Squeezing-out dynamics in free-standing smectic films

Flows Excited by Shear Stress in Freestanding Symmetric Smectic C Films

The purpose of this paper is to show some useful routes in describing the shear-driving flows in a freely suspended symmetric smectic C film stretched between two circular frames, the rest outer and rotating inner frames. Our calculations, based on a corresponding extension of the Eriksen–Leslie theory, show that the shear-driving flow in the film, excited by a rotating inner circular frame, causes a twisting rotation of the c^-director around the normal to smectic layers. It is found that the shear flow excited by the rotating frame in a positive sense (counterclockwise) causes a twisting rotation of the c^-director in a negative sense (clockwise) around the normal to smectic film. It is also shown that the twisting of the c^-director’s field has a jumping nature when a large reorientation is carried out in a short space of time. It was also shown that the twisting dynamics of the c^-director field strongly depends on the curvature of the inner rotating frame.

Theoretical explanation of rotational flow in the liquid-film motor

A liquid film that is under the action of two electric forces, an external electric field parallel to the film and a lateral voltage difference applied to both edges of the film, exhibits a universal rotational flow. In this article, we revisit this phenomena by considering an idealized so-called liquid-film motor and provide a theoretical description of the underlying physical mechanism that is responsible for the rotation. Based on this theory, the external electric field induces a non-uniform distribution of freely moving charges on the film. Then the internal field that is mainly resulted from the lateral voltage difference, will exert forces on induced charges and subsequently will result the rotational flow. We show, how the fields contribute in developing a universal flow pattern.

Structural, Optical and Dynamic Properties of Thin Smectic Films

The problem of predicting structural and dynamic behavior associated with thin smectic films, both deposited on a solid surface or stretched over an opening, when the temperature is slowly increased above the bulk transition temperature towards either the nematic or isotropic phases, remains an interesting one in the physics of condensed matter. A useful route in studies of structural and optical properties of thin smectic films is provided by a combination of statistical–mechanical theories, hydrodynamics of liquid crystal phases, and optical and calorimetric techniques. We believe that this review shows some useful routes not only for the further examining of the validity of a theoretical description of thin smectic films, both deposited on a solid surface or stretched over an opening, but also for analyzing their structural, optical, and dynamic properties.

Structural and optical properties of free-standing smectic films

We have carried out a complex numerical study of the structural, thermodynamic and optical properties of the partially fluorinated 5-n -alkyl-2-(4-n-(perfluoroalkyl-metheleneoxy)phenyl) free-standing smectic film in air under the action of the external electric field [Formula: see text]. Calculations, based upon the extended McMillan's mean-field theory with anisotropic forces, show a stepwise reduction of the value of the Helmholtz free energy and the reflectivity of the partially fluorinated smectic film in air, as the temperature is raised above the bulk smectic-A-isotropic transition value. It has been shown, by solving the self-consistent nonlinear equations for the orientational and translational order parameters, that the electric field [Formula: see text] may not only affect the layer-thinning transition sequences, but also change the first multilayer jump in the film thickness, whereas practically does not affect the reflectivity R(N) of the partially fluorinated N -layer smectic film in air. In the range of film thicknesses investigated, the reduction of the R(N) is, at least, qualitatively in agreement with the experimentally observed decrease of the optical reflectivity with the decrease of N.

Orientational relaxation in free-standing smectic C film driven by rotating circular frame

The pecularities in the cˆ-director reorientation in free-standing smectic C film without of defects and stretched between two circular frames, the rest outer and rotating inner, have been investigated theoretically based on the hydrodynamic theory including the cˆ-director motion and with accounting for backflow. Since the orientation of the cˆ-director is fixed at the rims of the smectic film, the shear flow induced by rotating frame winds up of the cˆ-director field. It is found that the higher shearing flow produces the greater twisting rotation of the cˆ-director around the normal to the smectic film directed in the opposite sense with respect to the direction of the angular velocity. Calculations also show that the relaxation dynamics of the cˆ-director field depends crucially on the curvature of the inner rotating frame.