive behavior of the present semi‐IPN was also affected by the electrolyte concentration of the external solution. The semi‐IPN also showed various degrees of increased bending behavior depending on the electric stimulus. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 915–919, 2004     

Photo-catalytic degradation of Metanil Yellow dye using TiO2 immobilized into polyvinyl alcohol/acrylic acid microgels prepared by ionizing radiation

Polyvinyl alcohol (PVA) microgels were prepared using electron beam irradiation. To improve the PVA microgel functionality and gel fraction, chains of polyacrylic acid (PAA) were incorporated into PVA microgel by radiation grafting technique. The increase in the acrylic acid (AA) content as well as PVA Mwt is accompanied by a mutual increase in the gel fraction and a decrease in the swelling%. Immobilization of different TiO₂ concentrations on the surface of the prepared PVA–AA microgel was carried out. The structural changes in the prepared PVA–AA microgel immobilized with TiO₂/were investigated using FTIR, EDX and XRD. Photodegradation efficiency of TiO₂/PVA–AA microgel against metnil yellow dyes was studied. TiO₂/PVA–AA microgel activity increases with the increase of the amount of TiO₂ and results in an increase in the rate of the photodegradation reaction. Easily recovery and reusability made TiO₂/PVA/AA of great important in practice use as a photocatalytic degradation composite, for dye removal from wastewater.