Equilibrium Degree Of Swelling Research Articles

Controlling of pore size and distribution of PDMAEMA hydrogels prepared by gamma rays

In this study, radiation synthesis and controlling of pore size and distribution of poly( N , N -dimethylaminoethyl methacrylate) (PDMAEMA) hydrogels have been investigated. Monomer mixtures containing various compositions of DMAEMA, water and ethylene glycol dimethacrylate (EGDMA) and poly(ethylene glycol) (PEG) have been prepared and irradiated. The molecular weight between cross-links of P(DMAEMA) hydrogels prepared in the presence of PEG increased with increasing amount of PEG in the initial mixture from 1% to 20%. Hydrogels with highest mesh size were obtained by using 20% PEG10 000. Upon PEG addition, an increase in the equilibrium degree of swelling ( Q ) was observed with increasing molecular weight of PEG until a molecular weight of 10 000. Maximum swelling was reached for systems containing 1% and 5% PEG10 000. SEM micrographs showed homogeneous pore structure of the hydrogels with open pores at lower pH.

Semi-interpenetrating networks based on POLY(N-isopropyl acrilamide) and POLY(N-vinylpyrrolidone)

Three series of semi-interpenetrating polymer networks based on cross-linked poly(N-isopropylacrylamide), PNIPA, and 1, 2 and 3 wt% of linear poly(N-vinylpyrrolidone), PVP, were synthesized in order to improve the mechanical properties of PNIPA gels. The effect of the incorporation of the linear PVP polymer into the temperature responsive networks on the phase transition temperature, swelling behavior and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25/1 to 100/1) of the monomer (N-isopropylacrylamide) to the cross linker (N,N'-methylene-bisacrylamide). The hydrogels were characterized by determination of the equilibrium degree of swelling at 25 ?C, the dynamic shear modulus and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. Furthermore, the deswelling kinetics of the hydrogels was also studied by measuring their water retention capacity. The inclusion of the linear hydrophilic PVP in the PNIPA networks increased the equilibrium degree of swelling, the highest values of which were obtained for samples with 2 and 3 wt% of PVP and the NIPA/MBA molar ratio of 75/1 and 100/1. The highest reinforcement effect, evaluated from the ratio of G'red(semi-IPN) to G'red(PNIPA), was obtained by incorporation of 2 wt% PVP. The tensile strength of the semi-IPNs reinforced with linear PVP was higher than that of the PNIPA networks. The elongation at break of these semi-IPNs varied between 22 and 55%, which are 22^11% larger than those for single PNIPA networks. The tensile measurements confirmed that the presence of 2 wt% of the linear polymer significantly reinforced the PNIPA network.

The use of poly(ethylene oxide) hydrogels as immobilization matrices for yeast cells

Hydrogels based on high molecular weight poly(ethylene oxide) (PEO) copolymers of ethylene oxide and propylene oxide, PEO/alginate and PEO/chitosan were synthesized by UV crosslinking of polymer aqueous solutions. These hydrogels were then characterized in terms of their gel fraction yield, degree of equilibrium swelling, shear storage and loss moduli. The physico-mechanical properties of the hydrogels were then correlated to their ability to sustain the viability and the activity of immobilized cells. The production of ethanol by immobilized Saccharomyces cerevisiae was used to test the suitability of the PEO based hydrogels as immobilization matrices. The PEO hydrogel with a value of 255 Pa for Gʹ and 11 Pa for Gʹʹ, showed the best mechanical properties of all the gels tested. Scanning electron microscope (SEM) analysis of the imobilized S. cerevisiae showed proliferation of the yeast cells entrapped inside the polymeric matrix.

Acetylation and molecular mass effects on barrier and mechanical properties of shortfin squid chitosan membranes

Chitosan samples with different N-deacetylation levels were obtained from β-chitin under heterogeneous alkali conditions. Oxidative depolymerisation was performed to attain low-acetylated chitosan samples with different molecular mass. Water vapour permeability, membrane swelling and tensile mechanical properties were analysed in plasticized self-supporting chitosan membranes. The main purpose was to describe unambigously the effect of the biopolymer molecular mass and acetylation degree on these properties. Commercially available chitosan samples derived from α-chitin were also studied for comparison. The equilibrium degree of swelling in water and the water vapour permeability increase by increasing the molecular mass or the degree of acetylation. Regarding the effect on the mechanical properties, generally harder and tougher membranes were obtained for chitosans with higher molecular mass or lower acetylation degree. These observations are tentatively explained based on the different structural characteristics of the polymer and can lead to a better understanding of the tools necessary to tailor a specific type of chitosan membrane.

Alginate–poly(vinyl alcohol) core–shell microspheres for lipase immobilization

AbstractA lipase [triacylglycerol ester hydrolase (EC 3.1.1.3)] was encapsulated in sodium alginate (AlgNa)/poly(vinyl alcohol) (PVA) microspheres. Spherical AlgNa/PVA beads were prepared by the ionotropic gelation of an AlgNa/PVA blend in the presence of calcium tetraborate (CaB4O7). The particles were spherical and had an average diameter of 400 μm. The microspheres were studied with differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, and water transport by the equilibrium degree of swelling. The elevation of the glass‐transition temperature of the microspheres indicated specific crosslinking reactions of the component polymers (AlgNa/PVA). FTIR spectra showed no evidence of a strong chemical interaction changing the nature of the functional groups of both AlgNa and PVA in the AlgNa/PVA blends. The water diffusion coefficients increased with increasing PVA content in the microspheres, indicating a decrease in the resistance to mass transfer through the AlgNa/PVA microsphere wall. The AlgNa/PVA microspheres were characterized by the Michaelis constant (KM) and the maximum reaction velocity (Vmax), which were determined for both free and immobilized lipases. The enzyme affinity for the substrate (KM/Vmax) remained quite good after immobilization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1553–1560, 2006

Structural properties of poly(ether) macromonomer based hydrogels

The major part of the present work discusses the synthesis and the properties of a series of hydrogels obtained by free radical copolymerization of α,ω-methacryloyloxy poly(ethylene oxide) (PEO) or poly(1,3-dioxolane) (PDXL) macromonomers. The influence of several parameters such as macromonomer molar mass, comonomer concentration, type of solvent, and crosslinking concentration on the weight degree of equilibrium swelling, the uniaxial compression modulus and the thermodynamic interaction parameter was investigated systematically. Hydrogels whose elastic chains are constituted of a short central PDXL block surrounded by two hydrophilic PEO blocks were prepared according to the same strategy. PDXL is known to be sensitive to acidic degradation due to the presence of acetal groups. Therefore, once placed in acidic media (in water or in an organic solvent) network degradation occurred. The solid-state properties of the different PEO or PDXL co-networks were examined by DSC, and compared to those of linear PEO or PDXL chains and to those of homopolymeric PEO or PDXL networks.

Swelling behavior of hydroxyapatite‐filled chitosan–poly(acrylic acid) polyelectrolyte complexes

AbstractA family of hydroxyapatite (HAP)‐filled chitosan (CHI)–poly(acrylic acid) (PAA) polyelectrolyte complexes was prepared for the development of a degradable biocompatible organic matrix with nascent HAP that will degrade in vivo over a period of time. The effects of complexation on the degradation profile of the composites as well as the interaction between the CHI–PAA matrix and HAP in the composite system were evaluated by studying the swelling behavior of these composites in phosphate‐buffered saline (PBS) by varying their CHI–PAA ratio and HAP content. All composite systems showed a general trend of three stages of swelling with the variation in the degree of equilibrium swelling. The percentage weight gain initially decreased in a linear way with increases in the HAP weight percentages, leading to a first equilibrium swelling, represented by the plateau; further increased to a greater extent; and finally stabilized. The CHI/PAA/HAP composites were stable in PBS up to a period of more than 45 days whereas the 50/50 CHI/PAA control sample showed a single equilibrium attained after a period of 288 h. Further exposure of the specimen to the medium led to its disintegration. It was also observed that, even though CHI and PAA were capable of binding HAP, because of the lack of efficient binding, the integrity of the CHI–HAP and PAA–HAP composites were lost within 48 h. The 50/50/80 CHI/PAA/HAP composition showed the minimum amount of swelling in the series. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4716–4722, 2006

Studies on radiation synthesis of polyethyleneimine/acrylamide hydrogels

Polyethyleneimine(PEI)/acrylamide(AAM) hydrogels were synthesized by γ-radiation-induced polymerization/crosslinking of aqueous mixtures containing different ratios of PEI and AAM. The gel percentage and equilibrium degree of swelling (EDS) of the synthesized hydrogels were investigated. The compositions of the hydrogels produced were found to be different from the feed composition. Ion-chromatography technique was used to determine the amount of Pb (II) and Cd (II) absorbed by the hydrogel. The maximum binding capacity of the PEI/AAM hydrogels, for Pb and Cd was found to be 19 and 12.6 mg/g, respectively, (at 100 ppm). PEI/AAM hydrogels had better metal uptake efficiency than the pure AAM hydrogel at concentrations less than 50 ppm. Pure PEI was observed to be highly degrading type polymer on exposure to gamma radiation. TGA and FT-IR techniques were used to characterize the prepared hydrogels.

Radiation Induced Synthesis of 2‐Hydroxyethyl Methacrylate‐Co‐Vinylbenzyltrimethylammonium Chloride Binary Hydrogel System‐I: Equilibrium Swelling Studies

High‐energy gamma radiation has been used to synthesize 2‐hydroxyethyl methacrylate‐co‐vinylbenzyltrimethylammonium chloride (HEMA‐co‐VBT) hydrogels. Unlike pure poly(vinylbenzyltrimethylammmonium chloride) gels, these gels had good strength and could be handled easily. The equilibrium degree of swelling of the gels was a linear function of the VBT content in the gels. The effect of ionic strength, temperature, pH, some solutes of biological importance such as glucose, urea, and surfactants such as Triton‐X, Deoxycholic acid, have been reported. An increase in temperature of the swelling medium did not affect the EDS but did affect the rate of swelling of the gels. HEMA‐co‐VBT hydrogels showed ionic strength responsive properties, and the reversible swelling‐deswelling action could be performed in NaCl‐water medium for several cycles without losing physical strength of the gel. The gels were also tested for uptake of monovalent anionic dyes namely acid blue 25 (AB25), acid yellow 99 (AY99) from dilute aqueous solutions and found to be suitable for dye uptake with high efficiency.

Synthesis of poly(acrylamide-co-methyl methacrylate) chemically cross-linked hydrogels and their application in controlled release of model drugs

Poly(acrylamide-co-methyl methacrylate) (poly(AAm-co-MMA)) hydrogels with chemical cross-links have been prepared using two monomers (acrylamide and methyl methacrylate) and cross-linker (N,N′-methylene bis acrylamide) (NN′-MBA) in different stoichiometric ratios. The effects of monomer ratio and cross-linking agent concentration on the swelling behaviour of poly(AAm-co-MMA)hydrogels were investigated. Swelling parameters such as equilibrium degree of swelling and swelling ratio, and network parameters such as molecular mass between cross-links (M c) and cross-link density (q) were determined. Depending on the monomer concentration, the M c values of hydrogels were varied from 1452.00 to 10 602.16 g/mol and q values of hydrogels were varied from 6.09 × 102 to 0.75 × 102. Depending on the cross-linking agent concentration the M c values of hydrogels were varied from 1463.57 to 2143.94 g/mol and q values of hydrogels were varied from 5.63 × 102 to 3.99 × 102. The ability of this co-polymeric hydrogel for use in controlled release of model drugs such as benzoic acid (BA), salicylic acid (SA) and p-nitroaniline (P-NA) was also studied.

Synthesis and characterization of novel aromatic azo bond-containing pH-sensitive and hydrolytically cleavable IPN hydrogels

Novel interpenetrating network (IPN) hydrogels, composed of pH-sensitive, aromatic azo group containing network as one component (Network A), and a hydrolyzable network as the other (Network B), were prepared by a sequential process. The first network was formed by crosslinking of a reactive polymer precursor (copolymer of N,N-dimethylacrylamide, acrylic acid, N-tert.butylacrylamide, and N-methacryloylglycylglycine p-nitrophenyl ester) with an aromatic azo group containing diamine (( N,N′- ε-aminocaproyl)-4,4′-diaminoazobenzene). The second network was formed by radical crosslinking copolymerization of N-(2-hydroxypropyl)methacrylamide with N,O-dimethacryloylhydroxylamine. The composition of the hydrogels was manipulated to determine the influence of hydrogel composition on the equilibrium degree of swelling, modulus of elasticity in compression, and on the rate of degradation of Network B. Modeling of network structure was accomplished using the statistical branching theory. The major advantage of IPN hydrogels, when compared to traditional pH-sensitive networks, is the linear swelling profile following abrupt change of pH from 2 to 7.4. This indicates the suitability of IPN as carriers for oral drug delivery.

Design and Properties of Degradable Networks Based on Free Radical Copolymerization of Poly(1,3-dioxolane) Macromonomers with Hydrophobic or Hydrophilic Comonomers in Water

Potentially degradable amphiphilic or hydrophilic copolymeric networks were synthesized directly in water by free radical copolymerization of α, ω-poly(1,3-dioxolane) (PDXL) macromonomers with vinyl monomers such as methyl methacrylate, butyl methacrylate, styrene or 2-hydroxyethyl methacrylate. Since PDXL macromonomers behave typically as amphiphiles, the rates of copolymerizations with hydrophobic comonomers are much higher than those of similar reactions carried out in organic solvents. Therefore crosslinking in water takes place rapidly. Once swollen to equilibrium in appropriate solvents, the physicochemical properties of the amphiphilic (or hydrophilic) copolymeric PDXL networks were investigated. The volume degree of equilibrium swelling and uniaxial compression modulus strongly depended upon the macromonomer molar mass (and concentration), and also the hydrophobic/hydrophilic balance. Their solid state properties were examined by DSC and compared to those of homopolymeric PDXL networks.

The effect of PEG(400)DA crosslinking agent on swelling behaviour of acrylamide-maleic acid hydrogels

Acrylamide (AAm)-maleic acid (MA) hydrogels with different monomer ratios were prepared in an aqueous solution by radical polymerization using a new crosslinking agent, polyethyleneglycol (400) diacrylate (PEG (400) DA) and also using N, N’-methylenebisacrylamide (NMBA) for comparison purpose. The hydrogels were characterized by acid group content and FTIR spectroscopy. Their swelling and deswelling behavior were studied as a function of maleic acid content, pH and crosslinking agent. Incorporation of MA in hydrogels significantly increased their swelling ability and their equilibrium degree of swelling (EDS) values changed between 100–269 g water/g polymer in water while AAm polymers swollen less (22–23 g water/g polymer). The AAm hydrogels showed Fickian type diffusion but the all AAm-MA hydrogels showed non-Fickian type behavior. Their swelling degree increased with the increase of pH of the external medium and an instantaneous increase was observed near a pH value of 7.0. The use of PEG (400) DA instead of NMBA as a crosslinking agent also increased the swelling rate and capacity of the gel. The swelling constant (K) and the diffusion coefficient (D) of hydrogels were also increased. The swelling-deswelling cycles in acidic-basic solutions showed that they could be used as pH responsive gels without any decrease in swelling capacity.

Studies on radiation synthesis of PVA/EDTA hydrogels

Aqueous solutions of polyvinyl alcohol (PVA) containing different amounts of ethylenediaminetetraacetic acid (EDTA) were gamma irradiated from a Co-60 source to form PVA–EDTA hydrogels. The effect of irradiation dose and EDTA content on the specific viscosity (in feed), gel percentage and equilibrium degree of swelling (EDS) was investigated. The amount of EDTA in the hydrogel matrix was found to be considerably lower than in the feed composition. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) technique was used to determine the amount of Pb(II), Cd(II) and Hg(II) absorbed by the hydrogel. The incorporation of EDTA moieties onto PVA network results in a hydrogel which has absorption affinity for Pb(II) and Cd(II). The maximum chelating capacities of the hydrogel were observed to be 8.5 mg/g for Pb(II) and 4.2 mg/g for Cd(II). No affinity for absorption of Hg(II) by the hydrogel was observed. The thermal stabilities of the prepared hydrogels were characterized by TGA. The efficiency of EDTA in the hydrogel matrix for chelation was observed to be approximately 10% of that of pure EDTA in solution.

Swelling behavior and pervaporation properties of new composite membrane systems: Porous polyethylene film‐poly(acrylic acid) hydrogel

AbstractA new type of composite membrane for pervaporation has been developed. These membranes were prepared by free‐radical copolymerization of acrylic acid with a macromolecular polyfunctional crosslinker (allylhydroxyethylcellulose) inside the porous polyethylene (PE) film. It was shown that the porous structure of the PE matrix is filled with poly(acrylic acid) (PAA), and a layer of acid is formed on the film surface. To investigate the effect of the porous matrix on the composite membrane properties, a hydrogel membrane of crosslinked PAA was also prepared without the matrix using the same procedure. PAA in both membranes was in the neutralized form (K+). Swelling behavior of the membranes and their separation characteristics for pervaporation were investigated in water–ethanol solutions depending on the ethanol concentration. All membranes exhibited a high degree of equilibrium swelling (Q = 20–50 g/g) in dilute ethanol solutions (0–30 vol %), and Q sharply dropped to 1.5–2 g/g at a EtOH concentration of 30–40 vol % due to collapse of the gel. All membranes under study were highly permeable and selective to water over a wide range of ethanol concentrations in the feed (50–96 vol %), but composite membranes had a higher separation factor due to the restriction effect of the matrix porous structure on swelling of PAA(K+) inside the pores. However, composite membranes were characterized by a lower permeation rate, compared to the crosslinked PAA membranes without a matrix, because of their lower effective surface for diffusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1461–1465, 2004

Effect of montmorillonite on the properties of thermosensitive poly(N‐isopropylacrylamide) composite hydrogels

AbstractThermosensitive composite hydrogels containing various amounts of sodium montmorillonite (NaMM) and poly(N‐isopropylacrylamide) (pNIPAAm) were synthesized. Their equilibrium degree of swelling (DS) was measured in NaCl solutions of different ionic strength and at various temperatures. The DS decreased when increasing the clay content and no substantial shift in the phase transition temperature was noticed. The composite hydrogels investigated had a NaMM content ranging between 1.0 and 5.7 wt % (in 0.1M NaCl at 25°C). A considerable enhancement in the response to thermal stimuli was observed for NaMM contents >2–3 wt %. It is suggested that when the NaMM concentration approaches a critical value, the clay platelets can inhibit the formation of the hydrophobic skin layer that hinders shrinking in conventional pNIPAAm hydrogels. The effect of montmorillonite on the mechanical properties of the hydrogels was investigated by uniaxial compression tests, which showed that the modulus increases with the NaMM content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1964–1971, 2004

Vinyl polymers based on L-histidine residues. Part 1. The thermodynamics of poly(ampholyte)s in the free and in the cross-linked gel form.

Amphiphilic vinyl polymers (in the free and cross-linked forms), carrying carboxyl and imidazole groups, were prepared by a radical polymerization of the purposely synthesized N-acryloyl-L-histidine. The protonation thermodynamic studies (at 25 degrees C in 0.15 M NaCl) showed high polyelectrolyte character of the soluble polymer. Unlike the linear decreasing trend of the basicity constant, over the whole range of alpha (degree of protonation), the enthalpy changes for the protonation of the imidazole nitrogen in the polymer showed a decreasing pattern only at alpha > 0.5. This was ascribed to the formation of hydrogen bonds between protonated and free neighboring monomer units. Viscometric data revealed a minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5), whereas at higher or lower pHs, the macromolecule expanded greatly as a consequence of the charged sites formation. This produced a preferential solvation of the protonated imidazole and carboxylate ions, the latter being surrounded by more water molecules in the hydration shell. The peculiar hydration behavior was confirmed in the cross-linked polymer. The hydrogel showed an equilibrium degree of swelling (EDS), strongly dependent on pH, in a similar manner as viscometric data of the soluble polymer. A linear relationship between the reduced viscosity and the EDS was found. The polymer was non toxic against the RAW264 cell line.

Radiation synthesis of superabsorbent poly(acrylic acid)–carrageenan hydrogels

A series of superabsorbent hydrogels were prepared from carrageenan and partially neutralized acrylic acid by gamma irradiation at room temperature. The gel fraction, swelling kinetics and the equilibrium degree of swelling (EDS) of the hydrogels were studied. It was found that the incorporation of even 1% carrageenan (sodium salt) increases the EDS of the hydrogels from ∼320 to ∼800 g/g. Thermal analysis were carried out to determine the amount of free water and bound water in the hydrogels. Under optimum conditions, poly(acrylic acid)–carrageenan hydrogels with high gel fraction (∼80%) and very high EDS (∼800 g/g) were prepared gamma radiolytically from aqueous solution containing 15% partially neutralized acrylic acid and 1–5% carrageenan. The hydrogels were also found to be sensitive to the pH and the ionic strength of the medium.

Volume Transition of Liquid Crystalline Gels in Isotropic Solvents

The equilibrium swelling and phase behavior of the side chain liquid crystalline (LC) networks in isotropic (nonmesomorphic) solvents has been investigated as a function of temperature. The LC networks swollen in di-n-amyl phthalate or di-n-butyl phthalate exhibit discontinuous volume transition driven by nematic ordering: The swollen isotropic gel is discontinuously transformed into the shrunken nematic gel at a characteristic temperature (TNIG). The transition temperature TNIG depends on the swelling solvent, and TNIG decreases as the degree of equilibrium swelling in the isotropic phase increases. The volume transition phenomena observed are satisfactorily described by a mean field theory for nematic gel.

Changing of network characteristics of acrylamide/maleic acid hydrogels by alteration of irradiation dose rate

Poly(acrylamide/maleic acid) P(AAm/MA) hydrogels were prepared by irradiating the ternary mixtures of AAm/MA and water by gamma rays at ambient temperature at very low (0.18 kGy/h), and moderate dose rate (3.0 kGy/h). The equilibrium degree of swelling (EDS) of hydrogels prepared at 3.0 kGy/h dose rate increased from 520% to 3900% with increasing MA mole content in the gel system from 0% to 5.2%. On the other hand, no systematic dependence of swelling on MA content was observed for hydrogels obtained at low dose rate irradiation due to formation of inhomogeneous network structure and large pores in the gel. Pore structure of hydrogels was monitored by using scanning electron microscope. Systematic swelling of P(AAm/MA) hydrogels prepared at moderate dose rates can be explained with homogeneous pore size distribution of network.