Swelling induced debonding of thin grafted hydrogel films

« With » Anusree Augustine, Yvette Tran and Emilie Verneuil
Collaboration with C.-Y. Hui and B. Zhu (Cornell Univesity) and M. Veillerot and N. Gauthier (CEA-LETI)

We investigate the delamination of thin hydrogel films grafted to silicon substrates under the action of swelling stresses. Delamination of Poly(dimetylacrylamide) (PDMA) films films from well controlled line defects with low adhesion is monitored under a humid water vapor flow ensuring full saturation of the polymer network. A propagating delamination of the film is observed under the action of differential swelling stresses at the debonding front. A threshold thickness for the onset of this delamination is especially evidenced which is increasing with grafting density while the debonding velocity is also observed to decrease with an increase in grafting density.

Debonding of a water-swollen PDMA thin film from a pre-existing defect line with low adhesion ; (a) images of the debonded film at increasing times showing the propogation of delamination both along the line defect and pependicular to it. (b) microscope image of the dried film showing telephone-cord instabilities.

These observations are discussed within the framework of a nonlinear fracture mechanics model which assumes that the driving force for crack propagation is the difference between the swelling state of the bonded and delaminated parts of the film. Using this model, the threshold energy for crack initiation is determined from the measured threshold thickness and discussed in relation to the surface density of reactive thiol groups on the substrate.

References

A. Augustine, M. Veillerot, N. Gauthier, B. Zhu, C.-Y. Hui, Y. Tran, E. Verneuil, & A. Chateauminois
Swelling induced debonding of thin hydrogel films grafted on silicon substrates.
Soft Matter In press (2023)