Polymer Brush Carbon Nanotubes as Nanofillers in Macro and Nano Size Composites

Author: Tony John Aitchison

Aitchison, Tony John, 2011 Polymer Brush Carbon Nanotubes as Nanofillers in Macro and Nano Size Composites, Flinders University, School of Chemical and Physical Sciences

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The work outlined in this thesis covers the many aspects of carbon nanotubes and polymers by combining the two into nanocomposite materials of macro and nano size. The issues of producing and combining the two are explored and results are provided. There are four major aspects to this work; 1. Polymer Brushed Carbon Nanotubes: multi-walled carbon nanotubes (MWCNT) are surface functionalized with polymer brushes produced by activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). A 'grafting from' approach was used as a higher grafting density would result and therefore it was necessary to functionalize the carbon nanotubes surface with hydroxyethyl-2-bromoisobutyrate (HEBI). This acted as the haloalkane (i.e. tertiary bromide) initiator sites in ARGET ATRP of styrene and methyl methacrylate. The successful growth of the polymer brushes were characterized for their chemical, kinetic and physical properties. In addition, polymer brushes of 2-hydroxyethyl methacrylate (HEMA) was grown by non-living means by attaching the HEMA monomer via the hydroxyl group to a carboxylic acid surface functionalized MWCNT and subsequently polymerized. 2. Macro-sized Composites: a composite of carbon nanotubes with homopolymers as the matrix, requires surface modification of the MWCNT to prevent nanotube aggregation. A homogeneous dispersion is necessary in order to produce improved properties for the composite. The 'macro' composite research involved the incorporation of polymer brush carbon nanotubes in concentrations of 0.1w/w% to 1w/w% (e.g. poly(methyl methacrylate) polymer brush carbon nanotubes in a poly(methyl methacrylate) matrix). The most improved composites obtained used polystyrene brushes in a polystyrene matrix, which was due to π-π stacking interactions. The composite material possessed improved mechanical strength, increased glass transition temperature and increased processability. Furthermore, the dispersion was maintained after processing with shear forces. 3. Pyrene as a Model System: 1-pyrenecarboxylic acid has a very similar architecture to MWCNT and for this reason was used to model the chemical synthesis of aspects '1' and '2' with polystyrene. The work showed similar enhancements in terms of mechanical strength, increased glass transition temperature and increased processability. Compared to polystyrene polymer brush carbon nanotubes the improvement was not as great, however the pyrene material did not exhibit limits of dispersion like the carbon nanotubes filler. 4. Nano-sized Composites: This research utilized a hexagonal-packed cylindrical phase of a di-block copolymer melt, in an attempt to align the carbon nanotubes to the cylindrical phase. To ensure their affinity for the cylinder phase, polymer brushes of polystyrene were used for a 30/70 poly(styrene-b-methyl methacrylate) melt. However, the nanotubes were found to disrupt the segregation process, and the phases did not form appropriately. This ultimately did not provide strong enough forces to align the carbon nanotubes, but indicates that because of their relative massive size, greater forces are required. Future work has been recommended with alternative polymer brush carbon nanotubes as fillers and using electric fields, as they have shown to better orientate a hexagonal-packed cylindrical phase from a parallel orientation to a perpendicular orientation. This is a suggested technique that might be able to align the carbon nanotubes.

Keywords: carbon nanotubes,copolymers,thin flims,ATRP,living polymerisation,polymer brushes

Subject: Nanotechnology thesis

Thesis type: Professional Doctorate
Completed: 2011
School: School of Chemical and Physical Sciences
Supervisor: Dr Milena Ginic-Markovic