Fig. 4.
Temperature dependence of the helix pitch of the NTB phase pTB(T) and of the birefringence Δn(T) (□) of CB7CB in the N and NTB phases. The pitch obtained from the FFTEM images (○) exhibits little variation with T (less than 5% over the whole NTB range). The solid circle (●) gives pTB from the MD computer simulation of Fig. 6. Birefringence grows on cooling in the N phase, as is typical. The deuterium magnetic resonance (DMR) splitting-determined orientational order parameter of deuterated 8CB solute in CB7CB, proportional to the solid green line (8), is a measure of Δn(T) in the N phase and is consistent with the optical Δn(T) in the N phase. In the NTB phase Δn(T) decreases with the onset of biaxial ordering, in a fashion different from the DMR splitting.