Combining modelling with experimental techniques in the development of novel (semi)-conducting nanocomposites

Polymer nanocomposites containing carbon nanotubes (NTs) can find applications in a wide variety of fields, owing to the many beneficial properties of carbon NTs such as their very good mechanical characteristics and a high intrinsic conductivity. The latter of these two properties justifies the use of carbon NTs for the preparation of conducting nanocomposites. To achieve good conductive qualities, NTs must form a percolating network, which requires a good dispersion of the NTs. Therefore, specialised techniques are often required, such as the recently developed latex technology, where surfactants are used to form aqueous polymer and nanotube emulsions, which are subsequently mixed, freeze-dried and compression-moulded 1,2. Recently, polydimethylsiloxane (PDMS) was also shown to readily disperse carbon nanotubes after mere high shear mixing 3. Using the double percolation concept, where the nanotubes are restricted to only one phase of a phase separated co-continuous polymer blend, can further aid to lower the percolation threshold and enable the development of novel (semi-)conducting nanocomposites 4.

In this work, first the interaction is modelled between carbon NTs and sodium dodecyl sulphate (SDS) as surfactant and polystyrene (PS) as polymer matrix, i.e. the system obtained when using the abovementioned latex technology. This analysis shows that addition of an extra component, such as low molar mass PS can increase polymer wetting of the NTs within the matrix, improving the electronic properties of the obtained nanocomposite 5. In a second part, the potential use of PDMS and polymethylphenylsiloxane (PMPS) in blends with PS as a matrix for novel conducting carbon NT nanocomposites was studied. Due to the large size of systems containing NTs and polymer chains, the semi-empirical AM1 method was chosen for modelling purposes. Theoretical results were compared to experimental analysis with modulated temperature differential scanning calorimetry (MTDSC), rheometry, conductivity measurements, atomic force microscopy (AFM) and scanning electron microscopy (SEM). With regard to pure PDMS and PMPS, the experimentally obtained results indicated good NT dispersion, behaviour that was not seen before for PMPS. Rheology and conductivity measurements indicate the formation of a percolating network. AM1 calculations indicate that while the PS/PDMS system is immiscible, which is well-known, the PS/PMPS shows interactions that may lead to miscibility. The partially miscible nature of this system was confirmed with MTDSC, SEM and AFM. The partial miscibility of PS and PMPS was not studied before, and together with the ability of PMPS to disperse NTs easily, may lead to new (semi-)conducting siloxane-based carbon NT nanocomposites.

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