Angewandte Fluororganische Chemie: Synthese ... - Fluorine

2. Struktur-Eigenschaftsbeziehungen
“Architecture” of Nematic Liquid Crystals
mesogenic core
structure
Temperature [ C]
tail
Δε > 0
polar
group
link
cyclic subunit
Δε < 0
Δε ~ 0
μ || , ε || , n ||
~ nematic phase director
~ long molecular axis
Display Specific Parameters:
Threshold Voltage V th and Switching Time
Threshold Voltage
V th
= π
Switching Time
τ
on
( K − 2K
)
K1
+ 3
4
ε Δε
2
γ 1d
=
2
2 ⎛V
⎞ on π K ⎜ −1
⎟
1 2
⎝ Vth
⎠
0
2
≅ π
γ d
τ off =
π
K1
ε Δε
0
2
1
2
K1
equilibrium
configuration
K 1
“splay”
K 2
“twist”
K 3
“bend”
μ ⊥ , ε ⊥ , n ⊥
Optimization of Mesophase Range - Side Chains
200
180
160
140
120
100
80
60
40
20
0
H 2m+1 C m
3/1 2/2 5/1 4/1 5/3 3/3 2/3 5/2 3/2 2/4 4/3 3/5 5/5 2/5 4/2 3/4 4/5 5/4 4/4
m/n
F
F
C n H 2n+1
nematic
crystalline
Dielectric Anisotropy: Maier, Meier, 1961
Δ = ε −ε
Δ || ⊥
n = n − n = n − n
P. KIRSCH: Angewandte fluororganische Chemie: Synthese, Pharmazeutika, Flüssigkristalle 38
ε ||
Electrooptic Characteristics and
Molecular Structure
⊥
e
o
2 ( 1−
3cos
) S
NhF
F
kBT
⎭ ⎬⎫
2
⎧ μ
Δε = ⎨Δα
−
β
ε 0 ⎩ 2
Birefringence: Vuks, 1966
Δε > 0
n
Δε < 0
2
ne −1
N ⎛ 2ΔαS
⎞
= ⎜α
+
2
⎟
n + 2 3ε
0 ⎝ 3 ⎠
2
no −1
N ⎛ ΔαS
⎞
= ⎜α
−
2
⎟
n + 2 3ε
0 ⎝ 3 ⎠
2
3
2 2
;
H7C3 C3H7 Δn ~ 0.043
2 ne
+ no
n =
• M. Bremer, K. Tarumi, Adv. Mater. 1993, 5, 842-848.
H11C5 Δn ~ 0.248
C5H11 • M. Klasen, M. Bremer, A. Götz, A. Manabe, S. Naemura, K. Tarumi, Jpn. J. Appl. Phys. 1998, 37, L945-L948.
Optimization of Mesophase Range - Fluorination
No. Structure Mesophases ( C)
1
2
3
4
5
6
7
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
F
F
F
F
F
F
F
F
F
C 2 H 5
C 2 H 5
C 2 H 5
C 2 H 5
C 2 H 5
C 2 H 5
C 2 H 5
C 171 S ? (160) N 217 I
C 118 N 189 I
C 104 N 164 I
K 125 N 195 I
K 125 N 164 I
K 111 S B 149 S A 168 I
K 69 N 175 I
Structure-Property Relationships - Birefringence ( n)
No.
1
2
3
4
5
6
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
H 7 C 3
Structure
C 2 H 5
CH 3
CH 3
CH 3
CH 3
C 2 H 5
n
0.064
0.082
0.167
0.255
0.281
0.364