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R. Lach, W. Grellmann, G. M. Kim, G. H. Michler:
"Indentation Methods for Characterising the Mechanical and Fracture Behaviour of Polymer Nanocomposites";
Talk: Chemical Congress 2008: Chemistry for Sustainable Development, Kathmandu (invited); 2008-05-23 - 2008-05-25; in: "Chemical Congress 2008: Chemistry for Sustainable Deveiopment", Nepal Chemical Society, Kathmandu (2008), ISBN: 978-9937-2-0535-1; 76.

Recent trends in materials research, process optimization and components development using nanostructured polymers such as block copolymers and polymer nanocomposites which are often only available with small volume of samples necessitate advanced testing procedures. In this context modern indentation methods are very advantageous compared with other approaches for characterising the mechanical performance and the fracture safety of these materials, structures and components.

Morphological analyses of nanocomposites based on polyurethanes (TPU) and polyhedral oligomeric silsesquioxanes (POSS) were performed using different techniques (transmission electron microscopy, small and wide X-ray scattering, differential scanning calometry) as a function of molecular weight of polyethylene glycol (PEG) and the PEG/POSS mol ratio. A strong interdependence in crystallisation behaviour between the two crystals specifies, i.e. the POSS nanocrystals about 5 nm in size and the crystals in the semicrystalline soft phase of TPU, were found. The mechanical properties (Vickers hardness under load and elastic modulus) determined using recording microindentation techniques at room temperature were significantly improved by POSS for two material formulations.

Based on the results from pure PMMA and PMMA/SiO2 nanocomposites containing 10 and 20 wt.-% well-dispersed spherical SiO2 nanoparticles, it has been shown that the indentation fracture mechanics is a powerful tool straightforwardly, cost- and time-effectively to analyze the fracture resistance for the novel polymer materials, such as brittle nanostructured polymer-ceramic hybrids. In contrast to pure PMMA, the R-curve effect, enhancement in crack resistance (R) as a function of crack size, was not observed in the nanocomposites investigated. The fracture toughness was found to be dependent on the content of SiO2 nanoparticles, of which maximum value was observed at 10 wt.-%. A significant reduction in fracture toughness occurred at 20 wt.-% SiO2 nanoparticles, which is associated with a percolation of the bound layers (interfacial layers) around the SiO2 particles. From DSC data, the thickness of the interfacial polymer layer was estimated to be about 9 nm. In situ mechanical investigations of thin films using transmission electron microscopy confirm the semiductile-to-brittle transition.

Recent trends in materials research, process optimization and components development using nanostructured polymers such as block copolymers and polymer nanocomposites which are often only available with small volume of samples necessitate advanced testing procedures. In this context modern indentation methods are very advantageous compared with other approaches for characterising the mechanical performance and the fracture safety of these materials, structures and components.

Morphological analyses of nanocomposites based on polyurethanes (TPU) and polyhedral oligomeric silsesquioxanes (POSS) were performed using different techniques (transmission electron microscopy, small and wide X-ray scattering, differential scanning calometry) as a function of molecular weight of polyethylene glycol (PEG) and the PEG/POSS mol ratio. A strong interdependence in crystallisation behaviour between the two crystals specifies, i.e. the POSS nanocrystals about 5 nm in size and the crystals in the semicrystalline soft phase of TPU, were found. The mechanical properties (Vickers hardness under load and elastic modulus) determined using recording microindentation techniques at room temperature were significantly improved by POSS for two material formulations.

Based on the results from pure PMMA and PMMA/SiO2 nanocomposites containing 10 and 20 wt.-% well-dispersed spherical SiO2 nanoparticles, it has been shown that the indentation fracture mechanics is a powerful tool straightforwardly, cost- and time-effectively to analyze the fracture resistance for the novel polymer materials, such as brittle nanostructured polymer-ceramic hybrids. In contrast to pure PMMA, the R-curve effect, enhancement in crack resistance (R) as a function of crack size, was not observed in the nanocomposites investigated. The fracture toughness was found to be dependent on the content of SiO2 nanoparticles, of which maximum value was observed at 10 wt.-%. A significant reduction in fracture toughness occurred at 20 wt.-% SiO2 nanoparticles, which is associated with a percolation of the bound layers (interfacial layers) around the SiO2 particles. From DSC data, the thickness of the interfacial polymer layer was estimated to be about 9 nm. In situ mechanical investigations of thin films using transmission electron microscopy confirm the semiductile-to-brittle transition.