Double-layer polarization induced transitions in suspensions of colloidal rods

Abstract

Polarization of electric double layers of colloidal rods due to an external alternating electric field is found to give rise to several phase/state transitions. Various phases and states are observed depending on the frequency and amplitude of the external electric field: i) non-chiral nematic domains (N-domains) in coexistence with an isotropic phase, ii) a chiral-nematic phase in the presence of the N-domains, iii) a chiral nematic phase, where now the N-domains are smaller and disconnected, and iv) dynamic states where the chiral nematic is melted, in the presence of disappearing and forming N-domains. Beyond a critical frequency (in the kHz range) the only stable state is the isotropic state. The phase/state diagram in the field amplitude vs. frequency plane is determined by means of polarization microscopy. In selected parts of the phase diagram, dynamic light scattering, electric birefringence and chiral-pitch measurements are performed to elucidate the nature of transition lines.