ATOMIC-FORCE MICROSCOPY OF STRUCTURES PRODUCED BY ELECTROSPRAYING POLYMER-SOLUTIONS

Solutions of synthetic [poly(ethylene oxides), polyvinylpyrrolidone, p olyacrylamide, and poly(vinylalcohol)] and natural linear polymers (si ngle- and double-strand DNA) have been electrosprayed onto mica surfac e and imaged with an atomic force microscope. Depending on the electro spray 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 solut ions such as are routinely used in mass spectroscopy studies of polyme rs. An increase in the polymer concentration resulted in formation of larger multimolecular globular clusters, then extended fibers, presuma bly consisting of single (0.2-0.5 nm high) and multiple (>0.6 nm high) polymer strands. Further increase in the polymer concentration produc ed complex structures including branched fibers, ''pins,'' and ''beads -on-a-string,'' Form ation of these structures is discussed in terms o f known mechanisms of ESI. (Int J Mass Spectrom 178 (1998) 143-159) (C ) 1998 Elsevier Science B.V.