Biomedical subjects

A Poniewierski

Publications and source records attributed to A Poniewierski.

17 recordsLinked to original sources

PubMed2005

Phase behavior of a nematic liquid crystal in contact with a chemically and geometrically structured substrate.

A nematic liquid crystal in contact with a grating surface possessing an alternating stripe pattern of locally homeotropic and planar anchoring is studied within the Frank-Oseen model. The combination of both chemical and geometrical surface pattern leads to rich phase diagrams, involving a homeotropic, a planar, and a tilted nematic texture. The effect of the groove depth and the anchoring strengths on the location and the order of phase transitions between different nematic textures is studied. A zenithally bistable nematic device is investigated by confining a nematic liquid crystal between the patterned grating surface and a flat substrate with strong homeotropic anchoring.

Journal Article↗

PubMed2003

Orientational phase transition and the solvation force in a nematic liquid crystal confined between inhomogeneous substrates.

A nematic liquid crystal confined between two identical flat solid substrates, with an alternating stripe pattern of planar and homeotropic anchoring, is studied in the framework of the Frank-Oseen theory. By means of numerical minimization of the free energy functional we study the effect of the sample thickness D on the location of the phase transition between a uniform alignment, either planar or homeotropic, and a distorted nematic texture. The solvation force f due to distortions of the nematic director is also studied. It is found that f is always attractive, and for D small compared to the periodicity of the surface structure it exhibits two distinct asymptotic behaviors: f approximately -D(-1/2) or f approximately -D(-1), depending on the relation between D and the extrapolation lengths.

Journal Article↗

PubMed2001

Uniform and nonuniform textures of a nematic liquid crystal in contact with an inhomogeneous substrate.

A semi-infinite sample of a nematic liquid crystal in contact with a flat solid substrate, possessing an alternating stripe pattern of planar and homeotropic anchoring, is studied in the framework of the Frank-Oseen model. The case of strong anchoring on one of the stripes is treated by means of bifurcation analysis, whereas the case of weak anchoring is studied by means of numerical minimization of the free energy functional. We find a second order phase transition between the uniform homeotropic or planar alignment and a distorted director configuration. The effect of the stripe width and the anchoring strength on the location of this transition and on the bulk orientation of the nematic director is also studied.

Journal Article↗

PubMed1996