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Contact and wetting properties of thin hydrogels films

A. Chateauminois, J. Delavoipière, Y. Tran and E. Verneuil

We investigate the interplay between elastic properties of thin (a few µm in the swollen state) films of hydrogel networks, their swelling state and their wetting and frictional properties based on contact and mist experiments. Model hydrogel networks 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

Poroelastic indentation response of hydrogel thin films is investigated geometrically within contacts with rigid spherical probes. Time-dependent indentation kinetics are described within the framework of an approximate contact model derived within the limits of confined contact geometries. This model provides simple scaling laws for the characteristic poroelastic time and the equilibrium indentation depth. Some deviations from this model are evidenced in the case of hydrogels networks experiencing a transition (glass transition, LCST) during the course of poreolastic drainage. These results emphasize the necessity of carefully considering the details of physical chemistry of hydrogel networks under such confined contact conditions or whenever the water content is reduced enough for drastic changes in the polymer network to happen, a point often overlooked in the literature. Further implications of these phenomena on the frictional properties of thin hydrogel films are currently under investigation.


Poroelastic drainage of a PDMA thin film mechanically confined within a contact between glass substrates. The progressive increase in lateral contact stiffness during the course of poroelastic indentation is induced by the glass transition of the drained network.

Other investigations are currently dealing with mist formation on these hydrogel films when cooled and submitted to an humid air.

References

J. Delavoipière, Y. Tran, E. Verneuil and A. Chateauminois, Poroelastic indentation of mechanically confined hydrogel layers, Soft Matter 12 (2016) 8049-8058