engleski

CHARACTERIZATION OF NANOSTRUCTURED COMPOSITE MATERIALS OF POLYMETHACRYLATES AND CARBON NANOTUBES

Composite materials have roused interest due to their advantageous properties when it comes to improved strength, stiffness, etc. Carbon nanotubes are recognized as fillers that can contribute significantly to the improvement of properties of composites. Therefore, in this work polymeric nanocomposite materials were synthesized using various pairs of methacrylic comonomers in different ratios to form polymeric matrices. Also, the multiwalled carbon nanotubes (MWCN) were added in various ratios as fillers. The procedure of introduction of nanotubes was performed ex-situ. The obtained copolymers were characterized with respect to their composition and structure, homogeneity of dispersion of nanotubes in polymeric matrix, dynamical-mechanical properties, as well as state of the surface. The copolymer composition determined by NMR displays a good match between experimental and theoretical values which is due to similar reactivity of comonomers. Dispersion of nanotubes, which is examined using scanning electron microscopy (SEM), shows significant diversity in a wide range of added nanotubes, between 0.1–5 wt.%. Mechanical properties, i.e. phase transition temperatures, storage (E’) and loss (E’’) moduli of pure copolymers as well as of composite materials after the MWCN addition were tested by dynamic mechanical analysis (DMA). The glass transition temperatures (Tg) increased with the decreasing length of methacrylate side chains in methyl methacrylate (MMA) and n-alkyl methacrylate (octadecyl, dodecyl, hexyl methacrylate) (ODMA, DDMA, HMA) copolymers. Additionally, the analogous behavior was seen with increasing portion of long chain methacrylate within the same system, e.g. MMA-ODMA, where an increase of 20 mol.% of ODMA caused the Tg increase of 25 oC. The introduced nanotubes did not significantly influence the Tg values. The Tg shift observed due to filler addition was smaller than the shift due to the change of n-alkyl methacrylate length and amounted only few degrees. Notably, there were some discrepancies attributed to the degree of homogeneity of composite samples. The hydrophobicity of obtained materials was tested by the sessile drop technique. The values of contact angles were mainly greater or close to 90 o from which we concluded that the polymeric samples were slightly hydrophobic. Furthermore, the contact angle increased with increasing amount of long-chain methacrylate characterized with long paraffinic groups that possessed considerable hydrophobicity. After introducing carbon nanotubes in the copolymer samples, the contact angle changed relatively to the pure copolymer ; however, the changes were minimal and did not show any recognizable trend.

nanostructured composite materials; polymethacrylates; carbon nanotubes

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