Equilibrium Degree Of Swelling Research Articles

Modified polyacrylamide hydrogels and their application in removal of heavy metal ions

Modified crosslinked polyacrylamides having different functional groups were prepared by Mannich reaction using different amine compounds such as ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA) and sulfomethylation reaction. Products were characterized by determination of their basic group content (BGC), hydroxymethyl group content (HMG), equilibrium degree of swelling (EDS) and FT-IR spectra. For Mannich reactions, BGC and EDS changed with amount of employed amine compounds, reaction time and temperature. Sulfomethylation reactions gave products with high BGC and very high EDS. FT-IR spectroscopic analysis confirmed that a parallel hydrolysis reaction occurred along with the expected modification reactions. The products were used for removal of Cu(II), Cd(II) and Pb(II) ion under competitive and non-competitive conditions at different pH. The metal ion removal capacities changed depending their BGC and EDS. While the Mannich products were selective towards Cu(II) ion, the sulfomethylation products were highly selective to Pb(II) ions. The polymers were used several times by regeneration without loss of adsorption capacity and changing of selectivity properties.

Volume transition of nematic gels in nematogenic solvents

Equilibrium swelling and phase behavior of liquid crystalline (LC) networks swollen in miscible nematogenic solvents has been investigated by polarizing microscopy as a function of temperature. Four systems, i.e., each of two different LC networks comprising dissimilar mesogens in two different nematic solvents, exhibit essentially the same swelling and phase characteristics. The swelling characteristics strongly correlate with the phases of the LC molecules inside and outside the gel. The two independent nematic-isotropic transition temperatures for the gel (TNIG) and the surrounding pure solvent (TNIS; TNIG>TNIS for all the systems examined) yield three characteristic temperature regions. In the totally isotropic and nematic phases (T>TNIG and T<TNIS, respectively), the degree of equilibrium swelling (Q) is almost independent of T, and the magnitudes of Q in these phases are comparable. Meanwhile, Q strongly depends on T in the region TNIS<T<TNIG where the LC phases inside and outside the gel are different, i.e., nematic and isotropic, respectively. Upon cooling down to TNIG from the totally isotropic phase, the nematic network and the miscible nematic solvent inside the gel form a single nematic phase, which causes a discontinuous decrease in gel volume: The swollen isotropic gel is discontinuously transformed into the shrunken nematic gel. As temperature decreases further, Q of the shrunken nematic gel surrounded by the isotropic LC solvent increases again, and Q at T≈TNIS reaches almost the same magnitude as that in the totally isotropic phase. The nematic ordering of the surrounding pure solvent takes place at TNIS, which yields an inflection of the Q-T curve without discontinuity. A mean field theory for nematic gel successfully describes the swelling and phase behavior observed. The theory also demonstrates that the nematic-isotropic transition of gel drives a volume transition; an increase in nematic order inside gel induces a further swelling of nematic gel surrounded by isotropic LC solvent.

External Stimuli Responsive Characteristics of Epoxy‐Polyamide/Starch Blend Films

Polymeric films of varying crosslink densities and of different molar‐concentrations were prepared from the epoxidized oil/diglycedyl ether of bis‐phenol A (DGEBA) epoxy/polyamide/starch by blending at ambient temperature. The influences of external stimuli such as pH, temperature, ionic strength of the swelling media, and the type of buffer on the equilibrium swelling properties were investigated. Polymeric films showed a typical pH and temperature response such as low‐pH and low‐temperature have maximum swelling while a high‐pH and high‐temperature show almost complete deswelling. A change in the ionic strength of the swelling solution from 0.01 to 0.2 M caused a decrease in the equilibrium degree of swelling of polymeric films. Oscillatory swelling was also observed and investigated in response to changes in the pH of the solution. The morphology of selected polymeric films were explained by scanning electron microscopy (SEM) and correlated with mechanical strength.

Preparation of modified polyacrylamide hydrogels and application in removal of Cu(II) ion

Modified polyacrylamide hydrogels were prepared by transamidation and Hofmann reactions using different amine compounds. Products were characterized by their amine value (AV), equilibrium degree of swelling (EDS) and FT-IR spectroscopy. In case of transamidation on crosslinked polyacrylamide (CPAAm) in aqueous media, AV increased with reaction time and temperature, but EDS decreased with time, especially for reactions at higher temperatures. On the other hand, transamidation reactions on linear polyacrylamide (LPAAm) gave products with higher AV, but quite lower EDS than aqueous media products. Hofmann reactions were carried out on CPAAm with different amounts of NaOCl in the presence of amine compounds, to yield products with higher AV and EDS compared with conventional Hofmann reactions. The products were used for removal of copper (II) ion at pH=5.5 by batch equilibrium technique. A maximum removal capacity of 2.93mmol Cu(II)/g was obtained after a regeneration cycle.

Release of PEGylated granulocyte-macrophage colony-stimulating factor from chitosan/glycerol films

We have prepared a new formulation for mucosal delivery of GM-CSF or PEGylated GM-CSF based on a chitosan carrier plus added glycerol to control the rate of release of the protein. Thin dry films comprised of various weight ratios of chitosan to glycerol and containing either granulocyte-macrophage colony-stimulating factor (GM-CSF) or PEGylated GM-CSF, PEG-(GM-CSF), were prepared. The amount of GM-CSF or PEG-(GM-CSF) released from the chitosan/glycerol films was determined using size exclusion high performance liquid chromatography (HPLC-SEC). The amount of PEG-(GM-CSF) released from the films decreased with an increase in the amount of glycerol present in the film. In parallel with this, films with higher glycerol content exhibited a lower degree of equilibrium swelling when immersed in release media. pH measurements of the release media and analysis of the dried films by Fourier-transform infrared spectroscopy (FTIR) suggested that the amount of residual acetic acid in the dry films decreased as the glycerol content increased. This indicates that glycerol may act by displacing and releasing bound acetic acid from the chitosan molecules, resulting in chitosan–glycerol hydrogen bond formation as the film dries. Further, it was found that the release rate and the amount of PEG-(GM-CSF) released decreased with increasing molecular weight of the conjugated PEG. This effect was not observed with films containing physical mixtures of PEG and GM-CSF. The decrease in the fraction of PEG-(GM-CSF) released with increasing PEG molecular weight is believed to be due to the increased steric hindrance of the PEGylated protein molecule during its diffusion out of the swollen chitosan/glycerol film.

Evaluation of the permeability and blood‐compatibility properties of membranes formed by physical interpenetration of chitosan with PEO/PPO/PEO triblock copolymers

AbstractIn order to develop blood compatible membranes with controlled porosity, we have fabricated and examined the properties of physical interpenetrating network (PIN) of chitosan and poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymers (Pluronics®). Degree of equilibrium swelling, scanning electron microscopy, and electron spectroscopy for chemical analysis (ESCA) were used to characterize the bulk and surface properties. Vitamin B12 and human serum albumin were used as permeability markers. Platelet adhesion and activation were used to determine the blood‐interaction properties of the PIN membranes. Unlike chitosan membranes that were nonporous, the chitosan‐Pluronic PIN membranes were highly porous with the pore size, depending on the type of incorporated Pluronic polyol. ESCA results showed a significant increase in the CO signal of C1s spectra on the PIN membranes that correlates with the presence of PEO chains on the surface. The permeability coefficients of vitamin B12 and albumin were higher in the chitosan‐Pluronic PIN membranes than in the control. The number of adherent platelets and the extent of activation were significantly reduced on the chitosan‐Pluronic PIN membranes. The decrease in platelet adhesion and activation correlated positively with the PEO chain length of the incorporated Pluronic polyols. The results of this study show that chitosan‐Pluronic PIN membranes offer a blood‐compatible alternative with a higher‐molecular‐weight cutoff for use in hemodialysis and related applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1274–1284, 2001

Synthesis and Absorption Power of New Polyelectrolyte Tetrazole-Containing Acrylic Hydrogels

The kinetic features of formation and equilibrium swelling in water and aqueous solutions of metals were considered for new hydrogels based on acrylic acid and methylenebisacrylamide modified with 2-methyl-5-vinyltetrazole in the polymerization stage. The influence of the concentration of the reactants on the gelation rate and the degree of equilibrium swelling was studied, as well as the influence of 2-methyl-5-vinyltetrazole on the properties of the copolymers prepared. Possible application fields for the new hydrogels were proposed.

“In situ” magnetic modification of polar elastomers

The paper presents the results of the research on the effect of a hard magnetic high coercive force fillers on rubber to filler interaction in polar elastomers based compositions. The changes in Brabender plasticorder curves, temperature characteristics of the process of mixing, equilibrium degree of swelling, bound rubber content and degree of crystallization are discussed. Reassuring evidences for the realization of polar elastomers magnetic modification “in situ” without external magnetic field application are considered.

Scaling behavior: Effect of precursor concentration and precursor molecular weight on the modulus and swelling of polymeric networks

End-linked poly(dimethylsiloxane) (PDMS) networks, containing a minimal number of defects, are prepared from vinyl-terminated PDMS chains in the presence of a theta (θ) solvent. Unreactive tri-methyl terminated PDMS of the same molecular-weight distribution as the reactive PDMS precursors were chosen as the θ solvent. Four precursor molecular weights ranging from 10 000 to 100 000 daltons were studied. The dependence of the initial modulus after cure, the dry modulus after solvent extraction, and the degree of equilibrium swelling on precursor concentration during cure were compared to recent scaling predictions. The experimental scaling exponents were found to be strong functions of the molecular weight of the precursor chains and their values approach the theoretical predictions for high-molecular-weight precursors. The relationship between the modulus of the fully swollen network and the degree of equilibrium swelling is found to be independent of precursor molecular weight and precursor concentration during cure and in better agreement with the corresponding, more robust, theoretical prediction.

Effect of kappa-carrageenan on the properties of poly(N-vinyl pyrrolidone)/kappa-carrageenan blend hydrogel synthesized by γ-radiation technology

A series of hydrogels in the form of rods were prepared from kappa-carrageenan (KC) and poly (N-vinyl pyrrolidone) (PVP) by gamma radiation with 60Co γ source at room temperature. The properties of the prepared hydrogels, such as the gel strength, gel fraction and swelling behavior were investigated. Incorporation of KC into the PVP/water system increased obviously the gel strength and equilibrium degree of swelling (EDS) of PVP hydrogel. The experimental analyses showed that the crosslinking reaction of PVP was quicker than the degradation of KC at a low dose (less than 30 kGy), and the degradation of KC was inhibited in the PVP/KC mixture system. So an interpenetrating polymer network (IPN) hydrogel composed of PVP (a chemical crosslinking network) and KC (a physical crosslinking network) was proposed here. The existence of different classes of water in this IPN system was shown by water melting curves using DCS.

An investigation of the effects of a silicalite type zeolite on PDMS-composites

The aim of this paper was to investigate the effect of a silicalite type zeolite on PDMS-zeolite composites. The obtained results show that the introduction of a silicalite type zeolite into polysiloxane matrices results in a change of the equilibrium degree of swelling of the composites in toluene, their hardness and their thermal stability. With increasing amount of zeolite, the time required to achieve the equilibrium degree of swelling (DSe) is reduced, the DSe decreases and the hardness increases. Two ranges of the effect of the zeolite concentration on the composite characteristics were noted. At zeolite concentrations up to about 12% there are significant changes of the DSe and the hardness with zeolite concentration, while these effects are considerably less pronounced at higher concentrations. The results obtained show that the silicalite type zeolite acts as a reinforcing filler. We believe that with increasing zeolite concentration in the composite the total number of established polymer-zeolite interactions increases, as does the spatial irregularity of the polymer network, but that the density of the interactions decreases. This could be the most probably explanation for the changes in the characteristics of the composite with changing zeolite concentration.

Investigation of the effects of NAA-type zeolite on PDMS composites

The aim of this article was to investigate the effect of a NaA-type zeolite on a polydimethylsiloxane (PDMS)–zeolite composite. The obtained results show that the introduction of a NaA-type zeolite into polysiloxane matrices results in a change of the equilibrium degree of swelling (DSe) of composites in toluene, their hardness, and their thermal stability. With increase in the zeolite, the time required to achieve the DSe is reduced, DSe decreases, and hardness increases. A double effect of the zeolite concentration on the change of the composite characteristics was noted. At zeolite concentrations of up to 20%, there is a drastic change of the DSe and hardness with zeolite concentration, while this effect is considerably less pronounced at higher concentrations. The results obtained show that a NaA-type zeolite plays the role of a reinforcing filler. A new mechanism of bonding the zeolite into the composite was suggested. According to this model, there is a possibility that bonds are established between the polymer and the zeolite via interaction of the π-bond of terminal vinyl groups of PDMS with the Na cation of the zeolite. With increase in the zeolite concentration in the composite, the total number of established polymer–zeolite bonds increases, but the density of the interaction decreases. This explains the change in the characteristics of the composite with the change of zeolite concentration. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1171–1176, 2000

Crosslinked dextran — a new capsule material for colon targeting of drugs

In the work presented here we have studied the application of glutaraldehyde crosslinked dextran as a capsule material for colon-specific drug delivery. A reaction mixture containing dextran, MgCl 2, glutaraldehyde and polyethyleneglycol 400 in water was applied onto molding pins of nylon producing capsule caps and bodies. The capsule materials were characterized by measuring of the mechanical strength in compression and equilibrium degree of swelling. Based on these results an optimal composition for the capsule material was selected. The dextran capsules were loaded with hydrocortisone and subsequently, drug release was studied. The release was found to be about 10% during the initial 3 h in a buffer solution. Over a period of 24 h the release was about 35%. However, when the dextran capsules were challenged with a dextranase solution, simulating the arrival of the drug delivery system to the colon, the capsules quickly broke and the drug was released as a dose dump. The study shows that the dextran capsules are promising candidates for providing a colon-specific drug delivery.

Hydrogels of poly(ethylene glycol): mechanical characterization and release of a model drug

Thermosensitive polymer networks were synthesized from poly(ethylene glycol), hexamethylene diisocyanate and 1,2,6-hexanetriol in stoichiometric proportions. By varying the amount of 1,2,6-hexanetriol and the molar mass of the poly(ethylene glycol), a wide range of networks with different crosslinking densities was prepared. The networks obtained were characterized by the temperature dependence of their degree of equilibrium swelling in water and by their Young's moduli. For each network, the molecular weight between crosslinks was estimated. The structure of the hydrogels was analysed with respect to scaling laws, and it was found that the results obtained with PEG 1500 and PEG 6000 hydrogels are in agreement with theoretical predictions, whereas those obtained with PEG 400 hydrogels are in disagreement. The release properties of PEG hydrogels were studied by the determination of the diffusion coefficient for acebutolol chlorhydrate and by an analysis of the effect of temperature on these coefficients. Finally, these release properties were correlated with the swelling and structural properties of the hydrogels.

Polyelectrolyte networks: elasticity, swelling, and the violation of the Flory-Rehner Hypothesis

This paper discusses the elastic behaviour of polyelectrolyte networks. The deformation behaviour of single polyelectrolyte chains is discussed. It is shown that a strong coupling between interactions and chain elasticity exists. The theory of the complete crosslinked networks shows that the Flory-Rehner Hypothesis (FRH) does not hold. The modulus contains contributions from the classical rubber elasticity and from the electrostatic interactions. The equilibrium degree of swelling is estimated by the assumption of a c∗-network.

PH-Responsive Gels of Hydrophobically Modified Poly(acrylic acid)

pH-responsive gels of hydrophobically modified (HM) weak polyacid were prepared from acrylic acid and n-alkyl acrylates (n = 8, 12, 18). The HM gels obtained bear up to 20 mol % of n-alkyl acrylate units randomly distributed along the network chains. The pH-driven swelling of these gels upon ionization in an aqueous medium was studied. The effect of the fraction and of the side chain length of n-alkyl acrylate groups on the equilibrium degree of swelling was examined. It was shown that the swelling transition shifts to alkaline pH with increasing hydrophobicity of the gel. This was explained by the stabilization of the collapsed state of the gel by hydrophobic aggregation of n-alkyl side chains. The formation of such aggregates, which break down in the course of gel ionization, was confirmed by the fluorescent probe method with pyrene as a probe and by NMR spectroscopy. Potentiometric titration data of HM poly(acrylic acid) (PAA) gels and of the corresponding linear copolymers evidence that the introduction of hydrophobic repeat units only slightly affects the apparent dissociation constant of PAA, except for the most hydrophobic gels.

Swelling behaviour of a polyelectrolyte network under load

The kinetics of swelling of a strongly charged hydrogel is studied. The influence of external load on the rate of swelling and on the equilibrium degree of swelling is experimentally investigated. With the help of a sensitive technique it is shown that two different mechanisms governing the process of swelling may be clearly determined. The first one (at the beginning of swelling) is connected with the ‘ordinary’ swelling of a neutral network, and the second one corresponds to the largest part of the kinetic curve and is connected with additional electrostatic interactions. The dynamics of hydrogel swelling, which corresponds to strong electrostatic interactions, is analysed by the equation of motion of the hydrogel boundary. The mathematical approach is based on the modern theory of the qualitative solution of differential equations. It allows one to obtain a correlation between static and dynamic parameters of the swelling process and the dependence of these parameters on applied load.

Evaluation of biodegradable hydrogels for colon‐specific drug delivery

AbstractThis paper summarizes the work carried out in our group over the last five years on biodegradable dextran hydrogels for colon‐specific drug delivery. Emphasis is placed on the recent developments in the design of dextran hydrogel capsules. The dextran hydrogels were shown to remain intact in the stomach and small intestine but were degraded by microbial dextranases in the colon. A large number of hydrogels with different structures have been studied and characterized in detail with respect to crosslinking density, equilibrium degree of swelling and modulus of elasticity. The release of hydrophilic and hydrophobic model drug molecules from dextran hydrogel discs and capsules have been studied. Biodegradation of the hydrogels was studied using a pure dextranase preparation, in vivo in rats and in vitro in human colon. Degradability was evaluated by measuring the time for complete dissolution of the hydrogels, the change in thickness and dry weight of the hydrogel discs and the production of short‐chain fatty acids. The surface characteristics of gels before and after degradation were studied by scanning electron microscopy.

Equilibrium Swelling and Elastic Modulus of End-linked Poly(dimethylsiloxane) Networks in Theta Solvent

The degree of equilibrium swelling and the dynamic Young's modulus for end-linked poly(dimethylsiloxane) networks in theta solvent are investigated as a function of polymer concentration at preparation. The experimental results agree well with the predictions of modified affine model, while they are not satisfactorily reproduced by the c* theorem.

Elastic modulus and equilibrium swelling of networks crosslinked by end-linking oligodimethylsiloxane at solution state

We have investigated the degree of equilibrium swelling and the elastic modulus of networks prepared by end-linking oligo(dimethylsiloxane)s (ODMS) in solution as a function of polymer concentration at crosslinking. The molecular weight of ODMS is so low that entanglement couplings are not formed in uncrosslinked state. It has been found from the preparation concentration dependence of elastic modulus in preparation state that trapped entanglements are formed by the introduction of crosslinks, and those considerably contribute to elastic modulus, even if the prepolymers are not entangled in uncrosslinked state. The experimental results for preparation concentration dependence of the degree of equilibrium swelling and the elastic modulus of equilibrium swollen networks are compared with the theoretical predictions by the two theories, i.e., the affine model and the c* theorem. It has been clearly shown that the affine model describes well the experimental results, while the discrepancies between the experimental results and the predictions by the c* theorem are considerable. These results strongly suggest that preparation concentration should be regarded as a reference state, and the displacement of crosslinks moves affinely on swelling, while the complete disinterpenetration of network chains in equilibrium swollen state, which is a postulate of the c* theorem, does not occur.