Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide) (original) (raw)
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Temperature dependence of swelling of crosslinked poly(N,N′-alkyl substituted acrylamides) in water
Journal of Polymer Science Part B: Polymer Physics, 1990
The swelling of crosslinked poly(N , N'-alkyl substituted acrylamides) in water was studied in relation to temperature changes. Conventional swelling theory and separation of the polymersolvent interaction parameter into enthalpic and entropic contributions were used to characterize the temperature dependence of swelling in water. The thermosensitivity of swelling can be attributed to the delicate hydrophilic/hydrophobic balance of polymer chains and is affected by the size, configuration, and mobility of alkyl side groups. A sharp swelling transition may occur at an optimum hydrophilic/hydrophobic balance but was found only in the N-isopropylacrylamide network among the networks tested. This swelling transition pattern was also reflected by the endothermic peak of the DSC thermogram of the swollen sample.
Network and swelling parameters of chemically crosslinked thermoreversible hydrogels
Polymer, 2001
Two series of hydrogels of poly(N-isopropylacrylamide-co-acrylic acid) have been prepared by copolymerisation in solution using tetrafunctional N,N H -methylene bis-acrylamide and a novel octafunctional crosslinker glyoxal bis(dially acetal) (GLY) as crosslinker. These thermoreversible hydrogels were swollen to equilibrium in water at 301 K and examined by gravimetric, dimensional and compression± strain measurements. The in¯uence of nature and content of crosslinker on swelling ratio, polymer±water interaction parameter, elastic moduli and effective crosslinking density (n e ) is reported and discussed. Both series exhibit low crosslinking ef®ciencies expressed as n e / (theoretical crosslinking density calculated from feed composition). The extremely low ef®ciencies for the GLY-crosslinked gels is responsible, at least in part, for the ultra-high swellability of these hydrogels. q
Morphological effect on swelling behaviour of hydrogel
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Hydrogels are hydrophilic polymer networks that are capable of imbibing large amounts of water. In this work, hydrogels prepared from natural and synthetic polymers were irradiated by using electron beam irradiation. The morphology of hydrogel inter-polymeric network (IPN) was investigated using Scanning Electron Microscopy (SEM). The studies reveal correlations between pore sizes of IPN with degree of cross-linking. This relation also has an effect on swelling properties of the hydrogel. The results indicated that hydrogel with smaller pore size, as a result of much dense IPN, would decrease water uptake capacity. Combination of natural and synthetic polymers to form hydrogel affects the pore size and swelling property of the hydrogel as compared to each component of polymer.
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Effects of Cross-linker Variation on Swelling Behavior of Hydrogels
Asian Journal of Pharmaceutics, 2020
Introduction: The main objective of this study is to find the effects of cross-linker variation on swelling behavior of hydrogels at different temperatures, that is, 30 min–120 min. Hydrogels are three-dimensional cross-linked structural arrangement of the polymeric materials with the ability to absorb huge amounts of water while maintaining their dimensional stability. Materials and Methods: A solution of 20% glutaraldehyde (GA) was prepared in 100 ml standard flask by dissolving 20.0 g GA in a standard flask (of capacity 100 ml) and make up the volume up to the mark using demineralized water (DMW). The gelatin-polyethylene glycol (PEG) composite hydrogels were prepared by simultaneous method, in which all the constituent component networks are polymerized concurrently. Different combinations of gelatin-PEG composite hydrogels were prepared with methylene blue (MB) dye in it. Swelling was studied with the help of the following equation: dssdW-WI=×100W Results and Discussion: The ob...
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.
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.
Swelling Behavior of Soft and Biological Materials
Key Engineering Materials, 2015
Injuries or other ailments can cause swelling of tissues in the body, or of ligaments and tendons surrounding the bones. Such inflammation can lead to discomfort, pain, or even serious illness. Knowledge of the biomechanics of soft tissues is essential for correct prognosis and diagnosis. This requires good modeling and simulation of soft skeletal tissues, which cannot be carried out without experimental material characterization. Behavior of organic tissues is quite similar to that of elastomeric materials that swell when immersed in certain fluids. This work investigates the effect of swelling on compression and bulk properties and the polymeric structure of a water-based elastomer. A drastic change in mechanical and structural properties is observed during the initial swelling period. Elastic and shear moduli decrease by nearly 90% within a few days, and then exhibit almost no change. An opposite trend can be observed for Poisson's ratio; dramatic increase in the beginning, then a near-constant behavior. Variation in bulk modulus is somewhat fluctuating, but the general trend is a decrease due to swelling. After ten days of swelling, value of Poisson's ratio becomes approximately 0.5. A sharp decrease in the first week of swelling can be observed in chain density, while cross-link average molecular weight shows the opposite trend of an increase with swelling (with minor fluctuations). Results of this study can provide the material input values for modeling and simulation of the behavior of tissues and other soft biological materials. This, in turn, can form a basis for more detailed analytical and computational studies in biomechanics and biomedical engineering.