Electro-optic properties of thiol-ene polymer stabilized ferroelectric liquid crystals

Electro-optic properties of polymer stabilized ferroelectric liquid crystal (PSFLC) systems are examined as a function of varying concentrations of either a linear or crosslinked thiol-ene polymer. The thiol-ene method of polymer stabilization is a drastic change from previous studies designed to avert the problem of polymer phase separation. FLC rise time and tilt angle measurements were used to determine the effects of the polymer network on the optical properties of the system. The addition of monomer impurities to both systems demonstrated a reduction in tilt angle, which translated into decreased switching speeds in both systems prior to polymerization. The crosslinked thiol-ene system showed increased switching times due to the creation of polymer in the interlayer spacing of the FLC, but exhibited minimal increase in the rotational viscosity of the system. In addition, the crosslinked polymer systems resulted in an increase in the liquid crystalline order, which produced an increase in the contrast ratio of the system. The linear polymer system showed drastically different results as compared with the crosslinked system. The rise time and tilt angle measurements decreased upon polymerization of the linear thiol-ene and the rotational viscosity and contrast ratio values also decreased. We suggest that the linear thiol-ene polymer phase separation from the interlayer spacing leads to a microscopic misalignment of the FLC molecules, causing a decrease in the optical properties of the LC.     

Electro-optic properties of thiol-ene polymer stabilized ferroelectric liquid crystals

Electro-optic properties of polymer stabilized ferroelectric liquid crystal (PSFLC) systems are examined as a function of varying concentrations of either a linear or crosslinked thiol-ene polymer. The thiol-ene method of polymer stabilization is a drastic change from previous studies designed to avert the problem of polymer phase separation. FLC rise time and tilt angle measurements were used to determine the effects of the polymer network on the optical properties of the system. The addition of monomer impurities to both systems demonstrated a reduction in tilt angle, which translated into decreased switching speeds in both systems prior to polymerization. The crosslinked thiol-ene system showed increased switching times due to the creation of polymer in the interlayer spacing of the FLC, but exhibited minimal increase in the rotational viscosity of the system. In addition, the crosslinked polymer systems resulted in an increase in the liquid crystalline order, which produced an increase in the contrast ratio of the system. The linear polymer system showed drastically different results as compared with the crosslinked system. The rise time and tilt angle measurements decreased upon polymerization of the linear thiol-ene and the rotational viscosity and contrast ratio values also decreased. We suggest that the linear thiol-ene polymer phase separation from the interlayer spacing leads to a microscopic misalignment of the FLC molecules, causing a decrease in the optical properties of the LC.     

Polymer nanotubes toward gelating organic chemicals

Crosslinked polymer nanotubes are large scale synthesized. The method is based on fast cationic polymerization using immiscible initiator nanodroplets. Nanoporous network processed from the nanotubes is superhydrophobic, which can absorb all the tested organic chemicals forming robust gels. The nanotubes are promising in the collection of spilled organic chemicals, detoxification and water treatment.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

Self-assembly of Peptide nanotubes in an organic solvent

The self-assembly of a modified fragment of the amyloid beta peptide, based on sequence Abeta(16-20), KLVFF, extended to give AAKLVFF is studied in methanol. Self-assembly into peptide nanotubes is observed, as confirmed by electron microscopy and small-angle X-ray scattering. The secondary structure of the peptide is probed by FTIR and circular dichroism, and UV/visible spectroscopy provides evidence for the important role of aromatic interactions between phenylalanine residues in driving beta-sheet self-assembly. The beta-sheets wrap helically to form the nanotubes, the nanotube wall comprising four wrapped beta-sheets. At higher concentration, the peptide nanotubes form a nematic phase that exhibits spontaneous flow alignment as observed by small-angle neutron scattering.     

Purification of HiPCO carbon nanotubes via organic functionalization

We report a new method for the purification of HiPCO single-wall carbon nanotubes (SWNT), which consists of the following sequence: (a) organic functionalization of the as-produced nanotubes (pristine tubes, p-SWNT), (b) purification of the soluble functionalized nanotubes (f-SWNT), (c) removal of the functional groups and recovery of purified nanotubes (r-SWNT) by thermal treatment at 350 degrees C, followed by annealing to 900 degrees C. Each of these steps contributes to the purification, but only their sequential combination leads to high-purity materials. Organic functionalization makes the SWNT more easy to handle, which results in a better manipulation for potential practical uses. The electronic properties of the purified tubes are investigated via Raman and NIR spectroscopies along with transmission electron microscopy.     

手性有机-无机杂化氧化硅纳米管的制备

依照文献以L-苯甘氨酸为手性源合成了一个手性阴离子两亲小分子化合物.利用圆二色谱表征了该化合物水中的自组装行为.通过溶胶-凝胶复制法,以该手性两亲小分子化合物和结构助剂的组装体为模板制备了右手螺旋有机-无机杂化氧化硅纳米管.圆二色谱表征结果表明,4,4′-亚联苯基氧化硅中的联苯基团呈手性堆积.     

一种光交联电光聚合物的合成及其外部电光测量

合成了一种新的带有光交联基团的电光聚合物,其高分子基体是双酚A环氧树脂,二阶非线性生色团对硝基苯胺和光交联基团肉桂酰氯都键接在高分子链上.将聚合物溶解后旋涂成膜,对薄膜进行电晕极化.极化的后阶段用紫外光照射,使聚合物体系交联成网络结构,形成生色团取向长时间稳定的聚合物电光薄膜.用这种聚合物电光薄膜构成外部电光调制系统,测量了共面波导上的电信号.     

Self-assembling vanadium oxide nanotubes by organic molecular templates

Vanadium oxide nanotubes were synthesized as the main product by hydrothermal self-assembling from ammonium metavanadate (NH(4)VO(3)) and organic molecules as structure-directing templates. Several kinds of templates including primary amines (C(n)H(2n+1)NH(2)), alpha,omega-diamines (H(2)N[CH(2)](n)NH(2)), and quaternary ammonium salt (CTAB) were demonstrated to be appropriate for the formation of nanotubes. The morphologies and structures of the nanotubes were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and thermal gravimetric analysis (TGA). The nanotubes were found forming together with the layered structures and the sheetlike structures. On the basis of the growth mechanism of WS(2) nanotubes proposed by our group, a possible rolling mechanism was proposed, which might be a suitable general formation mechanism for types of nanotubes from lamellar structures.     

Fundamental properties of single-wall carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) represent an excellent example of materials by design with many of their outstanding properties predicted by theory prior to their synthesis. Both experimental and theoretical work on these novel nanowires continue to increase at a breathtaking pace. Herein we describe some of their fundamental properties on which much of this work is built. After discussing their structure and symmetries, we emphasize their exceptional electronic properties. The standard one-parameter graphene sheet model of SWCNTs, introduced in the earliest published paper on extended SWCNTs, is discussed in terms of both its successes and limitations. The strong interplay between theory and experiment that this area has enjoyed is also discussed. In addition, several opportunities for further study are touched upon.     

pH-dependent electron-transport properties of carbon nanotubes

Carbon nanotube electrochemical transistors integrated with microfluidic channels are utilized to examine the effects of aqueous electrolyte solutions on the electron-transport properties of single isolated carbon nanotubes. In particular, pH and concentration of supporting inert electrolytes are examined. A systematic threshold voltage shift with pH is observed while the transconductance and subthreshold swing remain independent of pH and concentration. Decreasing pH leads to a negative shift of the threshold voltage, indicating that protonation does not lead to hole doping. Changing the type of contact metal does not alter the observed pH response. The pH-dependent charging of SiO2 substrate is ruled out as the origin based on measurements with suspended nanotube transistors. Increasing the ionic strength leads to reduced pH response. Contributions from possible surface chargeable chemical groups are considered.     

Sidewall functionalization of single-walled carbon nanotubes with organic peroxides

Single-wall carbon nanotubes (SWNTs) and their fluorinated derivatives (F-SWNTs) were reacted with organic peroxides including benzoyl and lauroyl peroxide to produce phenyl and undecyl sidewall functionalized SWNTs, respectively, which were characterized by Raman, FTIR, and UV-Vis-NIR spectra as well as TGA/MS, TGA/FTIR, and TEM data.     

Electro-optic and dielectric properties of new binary ferroelectric and antiferroelectric liquid crystalline mixtures

Several new binary liquid crystalline mixtures have been designed and their properties were studied by complementary methods. It has been shown that even both pure components used for the mixture design possess the ferroelectric behaviour; the induced antiferroelectric smectic phase has been detected for one of the prepared mixtures. The phase diagram has been constructed and the existence of the antiferroelectric phase was confirmed by switching time and dielectric spectroscopy measurements. Some of the resulted mixtures possess very high values of the tilt angle that reaches close below 45° degrees at saturation. Values of spontaneous polarisation were found within 50–200 nC/cm² in dependence of the mixture’s composition. Due to specific properties, the obtained mixtures might be interesting for further design of multicomponent mixtures and formulation of the advanced nanocomposite systems.     

Controlled fabrication of organic nanotubes via self-assembly of non-symmetric bis-acylurea

We present novel non-symmetric bis-acylurea organogelators that self-assemble into hollow tubular nanostructures upon cooling in solutions. The bis-acylureas have aliphatic end groups of different lengths divided by a spacer group [?NHCONHCO?(CH₂)₅?CONHCONH?, C5] with two hydrogen bonding sites. Due to the intermolecular biaxial hydrogen bonding, the molecules crystallize into 2D thin layers at first, and then their wrapping ultimately results in nanotubes. On the contrary, symmetric bis-acylureas form multilayered nanosheets which are stabilized by the van der Waals interaction between the stacked layers. The size and shape of the nanotubes can be controlled by varying the difference of the alkyl chain lengths. When the difference is big, for example, eight methylene units (BuC5DD, butyl (Bu) and dodecyl (DD)), uniform nanotubes of 65-nm mean outer diameter are obtained, while a non-symmetric bis-acylurea with one methylene unit difference (UDC5DD, undecyl (UD)) forms a mixture of nanosheets and nanotubes. Template-assisted formation of nanotubes was successfully performed via gelation in inorganic nanopores. We also synthesized a thiol-functionalized non-symmetric bis-acylurea, HS-UDC5Bu (thiol (HS)), which was used as a tubular template for gold nanoparticles.     

Cisplatin-encapsulated organic nanotubes by endo-complexation in the hollow cylinder

A bipolar glycolipid self-assembles into organic nanotubes upon its chelation with an anticancer drug cis-dichlorodiamineplatinum(ii) (CDDP). The facile synthesis of glycolipid, chelation-assisted formation of the nanotubes, and efficient loading and prolonged release of CDDP demonstrate a new approach to high-axial supramolecular drug nanocarriers.     

Thermoelectrical and optical properties of double wall carbon nanotubes:polyaniline containing boron n‐type organic semiconductors

The electrical conductivity, thermoelectrical, and optical properties of the polyaniline containing boron/double wall carbon nanotubes (CNTs) composites have been investigated. The electrical conductivities of the composites prepared with 1%, 5%, and 8% CNT concentrations at 300 K were found to be 5.31 × 10^?6, 2.72 × 10^?4, and 1.12 × 10^?3 (S/cm), respectively. The thermoelectrical results indicate that all the samples exhibit n‐type electrical conductivity. The optical band gaps of the samples were found to be 3.71 eV for 0% DWNT, 3.32 eV for 1% DWNT, 3.15 eV for 5% DWNT, and 3.12 eV for 8% DWNT. The obtained results suggest that the electrical conductivity of PANI‐B polymer is improved by DWNT doping. Copyright © 2008 John Wiley & Sons, Ltd.