| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 99 === The objectives of this research are the preparation and characterization of multiwalled carbon nanotubes (MWCNTs), functionalized MWCNTs, graphene, and functionalized graphene/epoxy nanocomposite for application to the thermal interfacial materials.
There are four parts in this dissertation.
The first part of this dissertation investigates the functionalized multi-walled carbon nanotubes (MWCNTs) which are used as cross-links between MWCNTs-epxoy interfaces to achieve homogeneous dispersion and strong interfacial bonding for developing fully integrated MWCNTs-epoxy nanocomposites. The monomer of glycidyl methacrylate (GMA) was grafted onto MWCNTs by free radical polymerization, and various grafted GMA quantities of functionalized MWCNTs by different compositions were obtained. In the GMA-MWCNTs/epoxy nanocomposites, GMA-MWCNTs can react with epoxy and becomes part of the cross-linked structure, rather than just a separate component. It was found that GMA-MWCNTs exhibited better dispersion in the epoxy matrix than that of pristine MWCNTs. The low grafted GMA quantity (7wt% organic compound on MWCNTs was obtained by TGA) of functionalized MWCNTs possesses better dispersion than that of higher grafted GMA quantity (8.2wt% organic compound on MWCNTs which was investigated by TGA) of functionalized MWCNTs. Moreover, results demonstrate that the thermal conductive property of the epoxy nanocomposite was improved dramatically, especially, adding low grafted quantity of functionalized MWCNTs. The thermal conductivity of MWCNTs/epoxy is increased from 0.19W/mK to 0.43W/mK, exhibiting 115 % improvement and the thermal interfacial resistance of nanocomposites is reduced from 0.51 to 0.16.
The second part of this dissertation studies a novel technology of the MWCNT interfacial insulation, to modify MWCNTs for uses in optical and semiconductor industry, which requires electrical insulation of the devices. The carboxylic functional group on the sidewalls of the acid oxidation MWCNTs will enhance the dispersion of MWCNTs in the epoxy matrix uniformly. For coating alumina nanolayer on the individual MWCNTs continuously, acid oxidized MWCNTs were reacted with 3-aminopropyl-triethoxysilane to generate siloxane functional group, which could enhance the chemisorption of MWCNTs with alumina precursor. The molecular interaction between the silane functionalized MWCNTs and alumina via sol-gol process was utilized to form alumina coated silane modified MWCNTs (Al2O3@SA-MWCNTs). The electrical resistivity and thermal conductivity of nanocomposites were investigated.
The volume electrical resistivity of Al2O3@SA-MWCNTs/epoxy composites can maintain the value of 5.2x1010 ohm*cm by adding 1phr Al2O3@SG-MWCNTs. However, a significant improvement on the thermal conductivity of Al2O3@SG-MWCNTs/epoxy composites, from 0.19W/mK to 0.45W/mK (enhanced 137%) can be achieved by adding 1phr Al2O3@SG-MWCNTs.
The third part of this dissertation investigates the synergistic effect of combining multi-walled carbon nanotubes (MWCNTs) and boron nitride (BN) flakes or aluminum nitride (AlN) particles on thermally conductive epoxy composite. The surfaces of these two fillers were functionalized to form covalent bonds between the epoxy and filler, thereby reducing thermal interfacial resistance. Results show that functionalized fillers improve the thermal conductivity of epoxy composites, due to the good dispersion and wettability. Furthermore, the hybrid fillers provide synergistic effect on heat conductive networks. The thermal conductivity of epoxy composites containing 25 vol% modified AlN and 1 vol% functionalized MWCNTs (1.21W/mK) is comparable to that of epoxy composites containing 50 vol% untreated AlN (1.25 W/mK). The thermal conductivity of epoxy composites containing 30 vol% modified BN and 1 vol% functionalized MWCNTs (1.91W/mK) is comparable to that of epoxy composites containing 40 vol% untreated BN (1.82 W/mK).
The fourth part of this dissertation studies the preparation and the indentification of graphene. Non-covalent functionalization was used to functionalize graphene nanosheets (GNSs) through π-π stacking of pyrene molecules with a functional segmented polymer chain, which results in a remarkable improvement on the thermal conductivity of GNS-filled polymer composites. The functional segmented poly(glycidyl methacrylate, PGMA) containing localized pyrene groups (Py-PGMA) was prepared by atom transfer radical polymerization(ATRP). The Py-PGMA on the GNS surface not only plays an important role to facilitate a homogeneous dispersion in the polymer matrix but also improve the GNS-polymer interaction, which results in a high contact area. Consequently, the thermal conductivity of integrated Py-PGMA-GNS/epoxy composites exhibited a remarkable improvement which is much higher than epoxy reinforced by multi-walled carbon nanotubes or GNSs. The thermal conductivity of 4phr Py-PGMA-GNS/epoxy is about 20% higher than that of pristine GNS/epoxy and 267% higher than that of pristine MWCNT/epoxy.
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