Microscopic origins of heliclinic phases in smectic liquid crystals

In a previous article [Phys. Rev. E 60, 1799 (1999)], the authors considered a model Landau free energy that explained the ferriclinic phases of chiral smectic liquid crystals as a series of short period helical modulations. In this paper we begin with a physically more realistic, more microscopic interlayer free energy and show how our previous work can be derived using only simple short-ranged interactions. We then discuss what additional information this provides about the Landau coefficients used previously to construct the phase diagram for the heliclinic phases of chiral smectic liquid crystals. Finally, we investigate a means for explicitly including chirality in our model

Twist modulated phases in chiral smectic liquid crystals

By considering short period helical planar modulations about the layer normal, we construct a model free energy for the ferriclinic phases observed in chiral smectic liquid crystals. We then use this free energy to construct the phase diagram for our model. The resulting phases are compared with the experimentally observed smectic-C* subphases (ferroclinic, antiferroclinic, and heliclinic). A strong coupling is found between the ferroclinic q=2π/a and the heliclinic q=2π/3a modes. This coupling was not considered in previous models. The resulting additional stability of this “locked in” phase is discussed

Routes to self-assembling stable photonic band-gap phases in emulsions of chiral nematics with isotropic fluids

Blue phases are stable phases with crystalline packing of interwoven topological defects in chiral nematic liquid crystals. We argue that chiral nematics with appropriate surfactants are likely to form blue phases for a wide range of parameters. We derive the transition curve for stable emulsified blue phases and find that the required low surface tension is within the accessible range of surfactants. These emulsified blue phases provide possible routes to photonic band-gap materials

Nematic electroclinic effect in a carbon nanotube-doped achiral liquid crystal

A small quantity of carbon nanotubes dispersed in an achiral liquid crystal matrix transmits chirality a short distance into the LC, and the LC+CNT mixture is found to exhibit a bulklike electroclinic effect in the nematic phase. The magnitude of the effect increases rapidly on cooling, showing significant pretransitional behavior on approaching the nematic -smectic-A transition temperature (T NA ) from above. The variation of the electroclinic coefficient is negligible over the frequency range 100 Hz -100 kHz in the in the nematic phase well above T NA and in the smectic-A phase, whereas the electroclinic coefficient falls off significantly with increasing frequency just above T NA

Orientational Susceptibility and Elastic Constants Near the Nematic-Isotropic Phase Transition for Trimers with Terminal-Lateral-Lateral-Terminal Connections

Magnetically induced Freedericksz measurements were performed in the nematic liquid crystal phase to extract the elastic constants of a terminal-lateral-lateral-terminal trimer, i.e., a trimer in which the connections to the first and third mesogens are at the end of the mesogen and both attachments to the central mesogen are lateral. Polymeric liquid crystals based on this unit have negative Poisson ratios. Additionally, electric field Kerr measurements were performed in the isotropic phase to extract the orientational susceptibility. The elastic constants were found to be similar to values obtained for typical monomers, albeit with a slightly enhanced ratio K-33/K-11 and reduced ratio K-11/K-22 especially near the transition temperature. The temperature dependence of the susceptibility was found to deviate significantly from that of typical monomers. The observed behavior is discussed in terms of coupled order parameters representing the terminal and core mesogens of the molecule

Pretransitional Behavior Above the Nematic-Isotropic Phase Transition of an Auxetic Trimer Liquid Crystal

Static Light scattering and electric field-induced Kerr measurements were performed above the nematic-isotropic phase transition of a terminal-lateral-lateral-terminal negative Poisson ratio trimer. Far both measurements the inverse susceptibility was observed to be nearly linear with temperature, a result inconsistent with our previously reported Kerr data [Phys. Rev. E 58, 2041 (1998)]. [S1063-651X(99)11010-9]

Spontaneous Liquid Crystal and Ferromagnetic Ordering of Colloidal Magnetic Nanoplates

Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magneto-mechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in absence of a field. Here we report a fluid suspension of magnetic nanoplates which spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field

Properties of uniaxial nematic liquid crystal of semiflexible even and odd dimers

A microscopic model is developed to describe statistical properties of a nematic phase consisting of semiflexible dimers. The effect of the spacer chain bonding the two mesogens is described by the local conditional probability in terms of a bare stiffness parameter $\Omega\sim E_{\rm B}/kT$ and a bare equilibrium angle $\theta_{0}$ between mesogenic monomers. In the framework of a molecular field approximaiton, taking into account long-range attraction and steric repulsion between monomers, we obtain a complete statistical description of the namatic phase with expressions for order parameter, mean-field potential, phase transition parameters and Frank elastic constants depending on details of specific molecular structure. Comparison of results for dimers that are straight and bent in equilibrium and for corresponding monomers reveals the effect of molecular biaxiality and biaxial fluctuations