Using Deuterium NMR Line Shapes To Analyze Lyotropic Liquid Crystalline Phase Transitions

John C. Blackburn and Peter K. Kilpatrick

Department of Chemical Engineering, North Carolina State University,

Raleigh, North Carolina 27695- 7905

Received January 27,1992. In Final Form: March 16, 1992

Deuterium quadrupole NMR line shapes were simulated to match experimental spectra of liquid crystalline phases observed in the cesium and sodium n-tetradecanoate-D₂0 systems. The line shapes of single-phase samples with both uniaxial and biaxial symmetry were accurately simulated. Line shape simulations were matched to experimental spectra by minimizing the sum of squared residuals on the basis of local intensity maxima and minima. The line shape parameters optimized were the quadrupole splitting DνQ, the spin-spin relaxation time T₂, and, in the case of biaxial spectra, the aggregate asymmetry parameter ή_D. The line shapes of multiple-phase samples were also accurately simulated by optimizing the relative amounts of each phase. The method can be used to accurately determine tie-line and tie-triangle end points in multiple-phase liquid crystal samples. Among the illustrative liquid crystalline transitions provided are hexagonal to ribbon phase, ribbon to lamellar phase, and ribbon to viscous isotropic phase.