Korea-Australia Rheology Journal December 2010 Vol. 22, No. 4 259 Korea-Australia Rheology Journal Vol. 22, No. 4, December 2010 pp. 259-264 Interphase control of boron nitride/epoxy composites for high thermal conductivity Jung-Pyo Hong 1 , Sung-Woon Yoon 1 , Tae-Sun Hwang 1 , Young-kwan Lee 2 , Sung-Ho Won 3 and Jae-Do Nam 4, * 1 Department of Polymer Science and Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Korea 2 Department of Applied Chemistry, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Korea 3 Department of Applied Chemistry, Dongyang Technical college 62-160 Kochuk-dong, Seoul 152-714, Korea 4 Department of Energy Science, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, South Korea (Received April 8, 2010; final revision received July 26, 2010; accepted July 29, 2010) Abstract The effects of the surface treatment of boron nitride (BN) particles on the thermal conductivity of BN/epoxy composite systems was investigated. By coating an amino silane compatibilizer on the BN surface, the interfacial space could be decreased so as to minimize the phonon scattering and thermal-interface resis- tance. When an excessive amount of silane compatibilizer was present at the BN/epoxy interphase bound- ary, it acted as a thermal insulation layer, resulting in the reduction of the thermal conductivity. Accordingly, the thermal conductivity was maximized when the optimal amount of silane compatibilizer was used, which was associated with the specific surface area or the size of the incorporated BN particles. In the case of the BN particles, whose specific surface areas were 14.3 m 2 /g and 11 m 2 /g (average particle size: 1 μm and 5 μm, respectively), the highest thermal conductivity was observed at 3.0 wt% and 2.5 wt% of the silane compatibilizer, respectively. By converting the particle size and specific surface area into the shape factor, the optimal amount of amino silane required to maximize the thermal conductivity was discussed in relation with the interphase structure and thermal resistance. Keywords : thermal conductivity, silane treatment, boron nitride 1. Introduction Boron nitride (BN) has a similar plate structure to graphite and thus superior thermal conductivity, but it is a noncon- ductor of electricity(Yung and Liem, 2007). BN has been stud- ied extensively as a filler to improve the thermal conductivity of a variety of polymer-based composite systems, most often in epoxy composite systems, which are applied to the pack- aging of electronic parts such as PCBs and EMCs(Lee et al ., 2006; Nagai and Lai, 1997; Yung et al ., 2006). On the other hand, heat transfer is restricted by phonon- scattering at the matrix-filler interface(Berman,1973). As the loading content of the filler is increased, the polymer- filler interfacial area increases, which subsequently increases the phonon-scattering. It was found that, in most cases, phonon scattering reduces the amount of heat trans- fer in composite material systems(Ishida and Rimdusit, 1998). Consequently, if the interfacial adhesion is not good and, thus, the extent of phonon scattering is significant in composites, the highly-conductive fillers may decrease the thermal conductivity with increasing filler-loading content. In addition, when the particles have different sizes, the numbers of interfaces along the path through which heat is transferred varies; therefore, composite materials with the same filler content have different values of the thermal conductivity(Nagai and Lai, 1997; Yung et al., 2007; Hsieh and Chung, 2006). In short, composite materials have dif- ferent thermal conductivities depending on the size or load- ing content of the particles, characteristics of the interfaces, or relative thermal conductivities of the particles and resin. The surface treatment of fillers is widely known to be an important factor for reducing the thermal resistance of the interfaces between the polymer and filler. Surface modi- fication using silane in particular is the most widely known method. Based on the results of research on the surface treatment of particles using silanes, it is known that surface treatment can indeed play an important role in reducing the thermal resistance between the filler and polymer depend- ing on the amount of silane; note, however, that the thermal conductivity may be reduced when an excessive amount of silane is used (Hsieh and Chung, 2006; Xu and Chung, 2000; Xie et al., 2004). In other words, using silane may initially increase the thermal conductivity, since it lowers *Corresponding author: jdnam@skku.edu © 2010 by The Korean Society of Rheology