Fluids Confined in Carbon Nanotubes Constantine M. Megaridis Micro/Nanoscale Fluid Transport Laboratory Mechanical and Industrial Engineering University of Illinois at Chicago 1
Background and Societal Impact Carbon nanotubes offer a relatively new platform for fundamental studies of fluid behavior in the spatial regime between molecular and macroscopic (a.k.a. continuum) length scales. Vacuum Fundamental understanding of Gas fluid behavior under extreme confinement is needed for the design and fabrication of new Liquid generation of nanofluidic devices, nano-analytical systems, sensors, Gas probes for medical applications, 50 nm etc. Phys. Fluids 14, L5-L8, 2002 2
Technical Principles Molecular Dynamics (MD) simulations have advanced the study of fluids under extreme confinement. But bridging the gap between MD modeling and the macroscale faces severe challenges. Experiments have lagged, but are now coming to the forefront. 3
Non-volatile Liquids in Open Nanotubes Gao & Bando, Nature 415, p. 599 (2002) 58 C 490 C 45 C Carbon nanothermometer containing gallium (metal): Height of continuous, unidimensional column of liquid Ga inside a carbon nanotube varies linearly and reproducibly in temperature range 50-500 C. Scale bar 75 nm. 4
Evaporative Transport in a Closed CNT a Upper Internal Closure x b x c x f Upper Internal Closure x gas Initial Interface d e gas Lower Internal Closure x 200 nm Nano Heat Pipe? x Final Interface Lower Internal Closure 200 nm J. Heat Transfer 126, p. 506 (2004) 200 nm 5
Fluid phenomena in CNT confinement: State-of-the-Art Experiments Modeling No through flows reviewed; see Whitby and Quirke, Nature Nanotech. 2, p. 87 (2007) 6
Membrane Rupture by Gentle e-beam e Heating 50 nm Appl. Phys. Lett. 86, 013109 (2005) 7
Continuum Modeling of Fluids inside CNTs Continuum approach, combines temperaturedependent mass diffusion with intermolecular interactions in the fluid bulk and in the vicinity of the carbon walls. No convection. J. App. Phys. 97, 124309 (2005) Mass concentration Temperature Liq. Gas 8
Reversible Condensation/Evaporation in CVD CNT (Environmental SEM) p = 5-6 Torr Rossi et al., Nano Letters 4, 989 (2004) 9
Does Water Wet the Interior Walls of CNTs? MD Simulation Phys. Fluids 14, L5-L8, 2002 Gas Vacuum Liquid Werder et al., J. Phys. Chem. B107, p. 1345 (2003) Model: Non-wetting 50 nm Gas Experiment: Wetting 10
MD Simulation Chemisorbed Positive Ions Increase Wetting MD Simulation contact angle (deg) Percentage of chemisorbed hydrogen Nanotech. 15, p. 232 (2004) Kotsalis et al., Chem. Phys. Lett. 11 412, p. 250 (2005)
Irregular G/L interfaces: Below continuum limit? Treated CVD Nanotubes Nano Letters 4, p. 2237 (2004) 12
Selective Intercalation of Polymers in CNTs PEO (600 kda) in water (0.01% wt.) PEO (2000 kda) in water (0.01% wt.) PEO (4000 kda) in water (0.01% wt.) PCL (80 kda) in MC (0.1% wt.) Langmuir (2007) 13
Infiltration of Solid Particles in Carbon Nanotubes 50nm polystyrene beads in CVD CNTs Magnetic nanoparticles in CVD CNTs Korneva et al., Nano Letters 14 5, p. 879 (2005)
Challenges Disparity of length and time scales between MD simulations and realistic experiments In computing, the major challenge is MULTISCALING and how to couple quantum - atomistic and continuum descriptions of systems In experiments, the major challenge is the limited analytical instrumentation available at these length scales Bio-nano interface: Very complex. Nanotubes can serve as theoretical and experimental model systems to study and control important biomolecular processes, e.g., water, ion, and proton conduction in aquaporins, ion channels and enzymes. Yeh and Hummer, Proc. Nat. Acad. Sci. 101, 12177 (2004) 15
Multiphysics: : Coupling Atomistic-Continuum Werder et al., J. Comp. Phys. 205, p. 373 (2005) Multi and All-scale Hydrodynamics - Embedding nanodevices in macrosystems Kotsalis et al., Phys. Rev. E 75, 046704 (2007) 16
Recommendations 1. Identify problems that can be tackled both computationally and experimentally. Use these to quantify uncertainty in MD simulations. 2. In the chemistry community there is quantum mechanics - molecular mechanics coupling expertise. In engineering there is expertise in Molecular Mechanics - Continuum. Coupling both worlds carries great promise. 3. Develop experimental diagnostics to analyze systems with nanometer resolution. 4. Catalyze the development of techniques capable of integrating CNTs into nanoscale/molecular devices. 17