Abstract
The objectives of this research are the preparation and characterization of poymer composite for the use in thermal interfacial materials (TIM). There are three parts in this study. The first part of this research is to develope the surface coating technologies for using these MWCNTs to template the assembly of silica and alumina nanoparticle. At first, the functionalized multi-walled carbon nanotubes (MWCNTs) were prepared via Friedle-Crafts acylation with Benzenetricarboxylic acid and Gallic acid. Raman spectra and X-ray photoelectron spectroscope (XPS) were utilized to characterize the functionalization of MWCNT.Thermogravimetric analysis (TGA) was used to calculate the organic contents of Benzenetricarboxylic acid and Gallic acid grafted MWCNT (BTC-MWNT and GA-MWCNT), which were 20.1wt% and 7.03wt%, respectively. Second, silane functionalized BTC-MWCNT and GA-MWCNT were prepared via amidation with (3-isocyanatopropyl) triethoxysilane. Raman spectra and X-ray photoelectron spectroscope (XPS) were utilized to characterize the functionalization of MWCNT. The ICPES-BTC-MWCNT and ICPES-GA-MWCNT were utilized as the nano-catchers for inorganic nanoparticles by the covalent incorporation between the silane functionalized MWCNTs and inorganic nanoparticles. The nano silica layer and nano alumina layer coated on the surface of MWCNTs can prohibit the conductive path of electrons. This part intends to investigate (1)the effect of functionalization on the structure of the MWCNTs by Friedel-Crafts modification；(2)the difference in the reactivity of functional groups on the surfaces of MWCNTs affect the morphology of inorganic nanoparticles coated on the MWCNTs；(3)the electrical properties and dispersion of inorganic nanolayer coated the MWCNTs. The ID/IG area ratio of prinstine-MWCNTs, acid treated MWCNTs, BTC-MWCNTs and GA-MWCNTs are 1.08, 1.29, 1.12 and 1.09, respectively. The ID/IG values of BTC-MWCNTs and GA-MWCNTs indicate this modification will functionalize the MWCNTs with slightly or no damage on the structure of MWCNTs. The morphology of inorganic nonoparticles coated on the surface of MWCNTs can be observed by TEM. The coating thickness of SiO2@BTC-MWCNT and Al2O3@BTC-MWCNT are about 7~20nm. The morphology exhibits partially continuous coating, and the silica layer is more smooth than alumina layer. The coating thickness of SiO2@GA-MWCNT and Al2O3@GA-MWCNT are about 5~15nm and the morphology exhibits more continuous coating than those of BTC-MWCNT series. The volume resistivities of SiO2@BTC-MWCNT and Al2O3@BTC-MWCNT increased 106Ω*cm comparising with prinstine-MWCNT (4.71Ω*cm). The volume resistivities of SiO2@GA-MWCNT and Al2O3@GA-MWCNT increased 108Ω*cm comparising with prinstine-MWCNT. Results confirm that the nano silica layer and nano alumina layer coated on the surface of MWCNTs can prohibit the electrical conductive path effectively. The second part of this research discusses the preparation and characteration of functionalized MWCNTs/epoxy composites. This study investigates the electrical property, dielectrical property, thermal property and thermal conductivity of nanocomposites with various contents of MWCNTs in epoxy matrix. The nanocomposite was prepared with 5phr Al2O3@MWCNTs. The volume resistivity and dielectrical constant of the Al2O3@MWCNTs/epoxy composite were 1.29*1014~5.78*1015Ω*cm and 3.72~4.56, respectively. The glass state CTE α1(coefficient of thermal expansion) and rubber state CTE of the Al2O3@MWCNTs/epoxy composite was decreased from 66.44 ppm/oC to 52.5~45.1ppm/oC (decreased 21~32%) and was decreased from 253.1 ppm/oC to 215~201.1 ppm/oC (decreased 15~20.5%), respectively. The thermal conductivity of the Al2O3@MWCNTs/epoxy composite was increased from 0.13 W/mK to 1.01~1.1W/mK (increased 677~746%). The third part of this research illustrates the preparation and characterization of functionalized MWCNTs/ alumina/ epoxy composites. This study investigates the electrical property, dielectrical property, thermal property and thermal conductivity of the hybrid composites with nano and micro fillers. The hybrid composite was prepared with 5phr Al2O3@MWCNTs、20Vol% alumina and 80Vol% epoxy matrix. The volume resistivity and dielectrical constant of the Al2O3/Al2O3@MWCNTs/epoxy composite were 8.4723*1013~2.1991*1015Ω*cm and 4.41~4.69, respectively. The glass state CTE (coefficient of thermal expansion) and rubber state CTE of the Al2O3@MWCNTs/epoxy composite decreased from 50.16 ppm/oC to 40.27~40.58ppm/oC (decreased 21~32%) and decreased from 201.4 ppm/oC to 143~162.7 ppm/oC (decreased 19~29%), respectively. The thermal conductivity of the Al2O3@MWCNTs/epoxy composite increased from 0.13 W/mK to 1.52~1.95W/mK (increased 1069~1400%). The enhancement of thermal conductivity of hybrid composite was more significant comparising with 60Vol% alumina/ epoxy composite (1.58 W/mK). The overall performance of hybrid composite with nano and micro fillers exhibited sinficant improvement.