Swelling Equilibrium of a Binary Polymer Gel (original) (raw)
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Equilibrium swelling properties of polyampholytic hydrogels
Chemical Physics, 1996
The role of counter ions and ion dissociation in establishing the equilibrium swelling of balanced and unbalanced polyampholytic hydrogels has been investigated experimentally and theoretically. The swelling dependence on both the net charge offset and the external bath salt concentration has been examined using an acrylamide based polyampholytic hydrogels. By careful consideration of the swelling kinetics, we illustrate the effects
Dependency of swelling on the length of subchain in poly(N,N-dimethylacrylamide)-based gels
The Journal of Chemical Physics, 1997
The equilibrium swelling degree of poly͑N,N-dimethylacrylamide͒ ͑polyDMAAm͒-based gels in water was systematically studied with various initial monomer (c m) and cross-linker (c xl) concentrations, and as a function of initial concentration of fully ionized co-monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid ͑AMPS͒. Proportionality of the length of a subchain (N) in the gels to [c xl (c m ϩc xl)] Ϫ1 was revealed, both theoretically and experimentally. Equilibrium swelling data indicate non-Gaussian elasticity of the gel network.
Polymer Journal, 2001
Networks of statistical copolymers of 1-vinyl-2-pyrrolidone and N-vinylcaprolactam (molar ratios of VPNCL= 1/0, 0.8/0.2, 0.6/0.4, and 0.5/0.5) with ionic comonomer, N,N-dimethyl-N,N-diallylammonium chloride (mole fractions x8 =0, 0.03, and 0.05) and crosslinker, 1-1'-divinyl-3,3'-(ethane-1,1-diy])di(1-vinyl-2-pyrrolidone), were prepared by radiation polymerization in a water/ethanol mixture (H20/EtOH = 0.5/0.5 by vol.). Swelling and mechanical behavior was investigated in water/acetone (w/a) mixtures. For charged copolymers, a first-order phase transition (collapse) was found. The extent of collapse (stepwise change in the gel volume), 1' >, and critical acetone concentration in the mixture at collapse, a" slightly increase with content ofVCL and ammonium salt in gels. Shift of transition to higher a, is caused by increasing hydrophobicity of network chains with VCL content. Decrease in swelling with increasing acetone concentration in w/a mixtures is accompanied by increase in equilibrium modulus, so that mechanical behavior is predominantly determined by swelling. The theory of swelling equilibria of polyelectrolyte networks, in which the effects of electrostatic interactions of the charges on the chain and finite chain extensibility are included, semiquantitatively describes the swelling data provided an effective concentration of charges (lower than x,) was introduced.
The Swelling Behavior of Charged Hydrogels
Macromolecular Symposia, 2006
We describe recent advances obtained in understanding the microscopic interplay of a charged hydrogel with its confined mobile counterions. Results of extensive computer simulations are compared to simple scaling descriptions for various solvent conditions. We will briefly discuss our simulation package ESPResSo which was used to perform the simulations. We demonstrate why simple scaling theories suffice to adequately describe the swelling behavior of these systems despite their enormous complexity. We will conclude with a presentation of ongoing results for polyelectrolyte networks under poor solvent conditions.
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.
Controlling the collapse/swelling transition in charged hydrogels
2004
In this paper, we investigate systematically the parameters controlling the swelling transition of charged hydrogels. Combining theoretical analysis and experimental investigations we characterize the transition pH and the width of the transition as a function of the hydrogel crosslink density (i.e. subchain molecular weight) and the solution salt concentration. We also investigate the effect of pendant polyethylene glycol (PEG) side chains on the swelling transition. Quite surprisingly, we find that (1) the degree of swelling varies non-monotonically with the solution salt concentration, first increasing and then decreasing with salinity, (2) even in the limit of high salt concentrations, where electrostatics are expected to play a minor role, we find that the degree of swelling is quite sensitive to the suspension pH, namely, to the gel degree of charging, (3) in the limit of long subchains the transition pH depends only on the chemistry of the gel charges, and the transition is quite sharp, (4) the transition pH shifts with decreasing subchain length and/or with decreasing salt concentration, and the width of the transition increases and (5) the overall degree of swelling increases significantly upon the incorporation of pendent PEG chains, while the transition pH remains unaffected and the width of the transition narrows significantly.
Functionalized Microgel Swelling: Comparing Theory and Experiment
The Journal of Physical Chemistry B, 2007
A comprehensive gel swelling model accounting for the effects of added salt, counterion/polyelectrolyte charge condensation, inter-cross-link chain length distribution, polyelectrolyte chain stiffness, and direct chargecharge repulsion between fixed polymer network charges has been applied to predict water fraction profiles in-COOH-functionalized microgels based on poly(N-isopropylacrylamide). The model can successfully order the microgels according to their rheologically measured water fractions and explains key differences in observed microgel swelling according to the different functional group and cross-linker distributions in the microgels. The cross-linking efficiency is used as an adjustable variable to match the magnitude of the different model predictions with the experimental water contents from rheological measurements. The resulting cross-linking efficiency predictions are correlated with the ability of the different comonomers to facilitate chain transfer and/or radical termination in the polymerization environment. The model can capture the differing responses of the microgels in the presence of different salt concentrations and can account for the impact of many key physical parameters and heterogeneities in microgel swelling which the Flory-Huggins model cannot directly address.
Rheological Characterization of Polysaccharide−Poly(ethylene glycol) Star Copolymer Hydrogels
Biomacromolecules, 2005
Binding interactions between low molecular weight heparin (LMWH) and heparin-binding peptides (HBP) have been applied as a strategy for the assembly of hydrogels that are capable of sequestering growth factors and delivering them in a controlled manner. In this work, the assembly of four-arm star poly(ethylene glycol) (PEG)-LMWH conjugate with PEG-HBP conjugates has been investigated. The interactions between LMWH and the heparin-binding regions of antithrombin III (ATIII) or the heparin interacting protein (HIP) have been characterized via heparin affinity chromatography and surface plasmon resonance (SPR); results indicate that the two peptides have slightly different affinities for heparin and LMWH, and bind LMWH with micromolar affinity. Solutions of the PEG-LMWH and of mixtures of the PEG-LMWH and PEG-HBP were characterized via both bulk rheology and laser tweezer microrheology. Interestingly, solutions of PEG-LMWH (2.5 wt % in PBS) form hydrogels in the absence of PEG-ATIII or PEG-HIP, with storage moduli, determined via bulk rheological measurements, in excess of the loss moduli over frequencies of 0.1-100 Hz. The addition of PEG-ATIII or PEG-HIP increases the moduli in direct proportion to the number of cross-links introduced. Characterization of the hydrogels via microrheology shows the gel microstructure is composed of polymer-rich fibrillar structures surrounded by polymer-depleted buffer. Potential applications of these hydrogels are discussed.