Internal structure, hygroscopic and reactive properties of mixed sodium methanesulfonate-sodium chloride particles

• DOI: 10.1039/c1cp20444k
• Publication Date: 2011-05-14T08:30:37Z
• Authors: Y. Liu; B. Minofar; Y. Desyaterik; E. Dames; Z. Zhu; J. P. Cain; R. J. Hopkins; M. K. Gilles; H. Wang; P. Jungwirth; A. Laskin
• Keywords: Mesylates; Kinetics; Surface Tension; Molecular Dynamics Simulation; Sodium Chloride; Nitric Acid; 01 natural sciences; 0104 chemical sciences

Internal structures, hygroscopic properties and heterogeneous reactivity of mixed CH(3)SO(3)Na/NaCl particles were investigated using a combination of computer modeling and experimental approaches. Surfactant properties of CH(3)SO(3)(-) ions and their surface accumulation in wet, deliquesced particles were assessed using molecular dynamics (MD) simulations and surface tension measurements. Internal structures of dry CH(3)SO(3)Na/NaCl particles were investigated using scanning electron microscopy (SEM) assisted with X-ray microanalysis mapping, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The combination of these techniques shows that dry CH(3)SO(3)Na/NaCl particles are composed of a NaCl core surrounded by a CH(3)SO(3)Na shell. Hygroscopic growth, deliquescence and efflorescence phase transitions of mixed CH(3)SO(3)Na/NaCl particles were determined and compared to those of pure NaCl particles. These results indicate that particles undergo a two step deliquescence transition: first at ∼69% relative humidity (RH) the CH(3)SO(3)Na shell takes up water, and then at ∼75% RH the NaCl core deliquesces. Reactive uptake coefficients for the particle-HNO(3) heterogeneous reaction were determined at different CH(3)SO(3)Na/NaCl mixing ratios and RH. The net reaction probability decreased notably with increasing CH(3)SO(3)Na and at lower RH.