Liquid Crystal Elastomer Dielectric Constant Measurements
description
Transcript of Liquid Crystal Elastomer Dielectric Constant Measurements
Liquid Crystal Elastomer Dielectric Constant
MeasurementsJeremy NealP.Palffy-Muhoray
Ferroelectric Workshop – Kent State University Saturday, June 23, 2007
Liquid Crystal InstituteKent State UniversityKent, Ohio
Liquid Crystal Elastomers• liquid crystal + rubber
• LC nematic monodmain• synthesize here - need to characterize
LC mesogen
polymer backbone
cross-linker
Experiment 1
Variac
Ne Trans.ITO Glass
Elastomer
Elastomer is suspended on a string between two parallel pieces of ITOcoated glass. Elastomer aligns along sufficiently strong applied field.
Video of Experiment
0 2 4 6 8 10 12 140
20
40
60
80
100
120Angle vs. Time
Time (sec)
Ang
le (D
eg)
Experimental DataField On
Field Off
Overview
dd
dtdI 2
2 torqueenergy
I moment of inertia
Want to solve
:Depends on
dielectric constant components
k spring constantmaterial properties
Directly fromexperimental data
TheoryEnergy of elastomer:
2
20
20
12 2
112 2
12 2
V D E k
V E E k
V E P E k
2 20
2
12 2
12 2
V E P E k
V P E k
k - spring constantV -volume
susceptibility
P polarization
orientationally invariant
Theory
n̂m̂
ˆ ˆ
ˆ ˆ ˆ ˆ( )
loc
loc locll ll
locll
P E
E n E m
nn I nn E
�
�
In general:
nnIPNEnnPNE
PEE
appllapp
apploc
ˆˆˆˆ00
0
�
polarizabilitydensity
N depolarizing tensor
where
Theory
0 0
ˆ ˆ ˆ ˆll app ll appP PP E nn E I nn
�
appllllll EInnnnIP��
ˆˆˆˆ1
00
0
1a
0
ll llb
appll EInnnnbIaP�� ˆˆˆˆ
Make substitutions:
then
cont’d
Theory
Choose A & B such that
InnBIAnnbIa���
ˆˆˆˆ
)( baabB
ba
BA
1
appll EInnnnBIAP�� ˆˆˆˆ
aA 1
appll EnnBABIAP�
ˆˆ)()(
appll EInnnnbIaP�� ˆˆˆˆ
then
Theory
dd
dtdI 2
2
212 2V P E k
2 2 2 2
2 2 2
1cos2 2
1cos2 2
app ll app
ll app
V ga AE B A B E k
V B A B E k
2cos sinll appd B A B V E kd
torque
Recall
Thus
Want to solve
orientationally invariant
Theory
)(0
llll1 ,ll
llo
o
1
2
202 ( 1) cos sinll app
d dI B A B V E kdt d
11 ( 1)ll ll
A BN
( 1) ( 1)(1 ( 1) )(1 ( 1) )
ll ll
ll ll
N NB
N N
Need the following: ,
, ,
app
N N depolarizing factors
E electric field
I moment of inertiak or free parameters
Also
So
where
Depolarizing Factors
2 2 2 202 ( ) ( )( )( ), ,
a b c dsNs a s b s c s
a b c ellipse semi axes
101.9.22
a mmb mmc mm
10
1.9
.2
.0076.0922
.9002
llN NNN N
Assume depolarizing factors for an ellipse can be used:
Elastomer Properties
l
w
d
2 2
9 2
8 3
1 ( )12
1.29 10
3.28 10
I m d l
x kg m
V x m
2.003.8.43.386
l cmw mmd mmm g
Electric Field Measurement
VinVout
R1
R2
55.95 10appVE x m
1
2
98.5526,800
R MR
Voltage divider:(110) 15,206(140) 19,353
in
in
V VV V
Thus
Experiment 2
Elastomer is sandwiched between aluminum plates and capacitance is measured with bridge
Capacitance Bridge Elastomer
Al plates
spacers
Vout
CBCU
Theory & Results
Without elastomer:0 ,10 air airs s
tot
AACd d
0 ,20 0air airs s etot
AA ACd d d
Find3.88s
Using1.00059air
With elastomer:
Find3.38
Results
8
3.29
3.38
1.13 10 /k x N m
2
2
d dIdt d
LHS RHS
Using:
0 1 2 3 4 5 6 7 8
-6.0E-06
-4.0E-06
-2.0E-06
0.0E+00
2.0E-06
4.0E-06
6.0E-06
8.0E-06 Torque vs. Time
LHS
RHS
Time (sec)
Torq
ue (
N m
)
Possible Future Work• Remove shape effects:
OR
• Remove anisotropy effects:
• Repeat experiments in magnetic field
Conclusions
• Electric field response used to determine elastomer dielectric constant values
• Would like to do similar magnetic field measurements
• Still a work in progress