Vacuum Filling an Assembled LC Cell

FILL STATION

PURPOSE:

Vacuum filling an assembled LC cell.

PROCEDURES:

1. Place a small amount of the liquid crystal in a filling trough.

2. Clip the cell, with the fill hole down, onto the holder with the four clips.

3. Place the trough with the liquid crystal under the cell and line them up so that when you lower the cell, it will come down level into the liquid crystal.

4. Use the toggle switch on the white controller box on the table next to the fill station to raise the cell a few inches above the trough so that when you start to pump down the chamber, the liquid crystal does not bubble up onto your cell.

5. Take the bell jar and place it over the filling apparatus and make sure that it sits flat on it’s base.

6. There are two valves for the vacuum which are located underneath the table. The roughing valve has a black knob, and the other, which leaks air back into the chamber, has a green knob. Make sure that both of these valves are closed (turned all the way clockwise).

7. Turn on the vacuum pump with the foot switch on the floor.

8. Slowly start to open the roughing valve (the black knob). The liquid crystal will start to bubble as it degasses. You have to be very careful to open the valve slow enough so that the bubbling does not get too vigorous and spill out of the trough. You may want to put the liquid crystal into the chamber before you fill your cell and degas it first. After it has been degassed once, it will not bubble up as much the next time.

9. Once you have opened the valve all the way, allow the chamber to pump down until the guage on the control box reads 10 to 15 millitorr.

10. Lower the cell down into the liquid crystal until the entire bottom edge of the cell has been wetted.

11. Once the liquid crystal has started to fill the cell you can close the roughing valve and allow the cell to fill. If you want the cell to fill faster, you can slowly leak air back into the chamber using the green valve, however this can cause the cell to fill too quickly and cause flow induced alignment.

12. If you haven’t done so, slowly leak air back into the chamber and allow it to come back to atmospheric pressure.

13. Remove the bell jar.

14. Lift the cell out of the liquid crystal using the switch on the control box, and remove it from the clips

SPECIAL CONCERNS:

All methods of filling cells are under extreme pressure. Do not touch the bell jar once it has begun to pressurize. If the jar were to break it would implode and could cause serious injury.