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MSE Seminar: Dr. Michael Strano, MIT Nanofluidic Platforms for Knowledge Gaps at the Water-Energy Nexus Abstract: Fluids confined inside single digit nanopores (SDNs) with pore dimensions comparable to the size of the fluid molecules can exhibit transport phenomena and thermodynamic properties, including phase transitions, which differ remarkably from those in the bulk phase. Here, we develop a high-throughput platform utilizing carbon nanotubes (CNTs) as SDNs to precisely investigate fluid phase transitions under strong confinement and characterize environmental coupling effects. By immersing CNTs, opened by focused ion beam (FIB), in water reveals phase transitions with concave-up trajectories dominated by the internal fluid desorption (adsorption) at high (low) temperatures. To model these water phase transitions, we have developed an equation of state (EOS) and utilize molecular simulations carried out in a hybrid statistical mechanical ensemble. This ensemble maintains the confined water in quasi chemical and thermal equilibrium with separate chemical potential and thermal reservoirs, respectively, under non-isothermal conditions. Importantly, this thermodynamic theory entails a self-consistent determination of the phase transition temperature as a function of the water-CNT interactions and CNT diameters, thereby enabling an accurate characterization of the enthalpy of phase change through fitting to the experimental data. Remarkably, as a control sample, local laser heating of as-grown CNTs in vacuum, we discovered thermally reversible radial breathing mode (RBM) downshifts of unopen CNTs by an extraordinary 10 to 15% with hyperbolic trajectories, which is attributed to a reversible increase in damping. The concave-down trajectories can be described using the harmonic oscillator model across 93 different Raman scans. Additionally, recent theoretical and experimental work by our laboratory has enabled the solution phase, irreversible polymerization of 2D polymers, specifically 2D Polyaramid 1 (2DPA-1). The monomers concatenated in two directions forming a molecular sheet, offering a novel ultra-strong 2D platform with stacked matrices and accessible porosity for gas or fluid transports through SDNs. Overall, our comprehensive experimental and theoretical investigations demonstrate the exceptional promise of CNTs as precision systems for various nanofluidic applications, and 2D polymers hold potential for molecular separations at the water energy nexus. This Event is For: Graduate • Faculty
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