Thermal positioning of point defects in smectic films: the thermal tweezer

Abstract

We have developed a simple, inexpensive, and easily incorporated technique for positioning point defects in free-standing smectic films, simplifying the study of defect structures in the moderate temperature window through probes such as depolarized reflected light microscopy. The technique exploits thermal flow in the smectic films to position and hold a point defect in place. We present details of the experimental design as well as measurements of the thermal flow induced by the device.

Notes

^†In [4] the motion of the SmC* defect in thin free-standing films was studied as a function of time during a period of 2 h. The experiment was done at a relatively low temperature (T≈55.1°C); thus the motion of the defect is somewhat limited. We plan to study the morphology of the five-arm defect on a curved surface. In free-standing films of the compound 2M4P9OBC, such a defect can only be observed at a moderate temperature (T≈76°C).

Schematic of the oven. The film is observed through the glass windows. The film-hole is ∼1 cm in diameter and is centred radially in the oven. The thermal tweezer is a 0.635 cm dia. brass rod, roughly 20 cm long, and centred on the film-hole. The tweezer is fed into the outer shell through an Ultra-Torr fitting so that it can be raised, lowered, and rotated with the outer stage holding vacuum