AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Shape and Structure of Alkane+CO2 Multicomponent Particles from FTIR Measurements
YENSIL PARK, Ruth Signorell, Barbara Wyslouzil, The Ohio State University
Abstract Number: 598 Working Group: Aerosol Physics
Abstract The shape and structure of particles can affect their growth as well as their aerodynamic and optical properties. When the particles are comprised of small molecules with relatively strong transition dipoles (> ~0.1 D), the shape and structure of the particles can affect the shape of the IR spectra. A specific example is the antisymmetric stretching vibration of CO2. Here, we investigate the structure of multicomponent nanoparticles comprised of n-alkane and CO2. The particles are formed by homogeneous and heterogeneous condensation in a supersonic Laval nozzle. In total, two different n-alkanes, pentane and hexane, were investigated at three different flow rate conditions (LF, MF, and HF) with ~12 % of CO2 and the carrier gas, Ar. The particles and the gas mixture were characterized using pressure trace measurements (PTM), small angle x-ray scattering (SAXS), and Fourier transform infrared spectroscopy (FTIR), and based on an integrated analysis of the experimental results, a few possible shapes and structures were determined. Exciton calculations were then performed to confirm and refine these structures. For the LFC5+CO2 and MFC5+CO2 conditions, experimental IR spectra suggest a core-shell structure where the core is the mixture of pentane and CO2 and the shell is pure CO2. For the LFC6+CO2 and MFC6+CO2 cases, both lens-on-sphere and core-shell are possible. The former corresponds to a hexane lens on a truncated cube shaped CO2 “sphere”, and the latter corresponds to a hexane core and thick CO2 shell. The shape of the IR spectra in the HFC6+CO2 case is quite different from the other cases, and is most consistent with elongated CO2 domains on the hexane particles.