(375d) Novel Approaches to the Understanding of Hydration Phenomena in Aqueous Electrolytes: Molecular-Based Tools Toward the Interpretation of Challenging Neutron Diffraction Experiments Conference: AIChE Annual MeetingYear: 2015Proceeding: 2015 AIChE Annual MeetingGroup: Engineering Sciences and FundamentalsSession: Thermophysical Properties and Phase Behavior I Time: Tuesday, November 10, 2015 - 1:50pm-2:10pm Authors: Chialvo, A. A., Oak Ridge National Laboratory Vlcek, L., Oak Ridge National Laboratory In this presentation we discuss a novel microstructural analysis of aqueous electrolytes and present a detailed account of crucial issues confronting the interpretation of neutron diffraction with isotopic substitution (NDIS) for the determination of accurate ion coordination numbers in ionic systems involving both halides anions and oxyanions (e.g., nitrates and sulfates) of alkali, alkaline earth, and transition metals. In particular, we address and confront the issues associated with the frequently overlooked ion-pairing phenomenon in the context of the determination of coordination numbers, and examine novel techniques to deal with the degree of ion-pairing and the correction of its effects on the experimentally measured quantities. Finally, we provide relevant examples for representative aqueous halides and oxyanions involving the use of heavy- and null-water as the aqueous media, the 15N/natN, 18ON/natON,,33S/natS and 18OS/natOS isotopic substitutions in the oxyanions, as well as the introduction of null-cation isotopic substitutions  via molecular simulation, as convenient dry runs for the challenging NDIS experiments to illustrate our new developments for the interpretation of ion coordination. Cited references: 1. Chialvo, A.A. and L. Vlcek, NO3-Coordination in Aqueous Solutions by 15N/natN and 18ON/natON Isotopic Substitution: What Can We Learn from Molecular Simulation? The Journal of Physical Chemistry B, 2015. 119(2): p. 519-531. 2. Chialvo, A.A. and L. Vlcek, Toward the Understanding of Hydration Phenomena in Aqueous Electrolytes from the Interplay of Theory, Molecular Simulation, and Experiment. Fluid Phase Equilibria, 2015. Invited submission for the special issue on aqueous electrolytes.