Nanodiamond-polymer composites

Ioannis Neitzel

doi:10.17918/etd-3987

Due to their favorable strength to weight ratio and low friction coefficients, polymer composite materials find numerous applications in structural, tribological, biomedical, sports and other industries. A nanocomposite by definition contains a filler smaller than 100 nm in one of its dimensions. At these small length scales, the specific surface area becomes large and polymer-filler interactions become increasingly important, changing polymer properties in the vicinity of the surface and forming a new phase called the "interphase". Tailoring the properties of the interphase holds the greatest potential for obtaining new or improved properties. The small 5 nm diameter of detonation nanodiamond (ND) particles, in combination with their superior mechanical properties (diamond properties) and rich surface chemistry, makes ND an optimal candidate for reinforcing polymer matrices. However, previous studies on polymer-ND composites are controversial: both significant increases and decreases in properties were reported. Reasons for these discrepancies are unclear, while understanding reinforcing mechanisms is true key for further progress in this field. Reinforcing effects of ND on polymers were systematically studied on various polymer matrices in this work. For thermosetting polymers, the effects of as-received and functionalized (aminated) ND-NH2 on the mechanical and tribological properties were investigated and demonstrated the advantages of covalent incorporation of ND into the structure of epoxy, resulting in a strong nanofiller-matrix interface. Multifunctional composites can be designed as well: in the case of an epoxy matrix, ultimate mechanical reinforcement was achieved by using high loadings of ND powder, along with an increased thermal conductivity and reduced friction coefficients. To reinforce a thermoplastic biodegradable polymer, poly(L-lactic) acid (PLLA), ND's surface was hydrophobized by grafting octadecylamine to match this hydrophobic polymer, resulting in an improved dispersion of ND in the matrix and better mechanical properties, along with biocompatibility and fluorescence. Several complementary mechanical characterization techniques including pin-on-disk, nanoindentation, Vickers, tensile, compression and AFM test were used to study the reinforcing mechanisms of ND. Results were compared with computer models. This research provides new insights in the reinforcing mechanisms of ND in polymer matrices. The findings allow for a new design of polymer nanocomposites, showing the potential of nanocomposites and suggest that further research efforts must focus on the uniform dispersion and de-agglomeration of ND in polymer matrices.

Nanodiamond-polymer composites

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Nanodiamond-polymer composites

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