Viscoelastic Gels

 

ABSTRACT: A polymeric gel is a cross-linked polymer network swollen with a solvent.  Much of the literature concerning the constitutive response of these materials is limited to elasticity coupled with fluid permeation.  Also, as is well known many polymeric materials exhibit viscoelastic behavior in their mechanical response.  To characterize the change in behavior due to swelling, we have developed an experimental procedure that includes mechanical testing when virgin, free swelling, mechanical testing when swollen, and mechanical testing after drying. Also, we have developed a continuum-level theory to describe the coupled fluid permeation and large viscoelastic deformation of polymeric gels.  The key finding of this work is that our results indicate that the viscoelastic behavior of initially dry VHB, reversibly, becomes essentially hyperelastic when swollen to equilibrium in multiple solvents.


Details:

  1. 1)Shawn A. Chester, 2012. A constitutive model for coupled fluid permeation and large viscoelastic deformation. Soft Matter, 8 8223-8233.

  2. 2)Nikola Bosnjak, Siva Nadimpalli, Dai Okumura, and Shawn A. Chester, 2019. Experiments and modeling of the viscoelastic behavior of polymeric gels. Journal of the Mechanics and Physics of Solids, 137 103829.


Simple Compression





















Stress as a function of time in simple compression. Here curves marked with a
correspond to the R = 5 mm case, while unmarked curves correspond to the R = 1 mm case. For both cases, the elastic (and coupled with fluid permeation) component of stress is given by dashed lines, the viscous component of stress by the dotted lines, and lastly the total stress by the solid lines. Note that the viscous component of stress for both cases lie directly on top of each other.


Fixed Depth Indentation


Contours of the polymer volume fraction after (a) 72 hours of free swelling; and then after indentation with an impermeable cylindrical punch at (b) 60 seconds, (c) 10 minutes, and (d) 6 hours. Here the mesh as been mirrored about one of the symmetry planes and only the outline of the punch shown for clarity. Note the change in scale for the contours each time.


Experimental Results


A subset of the experimental results showing the load-unload response for moderate rates displaying the clear affect of swelling on the behavior when fully swollen in the solvent indicated in the legend.