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In order to achieve the dispersion stability of multi-walled carbon nanotubes (MWCNT) in a fluorinated refrigerant (FC-72) used in various cooling purposes, fluorinated MWCNT (MWCNT-F) was prepared by a combined process of oxidation and fluorination. As a fluorine source, (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane was used to react with hydroxyl groups on MWCNT (MWCNT-OH) generated by chemical oxidation. Pristine MWCNT, MWCNT-OH, and MWCNT-F were dispersed in FC-72 and MWCNT-F was also dispersed in polar and nonpolar solvents. The MWCNT-F has excellent colloidal stability in FC-72 because of the chemical affinity between FC-72 and functional groups (-CFn) on the side walls of MWCNT. Through surface modifications, we could obtain the enhanced dispersion stability of MWCNT in a refrigerant. This homogenous MWCNT solution in FC-72 may be used to increase the heat transfer in FC-72 based nanofluids. [ABSTRACT FROM PUBLISHER]

Abstract: Alumina particles were incorporated in poly(dimethyl siloxane) (PDMS) matrix in company with multiwalled carbon nanotube (MWCNT) for improving the thermal and electrical conductivities. The concentration of MWCNT was increased from 0 to 10wt% to PDMS at fixed amounts of alumina (200 and 300wt% to PDMS). Thermal conductivity of PDMS composites was increased with the increasing amount of MWCNT and the excellent dispersibility of the incorporated pristine MWCNT was achieved. Thermal and electrical conductivities of the composites were increased with the increasing concentration of the alumina because the alumina particles help disperse MWCNT within the PDMS matrix due to the ball milling effect during compounding. The properties of the alumina and MWCNT incorporated PDMS composites were investigated in terms of the curing characteristics, electrical conductivity, and thermal conductivity. The MWCNT/alumina incorporated composite showed the high electrical conductivity to the level of the semiconductor. [ABSTRACT FROM AUTHOR]

Herein, the effect of the dispersion uniformity of multi-wall carbon nanotubes (MWNTs) on the thermal conductivity of nylon 610/MWNTs nanocomposite was investigated. Compared to raw MWNTs, the carboxylated MWNTs (MWNT-COOH) were well dispersed in aqueous hexamethylenediamine solution and the dispersion stability was further improved by the presence of poly(vinyl alcohol). By means of interfacial polymerization between the aqueous hexamethylenediamine solution containing the MWNTs and a sebacoyl chloride phase, nylon 610/MWNT composites were prepared. It was found that the stable dispersion state of MWNTs in aqueous solutions greatly improved the thermal conductivity of the ultimate nanocomposites. It is noted that the thermal conductivity of nylon 610/MWNT-COOH/PVA nanocomposite was 135% higher than that of nylon 610/raw MWNTs for the same 0.1 wt% content of MWNTs. [ABSTRACT FROM AUTHOR]

In order to enhance the thermal conductivity of MWCNT filled poly(dimethyl siloxane) (PDMS) composites, the MWCNT was coated with silica layer by three step reactions. The composites filled with raw and silica-coated MWCNTs were prepared and the properties were investigated in terms of the curing characteristics, mechanical properties, and thermal conductivity. Due to the poor compatibility between raw MWCNT and PDMS, raw MWCNT showed poor dispersion uniformity and wettability in PDMS. On the other hand, due to the chemical affinity between silica/MWCNT and PDMS throughout the hydrogen bonding, the silica-coated MWCNT filled PDMS showed improved mechanical properties in terms of tensile strength and 100% modulus, and good interfacial compatibility than raw MWCNT incorporated PDMS. Finally, the good wettability of silica/MWCNT in PDMS resulted in higher thermal conductivity caused from the facile phonon movement at the interface even with the smaller MWCNT contents. [ABSTRACT FROM AUTHOR]

Abstract: Recently, the fabrication of polymer composite nanofibers containing multi-wall carbon nanotube (MWCNT) by electrospinning has attracted much attention due to their potential advantages for the enhancement of properties such as electrical and thermal conductivity. In order to utilize the superior properties of MWCNT, in this study, MWCNT was covalently grafted with poly(ethylene glycol) (PEG) chains and PEGylated MWCNT-incorporated PVA nanofibers were prepared by electrospinning. To do so, MWCNT was firstly chemically oxidized to bear carboxyl groups and successively reacted with PEG molecules in ethanol. The PEGylated MWCNT was mixed with aqueous PVA solution and electrospinning was performed. The degree of surface modification of MWCNT by PEG was thoroughly investigated by FT-IR, XPS and TGA. Compared to the pristine MWCNT, the PEGylated MWCNT was uniformly dispersed PVA nanofibers without agglomeration. Because of the enhanced dispersion of PEGylated MWCNT in PVA nanofibers, the electrical conductivity of nanofibers with PEGylated MWCNT (1.0wt%) was increased by 4 orders of magnitude compared to that of nanofibers with pristine MWCNT (1.0wt%). [Copyright &y& Elsevier]

Herein, PEGylated multi-walled carbon nanotube (MWNT) was prepared for the successive fabrication of poly(vinyl alcohol) PVA/MWNT nanocomposite film by solution casting. The surface modified MWNT showed a good colloidal stability in a polar solvent, i.e., water. Also, the PEGylated MWNT had an improved dispersion stability in aqueous PVA solution. The mixture of PEGylated MWNT and PVA dissolved in water was film casted and the dispersion uniformity and corresponding improvement of electrical conductivity were investigated. The electrical conductivity of PVA/modified MWNT composite film was three-fold higher than that of PVA/pristine MWNT composite film due to the much improved distribution uniformity of modified MWNT in PVA matrix. [ABSTRACT FROM AUTHOR]

Abstract: The changes of electrical resistance of the polymer composites on exposure to chemical vapors have been applied for the production of vapor sensors. In this study, to confirm the ability of elastomer as chemical vapors sensors, polyurethane/PEG-modified MWCNT composite film was prepared by in situ condensation polymerization and solution casting. The responses of this elastomer composite film for various organic vapors (polar and non-polar solvents) were calculated by monitoring the change in the resistance of the composite film when exposed to the organic vapors. The changes of electrical resistance of the composite films were explained on the basis of volume expansion as swelling and polar interaction of various vapors on the composite. Therefore, we were able to interpret the behavior of the polyurethane/PEG-modified MWCNT composite film as a chemical vapor sensor through diffusion, sorption, and permeation coefficients of the polymer film–analyte systems. [Copyright &y& Elsevier]

Abstract: Herein, the effect of dispersion uniformity of multi-walled carbon nanotube (MWCNT) on the thermal conductivity of poly(dimethyl siloxane) (PDMS) composites was investigated by comparing experimentally obtained and calculated results based on simple models. Two different MWCNTs, i.e., raw and oxidized/masterbatched MWCNTs, were used and compared. For raw MWCNT, the dispersion in PDMS was poor, resulting in the significant reduction in the aspect ratio of MWCNT. However, for composites using masterbatched MWCNT, the thermal conductivity was always about 10% greater than those prepared with raw MWCNT and the aspect ratio calculated by the model equation was also 1.7 times greater. Above 1.5 phr masterbatched MWCNT concentrations, the aspect ratio of 430 was maintained. Finally, the results suggest that the thermal conductivity can be correlated with the degree of dispersion and aspect ratio obtained from the model equation used. [Copyright &y& Elsevier]

Abstract: Silica nanotubes were synthesized using the multi-walled carbon nanotubes (MWCNTs) as the template material. First, we prepared silica coated MWCNT composites by surface oxidation of MWCNTs using KMnO4 in the presence of a phase transfer catalyst and followed by grafting of 2-aminoethyl 3-aminopropyl trimethoxy silane, AEAPS. The amine groups in grafted AEAPS on MWCNTs could activate the silica shell formation by acid–base interaction. The synthesized silica was formed a uniform layer on MWCNTs with a controllable thickness and possessed sturdy 3-dimensional stability. After calcinations at 800 °C, the inner MWCNTs of the composite were completely decomposed and the outer silica shell layer maintained without distortion of its original shape. Finally, we could obtain the silica nanotubes having 13.0 nm of average layer thickness. [Copyright &y& Elsevier]