Properties of the Broad-Range Nematic Phase of a Laterally Linked H-Shaped Liquid Crystal Dimer

In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer have been synthesized and characterized. The distinct feature of the material is a very broad temperature range (about 50 oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.Comment: 30 pages (including Supplementary Information), 7 Figure

Formation of a Silicate L 3 Phase with Continuously Adjustable Pore Sizes

the magnitude of the gain. Thus, the delay time of ϳ0.5 s observed in REFERENCES AND NOTES ___________________________ Since the demonstration that surfactants could be used in the fabrication of silica mesophases (1), amphiphiles have been used to produce inorganic materials with a variety of mesomorphic structures, including lamellar, hexagonally packed tubular, and cubic forms (2-12). Surfactant-induced assembly of inorganic structures is now recognized as a way to make novel nanoporous materials with larger pore sizes than was previously possible. However, techniques developed thus far have limited capability to produce very large pores of a predetermined size. Here we describe the synthesis and characterization of a new, random, bicontinuous silicate mesomorph for which predetermined pore sizes, over a very large size range, may be obtained. Most procedures for forming mesoporous silicates rely on the micelle-forming properties of a surfactant, typically at a low surfactant concentration. The addition of an inorganic precursor, such as an alkoxysilane, leads to association and coassembly into a mesophase precipitant whose structural dimensions are controlled by the surfactant length. Polymerization of the inorganic precursor and removal of the surfactant results in a rigid silica shell conforming to the structural shape of the mesophase. However, the use of dilute surfactant solutions limits the ability to predict the topology of the mesophase. Also, the typical product of the process is a powder of micrometer-sized particles, thereby limiting uses in filtration, optical, or electronic applications, where large-area thin films or large uniform monoliths of material are required. Finally, the pore volume is filled with surfactant; that is, the surfactant must be removed before the pores can be accessed. These difficulties may be partially avoided by the use of high-concentration surfactant systems in which either the inorganic precursors minimally perturb a preexisting surfactant-water liquid crystalline (LC) structure or the LC nature of the system may be recovered under appropriate experimental conditions, as shown by Attard et al. (6). Also, because the inorganic precursor does not precipitate out of solution, the resultant material conforms to the shape of the container in which it forms, thereby allowing fabrication of large monoliths of a desired size and shape. However, even in these cases, the pore size is limited by the surfactant and the limited range of compositions on the phase diagram for a given mesomorphic structure. Applications of silicate mesophases as filtration media, optical materials, and nanocomposites would be facilitated if th