TN Liquid Crystal

TN (Twisted-Nematic) liquid crystal is put between crossed-Nicol polarizer/analyzer pair and then applied ramp wave voltage ranging from 2 V to 8 V with period 60 s. We can obverve what's called Freedericksz transition in which alignment of liquid crystal molecules changes.
Initially they are parallel to the wall (glass plate with ITO electrode), but as the electric field gets stronger, they are forced to be parallel to the electric field. We see colorful textures because I used white light for the microscope. White light contains all colors, and the color which can pass through polarizer/analyzer pair varies from place to place because of inhomogeneity of the sample. I'm sorry that I forgot which kind of TN liquid crystal we used.

We made this video for the exhibition at the university festival of Univ. of Tokyo, under advisory from Prof. Doi, Dr. Yamaue, Dr. Kaneko and Mr. Yamamoto of Doi laboratory ( http://rheo.t.u-tokyo.ac.jp/ ), and Prof. Ito and Dr. Kidowaki of Ito laboratry ( http://www.molle.k.u-tokyo.ac.jp/ ).

Category:

Science & Technology

Tags:

• liquid-crystal
• phase-transition
• 液晶
• 相転移

[keenhwi]

Interesting! Color of LC? is changed with specific intensity of electric field? right?

[kanodai]

Maybe so. The E-field is not completely uniform because ITO electrodes are spreaded using a simple spin-coat method, which may result in roughness of the electrodes. And even if the E-field is completely uniform, the transition threashould may vary place to place because of nonuniformity of LC sample.

Currently my major is ultracold atom physics; completely different field from soft matter physics. So parts of my memories about this experiment began to fade away...

[7Row7enn7]

What happens if you break open a calculator display? Will the LC burn you or somewthing?

[kanodai]

Typical liquid crystals do no harm to your health. Quotes from U. S. Environmental Protection Agency's report entitled "Life-Cycle Assessment of Desktop Computer Displays: Summary of Results":

> ... limited tests that have been conducted by manufacturers indicate that few liquid crystals have acute toxic potential to humans.

[kanodai]

And according to Display Devices Environment and Safety Committee, a part of Japan Electronics and Information Technology Industries Association, LD50 (median lethal dose) of typical liquid crystals are as low as table salt.

Moreover, even large LCDs contain less than 500 mg of liquid crystals (constitutes ~ 5 um thin layer between glass plates), which is mostly confined to the gap between glass plates and never flow out because of its surface tension.

[kanodai]

I updated the description. Thank you for watching!

[RamzGT]

great demonstration, this helped me understand the mechanics of twisted nematic better! thanks!!!!!

[sr903]

how did you build it?

[marsCubed]

ss20goku, Years ago I knew someone who had taken apart a circuit board for components. At some point he must have put his finger to his mouth, because soon afterwards he was in the casualty dept. at his local hospital with cyanide poisoning.

He lived, but it just goes to show; some very toxic substances are used in modern electronic devices.

[ss20goku]

i tore apart a calculater display, it was like from a (very) cheap one too. and i broke the glass, was afraid to get cut =/

and the inside, was like nothing....so i put my finger on it, it was slik and kind of slipper, so i quickly washed my hands cuz i didnt no wat the hell it was, and i like chemistry, its awesome, i no my grammer sucks, but its to make sentences shorter, but main topics is dont do sumthing if u dont no wat ur doin =)