title: Surface Potential of DPPC Monolayers on Concentrated Aqueous Salt Solutions.
abstract: The presence and exchange of electrical charges on the surfaces of marine aerosols influence their ability to act as cloud condensation nuclei and play a role in thundercloud electrification. Although interactions exist between surface-active inorganic ions and organic compounds, their role in surface charging of marine aerosols is not well understood. In this study, the surface potential of dipalmitoylphosphatidylcholine (DPPC) monolayers, a zwitterionic phospholipid found in the sea surface microlayer, is measured on concentrated (0.3-2.0 M) chloride salt solutions containing marine-relevant cations (Na(+), K(+), Mg(2+), Ca(2+)) to model and elucidate the electrical properties of organic-covered marine aerosols. Monovalent cations show only a weak effect on the surface potential of DPPC monolayers in the condensed phase compared to water. In contrast, Mg(2+) and Ca(2+) increase the surface potential, indicating different cation binding modes and affinities for the PC headgroup. Moreover, it is found that for divalent chloride salt solutions, the PC headgroup and interfacial water molecules make the largest dipolar contribution to the surface potential. This study shows that for equal charge concentrations, divalent cations impact surface potential of DPPC monolayers more strongly than monovalents likely through changes in the PC headgroup orientation induced by their complexation along with the lesser ordering of interfacial water molecules caused by phosphate group charge screening.
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Clayton B
authors.initials: CB
authors.lastname: Casper
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Dominique
authors.initials: D
authors.lastname: Verreault
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Adams
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Wei
authors.initials: W
authors.lastname: Hua
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors.forename: Heather C
authors.initials: HC
authors.lastname: Allen