November 1, 2019 at 7:45 pm

Chemistry Colloquium | Tracking Self-Assembly, Organization and Chemical Transformations at Complex Liquid/Liquid Interfaces using Nonlinear Vibrational Spectroscopy, Nov. 18

Benjamin Doughty, portrait

Benjamin Doughty

Ohio University’s Chemistry and Biochemistry Colloquium Series presents Dr. Benjamin Doughty on “Tracking Self-Assembly, Organization and Chemical Transformations at Complex Liquid/Liquid Interfaces using Nonlinear Vibrational Spectroscopy,” Monday, Nov. 18, at 4:10 p.m. in Walter Hall 145.

Doughty is an Research Scientist in the Department of Chemistry at Oak Ridge National Laboratories University of Tennessee.

The host is Dr. Katherine Cimatu.

Abstract: The interface between two liquids is a hotspot for self-assembly and anomalous chemical processes that ultimately dictate how species adsorb, order, and react. These key mechanistic steps ultimately dictate how molecules are transported from one phase to another and how chemical specificity is manifested on the molecular level, which differs greatly from the bulk. Despite the widespread interest in understanding these interfacial phenomena, particularly for applications in chemical separations and biological transport, the fundamental events governing selectivity and efficiency are not well understood. A key barrier to obtaining this insight is the current inability to directly probe the structure and dynamics of the molecularly thin interface using conventional methods without being overwhelmed by signals originating from the neighboring bulk phases. In this talk I will discuss new results using surface specific vibrational sum frequency generation spectroscopy to probe molecular self-assembly, hydrogen bonding, molecular ordering, and orientation in situ. The first part of my talk will focus on the self-assembly of well-defined amphiphilic oligomers that act as lipid mimics at the buried oil-water interface.  Out results show that tail conformations in the oil phase are ultimately directed by the electrostatic screening of charges in the aqueous phase.  These results point to design rules to alter the ordering and chemical makeup of these interfaces for applications in molecular electronics and robust bio-mimetic membranes. Building on this work, we turn attention to the long-standing problem of interfaces in the context of selective chemical separations. Our new results show dramatic changes to ligand ordering at the oil-water interface that are triggered by changes in bulk pH. These changes are linked to subsequent interfacial chemistry and associated kinetics that describe how the interface transforms during the extraction of a model divalent cation. Our results highlight the importance of ligand preorganization as moderated by unique interfacial hydrogen bonding structures assumed in the aqueous phase.  Our findings reveal new insight into the chemical and physical phenomena taking place at these complex interfaces that govern selectivity in chemical separations and molecular transport.

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