When fluids are confined to a nanometer scale channel, pore or volume, their molecular properties become distorted in ways that confounds existing theories. These systems are highly relevant for water purification, chemical separations, and understanding biological systems. The Strano group uses precision nanopores, such as the inside of a carbon nanotube or 2D membrane systems, to generate thermodynamic and transport data for confined fluids. These data are used to formulate and validate new theories of how such fluids behave.
Research Overview
When fluids are confined to nanometer scale volumes, the distortion of molecular orientations and the interacting with the confinement walls changes the thermodynamic and transport properties in ways not yet describable by theory. The Strano Group generates 1D and 2D solid-state nanopores and nano-confined systems to generate high-precision data on confined fluids, using this to design and validate new theories of these fundamental properties. The team has pushed experimental and theoretical frontiers to study these phenomena both in carbon nanotubes and nano-pore membranes, developing new experimental platforms for efficient, high-throughput characterization and theoretical models to explain fundamental phenomena. We conduct this work as a part of the Center for Enhanced Nanofluidic Transport (CENT), an DOE-ERFC that promotes strong collaboration between researchers across the country in top universities and national labs, working at the cutting-edge of fluid flow and molecular transport.
Nanopores and nano-confined systems
References
Carbon nanotubes as confined fluid test tubes
We study individual, millimeter-long carbon nanotubes synthesized on a substrate. Their supreme quality and direct accessibility make them an ideal testbed for nano-confined fluid phase transitions and transport. Carbon nanotubes are also extremely versatile and can be used for both experimental and computational exploration. Certain vibrational modes of these tubes are known to be susceptible to fluid-phase filling, a change in which can easily be detected by Raman spectroscopy. This allowed us to probe the extreme diameter-dependence of the freezing point of water confined within, which we found to even exceed +100 °C in some tubes [1]. We also investigate on the transport of different ionic species through carbon nanotubes, most prominently evidenced via stochastic pore-blocking behavior [2, 3]. The nanotube’s exterior can provide a transport channel which proved cation-selective in our experiment [4]. Recently, we demonstrated with remarkable precision the temperature dependence of the environmental vibration coupling of double-walled nanotubes, combining experimental work with a quantitative harmonic oscillator model to fully understand the effects of temperature and fluid-filling [5]. Current work focuses on understanding phase transitions and thermodynamic properties of a variety of critical fluids within carbon nanotubes, which has applications in nano-pore separations.
References
An Equation of State for Confined Fluids
A new research thrust in the Strano Group involves using mathematically simple thermodynamic equations of state to describe complex, nano-confined systems. In the last decade, there has been a strong push in the literature to derive accurate confined-fluid equations of state, given the critical need to be able to predict the properties of fluids under various degrees of geometric confinement. Important applications arise in membrane separations, heterogeneous catalysis, and corrosion-resistant materials development. Equations of state can be powerful tools to deduce important thermodynamic properties, such as adsorption enthalpies, while circumventing the need for vast computational resources. The Strano Group is currently exploring the capabilities of such equations of state in modeling the experimental behavior of fluids in carbon nanotubes, and other nano-confined systems such as graphene.CENT - Center for Enhanced Nanofluidic Transport
In October of 2018, Professor Strano, along with several other researchers from leading institutions in the United States, co-founded the Center for Enhanced Nanofluidic Transport (CENT). CENT is a Department of Energy Energy Frontier Research Center that addresses emerging and compelling gaps in our scientific knowledge of fluid flow and molecular transport in single digit nanopores. CENT applies precision model systems, transformative experimental tools, and predictive multiscale theories to understand fluid flow and molecular transport in single – digit nanopores, to identify conditions for enhanced flow at extreme confinement, to unravel structure of solid/liquid interfaces, and to design new mechanisms that deliver unprecedented molecular selectivity.