Atomic force microscopy of structures produced by electrospraying polymer solutions

Solutions of synthetic [poly(ethylene oxides), polyvinylpyrrolidone, polyacrylamide, and poly(vinylalcohol)] and natural linear polymers (single- and double-strand DNA) have been electrosprayed onto mica surface and imaged with an atomic force microscope. Depending on the electrospray ionization (ESI) conditions (concentration, solvent, sign of ion charge) each polymer studied could be imaged as globular or fibrillar forms. Globules were observed after electrospray (ES) of dilute solutions such as are routinely used in mass spectroscopy studies of polymers. An increase in the polymer concentration resulted in formation of larger multimolecular globular clusters, then extended fibers, presumably consisting of single (0.2-0.5 nm high) and multiple (>0.6 nm high) polymer strands. Further increase in the polymer concentration produced complex structures including branched fibers, "pins," and "beads-on-a-string." Formation of these structures is discussed in terms of known mechanisms of ESI.