Linear and non-linear viscoelastic rheology of hybrid nanostructured materials from block copolymers with gold nanoparticles |
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Authors: | Cesar Mendoza Nabil Gindy Manfred Wilhelm Amir Fahmi |
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Institution: | 1.School of Mechanical, Materials and Manufacturing Engineering,The University of Nottingham,Nottingham,UK;2.Institut für Technische Chemie und Polymerchemie,Karlsruher Institut für Technologie (KIT),Karlsruhe,Germany |
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Abstract: | A polystyrene-b-poly-4-vinypyridine (PS-b-P4VP) diblock copolymer is modified with a gold precursor to obtain an organic–inorganic (hybrid) block copolymer in bulk
with gold nanoparticles selectively incorporated in the P4VP block. In the linear viscoelastic regime, temperature sweep tests
over a series of these hybrid block copolymer systems revealed consistent shifts (ΔT) in the glass transition temperatures (both T
g\text-PS_{\rm g\text{-}PS} and T
g\text-P4VP_{\rm g\text{-}P4VP}) of the hybrid materials in comparison to the pristine polymers. Studying different volume fractions of the pyridine block,
a level-off point was found for block copolymers with f
P4VP > 0.26, where the shifts in T
g\text-P4VP_{\rm g\text{-}P4VP} consistently increased up to ΔT = 25°C. By artificially increasing the volume fraction of the pyridine block, the nanoparticles reduce the transition regime
determined in master curves. At higher volume fractions of the pyridine block, crossover frequencies were not detected after
the entanglement regime, indicating that the material does not relax from topological constraints (entanglements and nanoparticles)
into the terminal regime. Above a specific volume fraction of nanoparticles (Φ
P = 0.05), the flow behaviour of the hybrid materials becomes increasingly elastic, exhibiting wall-slip from the geometry
at lower strain values in comparison to the pristine material. In the non-linear viscoelastic regime, Fourier-transformed
rheology was used to analyse the raw signals from strain sweep experiments. It was clearly demonstrated the nanoparticle effect
by following the second and third harmonic (I
2/1, I
3/1) of the stress response. Comparing the behaviour of the third and second harmonics provided an unambiguous fingerprint for
the effect of the nanoparticles. |
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