Observed behavior similarities and differences

Similarities For all investigated nCB (from 5 to 8), and for the three substrates, there is a forbidden range of thickness (LB-UB) in the bulk nematic range of temperatures. Far below the Nl transition, the LB is a trilayer of molecules (3-4 nm), while the UB is around 20-30 nm. 

When approaching the Nl transition, both LB and UB increase they diverge at the transition. 

Partial similarities For all investigated nCB, and for the two liquid substrates, metastable states are observed. Several films with different thicknesses UB may be in contact with the LB film (see Fig. 5.8). The LB film may be in contact with thinner films. Contact between these thinner films and films UB is not observed during significant time scales. 

For all investigated nCB, and for the two liquid substrates, stripe patterns are observed in a well-defined range of thickness between the UB and an upper threshold D (0.5-1 pm). At a given temperature, the wavelength k depends only on the film thickness f. — A,(f) increases faster than linearly and is typically 100 times larger than f. A typical example is given in Fig. 5.10. 

Although stripe patterns are controlled by a competition between elasticity and anchoring, which both decrease strongly close to the N1 transition, the main effect on ) is the increase of the UB and seemingly a decrease of D. The curve itself depends only weakly on temperature. 

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