Interfaces with thin hydrogels layers : friction, debonding and wetting

We investigate the interplay between the swelling state of thin ( µm ) hydrogel films and their frictional and mechanical properties .
These investigations are based on model hydrogel networks which are elaborated using a click-chemistry route. By playing with the chemical nature of the constituents and their structure (crosslink density), hydrogels films with varied elastic and swelling properties are synthesized.

Synthesis of model hydrogel networks using a click-chemistry route

Friction of confined poroelastic hydrogel films

We investigate the contribution of poroelastic drainage to indentation and frictional response of thin hydrogel layers. The approach is based on dedicated contact experiments where the water content within the gel layer confined between glass substrates is continuously monitored during the course of poroelastic drainage. Experimental results are discussed in the light of a poroelastic contact model derived within the framework of a thin film approximation.

Frictional sliding : changes in the contact shape as a function of the Pe Number defined as the ratio of the characteristic poroelastic time to the contact time. When Pe<1, the contact is at the poroelastic equilibrium which would be achieved under a purely normal loading ; when Pe>>1 the decrease in the contact size is due to the developement of a pore pressure imbalance within the out-of-equilibrium contact.

Swelling induced debonding of grafted hydrogel films

Swelling induced debonding at the interface between thin hydrogel films and glass or silicon substrates are investigated in relation to the physical-chemistry of the interface (grafting density) and the swelling properties of the gel network. Debonding from well controled interface defects created using lithography techniques is monitored under humid water flow and analysed in the light of a fracture mechanics approach.

Swelling induced debonding of a grafted poly(dimethylacrylamide) (PDMA) hydrogel film 2 µm in thickness from a preexisting line defect at the interface with the silicon substrate.

Swelling Dynamics of Surface-Attached Hydrogel Thin Films in Vapor Flows

Te transfer of vapor from the atmosphere to hydrogel thin films is measured in a situation where water vapor flows alongside the coating which is set to a temperature lower than the ambient temperature. The effect of the physico-chemistry of the hydrogel film on the swelling kinetics is particularly investigated. By using model thin films of surface-grafted polymer networks with controlled thickness, varied cross-links density, and varied affinity for water, we were able to determine the effect of the film hygroscopy on the dynamics of swelling of the film. These experimental results are accounted for by a diffusion-advection model that is supplemented with a boundary condition at the hydrogel surface : we show that the latter can be determined from the equilibrium sorption isotherms of the polymer films. Altogether, this paper offers a predictive tool for the swelling kinetics of any hydrophilic hydrogel thin film.

References

L. Ciapa, J. Delavoipière, Y. Tran, E. Verneuil, and A. Chateauminois
Transient sliding of thin hydrogel films : the role of poroelasticity
Soft Matter 2020 10.1039/D0SM00641F

J. Delavoipière, B. Herteufeu, J. Teisseire, A. Chateauminois, Y. Tran, M. Fermigier and E. Verneuil
Swelling dynamics of surface-attached hydrogel thin films in vapor flows Langmuir 34 (2018) 15238-15244
 

J. Delavoipière, Y. Tran, E. Verneuil, B. Herteufeu, C.-Y. Hui and A. Chateauminois
Friction of poroelastic contact with thin hydrogel layers
Langmuir 34 (2018) 9617-9626
 

Poroelastic indentation of mechanically confined hydrogel layers
J. Delavoipière, Y. Tran, E. Verneuil and A. Chateauminois
Soft Matter 12 (2016) 8049