High Spatial Resolution Nonlinear Spectroscopy of Near-Critical Fluid in Pores of Nanoporous Glass International Laser Center and Physics Department of M.V. Lomonosov Moscow State University, Moscow 119991, Russia

Transparent nanoporous materials glass zeolites Pore radius: ~1 … ~100 nm Width of pore radius distribution: down to Angtsroms aerogel polymeric Porosity: up to 99 % Surface area: up to ~1000 m2/g

Nanoporous glass Vycor DV-1M Unit weight 1.5 g/cm3 Void space 28% Internal surface area 200 m2/g Average pore radius 2 nm (r~0.5 nm) 9 mm 4 mm DV-1M d, nm Unit weight 1.5 g/cm3 Void space 26% Internal surface area 100 m2/g Average pore radius 3.5 nm (r~0.5 nm)

Fluid inside a nanopore at different pressures gas 1st adsorbed layer liquid-like layer + condensed phase

Supercritical fluid (SCF) symmetric stretch asymmetric bending 1335 cm-1 0220 2003 cm-1 0330 1000 2000 cm-1 1388 cm-1 1285 cm-1 0200 667 cm-1 0110 2077 cm-1 1110 1932 cm-1 0310 0000 CO2 vibrational energy levels ν1 ν2 ν3 solid liquid Supercritical fluid (SCF) TCR=31.1 oC (no gas-liquid transition in bulk) TRoom is near-critical PCR Critical point PCR=72.8 atm Triple point gas pressure temperature TCR

CARS spectra at room temperature pore radius: 2 nm 3.5 nm

Experiment and calculations pore radius: 2 nm pressure, atm adsorption 32 ~1.3 monolayers (d=0.5 nm) 48 ~1.8 monolayers (d=0.7 nm) 52 ~2 monolayers (d=0.8 nm) condensation in pores 55 condensation in bulk 58

CARS spectra at near-critical temperatures spectral contributions subcritical 30.5 oC supercritical 33 oC Manifestation of critical point shift

CARS spectra at 22 C at low pressures pore radius: 2 nm liquid-like fluid gaseous fluid surface-adsorbed fluid