Chain extension in electrospun polystyrene fibres: a SANS study

Small angle neutron scattering techniques were used to quantify the size and shape of the chain conformation in electrospun fibres of atactic polystyrene prepared from solutions in methyl ethyl ketone. Aligned arrays of fibres were collected onto a rotating collector with tangential velocity varying between 0 ms(-1) and similar to 15 ms(-1). The measured radii of gyration of the polystyrene chains were found to be slightly higher than that expected for samples prepared from solutions in the concentrated regime. The ratio of the radius of gyration parallel and perpendicular to the chain axis was found to be similar to 1.05 in contrast to the substantial macroscopic shape transformation intrinsic to electrospinning. When the tangential velocity of the rotating collector was greater than the flight velocity of the fibres (ca. 4 ms(-1)), a further extension of the polymer chains was observed with a ratio of the radii of gyration increasing to 1.20 at the highest collector speeds. It is proposed that the heterogeneous processes involved, particularly solvent evaporation and the formation of a polymer skin during electrospinning play a significant role in determining the level of molecular anisotropy in the fibres.