Aggregation Kinetics of Colloidal Particles Measured by Gas-Phase Differential Mobility Analysis
De-Hao Tsai1, Leonard F. Pease III2, Rebecca A. Zangmeister2, Michael J. Tarlov2, and Michael Zachariah1. (1) University of Maryland and NIST, College Park, MD 20742, (2) National Institute of Standards and Technology, Gaithersburg, MD 20899
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 was determined. The latter enabled 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 to quantitatively probe the early stages of colloidal aggregation or as a preparatory tool for size election of aggregates.