Temperature and Frequency Effects on the Dielectric Properties of the Nematic Liquid Crystal 8CB

By

Dr. Chandra Prayaga

Ross Dickenson

Josh Barbee

Overview

• Liquid crystals defined• Applications of liquid crystals• UWF Department of Physics

research in liquid crystals• Results

Liquid Crystals

• Materials that have intermediate states between the solid and the liquid phases

Applications

• Display Technology– Laptop Computers– Digital Watches

• Aquarium Thermometers• Waveguide• Optical Switch

UWF Physics LC Research

• Optical Properties• Thin Films• Microscopy• Electrical: changes in dielectric

properties with frequency and temperature

RC - Circuit

+

VrResistor

-

Capacitor Made With Liquid Crystal

-

Vs

+

Capacitor Construction

Temperature Control

Experimental Apparatus

Data Collection Cycle

Φ = F (freq, Temp)

Set Temperature

Increase Temperature and Repeat

Record Phase Angle from Lock-In Amplifier

Select Frequencies

Graph of Data

Phase Shift Vs. Temperature and Frequency

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

25.00 27.00 29.00 31.00 33.00 35.00

Temperature (Dg C)

Ph

as

e S

hif

t (D

g)

.1 KHz

.05 KHz

.032 KHz

1 KHz

.5 KHz

.25 KHz

1.5 KHz

2 KHz

.32 KHz

.2 KHz

.75 KHz

Our Findings

• Combinations of Temperature and Frequency Contribute to Phase Angle

• Increasing Temperature at any frequency results in a lower phase angle

• At low frequency, room temperature, 8CB behaves like a normal dielectric

• 8CB’s behavior charges dramatically at transition temperature and medium frequencies

Future Efforts

• Refine temperature control• Gather more low frequency data in

the region of 26deg • Apply a magnetic field and

determine upper and lower bounds on the dielectric constant due to alignment of molecules