In a liquid crystal cell used for LCD the conductive substrates, usually made of ITO, are in contact with the liquid crystal. The question is: when a voltage is applied to the electrodes to reorient the molecules is there any current flowing through the liquid? The answer should be positive because LCs are conductive materials. But I know that the molecules should reorient themselves under an applied electric field for example between two plates like a capacitor even without being in contact with the LC. So why the electrodes are placed in contact with the LC and why LCDs consume electricity?


LCs materials are dielectric. But they are not perfect insulators and have some non-zero conductivity, allowing a leakage current to flow, slowly discharging the capacitor. This is caused by mobile ions in the liquid crystal and inside the polyimide layer [2]. Infact a liquid crystal cell can be modeled electrically as this circuit:

         |           |
         |     Cl    |

http://www.lintech.org/comp-per/03lcd.pdf‎ p.10-11
http://www.emdmillipore.com/showBrochure?id=200908.037 p.9

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