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