Comparison of the swelling kinetics of a partially neutralized poly(acrylic acid) hydrogel in distilled water and physiological solution (original) (raw)
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Journal of Applied Polymer Science, 2009
The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in buffer solutions of different pH values (5, 7, and 9) at temperatures ranging from 30 to 40 C were determined. The possibilities of applying the Fick kinetics model and the Peppas equation were examined. It was found that the applicability of these models were limited. The kinetics model of a first-order chemical reaction was found to describe the swelling kinetics of the PAA hydrogel in all the investigated buffer solution at all the investigated temperatures. Swelling kinetics is deter-mined by the rate of expansion of the network. The kinetic parameters (E a , ln A) of the swelling of the PAA hydrogel in buffer solutions of different pH values were determined. The activation energy and the pre-exponential factor of the swelling of the PAA hydrogel in buffer medium decreased with increasing pH value of the swelling medium.
Chemical Industry
Hydrogels are synthesized by the method of radical polymerization of monomers: N-isopropylacrylamide (NIPAM) and acrylic acid (AA). Characterization of poly(N-isopropylacrylamide- co-acrylic acid) hydrogels, p(NIPAM/AA), has been performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and by determination of the swelling behaviour in aqueous solutions at different temperatures (25, 31 and 37?C) and pH values (2.2, 4.5, 6 and 6.8). After lyophilisation in the solution at pH 6 and temperature of 25?C, p(NIPAM/AA) hydrogels have rapidly reached equilibrium degree of swelling, ?e, in comparison to non-lyophilized samples. The mechanism of solvent transport within matrix in lyophilized samples corresponds to less Fickian diffusion, whereas Super case II diffusion is characteristic for non-lyophilized samples. p(NIPAM/AA) hydrogel with 1.5 mol% of ethylene glycol dimethacrylate (EGDM) at the temperature of 25?C and pH 6.8, has reached the highest swelling equi...
Journal of Applied Polymer Science, 2006
Ionic poly(N-t-butylacrylamide-co-acrylamide) [P(TBA-co-AAm)] hydrogels were synthesized by the free-radical crosslinking copolymerization of N-t-butylacrylamide and acrylamide monomers in fixed amounts and the maleic acid (MA) comonomer in methanol in different amounts with N,N-methylene bis(acrylamide) as the crosslinker, ammonium persulfate as the initiator, and N,N,NЈ,NЈ-tetramethylenediamine as the activator. The swelling behavior of these hydrogels was analyzed in buffer solutions at various pHs. The polymer-solvent interaction parameter () and the average molecular weight between crosslinks of the ionic P(TBA-co-AAm) hydrogels were calculated from swelling studies in buffer solutions at various pHs and were related to the MA content. The results indicated that the swelling behavior of the ionic P(TBA-co-AAm) hydrogels at different pHs agreed with the modified Flory-Rehner equation based on the affine network model and the ideal Donnan theory. The enthalpy (⌬H) and entropy (⌬S) changes appearing in the parameter for the hydrogels were also determined with the modified Flory-Rehner equation. The negative values for ⌬H and ⌬S indicated that the hydrogels had a negative temperature-sensitive property in water, that is, swelling at a lower temperature and shrinking at a higher temperature. The experimental swelling data of the hydrogels at different temperatures agreed with the modified Flory-Rehner approach based on the affine network model, which ensured that the sensitive dependence of the parameter on both the temperature and polymer concentration was taken into account.
Journal of Applied Polymer Science, 1995
Incorporation of sodium polyacrylate (NaPAA) in poly(vinyl alcohol) (PVA) gels as small, uniformly distributed precipitates greatly accelerates their volume expansion during swelling in water to form hydrogels. In addition to the usual water absorption, the swelling process includes dissolution of the precipitates that leads to a locally high osmotic pressure that in turn causes a further increase in water penetration and volume expansion. During swelling, soluble NaPAA is released into the water phase with a high initial release rate that then decreases continuously. The release can be described by a n exponential decay function with a power dependent rate coefficient. Because the diffusion of NaPAA through the PVA walls is too slow to account for this release rate, a morphology of a closed cell foamlike structure with interconnecting channels is proposed. An aqueous solution of NaPAA seems to diffuse out of the hydrogel through these channels. 0 1995 John Wiley & Sons, Inc.
pH-induced swelling kinetics of polyelectrolyte hydrogels
Journal of Applied Polymer Science, 1995
Through swelling experiments on polyelectrolyte (HEMA/DMA) hydrogels, pH-induced swelling kinetics is found to be best described by a diffusion-mechanical relaxation incorporated model. The theory of equilibrium swelling is quantitatively combined into the model of swelling kinetics. By doing so, the advantage is taken of applying relatively more matured knowledge of gel swelling thermodynamics to predict less knowledgeable dynamic behavior of gels.
Journal of Research Updates in Polymer Science, 2013
The ter-polymeric hydrogels of vinylacetate (VA), methacrylate (MA) and acrylicacid (AA) were prepared using ethyleneglycoldimethacrylate (EGDMA) as a cross linker and benzoylperoxide (BPO) as an initiator. The effect of acrylic acid concentration on various swelling parameters was studied at different pHs (1.0, 4.0, 5.5, 7.4 and 8.0). A promising relationship was found to exist between media penetration velocity and equilibrium media content of hydrogels at all pH values for various concentration of acrylic acid. The fastest dynamic swelling was observed for the highest concentration of acrylic acid (40 mol % of AA) at pH 8.0. In the kinetic study, during the first hours, a first order kinetics (Fick Model) was observed at pH higher than the value of pKa (4.75) of acrylic acid, the hydrogels exhibiting non-Fickian diffusion mechanism. Whereas, for the acidic media pH, a second order kinetics was observed (Schott Model). Network parameters strongly support the swelling out comes. The relaxations of the ter-polymeric chain were observed after swelling at pH 8.0 via SEM pictures. Thermo gravimetric analysis and differential scanning calorimetric analysis also agree with the above conclusions. Well controlled swelling behavior, network properties, SEM out comings and thermogravimetric analysis support the idea to use these hydrogels for targeted drug delivery in the colon part of the digestive tract.
2007
The poly (acrylamide) (PAAm) and methyl cellulose (MC) hydrogels were prepared with a crosslinker using N, N'methylene bisacrylamide (NNMBA) and glutaraldehyde (GA). In order to do this, it was necessary to modify the percentages of catalyst (potassium persulfate, KPS) and crosslinker (NNMBA) for poly (acrylamide). To evaluate their maximum degree of swelling and to determine the swelling kinetics, the quantity of fluids absorbed by films was measured at different temperatures (20, 30, and 40°C) and pH's (acidic, basic, and neutral). According to the results obtained from the experiment, the most suitable temperature and pH were 30°C and neutral, conditions under which the highest swelling values were obtained. In the kinetic study, during the first hours, a first order kinetic (Fick Model) was observed. The results were non-Fickian, revealing that the chain's diffusion and relaxation processes occur at the same time during the absorption of the solution. For longer periods of time, with the exception of a 40 °C temperature (where the first order kinetic was identified), a second order kinetic was observed (Schott Model), indicating that there is no polymeric chain relaxation, but rather, contraction and collapse of the material. The relaxations of the polymer chain were observed after swelling via SEM pictures.
Journal of Applied Polymer Science, 1998
A series of hydrogels were prepared from acrylamide and 2-acrylamido-2methylpropanesulfonic acid (AMPS) monomers with 0 -80 mol % AMPS and using N,NЈ-methylenebis(acrylamide) as the crosslinker. The swelling capacities of hydrogels were measured in water and in aqueous NaCl solutions. The volume swelling ratio q v of hydrogels in water increases sharply when the mole fraction f c of AMPS increases from 0 to 0.06. At higher values of f c from 0.06 up to 0.18, no change in the swelling capacities of hydrogels was observed; in this range of f c , q v becomes nearly constant at 750. However, as f c further increases, q v starts to increase again monotonically over the entire range of f c . At a fixed value of f c , the swelling ratio of hydrogels decreases with increasing salt concentration in the external solution. The results of the swelling measurements in aqueous salt solutions were compared with the predictions of the Flory-Rehner theory of swelling equilibrium. It was shown that the theory correctly predicts the swelling behavior of hydrogels up to 80 mol % charge densities. The method of estimation of the network parameters was found to be unimportant in the prediction of the experimental swelling data. The network parameters used in the simulation only correct the deficiency of the swelling theory.
Swelling characterization of anionic acrylic acid Hydrogel in an external electric field
2006
A polymer gel is a cross-linked polymer which undergoes a reversible volume and/or sol-gel phase transition in response to physiological (temperature, pH and presence of ion in organism fluids) or other external (electric field, light) stimuli. In structurally soft gels, the motion of polymer network and the diffusion of ions easily take place by an external stimulus. A typical function of gel containing ionic groups is to swell under the influence of an electric field, making it useful for wide biomedical applications. In this study, poly(acrylic acid) (PAA) hydrogel network was prepared by free radical polymerization whose average molecular weight between crosslinkes was calculated as 18500 g/mol and its homogeneity assessment evaluated by comparing 30 samples swelling ratios after 48 h soaking in distilled deionized water. The swelling behaviour of PAA under an electric field application was also investigated as a function of cross-linking agent and electric field intensity variation. It is seen that equilibrium swelling ratio of PAA gel increases from 16 (no electric field) to 30 (by application of 300 V/m electric field), however this variation is dependent on the sample location relative to electrodes. The normalized swelling ratio of sample changes by 4.8 to 0.9 relative to its distance from positive electrode. Increasing the concentration of cross-linking agent (EGDMA) from 0.14 to 0.71 molar percent of monomer resulted in 45% decrease of gel volume fraction. It is proven that applying an external electric field can make an improvement in the time-response of the hydrogel expansion phase and swelling behaviour.
Cationic copolymer gels of acrylamide and [(methacrylamido) Propyl] trimethyl ammonium chloride (MAPTAC) were synthesized by free radical aqueous solution polymerization. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the equilibrium swelling capacity of the hydrogels. Based on Taguchi method a standard L 16 orthogonal array with five factors at four levels was designed and experiments were done in accordance with it. The effects of network composition such as cross-linker density, ionizable monomer and total monomer concentration together with the initiator concentration on the equilibrium swelling capacity of hydrogels in distilled water were studied. From the analysis of variance (ANOVA) of the test results, the most effective factor controlling equilibrium swelling capacity was obtained and maximum water absorbency of the optimized hydrogel was found to be 3570 g/g. The presence of counterions in the external solution suppressed swelling of optimized hydrogel and this effect was pronounced with bivalent counterions. By using the thermodynamic model, the experimental data were analyzed and the cross-linking efficiency for the polymerization reaction was calculated to be about 40%.