Yielding and recovery of conductive pastes for screen printing

We investigate the yielding and recovery of silver pastes with industrial applications under dynamic shear conditions by means of the recently developed sequence of physical processes (SPP) approach. The SPP framework is unique as it allows insights to be gained regarding yielding and recovery processes on timescales significantly faster than the period of oscillation, with the temporal resolution limited only by the data acquisition time. This resolution allows for the accurate determination of yielding of soft materials under any predetermined preshear history, and at timescales that are relevant to the applications of these materials. The behavior of these pastes is shown to be significantly different than previously assumed, with yielding occurring shortly after the reversal of strain in an oscillation, and the observation of a rate-dependent shear-thickening effect. Yielding is also shown to occur far below what would typically be defined as the flow condition. The relative rates and timescales for yielding and recovery are also assessed. The results in this paper are an important step toward a more comprehensive understanding of the yielding and recovery of yielding materials.