pH-induced swelling kinetics of polyelectrolyte hydrogels (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.
International Journal of Pharmaceutics, 2020
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Journal of the Serbian Chemical Society, 2007
The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in distilled water and physiological solution at temperatures ranging from 20 to 40 ºC were determined. The possibility of applying both the Fick's kinetics model and kinetics model of the first order chemical reaction to the swelling kinetics of the PAA hydrogel in distilled water and physiological solution were examined. It was found that the possibilities of applying these models were limited. The new model of the kinetics of swelling in distilled water and physiological solution was established. The kinetic parameters (E a , ln A) for the swelling in distilled water and physiological solution were determined. The decrease of the equilibrium degree of swelling and the saturation swelling rate of the swelling of the PAA hydrogel in physiological solution compared to swelling in distilled water could be explained by the decreased differences in the ionic osmotic pressures between the hydrogel and the swelling medium. The increase of the initial swelling rate in the physiological solution might be caused by an increased density of charges at the network and by an increased affinity of the network towards the water molecules. The increase of the activation energy of the swelling of the PAA hydrogel in the physiological solution is a consequence of its additional "ionic crosslinking".
European Polymer Journal, 2007
In this study, swelling behavior and mechanical properties of polyelectrolyte cationic hydrogels of poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA), and poly((2-dimethylamino) ethyl methacrylate-co-butyl methacrylate) (P(DMAEMA-co-BMA)), were investigated. Hydrogels were prepared by free-radical solution copolymerization of DMA-EMA and BMA using ethylene glycol dimethacrylate (EGDMA) as the crosslinking agent. Compression-strain measurements were used to analyze the mechanical properties of the hydrogels. It was found that increasing the amount of BMA comonomer in the gel structure increases the compression modulus of the material. The results of mechanical measurements were used to characterize the network structure of the hydrogels, namely the effective crosslinking density (m à e Þ. It was found that m à e exceeds the theoretical crosslinking density (m t) calculated from the initial amount of EGDMA used for hydrogel synthesis. These hydrogels demonstrated dual sensitivity to both pH and temperature. It was shown that the pH-sensitive or temperature-sensitive phase transition behavior of the gels can be changed by changing the temperature or pH of the swelling medium at constant hydrogel composition. Increasing the temperature decreased the transition pH of the pH-sensitive phase transition. On the other hand, increasing the pH of the surrounding medium decreased the transition temperature of the temperature-sensitive phase transition. Incorporation of BMA in the gel structure has a significant effect on the transition point of the gel. Increasing the BMA content reduced the transition pH and temperature of the pHand temperature-sensitive phase transition, respectively. The similar effect of increasing temperature or BMA content can be explained by the role of hydrophobicity in the phase transition behavior of hydrogels. Finally, the results of equilibrium swelling and compression-strain measurements were used to calculate the polymer-solvent interaction parameters of these hydrogels using the Flory-Rehner equation of equilibrium swelling.
A theory of constrained swelling of a pH-sensitive hydrogel
2010
Many engineering devices and natural phenomena involve gels that swell under the constraint of hard materials. The constraint causes a field of stress in a gel, and often makes the swelling inhomogeneous even when the gel reaches a state of equilibrium. This paper develops a theory of constrained swelling of a pH-sensitive hydrogel, a network of polymers bearing acidic groups, in equilibrium with an aqueous solution and mechanical forces.
Deformation kinetics of pH-sensitive hydrogels
Polymer International, 2013
Polymeric gels can undergo large deformation when subjected to external solutions of varying pH. It is imperative to understand the deformation process of pH-sensitive hydrogels for the effective application of these attractive materials in the biomedical and microfluidic fields. In the modeling of these multi-phase materials, finite element (FE) modeling is a useful tool for the development of future applications, and it allows developers to test a wide variety of material responses in a cost-effective and efficient manner, reducing the need to conduct extensive laboratory experiments. Although a FE user-defined material model is available for the equilibrium state, the transient response of pH-sensitive gels has not been effectively modeled. Based on our recent work using the heat transfer analogy to tap into the readily available coupled temperature-displacement elements available in the commercial FE software ABAQUS for simulation of the transient swelling process of neutral hydrogels, the transient swelling process of a pH-sensitive hydrogel is studied and a FE model is further developed to simulate the transient phenomena. Some benchmark examples are investigated to demonstrate the model's capabilities in the simulation of nonlinear deformation kinetics relevant to several applications of pH-sensitive hydrogels.
The Swelling Responsiveness of pH-Sensitive Hydrogels in 3 D Arbitrary Shaped Geometry
2013
The pH-sensitive hydrogels are physically responsive to a change in the pH of surrounding solution, which often resemble to biomaterials. These hydrogels can expand up to 4 times to its original dimensions under certain pH of surrounding buffer. We present the simulation of swelling characteristic of 3Darbitrary-geometry, pH-sensitive hydrogel in steady state conditions. Three nonlinear partialdifferential equations that are representing responsible physical phenomena namelychemical, electrical, and mechanical can describe the swelling responses to a chemical change in surrounding solution. Finite element analysis used for present study was carried out by full coupling of above three partial-differential equations with variable material properties in COMSOL Multiphysics®. Employing a moving mesh method for 3D geometry, the FEM simulation was performed to account for largeswelling of the pH-sensitive hydrogel.
Polymer Bulletin, 2001
Influence of some simulated physiological body fluids on the dynamic swelling behaviour of polyelectrolytic hydroxamic acid hydrogels (PHA) was investigated at 37 °C in vitro. The simulated physiological body fluids are distilled water, human sera, physiological saline (0.89 % NaCl), isoosmotic phosphate buffer at pH 7.4, gastric fluid at pH 1. 1, (gylicine-HCl buffer), urea (0-3 mol L-1), and the aquatic solutions of K 2 HPO 4 and KNO 3 (the sources of K +). The values of equilibrium swelling of PHA hydrogels varied in the range of 130-4625%, while the values of equilibrium fluid content of the hydrogels varied in the range of 57-97%. The initial rate of swelling, diffusional exponent, and, diffusion coefficient were calculated using swelling kinetics data. Diffusion of the fluids into the hydrogel was found to be non-Fickian character. The diffusion coefficients of the hydrogel varied between 0.6x10-6-8.1x10-6 cm 2 s-1 .
Analysis of a model for pH-sensitive hydrogels
Polymer, 2012
A mathematical model comprising conservation of mass, momentum, and ions for a hydrogel subject to alterations of the solution pH is derived, analyzed, validated and presented. Good agreement between model predictions and their experimental counterpart are achieved. To gain a physical insight into the deformation behavior of the pH-sensitive hydrogel, a scaling analysis coupled with a parametric study is carried out for key physical and operational parameters. The results suggest the significance of initial fixed-charge density, solution ionic strength, Poisson ratio and Young modulus in determining swelling degree of the hydrogel. In addition, it is noted that changes in acid dissociation constant and temperature lead to a notable shift in equilibrium swelling curves. Permeability and size of the hydrogel were found to significantly affect the deformation kinetics: A hydrogel with higher permeability and/or smaller size exhibits faster deformation. These findings and the characteristic scales could provide important guidelines in designing systems utilizing pH-sensitive hydrogels.
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...