Nuclear magnetic resonance and phase behavior studies of Aerosol OT, TR, and IB

Author

Craig Arlen Martin

Date of Award

12-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Linda J. Magid

Committee Members

Richard Pagni, D. C. Kleinfelter, Leaf Huang, Clifton Woods

Abstract

¹³C Nmr was used to study the conformational and dynamic changes which occur when water is added to Aerosol OT (AOT) inverted micelles in apolar solvents. Upon addition of water, the ¹³C chemical shifts of AOT's carbonyls move sharply upfield in cyclohexane solution, while changes were observed in the fine structure of the carbonyl region of the dispersive ir spectra. The spin-lattice relaxation times (T₁) of all of AOT's carbons increase in this solvent up to R = [H₂0]/[A0T] = 5 - 10, then level off or increase slightly throughout the w/o microemulsion domain. The segmental mobility of AOT's alkyl chains decreases dramatically as the inverted micellar domain is transversed in cyclohexane. These results indicate an increased mobility and that gauche to trans conformational changes occur throughout the AOT molecule as water is added.

T₁'s of AOT are larger in benzene and carbon tetrachloride than in cyclohexane. The segmental mobility of AOT inverted micelles at R = 0 decreases in the following solvent series: cyclohexane > carbon tetrachloride > benzene. This is due to the latter two solvents intercalating AOT's alkyl chains, while in cyclohexane the voids are filled by the hydrocarbon tails. Solvent penetration decreases in the following order: benzene > carbon tetrachloride > cyclohexane.

The relaxation of carbons nearest the sulfonate head group is primarily influenced by the overall motion of the AOT molecule. At low R values, the major contribution is from overall aggregate tumbling; at high R, relaxation is due to lateral AOT diffusion along the AOT/ water interface.

Frequency dependent T₁'s of AOT inverted micelles in cyclohexane indicate that a distribution of correlation times affect the relaxation of all carbons. The motion of AOT's alkyl tails in the w/o microemulsions can be described using a single correlation time.

Motional differences are observed in the AOT alkyl chains when going from the inverted micelles to the w/o microemulsions. Calculations show that the w/o microemulsions cannot be spherical at the highest water contents.

Also studied was the ternary phase behavior of AOT, Aerosol TR (ATR), and Aerosol IB (AIB) in water/oil solutions at 45°C using cyclohexane and benzene as the hydrocarbon. AOT solubilizes less water in benzene than in cyclohexane. ATR takes up a smaller amount of water in either solvent than AOT does. AIB/water solutions solubilize moderate amounts of both benzene and cyclohexane. In benzene, AIB takes up significant amounts of water, while solid AIB precipitates from cyclohexane solutions when water is added.

The effects of cosurfactants of the opposite HLB on the phase behavior of ATR and AIB were investigated. Large, isotropic, one phase regions dominated the pseudoternary phase diagrams when 2:3 (w/w) ATR/2-propanol or AIB/1-hexanol was used as the emulsifier. Attempts to characterize the aggregates in the ATR one phase solutions using ¹³C and ¹H nmr were inconclusive, but provide the basis for further work.

Recommended Citation

Martin, Craig Arlen, "Nuclear magnetic resonance and phase behavior studies of Aerosol OT, TR, and IB. " PhD diss., University of Tennessee, 1981.
https://trace.tennessee.edu/utk_graddiss/13476