Characterisation of the surface composition in electrospun nanowebs with static secondary ion mass spectrometry (S-SIMS)

Electrospinning is a recently rediscovered method to produce non-woven nanowebs of which the individual polymer fibres have diameters of 50-500 nm. Applications require specific functionalities to be present at the surface. The use of additives in the electrospun solution provides an elegant alternative to functionalised polymers. This study has focused on the use of the static secondary ion mass spectrometry (S-SIMS) to characterise the surface composition of nanofibres electrospun from acetone solutions containing 15% (w/w) of poly(?-caprolactone) (PCL, molecular weight 40,000) and 0-15 mol% (relative to PCL) cetyltrimethylammonium bromide (CTAB). Specifically, the calibration of the relative signal intensities of structural ions from PCL and CTAB as a function of the local concentrations requires adequate reference samples to be prepared. In general, this step becomes a major bottleneck in nanoscale analysis. A relatively simple method using a combination of spincoating and hand barcoating of solutions has been developed. Its applicability and limitations for monitoring the surface enrichment of CTAB in PCL nanowebs are discussed.