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Robert B Meyer

Publications and source records attributed to Robert B Meyer.

5 recordsLinked to original sources
PubMed2006

Textural transformations in islands on free standing smectic-C* liquid crystal films.

We report on and analyze the textural transformations in islands, thicker circular domains, floating in very thin free standing chiral Smectic-C* liquid crystal films. As an island is growing, an initial pure bend texture of the director changes into a reversing spiral at a critical size. Another distinct spiral texture is induced by changing the boundary condition at the central point defect in the island. To understand these transformations from a pure bend island, a linear stability analysis of the c-director free energy is developed, which predicts a state diagram for the island. Our observations are consistent with the theoretical phase diagram.

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PubMed2006

Buckling instability in liquid crystalline physical gels.

In a nematic gel we observe a low-energy buckling deformation arising from soft and semisoft elastic modes. We prepare the self-assembled gel by dissolving a coil-side-group liquid-crystalline polymer-coil copolymer in a nematic liquid crystal. The gel has long network strands and a precisely tailored structure, making it ideal for studying nematic rubber elasticity. Under polarized optical microscopy we observe a striped texture that forms when gels uniformly aligned at 35 degrees C are cooled to room temperature. We model the instability using the molecular theory of nematic rubber elasticity, and the theory correctly captures the change in pitch length with sample thickness and polymer concentration. This buckling instability is a clear example of a low-energy deformation that arises in materials where polymer network strains are coupled to the director orientation.

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PubMed2002

Isotropic-cholesteric transition in liquid-crystalline gels.

In a nematic gel, the appearance of nematic order is accompanied by a spontaneous elongation of the gel parallel to the nematic director. If such a gel is made chiral, it has a tendency to form a cholesteric helical texture, in which local elongation of the gel parallel to the nematic director is suppressed due to the requirement of elastic compatibility. We show that a conical helix in which the director makes an oblique angle with respect to the helix axis serves as an energy minimizing compromise between the competing tendencies for elongation and twisting. We find the dependence of the helical cone angle and pitch on the strength of the chirality, and determine the change in sample shape at the isotropic to cholesteric phase transition.

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PubMed2002

Electroclinic effect and modulated phases in smectic liquid crystals.

We explore the possibility that the unusually large electroclinic effect observed in the smectic-A phase of a ferroelectric liquid crystal arises from the presence of an ordered array of disclination lines and walls in a smectic-C* phase. If the spacing of these defects is in the subvisible range, this modulated smectic-C* phase would be similar macroscopically to a smectic-A phase. The application of an electric field distorts the array, producing a large polarization, and hence a large electroclinic effect. We show that with suitable elastic parameters and sufficiently large chirality, the modulated phase is favored over the smectic-A and helically twisted smectic-C* phases. We propose various experimental tests of this scenario.

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