Sacha Noimark, March 2015: Further work on developing new coating strategies for laser generated ultrasound and optimisation of MWCNT coatings

• Functionalise MWCNTs for dispersion in aqueous solutions. Used CTAB and extensive sonication – optimised MWCNT at 1 mg/mL.
• Electrospin CTAB-functionalised MWCNTs/ PEO solutions – optimised and achieved thick mesh. Route for alignment of MWCNTs within fibres – fibre diameter < 0.5 micron, MWCNT length 5 micron. Next step to align CTAB-functionalised MWCNT/PEO fibres themselves such that MWCNTs aligned within aligned fibres. Achieve good alignment but films very thin and not very absorbing. Need to optimise experimental setup (use of motor).
• Collaboration with Manchester University – NMP dispersed graphene. Aim to develop graphene-PDMS coatings for laser-generated ultrasound – compare efficiency with MWCNT coatings).
• Extensive attempts to deposit graphene as film on planar substrate. Key issue is that NMP solvent has very high boiling point and therefore evaporates very slowly at RT (>days) – dip coating which proves effective for fMWCNT/xylene, is not an option here. Can form uneven graphene films on glass substrate using drop casting deposition technique, with solvent evaporation at high temperature (ca. 200 ºC), however, this may not be suitable for translation onto optical fibres. Further attempts included deposition onto painted glass substrate and swell-encapsulation into PDMS. The former resulted in patchy graphene films and the latter did not work. Swell-encapsulation into a rubber band – as described in the literature – worked, although at this stage not useful for project. Further discussion with collaborators necessary.
• Optimise fMWCNT solution as ink for printing.
• Collaboration with Liverpool university – inkjet printing using fMWCNT ink developed for printing onto planar substrates, with a view to print directly onto optical fibres as an alternative coating deposition strategy. Prepared series of inks and polymers and visited their inkjet printing labs. Successfully printed fMWCNTs; 10 x 10 arrays, with multiple passes. Printing needs further optimisation of wave formula. Left inks at Liverpool for further optimisation.
• Laser-generated ultrasound study #2: 200 micron fibres: MWCNT (1 dip) x 4 fibres, MWCNT (2 dip) x 4 fibres with paint overcoat, MWCNT (1 dip) x 4 fibres, MWCNT (2 dip) x 4 fibres with PDMS overcoat compared to previous integrated fibres. Bilayer MWCNT+PDMS fibre coating results in enhanced ultrasound pressures and wider bandwidth spectra.
• Characterisation: UV Vis (absorption and transmission measurements), Optical microscopy (stereo microscope), Scanning electron microscopy.
• SEM shows evidence of PDMS infiltration through dense nanotube mesh.

 

Sacha Noimark