Acoustic excitations in suspensions of soft colloids

Vibrational modes in suspensions of soft colloids in a fluid can be detected experimentally by Brillouin light scattering. Besides the usual acoustic mode, being essentially the longitudinal phonon of the liquid matrix, an "opticlike" mode is observed in giant starlike micelles at low volume fractions. We propose that this opticlike mode is due mainly to the internal vibration of each hairy particle.