Dipolar interactions in molecules aligned by strong AC electric fields

Insertion of liquid crystal molecules into hydrocarbon monolayers

Atomistic molecular dynamics simulations were carried out to investigate the molecular mechanisms of vertical surface alignment of liquid crystals. We study the insertion of nCB (4-Cyano-4'-n-biphenyl) molecules with n = 0,…,6 into a bent-core liquid crystal monolayer that was recently found to provide good vertical alignment for liquid crystals. The results suggest a complex-free energy landscape for the liquid crystal within the layer. The preferred insertion direction of the nCB molecules (core or tail first) varies with n, which can be explained by entropic considerations. The role of the dipole moments was found to be negligible. As vertical alignment is the leading form of present day liquid crystal displays (LCD), these results will help guide improvement of the LCD technology, as well as lend insight into the more general problem of insertion of biological and other molecules into lipid and surfactant layers.

Structure determination of aligned systems by solid-state NMR magic angle spinning methods

Single crystal rotational echo double resonance (REDOR) experiments can be used to determine the three-dimensional orientation of heteronuclear bond vectors in an amino acid, as well as the crystal's orientation relative to the rotor fixed frame (RFF). We also demonstrate that for samples uniaxially aligned along the rotor axis, the polar tilt angle of a bond vector relative to the RFF can be measured by use of an analytical expression that describes the REDOR curve for that system. These bond orientations were verified by X-ray indexing of the single crystal sample, and were shown to be as accurate as +/- 1 degrees .

Spontaneous organization of single CdTe nanoparticles into luminescent nanowires

Nanoparticles of CdTe were found to spontaneously reorganize into crystalline nanowires upon controlled removal of the protective shell of organic stabilizer. The intermediate step in the nanowire formation was found to be pearl-necklace aggregates. Strong dipole-dipole interaction is believed to be the driving force of nanoparticle self-organization. The linear aggregates subsequently recrystallized into nanowires whose diameter was determined by the diameter of the nanoparticles. The produced nanowires have high aspect ratio, uniformity, and optical activity. These findings demonstrate the collective behavior of nanoparticles as well as a convenient, simple technique for production of one-dimensional semiconductor colloids suitable for subsequent processing into quantum-confined superstructures, materials, and devices.

Partial alignment of biomolecules: an aid to NMR characterization

Partial alignment of biomolecules in solution has added a new dimension to structural investigation by high-resolution NMR methods. Applications to proteins, nucleic acids and carbohydrates now abound. Limitations initially associated with compatibility of biomolecules with the liquid-crystal media commonly used to achieve alignment have begun to disappear. This is, in part, a result of the introduction of a wide variety of new media. Future applications to biologically important problems such as the structural organization of multi-domain proteins and multi-protein assemblies look very promising.