Characterization of microscopic deformation in polymeric thin films using particle image velocimetry

The effectiveness of a technique based on particle image velocimetry (PIV) for measuring the instantaneous deformation field in planar polymeric films is investigated. Detailed deformation of polymeric films under complex stretching conditions will be very useful in characterization as well as optimization of mechanical properties. PIV is a method for measuring velocity fields in many fluid mechanics applications. In this technique, light scattering from glass micro-particles is used for estimating flow fields. In this work, the particles are spread on the surface of a polymeric film. The film is kept in a laser sheet while the deformation takes place. Two consecutive images of areas as large as 100 cm 2 are taken, separated by small time interval Δt. Displacement of seed particles over this time interval is estimated using cross-correlation. The polymer film was stretched uniaxially at constant rates. The deformation fields in the thin films over the time of stretching were evaluated. Films with introduced defects were also investigated for the measurement of the planar deformation fields. It is shown that the technique has potential to quantify the instantaneous deformation rate and strain fields for a large area in the plane of a film.