The Surfactant CTAB At Interfaces Studied By Broadband Vibrational Sum Frequency Generation Patrick L. Hayes and Franz M. Geiger Northwestern University Department of Chemistry Evanston, IL International Symposium on Molecular Spectroscopy 62nd Meeting June 20th, 2007

Application of surfactants to oil recovery U.S. Crude Oil Production: Kern River Oil Field near Bakersfield, California. Taken from: Jad Mouawad, “Oil Innovations Pump New Life Into Old Wells” The New York Times, March 5th, Average oil recovery rates are 20 to 40% of field’s total oil! U.S. Department of Energy (Accessed June 2007) Adapted from: Energy Information Administration Arctic National Wildlife Refuge

Application of surfactants to oil recovery Surfactant containing fracturing fluids can improve recovery rates to 30 to 60%. Taken from: Armstrong, K. et al. “Advanced Fracturing Fluids Improve Well Economics” Oilfield Review, Autumn Fractured Unfractured Crude flows through pores in well wall into fractures. Sandstone Sand- stone Well Bore Well Bore U.S. Crude Oil Production: Adapted from: Energy Information Administration U.S. Department of Energy (Accessed June 2007)

Chemical Questions Regarding Fracturing Fluids Are surfactants retained in the pores of the sandstone matrix? Under what conditions do monolayers form? Bilayers? Multilayers? (Potential experimental parameters: ionic strength, pH, [surfactant], etc.) Scanning electron microscope image of oilfield sandstone: Pore Quartz Grain

CTAB at the fused quartz/water interface 1) Real-time monitoring of CTAB adsorption at the fused quartz/water interface using Second Harmonic Generation (SHG). Taken from: Velegol et al. Langmuir 2000, 16, AFM images of adsorbed CTAB layers. 2) Characterization of adsorbed surfactant structure through sum frequency generation (SFG). Fused Quartz Cetyltrimethylammonium Bromide (CTAB)

SHG -- Experimental setup Hayes, P. L. et al. J. Phys. Chem. 2007, ACS ASAP. Gibbs-Davis, J. M.; Hayes, P. L.; Scheidt, K. A.; Geiger, F. M. J. Am. Chem. Soc. 2007, 129, Teflon Reservoir Aqueous Phase SiO 2 I time PMT fsec Laser Inject CTAB

SHG -- The  (3) technique Fused Quartz More negative surface charge Less negative surface charge Salafsky, J. S.; Eisenthal, K. B. J. Phys. Chem. B 2000, 108, Xiao, X. D.; Vogel, V.; Shen, Y. R. Chem. Phys. Lett. 1989, 163, 555. Zhao, X.; Ong, S.; Wang, H.; Eisenthal, K. B. Chem. Phys. Lett. 1993, 214, 203. Gouy-Chapman Model:

SHG -- CTAB adsorption experiments Adsorption Isotherm (pH=6) 400 mM NaCl Surface saturation occurs at ~1.5 mM CTAB CTAB CMC Adsorption Trace (pH =6.5) 0.5 mM CTAB 400 mM NaCl 400 mM NaCl

SFG -- Experimental setup Mono/ CCD Delay Stage IR: 3-10  m Visible: 800 nm Stokes, G. Y. et al. J. Am. Chem. Soc. 2007, ACS ASAP. Voges, A. B. et al. J. Phys. Chem. B 2004, 108, Voges, A. B. et al. J. Phys. Chem. C 2007, 111, Sample Preparation: (1) Exposed glass slide to 5-mM solution of CTAB for 2-hours. (2) Removed and dried under N 2 gas. Following similar procedure, adsorbed layer thickness of 1.4(2)-nm determined for silica/air interface. (From Eskilsson et al. Langmuir 1998, 14, 2444.)

SFG Spectra Assignments based on literature assignments for IR and Raman spectra cm -1 : Symmetric CH 2 stretching mode 2880 cm -1 : Symmetric hydrocarbon CH 3 stretching mode 2937 cm -1 : Symmetric CH 3 -(N + ) stretching mode 2958 cm -1 : Anti-symmetric hydrocarbon CH 3 stetching mode Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, 263. SSP +

PPP SFG Spectra PPP Spectrum: 2890 cm -1 : Fermi resonance of the symmetric CH 2 stretch 2956 cm -1 : Anti-symmetric hydrocarbon CH 3 stetching mode (Present in both SSP and PPP) 2967 cm -1 : Combination of anti-symmetric CH 3 hydrocarbon stretch and symmetric CH 3 -(N + ) stretch. Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, 263. SSP +

PPP SFG Spectra Sau, T. K.; Murphy, C. J. Langmuir 2005, 21, Campbell, R. A.; Parker, S. R. W.; Day, J. P. R.; Bain, C. D. Langmuir 2004, 20, Wang, W.; Gu, B.; Liang, L.; Hamilton, W. A. J. Phys. Chem. B 2004, 108, Kung, K. S.; Hayes, K. F. Langmuir 1993, 9, cm -1 : Combination of anti-symmetric hydrocarbon stretch and symmetric CH 3 -(N + ) stretch Fused Quartz cm -1 mode consistent with interdigitated CTA + bilayer (observed previously in literature.)

Conclusions & Future Work 1)Use deuterated CTAB to verify assignments in SFG spectra. 2) Further SFG studies of CTAB at quartz/water interface to compliment current work at quartz/air interface. In particular, probe for further evidence of interdigitated bilayer structures (or other surface structures) at these interfaces. + Fused Quartz Water

Conclusions & Future Work 3) Proof-of-concept:  (3) technique can be used to track surfactant adsorption to the fused quartz/water interface, and will be used to determine conditions under which adsorption is reversible. 0.5 mM CTAB 400 mM NaCl 400 mM NaCl Optimizing conditions for surfactant removal (desorption) in oil wells allows for improving recovery rates up to and beyond 60%! Sandstone Well Bore

Acknowledgements Funding Schlumberger Oilfield Chemical Products Northwestern University The Alfred P. Sloan Foundation The Geiger Group