Characterization of Nanoscale Transport Phenomena at the Solid-Fluid Interface

Rapid development in nanoscale fabrication and manufacturing is transforming application-driven research in areas such as water treatment and desalination, biosensing, and energy conversion. Nanoscale features exhibit an array of new forces and new phenomena, creating new problems at the nanoscale that severely impact the performance of these technologies due to their macroscopic manifestations. The relevant nanoscale phenomena include inter-molecular forces, such as van der Waals and nanocapillary forces, Hofmeister and hydrogen bonding hydrophilic/hydrophobic effects, concentration polarization due to Debye layer overlap, short-wavelength interfacial phonon thermal transport during plasmonic heating of nanoparticles, non-continuum viscous/thermal slip effects and confinement effects during hysteretic liquid/gas transitions. These phenomena often involve cooperative dynamics, such that non-equilibrium water structures, ion polarization, and metastable states exist sufficiently long to produce important but anomalous effects like bubble cavitation, ion-selective membrane translocation, and localized thermal hotspots. In some cases, nanoscale phenomena can have deleterious effects, such as limiting currents and loss of selectivity in electrodialysis and bubble attachment at plasmonic nanoparticles, each of which reduces efficiency for the respectively associated desalination technologies. This talk concerns the study and characterization of nanoscale transport phenomena and the surface properties responsible for giving rise to these phenomena in two very different systems: ion-selective membranes/nanochannels and suspended, functionalized core-shell nanoparticles. An emerging common theme between the two systems is the critical role played by hydrogen bonding and water structure. In fluidic systems, water structure is responsible for ion-specific transport effects and surface-fluid interactions, while in the nanoparticle system, hydrogen bonding between functional groups on the NP surface and the fluid enhance interfacial thermal conductance.