Deuterium NMR is used to examine the molecular order exhibited by an organosiloxane tetrapode giving the first experimental evidence, using a bulk sample, for the existence of a biaxial nematic phase in this type of compounds. The temperature dependence of the averaged quadrupolar coupling constant and asymmetry parameter was determined in the compound's nematic phase. Two distinct regimes could be identified, one with a vanishing asymmetry parameter corresponding to a uniaxial nematic phase and another with a significant temperature dependent asymmetry parameter, corresponding to a biaxial nematic phase. The high values obtained for the asymmetry parameter at the lower end of the nematic range are well above experimental error and constitute a definite proof of the biaxial nature of the nematic phase exhibited by the studied compound for those temperatures.

Optical coherence tomography is an imaging technology that produces high-resolution cross-sectional images of turbid media and internal microstructures including inside living tissue. In this work, three-dimensional images of a dental microstructure, that can be used to make both qualitative and quantitative assessments of oral tissue health, were obtained. It was possible to detect subclinical caries in third molar human teeth, showing that the lesion is located below the surface at 10μm with a maximum depth lesion of 50μm. A three-dimensional image was constructed confirming that it is possible to observe different planes inside the sample. It is important to notice that the optical changes induced by the carious disease in dental tissue can be readily detected by the optical coherence tomography method, before structural changes become apparent.

We have shown in this work that a tunable topographical system can be obtained from aqueous hydroxypropylcellulose (HPC) liquid crystalline solutions. The HPC solid films were prepared by casting isotropic and liquid crystalline solutions under shear. Atomic force microscopy (AFM) measurements of their topographical features were performed. The features of the film surface can be affined by controlling the processing conditions. We have demonstrated that the films prepared from liquid crystalline solutions (HPC/water ratio:  50−65% w/w) show two periodic structures, primary and secondary set. The former consists of the bands perpendicular to the shear direction while the latter has the bands slightly tilted from that direction. An out-of-plane angle variation (9°−13°), of the sinusoidal molecular orientation, is also reported. A fractal analysis of these surfaces indicates a scale-invariant nature between 300 nm and 4 μm.

A proton nuclear magnetic resonance ͑NMR͒ relaxation study of molecular dynamics in the liquid crystal 4-octylphenyl 2-chloro-4-͑4-cyanobenzoyloxy͒benzoate ͑DB 8 Cl͒ is presented. DB 8 Cl molecules possess a strong polar terminal group and form, in addition to the nematic phase, three different smectic phases: bilayer smectic A, bilayer smectic C, and anticliniclike smectic C phase. The proton spin-lattice relaxation times were measured in all mesophases over a broad frequency range of six decades by applying conventional and fast field-cycling NMR techniques. The parameters obtained in the analysis of the experimental data give quantitative information on molecular motions, particularly for the tilted smectic phases of DB 8 Cl. In contrast to former conjectures, we found that the low-frequency relaxation in the bilayer smectic C phases results from director fluctuations about the layer normal, which occur without distortion of the layers, and from layer undulations, similar to those in the smectic A phase. In the low-temperature bilayer smectic C phase, a considerable slowing-down of molecular translational diffusion is observed. It confirms indirectly the anticlinic character of this mesophase. Measurements of angular dependence of the relaxation times at 60 MHz support the conclusions obtained from the frequency dispersion data.