Light scattering with swollen hexagonal phases

We investigate, using quasi-elastic light scattering, some features of the long-wavelength, low-frequency modes of the hexagonal phase often encounter ed in the study of lyotropic (surfactant-solvent) systems. The hexagonal ph ase is swollen bg an oil-based ferrofluid, allowing magnetically aligned sa mples to be prepared. We show experimentally the anisotropy of the two lowe st-frequency modes. We develop a model which predicts that these slow modes are associated to particle diffusion and tube motion. With the help of mic roscopic as well as phenomenological analyses: we suggest that the latter p resumably corresponds tu a peristaltic mode. Confinement effects on the one -dimensional, Brownian diffusion of the colloids along the tube axis togeth er with the coupling between the two modes are studied experimentally, vary ing the tube diameter to particle size ratio.