ABSTRACTThe effect of the polymeric crosslink density on the thermal conductivity of an epoxy nanocomposite was investigated by adding two different diamine-functionalized multiwalled carbon nanotubes (diamine-MWNTs) to the epoxy resin as co-curing agents and conducting fillers. Tetramethylenediamine (TMDA)-MWNTs resulted in an epoxy nanocomposite with a higher crosslink density than octamethylenediamine (OMDA)-MWNTs. Interestingly, epoxy/TMDA-MWNT nanocomposites under 1.5 wt % nanotube concentration, showed a higher thermal conductivity than an epoxy/OMDA-MWNT nanocomposite with the same concentration of nanotubes. In contrast, for higher diamine-MWNT concentrations (over 2.0 wt %), the thermal conductivity of the epoxy/OMDA-MWNT nanocomposite was higher than that with TMDA-MWNTs. We observed that for low MWNT concentrations, where a percolating network was not formed, a high crosslink density enhanced the thermal conductivity via phonon transport. However, for high MWNT concentrations, a high crosslink density hinders the formation of a percolating network and lowers the thermal conductivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44253.

•Porous polymer cryogels from blend of polyimide and polyethyleneoxide are prepared.•Porous carbons are prepared by carbonizing polymer cryogels with various contents.•Channel structures of the cryogels are maintained in the carbon cryogels.•Specific surface areas of carbon cyrogel derived from PAEO 5 wt% is 2646 m2/g.•Electrochemical application of the carbon cyrogels is demonstrated.A facile fabrication of a porous carbon cryogel from a blend (PAEO) of fluorinated poly(amic acid) and poly(ethylene oxide) (PEO) is demonstrated. The porous carbons are prepared by carbonizing the freeze-dried cyrogels of polymer blend with various contents. The original channel structures of the cryogels with PEO content below 5 wt% are perfectly maintained in the carbon cryogels. In particular, the carbon cyrogel derived from the blend (PEO content: 5 wt%) shows very high specific surface areas, 2646 m2/g. From investigation of the carbonization mechanism, it is found that the incorporation of PEO creates mesoporous structure without generating hydrophobic or ambiphilic components, while elimination of fluorine moiety affects the formation of microporous structure in resulting-carbon. In addition, the porous structure in carbon cryogels of high PEO loading is shrunk because PEO component reduces the rigidity of the structure. Lastly, the performance of the carbon cryogels as a capacitor is investigated.Download high-res image (308KB)Download full-size image

To develop advanced thermally conductive epoxy resins with liquid crystallinity, three novel liquid crystalline epoxies (LCEs) were synthesized via the substitution of phenylcyclohexyl (PCH) mesogenic moieties into the 2,5 positions of diglycidyl terephthalate. Mesomorphic properties of LCEs were evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). All LCEs exhibited an enantiotropic smectic phase on heating and cooling. Remarkably, the smectic phase with a wide temperature range of 98–145 °C was observed for the eutectic mixtures of a family of stable smectic LCEs. The selection of optimum curing agents, compositions of LCEs and curing agents, and curing conditions were determined based on physical, chemical, and thermal properties of LCEs and curing agents. The thermally cured LCEs at the LC phase exhibited a high thermal conductivity of 0.4 W m−1 K−1.

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.

•Microcellular polystyrene (PS) cryogel template was prepared by freeze-drying.•PS template/poly(amic acid) (PAA) was prepared by adsorption of PAA into the PS template.•Microcellular meso & microporous carbon material was prepared by carbonization of PS template/PAA.•Carbon material from PS template/PAA showed SSA of 2443 m2/g and micropore volume of 0.90 cm3/g.•Pendent groups containing fluorine atom helped to form highly microporous structure.In this work, a highly microporous carbon material was synthesized through the combination of fluorine-containing poly(amic acid) (F-PAA), which can produce a microporous carbon material upon carbonization, and a mesoporous polystyrene (PS) cryogel. Carbonization of F-PAA at 1000 °C yielded a microporous carbon material with high specific surface area (SSA, ∼1300 m2/g). In addition, we prepared a PS cryogel template with microcellular structure by freeze-drying the PS solution in 1,4-dioxane. The template was then impregnated with F-PAA, followed by carbonization at 1000 °C. Interestingly, the carbon material obtained through this approach maintained the microcellular structure of the PS cryogel template even after template pyrolysis during carbonization. Moreover, the microcellular carbon material exhibited a high SSA and a large micropore volume (∼2400 m2/g and 0.90 cm3/g, respectively).

•Helical carbon, carbon microtubes, and carbon rods were synthesized by carbonizing mercerized cotton fibers.•The surface area of carbonized cotton fiber without mercerization was 203 m2/g.•The surface area of carbonized cotton fiber with mercerization was improved to 726 m2/g.In this study, we used mercerized cotton fibers as carbonization precursors to fabricate carbon materials having different structures. The morphologies of the synthesized carbon materials were successfully controlled by varying the mercerization time. Twisted ribbon-like carbon structures, carbon microtubes, and carbon rods could be synthesized by carbonizing non-mercerized cotton fibers, cotton fibers mercerized for 40 min, and fully mercerized cotton fibers (i.e., fibers mercerized for 60 min), respectively. Interestingly, along with the morphological changes, the specific surface areas of these carbon materials were also changed to 203.7, 726, and 276.7 m2/g, respectively. This method of fabricating carbon materials should lead to the synthesis of novel, structured carbon materials with various functionalities as it exploits both the natural structure of cotton fibers and artificial chemical processes.

•Microcellular polypyrrole (PPy) was synthesized using a freeze-dried polystyrene template.•Microcellular PPy exhibited bamboo-like honeycombed channel structure similar to the template.•Microcellular carbon material was prepared by iodine doped microcellular PPy.The facile fabrication of polypyrrole (PPy) foams via vapor phase polymerization using microcellular polystyrene, prepared by unidirectional freeze-drying, as a template was demonstrated. Remarkably, the PPy foams maintained the porous morphology of the template, which exhibited a bamboo-like honeycomb channel structure. In addition, the PPy foams were carbonized at 800 °C with iodine doping and the carbon products showed similar morphologies to that of the precursor. The carbon foams were characterized by Raman spectroscopy and XRD analysis and were confirmed to be amorphous carbon with a nitrogen content of about 7%.

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 × 103 S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn.Keywords: carbon nanotube fiber; FeCl3; intramolecular cross-dehydrogenative coupling;

•LC-MWNTs synthesized by esterification showed good dispersion stability in ethanol.•LC-MWNTs exhibited good miscibility in a host thermotropic nematic LC (N-LC).•LC-MWNTs in the N-LCs showed well aligned parallel to the applied magnetic field.Liquid crystal (LC)-functionalized multi-walled carbon nanotubes (MWNTs) were synthesized by substituting decyloxy and phenylcyclohexyl (PCH) mesogenic moieties into MWNT surface through covalent linkage. The LC-functionalized MWNTs (LC-MWNTs) showed good dispersion stability in ethanol as well as good miscibility in a host thermotropic nematic LC (N-LC). A polarizing optical microscope image demonstrated that the LC-MWNTs could be well dispersed in the host N-LC within 5 wt% content of LC-MWNTs without aggregation, which is ascribed to the substantial affinity between the PCH moieties and the host N-LC molecules. It was found that the LC-MWNTs in the host LC matrix could be well aligned parallel to the direction of the applied magnetic field of 5 T. Then the high order parameter of 0.46 for LC-MWNTs was obtained from the measurement of polarized Raman spectroscopy.