Self-healing slip pulses and the friction of gelatin gelsT. Baumberger, C. Caroli and O. Ronsin
Groupe de Physique des Solides (Associé au Centre National de la Recherche Scientifique et aux Universités Paris 6 et 7.) , 2 place Jussieu, 75251 Paris, Cedex 05, France firstname.lastname@example.org
(Received 7 March 2003 / Published online: 11 June 2003)
We present an extensive experimental study and scaling analysis of friction of gelatin gels on glass. At low driving velocities, sliding occurs via propagation of periodic self-healing slip pulses whose velocity is limited by collective diffusion of the gel network. Healing can be attributed to a frictional instability occurring at the slip velocity . For , sliding is homogeneous and friction is ruled by the shear-thinning rheology of an interfacial layer of thickness of order the (nanometric) mesh size, containing a solution of polymer chain ends hanging from the network. In spite of its high degree of confinement, the rheology of this system does not differ qualitatively from known bulk ones. The observed ageing of the static friction threshold reveals the slow increase of adhesive bonding between chain ends and glass. Such structural ageing is compatible with the existence of a velocity-weakening regime at velocities smaller than , hence with the existence of the healing instability.
46.50.+a - Fracture mechanics, fatigue and cracks.
46.55.+d - Tribology and mechanical contacts.
83.80.Rs - Rheology: Polymer solutions.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003