Anisotropy and acoustic modes in β-FeOOH suspensions

Studies on the electro-optic behavior of isotropic colloidal systems demonstrated the sensitivity of the electric light scattering method to induced density fluctuations. Thus, the separation of acoustic and anisotropy modes in the electro-optic responses of anisotropic colloidal samples becomes a basic problem in the electro-optic analysis. This paper presents an electro-optic investigation of the electrically induced modes in suspensions of highly monodisperse β-FeOOH particles. The analysis shows that the translation modes are detected at low frequency and intensity of the applied field, even in the case of noninteracting systems. The influence of density fluctuations increases with particle volume fraction and can be significant far below the critical concentration of interparticle interaction.