  The debonding criterion of fibrils of soft adhesive materials is a key
element regarding the quantitative modelisation of pressure sensitive adhesive
tapes peeling energy. We present in this article an experimental study of the
detachment of a commercial acrylic adhesive tape from the top surface of a
single micrometric pillar of PDMS elastomer. During an experiment, the pillar
and the adhesive, after being put in contact, are separated at a constant
displacement rate, resulting in the formation, the elongation and the final
detachment of a fibril of adhesive material. A systematic study allows us to
uncover power laws for the maximum force and the critical elongation of the
fibril at debonding as a function of the diameter of the cylindrical pillar
which controls the diameter of the fibril. The scaling law evidenced for the
critical elongation appears as a first step toward the understanding of the
debonding criterion of fibrils of soft adhesive materials. In addition,
viscoelastic digitation at the triple debonding line is observed during
detachment for large pillar diameters. The wavelength and penetration length of
the fingers that we report appear to be consistent with existing models based
on pure elastic mechanical response.
