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Development of a Sheath-Flow Supercritical Fluid Expansion Source for Vaporization of Nonvolatiles at Moderate Temperatures
Bradley M. Gibson and Jacob T. StewartDepartment of Chemistry, University of Illinois at Urbana-ChampaignBenjamin J. McCall Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign
What is a supercritical fluid?
Figure from: http://en.wikipedia.org/wiki/Supercritical_fluid {2}
Why use supercritical fluids?
Figures from: B. Brumfield. Development of a quantum cascade laser based spectrometer for high-resolution spectroscopy of gas phase C60. UIUC, 2011. {3}
C60 Vapor Pressure
Why use supercritical fluids?
Figures from: B. Brumfield. Development of a quantum cascade laser based spectrometer for high-resolution spectroscopy of gas phase C60. UIUC, 2011. {4}
Why use supercritical fluids?
Figure from: B. E. Brumfield et al. Rev. Sci. Instrum. 81, 063102 (2010). {5}
Why use supercritical fluids?
Figures from: J. T. Stewart. High-resolution infrared spectroscopy of large molecules and water clusters using quantum cascade lasers. UIUC, 2013. {6}
Estimated:
Observed:(NEA ~0.6 ppm)
Why use supercritical fluids?
{7}
Inefficient Vibrational Cooling• Large partition function• Poor density of states at low energy
2000
1500
1000
500
0
Vib
ratio
nal T
empe
ratu
re (
K)
100
101
102
103
104
Qvib
300250200150100500Temperature (K)
How does the source work?
{8}
How does the source work?
{9}
How does the source work?
{10}
How does the source work?
{11}
What affects the final temperature?
• Extraction chamber temperature• Pure CO2: > 305 K• 7:3 CO2:toluene: ~ 450 K• 96:4 CO2:naphthalene: ~ 340 K
• Nozzle temperature• Aerosol-formation limited • 7:3 CO2:toluene: ~ 400 K
• Argon backing pressure• Expansion composition• Velocity matching
Figures adapted from: S. R. Goates, N. A. Zabriskie, J. K. Simmons, B. Khoobehi. Anal. Chem. 59, 2927 (1987)C. H. Sin, M. R. Linford, and S. R. Goates. Anal. Chem. 64, 233 (1992) {12}
How can we test the source?
{13}
Methylene Bromide• Solubility unknown• No signal observedPyrene• Solubility in pure CO2 too low• Solubility with cosolvents unknown• No signal yet• Visible pyrene output – mg/ hr scaleD2O• Very strong monomer signals observed• Poor for vibrational temperature estimates
Does the source cool efficiently?
{14}
D2O Tests• 111←000 rovibrational transition• Clear evidence of cooling (Trot < 16 K)• Works from 400 - 500 K nozzle• 350-370 K mixing chamber (limited by heater)
400
300
200
100
0
Loss
Per
Pas
s (p
pm)
1199.7701199.7681199.7661199.7641199.7621199.7601199.758
Frequency (cm-1
)
Background GasFWHM ~105 MHz
Jet-Cooled Gas
300
250
200
150
100
50
0
Loss
Per
Pas
s (p
pm)
1199.7701199.7681199.7661199.7641199.7621199.7601199.758
Frequency (cm-1
)
Subtracted Line Gaussian Fit
FWHM ~27 MHz
What molecules can we target?
{15}
Nonvolatile Molecules• Fullerenes• Polycyclic aromatics
• Perylene• Coronene
What are the source’s limitations?
{16}
Fundamental Limitations• Low vapor production rate• Minimum “starting” temperature• Appropriate solvent system required
Design-Specific Limitations• Clogging / multi-phase behavior• Limited temperature range (<370 K)• Limited pressure range (<3600 psi)
Conclusions
{17}
• Should allow vaporization at moderate temperatures• Prototype source completed• Tests with D2O appear promising• Numerous interesting targets available• Design improvements and additional testing underway
Acknowledgements
{18}
• McCall Group• Claire Gmachl• Steven Goates