Jinho Hong

Fabrication of silica nanotubes using silica coated multi-walled carbon nanotubes as the template.

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 KMnO(4) 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 degrees 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.

A Review on Thermal Conductivity of Polymer Composites Using Carbon-Based Fillers : Carbon Nanotubes and Carbon Fibers

Recently, the use of thermal conductive polymeric composites is growing up, where the polymers filled with the thermally conductive fillers effectively dissipate heat generated from electronic components. Therefore, the management of heat is directly related to the lifetime of electronic devices. For the purpose of the improvement of thermal conductivity of composites, fillers with excellent thermally conductive behavior are commonly used. Thermally conductive particles filled polymer composites have advantages due to their easy processibility, low cost, and durability to the corrosion. Especially, carbon-based 1-dimensional nanomaterials such as carbon nanotube (CNT) and carbon nanofiber (CNF) have gained much attention for their excellent thermal conductivity, corrosion resistance and low thermal expansion coefficient than the metals. This paper aims to review the research trends in the improvement of thermal conductivity of the carbon-based materials filled polymer composites.

Electrical, thermal, and rheological properties of carbon black and carbon nanotube dual filler-incorporated poly(dimethylsiloxane) nanocomposites

AbstractConductive nano-sized carbon black (CB) and carbon nanotube (CNT) are widely used in the polymer industry due to their excellent electrical and thermal conduction behavior and reinforcing ability. Herein, poly(dimethylsiloxane) (PDMS) nanocomposites filled with both conductive CB and CNT were fabricated using a planetary mixer and two-roll mill. Due to excellent thermal, electrical, and physical properties of CB and CNT, both the thermal and electrical properties of the composites and the dynamic mechanical properties were improved by the incorporation of CB and CNT into PDMS. The thermal conductivities of the composites linearly increased with filler concentration, and the electrical threshold was determined to be low. The rheological properties of the PDMS/CB and PDMS/CB/CNT nanocomposites were significantly influenced by filler incorporation.

Polyelectrolyte-assisted synthesis of polystyrene microspheres by dispersion polymerization and the subsequent formation of silica shell

Polystyrene (PS) microspheres were synthesized via dispersion polymerization in alcoholic media. A cationic polyelectrolyte, polyethyleneimine (PEI) was successfully used as a steric stabilizer. The concentration of initiator, monomer, and the solubility parameter of medium showed typical phenomena observed in dispersion polymerization. However, the sensitivity to the change in the particles size was almost twofold greater than conventional stabilizers. Spherical PS particles were synthesized with the PEI concentrations ranging from 5 to 20 wt.% to styrene, but conversion over 95% was achieved over 10 wt.% PEI. As-prepared PEI-stabilized PS microspheres were used as the template for the subsequent formation of a silica shell. As a result, a robust silica layer was fabricated on PS microspheres due to the increased interaction between PEI and tetraethyl orthosilicate (TEOS).

Synthesis of Positively Charged Silica-Coated Polystyrene Microspheres via Dispersion Polymerization Initiated with Amphoteric Initiator

The positively charged silica-coated polystyrene microspheres are synthesized by dispersion polymerization using an amphoteric initiator, 2,2′-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] (HOOC(CH2)2HN(HN˭)C(CH3)2CN˭NC(CH3)2C(˭NH)NH(CH2)2COOH. The effects of silica addition time and the amount of silica on the polymerization behavior and the properties of the ultimate particles are investigated in terms of the rate of polymerization, morphology, size distribution, and dispersion stability. It is found that the fastest polymerization is achieved when the silica is present at the beginning of the polymerization and the optimum silica content is 12–15 wt% to monomer. Herein, amphoteric polystyrene microspheres stabilized by positively charged silica can be prepared since the silica serves as an inorganic stabilizer providing electrostatic repulsion. Also, the silica promotes the nucleation, that is, generation of growing particles and also accelerates the rate of polymerization.

Significance of the Dispersion Stability of Carbon Nanotubes on the Thermal Conductivity of Nylon 610 Nanocomposite

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.