Structure-Specific Liquid Crystal Anchoring Induced by the Molecular Combing of Short Oligonucleotides.

Surface-immobilized oligonucleotides were "combed" by meniscus motion and exposed to a nematic liquid crystal (LC). Although the oligonucleotides were as short as 16 bases, they were apparently oriented by this process and, in turn, successfully biased the orientation of the adjacent LC material. Single-stranded DNA (ssDNA) induced LC orientation in the combing direction, while hybridized double-stranded DNA (dsDNA) rotated the azimuthal LC orientation by ∼30° from the combing direction. The sensitivity of the chiral response to mixed ssDNA/dsDNA surfaces was characterized by employing complementary DNA that was longer than the immobilized DNA, resulting in single-stranded overhangs of various lengths. A rotated LC orientation was observed even when more than 70% of the DNA was single-stranded, and the transition from the rotated to nonrotated response was apparently discontinuous as a function of ssDNA surface coverage. These phenomena represent a sensitive DNA hybridization detection strategy that can potentially comprise a multiplexed assay.

Anisotropic molecular hopping at the solid-nematic interface.

Single molecule tracking was used to observe intermittent and anisotropic molecular motion at the solid-nematic interface. Although the interfacial diffusion was dramatically slower than self-diffusion in the nematic, the diffusion anisotropy was the same at the interface and in bulk, supporting the desorption-mediated mechanism of interfacial diffusion, where molecules sample the physical properties of the vicinal fluid phase during flights, and the magnitude of the interfacial diffusion coefficient is primarily determined by the distribution of waiting times between flights.

Nanostructures of nematic materials of laterally branched molecules.

The synthesis and small-angle X-ray scattering (SAXS) characterization is reported for 20 laterally branched mesogenic molecules, which are derived from the common rod-shaped 2,5-bis([4-(octyloxy)phenyl]carbonyloxy) benzoic acid unit. These compounds have a varying degree of flexibility, in that their lateral branch is formed upon conversion of the acid to either an ester or an amide, and most laterally branched molecules exhibit relatively wide nematic liquid-crystal phases with a direct nematic-to-crystal transition at lower temperatures. SAXS studies reveal the presence of smectic-like nanostructures (clusters) with short-range order in the nematic phase, with characteristic correlation lengths from 3 to over 10 nm. The smectic layers that are contained in these clusters are tilted with respect to the nematic director by angles ranging from 0° (i.e. untilted) to 55°. In some compounds, the intensity of the SAXS peak corresponding to the smectic layer spacing depends strongly on temperature. The main features of the nanostructures can be understood based on the molecular structure; therefore, guiding future synthetic work towards more precisely controlled and technologically useful nanostructures in nematics.

Shape-independent lateral force calibration.

Current methods for lateral force calibration are often time-consuming, expensive, or cause significant wear of the tip. A quick and simple alternative is presented in which the linear relationship between force and voltage is exploited. The technique is independent of the shapes of the sample and cantilever and eliminates common problems, while maintaining better than 10% precision. This advance will facilitate quantitative comparisons between experiments.