Transcript seastars_LC_RC_04-26..

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
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Optical Properties
Thin Films
Microscopy
Electrical: changes in dielectric
properties with frequency and
temperature
RC - Circuit
Capacitor Made With Liquid Cry stal
+
Vs
-
+
Resistor
Vr
-
Capacitor Construction
Temperature Control
Experimental Apparatus
Data Collection Cycle
Set
Temperature
Select
Frequencies
y
Record Phase Angle
from Lock-In Amplifier
1
0.5
Φ = F (freq, Temp)
0
0
1.25
2.5
3.75
5
x
-0.5
-1
Increase Temperature and Repeat
Graph of Data
Phase Shift Vs. Temperature and Frequency
80.0
70.0
Phase Shift (Dg)
60.0
50.0
40.0
2 KHz
1.5 KHz
1 KHz
.75 KHz
.032 KHz
30.0
20.0
.5 KHz
.32 KHz
.25 KHz
.2 KHz
.05 KHz
.1 KHz
10.0
0.0
25.00
27.00
29.00
31.00
Temperature (Dg C)
33.00
35.00
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