Molecular Beams of Macroions. II

Abstract

Using the electrospray technique and nozzle–skimmer system previously described, the influence of polystyrene concentration in the sprayed solution on the magnitude and substructure of the macroion current in the molecular beam has been investigated. Other variables studied include polarity of the beam, needle–nozzle and nozzle–skimmer distances, shape of spray, etc. Attempts to produce isolated macroions in the beam by carrier gas atomization were not successful; operation at reduced pressures and elevated temperatures was not found to be advantageous. In the case of positive macroions the current–repeller-voltage curves had less substructure than in the case of negative beams, and the first stopping potential was more dependent upon the solution concentration, especially when using a relatively large nozzle–skimmer distance. For molecular weights of the polystyrene from 600 to 97 200 the relative macroion positive charge was roughly proportional to the surface area of the macroions, assuming the latter to be spheres and as calculated from the first measured stopping potential. In the case of negative beams the current at zero repeller voltage and at a solution concentration of 2.2 × 10−6 Mw was proportional to the third power of the molecular weight at the lower solute molecular weights, as is predicted for a diffusional charging process.

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Affiliated Institutions

• Northwestern University US

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