Direct observation of the spatial distribution of charges on a polypropylene fiber via Electrostatic Force Microscopy

The spatial distribution of electrical charges along the longitudinal axes of a polypropylene electret fiber was determined using Electrostatic Force Microscopy (EFM). EFM mapping on highly curved surfaces, such as those of polymeric fibers, is a challenging endeavour and most work reported in the scientific literature has been limited to single line-scan analysis or flat specimens. Charged polymeric fibers, electrets, are extensively used in high performance filtration applications and methods to determine the amount and magnitude of the charges on these fibers remain elusive. Electrical charge maps of individual fibers were obtained by biasing the tip to -10 V and maintaining a constant tip-sample distance of 100 nm. Spatially dependant EFM phase and magnitude gradients were determined and the developed technique may provide a unique understanding into the heterogeneous charge distribution on electrets fibers. Direct mapping of the charge distribution in electrets fibers can offer new insights in the development of antistatic additives, new means to facilitate electrostatic self-assembly of nano-moieties on the surface of fibrous materials and a quantitative metrics capable of determining discharge dynamics and predicting the shelf-life of filtration media.