YIELDING AND REARRANGEMENTS IN DISORDERED EMULSIONS

We use diffusing-wave spectroscopy to measure the motion of droplets i n concentrated emulsions subjected to a periodic shear strain. The str ain gives rise to periodic echoes in the correlation function which de cay with increasing strain amplitude. For a given strain amplitude, th e decay of the echoes implies that a finite fraction of the emulsion d roplets never rearranges under periodic strain while the remaining fra ction of droplets repeatedly rearranges. Yielding occurs when about 4- 5% of the droplets rearrange.