Swelling and deswelling pathways in non-ionic poly(N-isopropylacrylamide) hydrogels in presence of additives (original) (raw)
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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.
European Polymer Journal, 2002
Deswelling kinetics of water and terbinafine hydrochloride adsorbed poly(N-vinyl-2-pyrrolidone/itaconic acid) P(VP/IA) hydrogels were investigated. Hydrogels were prepared by irradiating the ternary mixture of VP/IA and crosslinking agent ethylene glycol dimethacrylate (EGDMA) in water by c-rays at ambient temperature. Hydrogels swelled in pure water and terbinafine hydrochloride (TER-HCl) solutions at room temperature and deswelling or water loss were investigated between 4 and 45°C temperature range and on human skin. The influence of IA content, % swelling, temperature and TER-HCl content on the water loss from gel matrix were investigated. Induction time for 80% water loss from hydrogel systems are found to increase from 9.6 to 21.2 h by increasing IA content in the gel system at 25°C and decreased by 11 h with addition of TER-HCl in the gel system. Kinetic analyses had shown that the basic properties affecting the water loss behavior of these hydrogels are the IA and TER-HCl content and temperature of the medium. Ó
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".
The Journal of Physical Chemistry B, 2007
The number of variables controlling the behavior of ionic gels is large and very often some of them are unknown. The aim of this work is to interpret quantitatively the swelling behavior of pH sensitive gels, with the minimum number of simplifying assumptions. With this purpose, the equilibrium degree of swelling (S) and protonation (R) of chemically cross-linked poly(N-vinylimidazole) (PVI) immersed in aqueous salt solutions were measured as a function of the ionic strength (µ), in the whole range of pH. In acid solutions with pH in the range 0 to 4, imidazole moieties become protonated, and PVI behaves as a polyelectrolyte gel: S decreases upon increasing µ both for NaCl and for CaCl 2 , with HCl as protonating acid. In aqueous solutions with larger pH, between 4 and 12, the hydrogel is practically neutral, and S increases as µ rises, showing a salting-in effect. From the quantitative analysis of these results, the following facts emerged. Protonation induces chain stiffness (as measured by the non-Gaussian factor) and worsening of the solvent quality of the aqueous media (as measured by the polymer-solvent interaction parameter). For R below 33%, swelling seems to be governed by the excess of mobile counterions inside the gel with respect to the bath, with a minor but still significantly negative contribution of the osmotic swelling pressure due to polymer-solvent mixing. Above 33% protonation, it is necessary to consider Manning counterion condensation to get parameters with physical meaning. The crossover between polyelectrolyte and salting-in effects corresponds to R and µ values with the same ionic and mixing contributions to the osmotic swelling pressure. The formation of ionic nonpermanent cross-links, with H 2 SO 4 as the protonating acid, was discarded.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 1999
A microgel particle is a cross-linked latex particle which is swollen by a good solvent. Particle swelling is intrinsically related to the nature of the interaction between the polymer and continuous phase. Microgel particles based on PNP [PNP=poly(N-isopropylacrylamide)] are particularly interesting since the parent homopolymer undergoes a coil-to-globule transition in water when the temperature increases above 32°C. In this work, PCS (photon correlation spectroscopy) and SANS (small-angle neutron scattering) are employed in a complementary manner to study the environmentally induced de-swelling of PNP particles. Further, we show that particle de-swelling may be induced at room temperature by addition of alcohols or excluded free polymer (i.e. non-adsorbing free polymer) to the continuous phase. (The extents of particle de-swelling observed using these additives are similar to those achieved by heating the pure microgel particles in water above 32°C.) Particle de-swelling in the presence of added alcohol or free polymer arises from “co-non-solvency” and osmotic de-swelling effects, respectively.Copolymerization of N-isopropylacrylamide (NP) with acrylic acid yields microgel particles whose diameters are sensitive to both pH and temperature. These particles adsorb PbII ions from solution in a reversible manner. The latter property has potential application in water purification.
European Polymer Journal, 2001
Hydrogels were prepared by free radical polymerisation in aqueous solution of N-isopropylacrylamide (NIPA) and of NIPA with di-npropylacrylamide (DPAM), di-n-octylacrylamide (DOAM) or di-dodecylacrylamide (DDAM) as hydrophobic comonomer. N,N-methylene bisacrylamide (BIS) and glyoxal bis(diallyacetal) (GLY) were used as crosslinkers. A series of copolymers with three different comonomer contents was synthesised and for some polymers three different crosslinker concentrations were employed. The swelling equilibrium of these hydrogels was studied as a function of temperature, hydrophobic comonomer species and content in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS). In pure water the gels showed a discontinuous volume phase transition at 33 and 30 8C for PNIPA and hydrophobically modi®ed PNIPA copolymeric hydrogels, respectively. The swelling ratio r and the transition temperature (LCST) increased at low temperatures with the addition of SDS, this is ascribed to the conversion of non-ionic PNIPA gels into polyelectrolyte gels through the binding of SDS. At SDS concentration below 0.5 wt%, gels exhibited a single discontinuous volume transition at 36± 38 8C. However, for SDS concentration above 0.5 wt%, two discontinuous volume transitions at 36±40 and 70 8C were observed. Additionally, the replacement of BIS by the novel octafunctional crosslinker glyoxal bis(diallylacetal) (GLY) yielded an increase in the swelling ratio. q
Journal of Membrane Science, 1994
Temperature-responsive poly (N-isopropylacrylamide-co-butyl methacrylate) gels exhibit "on-off" regulation of drug release in response to temperature. In a previous study, swelling kinetics of these gels from deswollen to swollen states at several temperatures were investigated. It was demonstrated that the swelling behavior of the gel changed at various temperatures, yielding several patterns of drug release profiles. At 20' C, gel swelling increased with time, which was explained using a Case-II transport mechanism. In this mechanism, the glassy polymer matrix core acts to suppress the swelling of the outer region when swelling forces dominate. By reducing the experimental temperature to 10' C and utilizing the greatly enhanced hydration of polymer chains after disappearance of the glassy core, a sigrnoidal swelling pattern gives rise to novel drug release profiles. In this study, these swelling mechanisms have been verified in detail by theoretical analysis. The existence of a swelling front was confirmed by observation of the colored gel using a dye. When the thickness of gel was changed, the acceleration of swelling was delayed with increasing thickness, and the acceleration times agreed with theoretical values predicted from the model. The observed changes in diameter and thickness of the gel also supported the model. These results demonstrate the validity of the model presented in the previous paper.
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.