title: Aggregation kinetics of colloidal particles measured by gas-phase differential mobility analysis.
abstract: We demonstrate the utility of electrospray gas-phase ion-mobility analysis as a new method to investigate nanoparticle flocculation, or aggregation. Au nanoparticle (Au-NP) solutions were sampled via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the particle mobility distribution. Multimodal size distributions obtained with ES-DMA indicated the presence of single Au-NPs (monomer) as well as larger Au-NP clusters such as dimers, trimers, and tetramers under specific solution conditions. The fraction of each aggregate species as a function of time was quantitatively characterized, from which the degree of aggregation, aggregation rate, and stability ratio at different ionic strengths were determined. The latter enabled the extraction of a surface potential (or surface charge density) of 64 +/- 2 mV for 10 nm Au-NPs, which is in good agreement with values obtained from other methods, thus validating our approach. Our results show that ES-DMA is a valuable tool for quantitatively probing the early stages of colloidal aggregation or as a preparatory tool for the size election of aggregates.
authors.affiliation: Department of Chemistry and Biochemistry and Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: D-H
authors.initials: DH
authors.lastname: Tsai
authors.forename: L F
authors.initials: LF
authors.lastname: Pease
authors.forename: R A
authors.initials: RA
authors.lastname: Zangmeister
authors.forename: M J
authors.initials: MJ
authors.lastname: Tarlov
authors.forename: M R
authors.initials: MR
authors.lastname: Zachariah