Swelling and de-swelling of gels under external elastic deformation (original) (raw)

Quantifying deformation in gel swelling: Experiments and simulations

AIChE Journal, 2000

A technique for the real-time ®isualization of material line mo®ement during transparent gel deformation was de®eloped based on caged photo-acti®ated fluorophores co-®alently attached to the gel network. It is used to quantitati®ely monitor the swelling of ( ) sodium polyacrylate and poly acrylamide-sodium acrylate gels in quasi two-dimensional constrained geometries. The experimentally obtained profiles for the Finger deformation tensor and the polymer concentration are compared with transient simulations of a model of transport in polyelectrolyte gels.

Transient analysis of swelling-induced large deformations in polymer gels

Journal of the Mechanics and Physics of Solids, 2013

The purpose of the research is to describe the swelling-induced large deformations in polymer gels: a theoretical model is developed, and then implemented and solved using the finite element method. The model is firstly assessed with two well-known benchmark problems; moreover, the proposed approach is benchmarked against a recent experiment involving localized exposure of the gel boundary to a solvent, where large bending deformations appear during solvent absorption. In both cases, our results are quite satisfying.

Dynamic deformation visualization in swelling of polymer gels

Chemical Engineering Science, 2000

A technique for the real-time visualization of transparent gel deformation is developed, based on caged photo-activated #uorophores covalently attached to the gel network. The technique is used to quantitatively monitor the swelling of quasi two-dimensional sodium polyacrylate gels in a constrained geometry.

Nonmonotonic swelling and compression dynamics of hydrogels in polymer solutions

Physical Review E, 2020

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Non-affine deformations in biological gels

Bulletin of the American Physical …, 2008

This paper reviews the current understanding, both theoretical and experimental, of non-affine deformations in polymer hydrogels.

Cross-linking patterns and their images in swollen and deformed gels

Using the theory of elasticity of polymer gels we show that large-scale cross-link density patterns written into the structure of the network in the melt state, can be revealed upon swelling by monitoring the monomer density patterns. We find that while isotropic deformations in good solvent yield magnified images of the original pattern, anisotropic deformations distort the image (both types of deformation yield affinely stretched images in Θ solvents). We show that in ordinary solids with spatially inhomogeneous profile of the shear modulus, isotropic stretching leads to distorted density image of this profile under isotropic deformation. Using simple physical arguments we demonstrate that the different response to isotropic stretching stems from fundamental differences between the theory of elasticity of solids and that of gels. Possible tests of our predictions and some potential applications are discussed.

Mapping the Local Osmotic Modulus of Polymer Gels

Langmuir, 2009

Polymer gels undergo volume phase transition in a thermodynamically poor solvent as a result of changes in molecular interactions. The osmotic pressure of gels, both synthetic and biological in nature, induces swelling and imparts the materials with the capacity to resist compressive loads. We have investigated the mechanical and swelling properties of poly(vinyl alcohol) (PVA) gels brought into the unstable state by changing the composition of the solvent. Chemically cross-linked PVA gels were prepared and initially swollen in water at 25°C, and then n-propyl alcohol (nonsolvent) was gradually added to the equilibrium liquid. AFM imaging and force-indentation measurements were made in water/n-propyl alcohol mixtures of different composition. It has been found that the elastic modulus of the gels exhibits simple scaling behavior as a function of the polymer concentration in each solvent mixture over the entire concentration range investigated. The power law exponent n obtained for the concentration dependence of the shear modulus increases from 2.3 (in pure water) to 7.4 (in 35% (v/v) water + 65% (v/v) n-propyl alcohol mixture). In the vicinity of the Θ-solvent composition (59% (v/v) water + 41% (v/v) n-propyl alcohol) n ≈ 2.9. Shear and osmotic modulus maps of the phase separating gels have been constructed. It is demonstrated that the latter sensitively reflects the changes both in the topography and thermodynamic interactions occurring in the course of volume phase transition.

Wrinkling of a Polymeric Gel During Transient Swelling

Journal of Applied Mechanics, 2014

When exposed to an external solvent, a dry polymeric network imbibes the solvent and undergoes large deformation. The resulting aggregate is known as a hydrogel. This swelling process is diffusion driven and thus results in differential swelling during transient swelling. When subjected to external geometrical constraints, such as being rigidly fixed or attachment to a compliant substrate, wrinkles have been shown to appear due to mechanical instabilities. In the case of free swelling, there are no external constraints to induce the instabilities accounting for wrinkling patterns. However, during the transient swelling process, the swelling differential between the gel on the exterior and the interior causes compressive stresses and gives rise to mechanical instabilities. It is also observed that the time dependence of the swelling profile causes the wrinkles to evolve with time. In this work, we investigate this interesting phenomenon of transient wrinkle mode evolution using the f...

Elastic Modulus and Equilibrium Swelling of Polyelectrolyte Gels

Macromolecules, 1996

We present a scaling theory for the modulus G of polyelectrolyte gels as a function of strand length between cross-links, monomer concentration c, salt concentration cs, and preparation conditions (monomer concentration c0 and salt concentration cs°). The theory assumes affine displacement of the junction points when the concentration is changed. With no added salt (cs ) cs°) 0), we predict a new concentration dependence of the modulus G ∼ c 5/6 . In the high-salt limit, we predict the usual concentration dependence for uncharged polymers but a novel dependence on salt concentration, G ∼ c 7/12 cs 1/4 . We also predict the modulus to decrease as charge is added to the gel strands. The predicted effects of added salt and charge on modulus have recently been observed by Candau and co-workers. At low concentrations, we discuss the strong stretching of network strands and its effect on modulus and equilibrium swelling.