Materials Literature
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The polymer network-ferroelectric liquid crystal (FLC) microcomposites are prepared by UV crosslinking of a chiral prepolymer diluted in a FLC. A fast cross-linking process involving 20 mW cm-2 UV intensity produces material with ferroelectric properties which have strongly deteriorated compared with the pure FLC. By…
In five double-swallow-tailed compounds a weakly birefringent high temperature phase occurs which exhibits a characteristic optical texture. On the basis of X-ray diffraction measurements on well oriented monodomains, the structure of this phase could be described by a rhombohedral lattice of space group R3c or R32/c;…
Poly(ε-caprolactone-b-perfluoropolyether-b-εcaprolactone) (PCL–PFPE–PCL) block copolymers having different PCL block lengths and end-capped with methacrylate groups were prepared and characterized. Spectroscopic analyses confirmed the expected molecular structure of the products. After UV curing, the films revealed th…
A theoretical analysis of carbon nanotube based field-effect transistors fabricated by two different groups [Tans et al., Nature (London) 393, 49 (1998); Martel et al., Appl. Phys. Lett. 73, 2447 (1998)] is presented. The metal (electrode)-semiconductor (nanotube) contact influences subthreshold channel conductance ve…
Seven homologous symmetric dimeric liquid crystals are presented where two three-ring mesogenic units are connected by a bis(carbonyloxy)alkylene spacer. For homologues with terminal heptyloxy, octyloxy and nonyloxy chains, the unusual phase sequence SmA-SmC with increasing temperature was detected by the study of the…
Thin films of hexadecafluorophthalocyaninatooxovanadium (F 16 PcVO) are vapor-deposited under organic molecular beam epitaxy (OMBE) conditions on the (100) surfaces of NaCl, KCl, and KBr and on quartz glass. Beginning at submonolayer coverages and extending to a film thickness of several tens of nanometers the film st…
We report single-layer holographic polymer-dispersed liquid-crystal materials with multiple reflection and/or diffraction gratings. Three switchable gratings are observed in a single film formed in a three-beam interference pattern. Two reflection gratings and one transmission grating are formed, corresponding to each…
A new adsorption site for adsorbed acetylene on Si(100) is observed by photoelectron imaging based on the holographic principle. The diffraction effects in the carbon 1s angle-resolved photoemission are inverted (including the small-cone method) to obtain an image of the atom's neighboring carbon. The chemisorbed acet…
The diffusion of amine stabilizers in vulcanized natural rubber formulations used in tires was investigated. Experiments were undertaken using a “sandwich” system composed of a sample disk containing the additive (source disk) between two external disks of nonadditivated rubber (reception disks). Diffusion coefficient…
Nitrilic rubbers containing 29 or 45% of acrylonitrile were blended with polyaniline doped with different acids (chloridric, dodecylbenzenesulfonic, tetrapropylbenzenesulfonic, and p-toluenesulfonic acids). The blends were prepared by mechanical mixing in a roll-mill and vulcanized in a hot press. The volumetric condu…
A cubic mesophase is found in an extended rod-like mesogen in which the terminal chains are perfluorinated.
A research area that has obtained increasing interest during the last decade concerns improvement of macromolecular properties by changes in the macromolecular architecture. One group of these materials is dendritic polymers, which are highly branched structures exhibiting very different properties compared with linea…
A new homologous series of achiral banana-shaped mesogens ('Cn') has been synthesized and studied by classical techniques (optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optic investigations). Complete miscibility with compounds of the n-OPIMB series shows that the short homologue…
The behaviour of a liquid crystalline azobenzene material possessing a nematic phase was studied under UV illumination. It was found that a uniformly aligned planar sample of the azobenzene undergoes a reversible orientation transition to homeotropic; this can be interpreted as an anchoring transition caused by the ph…
Raman scattering measurements were carried out in self-organized Ge quantum dot superlattices. The samples consisted of 25 periods of Ge quantum dots with different dot sizes sandwiched by 20 nm Si spacers, and were grown using solid-source molecular-beam epitaxy. Optical phonon modes were found to be around 300 cm−1,…
Porous poly(L-lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution-cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film por…
A chemically cross-linked and water-swollen poly(3-thiopheneacetic acid) (P3TAA) gel was synthesized, and its swelling and spectral changes associated with its ionization were studied. The gel undergoes an abrupt red shift in the electronic spectra at a certain pH, suggesting that a conformational transition due to io…
The most important methods of synthesis and purification of carbon nanotubes, a new form of material, are described. The prospects for increasing the scale of preparation processes and for more extensive application of nanotubes are evaluated. The bibliography includes 282 references.
Rheological and morphological studies were performed on polymer blends of ethylene-octene copolymer [polyethylene elastomer (PEE)] and polypropylene (PP). The viscosities of PEE, PP, and PEE/PP blends were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200. A non-Newtonian…
X-ray diffraction was used to monitor the structure of 45 A diameter CdSe nanocrystals as they transformed repeatedly between fourfold and sixfold coordinated crystal structures. Simulations of the diffraction patterns reveal that a shape change occurs as the crystals transform. They also show that stacking faults are…