Phenomenological theory of the formation of cubic phases in complex fluids

A unifying phenomenological model is proposed, which describes the cubic meso phases found in complex fluid systems. The order-parameter symmetries associated with the formation mechanism of the mesophases are determined. The different configurations associated with the same cubic symmetry are described in the case of the gyroïd phase

Theory of the non-planar surface phase in tilted smectic films under electric field

We present a phenomenological theory of the non-planar tilted surface phase recently observed in freely suspended smectic films. We show that the three phases —Synclinic, Anticlinic, and non-planar (Axial)— stable in non-chiral systems, merge into a single phase in chiral systems. We discuss some experimental consequences of this specific chiral feature. We predict the effects of electric field application parallel to the smectic layers on the stability of the various zero-field surface phases, and determine the conditions for the observation of field-induced chiral Anticlinic/Synclinic crossovers. In thin films they depend only on the ratio between the bulk electroclinic coupling energy and the surface electric-field-tilt coupling

Multigap ferroelectric and antiferroelectric smectic phases

We present a phenomenological model describing spatial modulations of the (anti)polarization in chiral tilted smectic phases. The helical instability of the polarization field direction combines with a second instability associated with the polarization amplitude. We predict new structures exhibiting a mismatch between the helix pitch and the amplitude modulation length. These incommensurate phases display extraordinary optical properties, resulting from a multi-gap band structure in their electromagnetic dispersion relations. Such structures could be used as natural photonic crystals

Theory of the incommensurate smectic-A phases in dimesogenic liquid crystals

A mechanism assuming a mismatch between the basic smectic periodicity and the amplitude and phase modulations periods of the mass density wave order parameter is proposed, for describing the incommensurate smectic-A structure found in dimesogenic liquid crystals. The different sequences of phases found in this family of compounds are described theoretically

Packing of ovaloïd atoms in actinide structures

The atomistic mechanisms which result in the structures of eleven actinide elements are deduced from a parent bcc structure. The rich polymorphism and idiosyncratic structures found in uranium, neptunium and plutonium are interpreted in terms of close packings of ovaloïd atoms. The incommensurate structure found in α-U is discussed in this framework