10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


The Development and Characterization of a “Store and Create” Microfluidic Device to Study Ice Nucleation Particles

THOMAS BRUBAKER, Michael Polen, Leif Jahn, Perry Cheng, Vinay Ekambaram, Shelley Anna, Ryan Sullivan, Carnegie Mellon University

     Abstract Number: 782
     Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds

Abstract
Characterization of heterogeneous ice nucleation by ice nucleating particles (INPs) is hindered by the analytical challenge of accurately determining the freezing temperature spectrum and atmospheric concentration of these rare one-in-a-million ice nucleating particles (INPs). We have developed a microfluidic device interfaced with our cold plate system with a greatly improved background homogeneous freezing background signal from pure water droplets compared to droplets on a substrate methods. The lower consistent background freezing temperature spectrum enables measurements of weaker but often more abundant INPs that induce freezing near -30 °C, such as found in biomass burning aerosol. We used soft lithography techniques to fabricate our microfluidic device from PDMS. A “store and create” method is used to form and trap an array of uniformly sized droplets. The aqueous droplets have minimal surface interactions with the rigid device since the surfactant-less oil preferentially coats the hydrophobic walls, ensuring the droplets do not contact the polymer surface. Our homogeneous background freezing signal has a median freezing temperature of T50=-33.88± 0.46 °C. The freezing of the droplets was imaged on a gold-plated silicon wafer using reflectance microscopy. An automated script analyzes the images producing the frozen fraction curves and size distribution of our droplets. We characterized our system using SnoMax, illite, Arizona test dust particles, pure water, aged and fresh biomass burning aerosol, and commercially available 100 nm metal oxide nanoparticles. The metal oxide nanoparticle’s near-monodispersed surface properties enable us to begin decoupling different ice nucleation pathways and study INP behavior in a systematic fashion.