Swelling of Rubber under Nonuniform Stresses and Internal Migration of Swelling Liquid When the Stresses Are Removed

Abstract

As shown by Treloar, the degree of swelling of a rubber sample is strongly affected by applied stress. His work suggests that the degree of swelling will vary from point to point in a sample, in accordance with the local stress field. Thus, when rubber sheets are bent, they are expected to swell more on the tension side and less on the compression side, and when the bending constraint is removed, recovery toward the initial flat state is expected to be only partial at first and then followed by a slow further recovery. These effects are explored here for natural rubber sheets swollen by dodecane. The measured "set" following release from bending is found to be in accord with simple swelling theory. The time dependence of later recovery is shown to be in agreement with the rate of diffusion of the swelling liquid. It is concluded that internal migration of compatible liquids will cause temporary delays in deformation kinetics and make a significant contribution to energy losses. Also, the bending experiment itself appears to provide a simple and generally applicable method for determining the internal diffusion coefficients of absorbed liquids.

Swelling thermodynamics and phase transitions of polymer gels

“…The free energy therefore decreases when p points alongn, describing a situation in which solvent mass is greater towards the outer radii of the torus and there is more polymer mass near the 'hole' region; this is confirmed by experiment (see figures 16(f)-(j)). This curvature-solvent distribution coupling has been observed in bent rubber and is due to the effect of internal stress on a material's ability to swell [88]; swelling is promoted in regions under tension and impeded in regions under compression. Furthermore, with such a polarization of the solvent distribution, the similar coupling with Δω m implies that free energy is decreased if the torus deforms such that curvature increases.…”

Bending and twisting of soft materials by non-homogenous swelling

“…26 Very recently, several papers have focused on coupling equilibrium swelling information with dynamic deformations for liquid crystal elastomers, rubber, and paper. [27][28][29][30] In this paper, we study the impact of material geometry and nonhomogenous swelling on the dynamics of deformation of soft materials.…”

Swelling-induced deformations: a materials-defined transition from macroscale to microscale deformations

“…These include buckling, [10][11][12] creasing, 13 and wrinkling instabilities, [14][15][16][17][18][19] and the curling of paper and rubber. [21][22][23][24] In addition, porous thin lms, such as fuel cell membranes, 25,26 are highly susceptible to swelling-induced delamination and buckling, which cripple their functionality. For materials to adequately accommodate different uid-structure environments there must be an accurate understanding of both the global and surface-conned deformations that can occur.…”

“…32,37 At short times, the outer surface of the beam is under more stress than the bulk, and will elongate and bend into an arch. [22][23][24]38,39 However, bending of the structure will only occur if the swelling stress is greater than the stress required to bend the beam.…”