Munju Goh

Powerful helicity inducers: axially chiral binaphthyl derivatives

Axially chiral binaphthyl derivatives with highly twisting powers were synthesised by substituting phenylcyclohexyl (PCH) mesogenic moieties into 2,2′ positions or 2,2′,6,6′ positions of binaphthyl rings. The di‐ and tetra‐substituted binaphthyl derivatives were adopted as chiral dopants to induce chiral nematic liquid crystals (N*‐LCs). The helical twisting power (βM) of tetra‐substituted binaphthyl derivative, D‐3, having direct linkages between the PCH moieties and the binaphthyl rings at the 6,6′ positions, was 449 µm−1. This is ca. 2.6 times larger than that (171 µm−1) of di‐substituted one, D‐1. For systematic investigation of helical twisting power in the binaphthyl derivatives, several tetra‐substituted binaphthyl derivatives (D‐2–D‐9) were synthesised by introducing different aromatic moieties into the 6,6′ positions of the binaphthyl rings without methylene spacer. When the substituents group changed from p‐hexaoxyphenyl to p‐hexaoxybiphenyl, the helical twisting powers of the binaphthyl derivatives increased from 234 to 757 µm−1. Interestingly, D‐3 and D‐9 exhibited liquid crystallinity. Although the liquid crystallinity of the chiral dopant has no direct influence on the helical twisting power of the N*‐LC, it plays a role in increasing the miscibility of the chiral dopant to host N‐LC, leading to a raise of the upper limit in concentration of the chiral dopant. Consequently, both the high helical twisting power and the high miscibility of D‐3 allowed us to prepare a highly twisted N*‐LC, the helical pitch of which is in the nano‐order, e.g. 270 nm.

Enhancement of the crosslink density, glass transition temperature, and strength of epoxy resin by using functionalized graphene oxide co-curing agents

We synthesized diamine-functionalized graphene oxide, DDS–GO and HMDA–GO, by introducing 4,4′-diaminodiphenyl sulfone (DDS) or hexamethylenediamine (HMDA) into the carboxylic acid groups on graphene oxide (GO) via amide bonds. The introduction of diamines was confirmed by analytical methods such as FT-IR, TG-DTA, XPS, AFM, and optical microscopy. Then, we applied DDS–GO and HMDA–GO as co-curing agents for epoxy (EP) nanocomposites that were prepared by mixing bisphenol-A type EP and DDS curing agent (ca. 21 wt%). Interestingly, when 1.0 wt% of DDS–GO was added to the EP/DDS mixture, the crosslink density (CD) increased from 0.028 to 0.069 mol cm−3. Due to the higher CD, both the glass transition temperature and tensile strength of the EP/DDS/DDS–GO nanocomposite effectively improved from 160.7 °C to 183.4 °C and from 87.4 MPa to 110.3 MPa, respectively.

Defect healing of reduced graphene oxide via intramolecular cross-dehydrogenative coupling

A chemical defect healing of reduced graphene oxide (RGO) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G-band to the D-band, the IG/ID ratio, of the RGO was increased from 0.77 to 1.64 after the ICDC reaction. From XPS measurements, the AC=C/AC-C ratio, where the peak intensities from the C=C and C-C bonds are abbreviated as AC=C and AC-C, of the RGO was increased from 2.88 to 3.79. These results demonstrate that the relative amount of sp(2)-hybridized carbon atoms is increased by the ICDC reaction. It is of great interest that after the ICDC reaction the electrical conductivity of the RGO was improved to 71 S cm(-1), which is 14 times higher than that of as-prepared RGO (5 S cm(-1)).

Entanglement-free fibrils of aligned polyacetylene films that produce single nanofibers

An aligned polyacetylene (PA) film was synthesized in a macroscopically-aligned nematic liquid crystal (N-LC) solvent using a gravity-flow method. Long and single nanofibers of less than 100 nm in radius were successfully prepared by ultrasonication of the aligned PA film immersed in ethanol. The usual PA film was synthesized in an isotropic solvent, such as toluene, only yielding short and non-dispersed fibers after the ultrasonication due to the entangled fibril morphology. Entanglement-free fibrils of the aligned PA were well-separated into single fibrils through ultrasonication, even without a surfactant.

A facile method for transparent carbon nanosheets heater based on polyimide

In this work, a novel film heater in nanometer-scale thickness based on catalyst-free and transfer-free carbon nanosheets (CNSs) with properties similar to graphene is fabricated. Here, poly(amic acid) (PAA), which is composed of several aromatic hydrocarbon rings, is used as the carbon precursor of CNS films. Altering the polymer concentration easily controls the morphological, optical, and electrical properties of the CNS films obtained by carbonization of PAA thin films. The CNS films with different thicknesses of 7.53–28.40 nm are simply prepared through spin-coating on a quartz substrate and post heat-treatment. Finally, their direct use as transparent film heaters is deeply investigated by considering electrical conductivity, temperature response rapidity, achievable maximum temperature, and electric power efficiency. For instance, an electrically conductive and optically transparent CNS film with 28.40 nm thickness exhibits excellent electric heating performance achieving well-defined steady-state maximum temperatures of 24–333 °C at low input electric power per unit film area of 0.027–1.005 W cm−2 in a relatively short time of ∼100 s.

Chemical method for improving both the electrical conductivity and mechanical properties of carbon nanotube yarn via intramolecular cross-dehydrogenative coupling.

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G band to the D band (IG/ID ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the AC═C/AC-C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10(3) S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn.

Chirality transfer from atropisomeric chiral inducers to nematic and smectic liquid crystals – synthesis and characterization of di- and tetra-substituted axially chiral binaphthyl derivatives

The chirality transfer of axially chiral binaphthyl derivatives bearing liquid crystal (LC) moieties at the n,n′ positions (n = 3, 4, 6) of the binaphthyl rings to nematic (N) and smectic (S) LCs is investigated. Chiral nematic LCs (N*-LCs) are prepared by adding a small amount of the chiral binaphthyl derivative into host N-LCs composed of cyanobiphenyl mesogen cores. The binaphthyl derivative with phenylcyclohexyl (PCH) type LC moieties at the 4,4′ positions of the binaphthyl ring [D-4,4′] exhibits a low helical twisting power (HTP) of 11 μm−1. In contrast, those with LC moieties at the 3,3′ and 6,6′ positions of the binaphthyl rings [D-3,3′ and D-6,6′] exhibit high HTPs of 153 μm−1 and 154 μm−1, respectively. Next, the binaphthyl derivatives are added into two types of S-LCs with phenylbenzoate mesogen cores: 4-(4-methylpentyloxy)phenyl-4-(decyloxy)benzoate [PhB1] and 4-(3-methylpentyloxy)phenyl-4-(decyloxy)benzoate [PhB2]. The mixture of the host LC, PhB1 or PhB2 with the chiral dopant, D-3,3′ or D-6,6′ shows chiral smectic LCs C (SC*-LCs). The highly twisted SC* phases with helical pitches of 1.2–1.4 μm are prepared in PhB1 and PhB2 by using the chiral dopant of D-6,6′. It is concluded that D-6,6′ has a large helical twisting power and is the most favourable atropisomeric chiral inducer for chirality transfer to both N-LCs and S-LCs.

Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers

Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m−1 K−1 near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed ...

Probing Spin-charge Relation by Magnetoconductance in One-dimensional Polymer Nanofibers

Polymer nanofibers are one-dimensional organic hydrocarbon systems containing conducting polymers where the non-linear local excitations such as solitons, polarons and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here we report our observations of a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite) MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge).

Synthesis and preparation of alkyl-functionalized graphene oxide/polyimide nanocomposites

Abstract