Equilibrium Swelling Study of Cationic Acrylamide-Based Hydrogels: Effect of Synthesis Parameters, and Phase Transition in Polyelectrolyte Solutions (original) (raw)
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Macromolecular Symposia, 2012
Stimuli-responsive polyampholyte hydrogels were synthesized by the copolymerization of acrylic acid (AAc) and acrylamide (AAm) by thermal methods. Polyampholytic hydrogels are crosslinked networks composed of positively and negatively charged repeating units that show entirely different properties from their origins. In this work, polyampholytic poly (acrylic acid acrylamide) hydrogels prepared in different molar ratio in feed composition by thermal methods. The structures of hydrogels were characterized by FTIR analysis. Thermal stabilities of the hydrogels were investigated using TGA analysis. The swelling behavior of hydrogels investigated by some parameters such as pH, salt concentration and temperature. We determined this swelling capacity in different temperatures (25, 50 and 70 8C) and different pH (2, 7 and 12). In addition, we investigated the effects of different salts such as LiCl, CaCl 2 , Na 2 SO 4 and NaCl with concentration of 0.1, 0.2 and 0.3 M on swelling properties.
Journal of Macromolecular Science, Part A, 2007
An investigation of water uptake behavior of a novel poly(acrylonitrile-co-2-acrylamido-2-methylpropane sulfonic acid-coN ,N 0-methylenebisacrylamide) hydrogel system was carried out with two major objectives. First, the study was initiated to understand the effect of various synthesis conditions, i.e., reaction temperature, initiator content, crosslinker content and pH,on the water absorbency of resulting hydrogels. The second reason was to evaluate these hydrogels after reaction with hydroxylamine hydrochloride to convert the CJN (nitrile) groups to-C5 5N-OH (amidoxime) groups. The optimum amidoximation conditions was determined. The structure of the hydrogels, before and after amidoximation, was analyzed with FTIR and thermal methods. The optimum synthesis temperature, initiator concentration and crosslinker content were found to be 558C, 1.5 (wt.%) and 1.5 (wt.%), respectively. The equilibrium water uptake increases with an increase in initiator (K 2 S 2 O 8) concentration and crosslinker (BAAm) content up to 1.5% and then it begins to decrease with a further increase in K 2 S 2 O 8 and BAAm content. The gel undergoes a drastic volume change in the pH range 5, thus indicating the dissociation of NH groups of acrylamidoxime. The pH increased at 7, and this pH shift may be attributed not only to the acidic region, but also the basic region. A drastic volume change is also observed at pH:10, which may be due to the dissociation of the AMPS SO 3 H groups. The swelling ratio of the hydrogel sample in sea water, tap water and distilled water are collected. According to the results, the maximum swelling ratio was observed in the distilled water. Finally, the nitrile groups can be easly converted into amidoxime groups via treatment with a solution of hydroxylamine. The swelling behavior of hydrogels are in good agreement, before and after amidoximation.
Swelling equilibria for acrylamide-based polyampholyte hydrogels
Macromolecules, 1992
Polyampholyte hydrogels show promise for use in applications that require the material to maintain appreciable swelling capacity in highionic-strength aqueous media. Polyampholyte hydrogels were synthesized by copolymerizing acrylamide (AAm) with the cationic monomer methacrylamidopropyl trimethylammonium chloride (MAPTAC) and the anionic monomer sodium styrene sulfonate (SSS). The total nominal charge density of the hydrogels was held constant at 4.7±0.1 mole percent (dry basis), while the molar ratio of anionic to cationic moieties within the hydrogels was varied. Swelling equilibria were measured in water and in 0. aqueous sodium chloride solutions ranging in ionic strength from 10-5 to 1.0 M. The hydrogels show increasing insensitivity to ionic strength as the molar ratio of anionic to cationic moieties in the hydrogel approached unity. At ionic strengths of 0.1 M and above, all hydrogels prepared show an increase in water content with rising NaCl concentration.
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.
Polymer, 2007
In this work, the influence of the incorporation of a small amount of carbohydrate-containing monomer N-acryloyllactosylamine (LAM) on the swelling behavior of covalently-crosslinked polyacrylamide hydrogels in water has been reported. The incorporation of LAM into the copolymer was assessed by ATReFTIR and thermogravimetric experiments. The main result is that the equilibrium water uptake was significantly decreased as soon as the hydrogel contained LAM considering a constant amount of crosslinking agent. The greatest difference of water uptakes between carbohydrate-free hydrogel and carbohydrate-containing hydrogel occurred for the lowest crosslinker amount of 1 mol%. In that case, the value of the water uptake reached w56-fold for the carbohydrate-free hydrogel and decreased down to 41-fold for the 10 mol% LAM hydrogel. Additional NMR experiments were used to measure the amount of non-crystallizable water which was higher for carbohydrate-free hydrogel than that for lactose-containing hydrogel confirming the water uptake results.
Structural parameters of polyacrylamide hydrogels obtained by the Equilibrium Swelling Theory
In this paper, the synthesis and structural characterization of a series of polyacrylamide hydrogels with different degrees of reticulation are reported. Although the Equilibrium Swelling Theory was recognized as a simple and reliable tool for the determination of structural hydrogels network parameters like equilibrium degree of swelling, cross-link ratio and mesh size, this is the first application of this methodology for polyacrylamide hydrogels. By changing the total monomer content in the synthesis solution (%T) from 5 to 30%, at a fixed value of cross-linker content in the total monomer amount (%C) of 5%, the final parameter obtained, the mesh size, can be tuned from 2 to 0.3 nm. It was also possible to change the mesh size (0.19-0.35) by varying %C from 5 to 12% (at %T = 20%). Scanning Electron Microscopy images for the most different formulations are shown and corroborate data obtained from the theory.
Colloid and Polymer Science, 2008
We synthesized, thermo-and pH-sensitive gels and tested them as skin extenders. Our aim is the development of copolymer and composite hydrogels that, when implanted under the human skin, swell osmotically and thereby induce skin growth. In the course of the polymerization reaction, we produced copolymers with variable compositions, starting from different acrylic compounds [N-isopropyl-acrylamide (NIPAAm), acrylamide (AAm), and acrylic acid (AAc)]. The mechanical strength and the swelling stability of the gels are enhanced by the addition of fillers [Na-montmorillonite and Namontmorillonites organophilized with alkylammonium ions (C n -m.), n=4, 12, 18]. With this method we synthesized composite hydrogels. We observed that in the case of composites synthesized with the addition of fillers, relatively low filler contents (1-5 wt.%) resulted in more extensive swelling and stronger gel structure. During the experiments, the monomer composition (0/100-100/0 mol% NIPAAm/ AAm or AAc) and the cross-link density (50-1500 mol%) of the gels (M/C ratio) and, in the case of composites, the quality and quantity of fillers are varied. The filler content of composites varies between 1 and 25 wt.%. The extent of swelling and the viscoelastic properties can be manipulated through the ratios of these parameters. In the case of certain copolymer and composite gels, values of desorption enthalpy (ΔH m ) corresponding to the actual water contents were also determined by thermoanalytical measurements (differential scanning calorimetry, DSC). Swelling values determined by gravimetry and enthalpies calculated from DSC measurements were found to be in good correlation. Even in the case of the relatively hydrophobic poly(NIPAAm)based gels, an enthalpy value of 98.41 kJ/mol was obtained, which is twice the value measured in pure water (41.74 kJ/ mol). Evaluation and comparison of the rheological and DSC results also allowed conclusions to be drawn concerning the types of interaction operating among the three components of the system, i.e., the polymer skeleton and the filler and water molecules.
Poly(hydroxamic acid) hydrogels from poly(acrylamide): preparation and characterization
Polymer Bulletin, 2001
Poly(hydroxamic acid) (PHA) hydrogels from crosslinked poly(acrylamide) (PAAm) hydrogels containing different type crosslinkers such as such as N, N'methylene bisacrylamide (N) and ethyleneglycol dimethacrylate (E). The effect of crosslinkers on some physical properties was investigated. The structure of hydrogels was characterized spectroscopically and thermally. The swelling parameters of PHA in distilled water, such as percent equilibrium swelling (S eq %), initial swelling rate (r o), maximum equilibrium swelling (S max), diffusional exponent (n), network parameter (k) and diffusion coefficient (D) were calculated. It has been found that the ionogenity of PHA and the structure of the used crosslinkers during the synthesis have been effective on the swelling behaviour of the hydrogels.
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.