Soft Matter Interest Group Virtual Seminar
SPEAKER: Heather C. Allen (Professor, Department of Chemistry, The Ohio State University)
TITLE: Anion-Triggered Organization at Aqueous Surfaces
ABSTRACT: Studies from the air-water interface are presented with focus on hydration and binding phenomena. Amphiphilic molecules are essential for the creation of the functional and dynamic aqueous interfaces seen across natural and artificial systems. These interfaces typically rely on molecular recognition for their formation or environmental response but the interfaces also influence binding that motivate fundamental studies aimed at understanding the underlying driving forces. Anion binding and the resulting amphiphile complex that forms as the trigger to drive self-organization into highly ordered monolayers at the air-water interface is presented. A neutral and entirely hydrophobic synthesized molecule showed poor organization and formed an abundance of aggregates at the surface of a pure water solution as seen by Brewster angle microscopy (BAM) and surface pressure area isotherms. Chloride (Cl–) was added as a hydrophilic anion that has low chemical selectivity for this class of macrocycles while phosphate (H2PO4–) is another hydrophilic anion with good affinity for this class of macrocycles. Both retain the highly disordered surface aggregates of the hydrophobe. When hexafluorophosphate (PF6–) and perchlorate (ClO4–), are in the aqueous subphase, the macrocycles assemble into organized architectures that now display surfactant character. Infrared reflection absorption spectroscopy (IRRAS) reveal bound anions, and interesting, chain disorganization upon binding. Vibrational sum frequency generation (VSFG) spectroscopy showed the presence of a highly charged aqueous interface consistent with PF6– and ClO4– anion-hydrophobic molecule interfacial complexation. This is the first study showing anion-triggered monolayer formation using a shape-persistent macrocycle and molecular recognition principles. I will also show other work from our laboratory including new advances in surface potential measurements of halides.
Meeting ID: 942 2008 0385