Bent-Core LC Elastomers and Side-Group LC Polymers Using ...€¦ · Bent-core (banana) liquid...
Transcript of Bent-Core LC Elastomers and Side-Group LC Polymers Using ...€¦ · Bent-core (banana) liquid...
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Bent-Core LC Elastomers and Side-Group LC Polymers Using
Reactive Bent Core LCs
Thursday, September 24
Rafael Verduzco1,2, Brad Lokitz2, Seung Hong3, Martin Chambers3,4, Paul
Luchette4, John Harden4, Peter Sálamon4, Peter Palffy-Muhoray4, Elaine
DiMasi5, Antal Jákli4, Samuel Sprunt3, and James T. Gleeson3
1Department of Chemical and Biomolecular Engineering, Rice University2Center for Nanophase Materials Sciences Oak Ridge National Laboratory
3Department of Physics, Kent State University4Liquid Crystal Institute, Kent State University
5Brookhaven National Laboratory
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Bent-core (banana) liquid crystals exhibit spontaneous polarity
OO
OO
N
OR
N
RO
• Restricted rotational freedom
• Supramolecular chirality
• Polar order
• Unique LC phases
Temperature
IsotropicNematicColumnar
(B1)
Tetrahedratic;
Dark
congolmerate
Lamellar
(SmCP, B6)
Crystal
Reddy, R. A.; Tschierske, C. J. Mater. Chem. 2006, 16, 907-961. (Review)
Etxebarria, J.; Blanca Ros, M. J. Mater. Chem. 2008, 18, 2919-2929. (Review)
Lubensky, T. C.; Radsihovsky, L. Phys. Rev. E., 2002 , 66, 031704.(Phase Behavior)
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Bent-core LCs show a large flexoelectric coupling
Measurement of Flexoelectric
coefficientsNo net
polarization
++
+ ++ + + + +
++
++
+ ++ + + + +
++
Banana
Rod-like
Meyer, Phys. Rev. Let., 22, 918, 1969.
Pd = e1 n (div n) + e3 (curl n) x n
Dewar, et al., J. Chem. Phys., 123, 174907,
2005.
Mechanically induced
polarization
Harden, et al., Phys. Rev. Let., 97, 157802,
2006.
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Bent-Core Polymers and Networks for Flexoelectric Networks
• How can we prepare a free-standing bent-core LC material?
• How does the LC-polymer coupling influence or enhance the
properties observed for bent-core LCs?
• How does the presence of a polymer network affect mesophase
ordering?
• Preparation/Characterization of bent-core LCs
• Route 1: Polysiloxane elastomers swollen with bent-core LCs
• Route 2: Preparation of pure bent-core elastomers
• Route 3: Controlled Polymerization of bent-core LC
Outline:
LC polymer gels/elastomers: Finkelmann, Warner, Kornfield, Hammond, Urayama, Mather
Bent-core LC polymers: Tschierske, Ikeda, Hsiao
Bent-Core LCPolymer/Rubber
elasticity
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X-ray Scattering can reveal pretransitional phenomena and cybotactic clustering
Pretransitional phenomena in Calamitic
LCs:
McMillan, et al., Phys. Rev. A, 6, 936, 1972.
Pretransitional phenomena in Bent-Core
LCs (?):
Bailey, Jakli et al.
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Route 1 towards bent-core LC elastomers
Finkelmann, H.; Greve, A.; Warner, M. Eur. J. Phys. E 2001, 5, 281 crosslink LC side-group
Polymer network
OO
OO
OR2R1O
Cl Cl
Chambers, M., Verduzco, R., Sprunt, S, Gleeson, Jakli, Advanced Materials, 2009
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Materials: Bent-Core Liquid Crystals
Material R1 R2 TI-N(oC)
TN-C(oC)
BC2-ss C8H17 C8H17115 82
BC2-us C8H15 C8H17106.9 58
BC2-uu C8H15 C8H1592.7 38
Material R TI-N(oC)
TN-S(oC)
TS-C(oC)
BC1-ss C10H21 89 62 55
BC1-uu C10H19 106.9 17.4 58
OO
OO
OOC
OR
C
RO
O O
Cl
OO
OO
OR2R1O
Cl Cl
“Giant” Flexoelectricity (Harden, et al.,
Phys. Rev. Lett. 2006, 157802)
BC1: Fodor-Csorba et al., J. Mater. Chem. 2004, 14,2499-2506
Monotropic nematic phase
Enantiotropic nematic phase
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OO
OO
OR2R1O
Cl Cl
Cl Cl
OO
O O
O O
Cl Cl
OO
O O
O O
Cl Cl
OO
O O
O O
BC2-ss
BC2-us
BC2-uu
Materials: Bent-Core Liquid Crystals
BC1: Fodor-Csorba et al., J. Mater. Chem. 2004, 14,2499-2506
BC1
Monotropic
Nematic Phase
“Giant”
Flexoelectricity
Harden, et al.,
Phys. Rev. Lett.
2006, 157802
OO
OO
OOC
O
C
O
O O
Cl
OO
OO
OOC
O
C
O
O O
Cl
BC1-uu
BC1-ssOO
OO
OOC
OR
C
RO
O O
Cl
BC2
Enantiotropic
Nematic Phaseelectr
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Bent-Core LCs swell Calamitic LC Elastomers
Chambers, M., Verduzco, R., Sprunt, S, Gleeson, Jakli, Advanced Materials, 2009.
0 5000 10000 15000 20000 25000 30000
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 1/ /0 1
t te e
t0 =3 60s, t
1 = 176
t (s)
t = 0 h
t = 3 h
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Bent-Core LCs swell Calamitic LC Elastomers
LCE
solvent
V/Vo c
(% mol)
TI-N(oC)
TN-SmX(oC)
TSmX-C(oC)
Tg(oC)
LCE 1.0 0 73.8 -- -- -6.0
BC1-ss 1.93 32 81.0 52.4 30.2 --
BC1-uu 1.70 39 85.9 65.4 29.3 --
BC2-ss 2.11 35 99.1 66.7 21.8 --
BC2-us 2.29 41 85.4 -- -- -1.2
BC2-uu 2.13 30 86.8 -- -- -3.6
Chambers, M., Verduzco, R., Sprunt, S, Gleeson, Jakli, Advanced Materials, 2009.
V/Vo: Ratio of the final swollen volume to the initial unswollen volume
c: Molar concentration of LC in the swollen elastomer at equilibrium
TI-N: Isotropic to Nematic phase transisition temperature on cooling
TN-SmX: Isotropic to Smectic phase transisition temperature on cooling
Tg: Glass-transition temperature
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Swollen LC Elastomer Exhibits Flexoelectricity
OO
OO
OR2R1O
Cl Cl
R1 = C8H15R2 = C8H17
Chambers, M., Verduzco, R., Sprunt, S, Gleeson, Jakli, J. Mater. Chem., in press.
See presentation this Saturday by John
Harden for details on flexoelectric
measurements (RA3, 11:05 on Saturday)
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X-ray scattering of magnetically aligned bent-core LCs reveals four-peak structure
T > TNI T < TNI T
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Swollen elastomers exhibit a broad-low angle peak
95 ℃ 70 ℃ 30 ℃
I N Sm86.8 oC 25.0 oC
Chambers, M., Verduzco, R., Sprunt, S, Gleeson, Jakli, et al., J. Mater. Chem., in press.
25
30
35
40
45
50
55
0.05 0.25
Inte
ns
ity (
a.u
.)
q (Å-1)
38
30
29
85 oC
T
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BC2-us
Monofunctional Bent-Core Liquid Crystals for Bent-core Elastomers and Polymers
BC2
Enantiotropic
Nematic Phase
Cl Cl
OO
O O
O O 66
Polymerizable bent-
core LCele
ctron
ic-Liq
uid C
rystal
Pres
entat
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Synthesis of asymmetric bent-core LC
O
O
HO
DMF, K2CO3
OTs
O
O
O87 %
recryst. EtOH
EtOH, KOH
90 oC, 12 hreflux, 12 h
94 %
SOCl2reflux, 12 h
6
ClCl
OHHO
THF, TEA
OH
O
O
6
Cl
O
O
ClCl
OHO
O
O24 h, 75 %
6
THF, TEA
6
Cl
O
O
24 h, 85 %
Cl Cl
OO
O O
O O 66
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Route 2: Pure Bent-Core Elastomers
BC2-us
crosslink
Bent-core
LC side-group
Polymer network
OO
OO
OR2R1O
Cl Cl
Luchette, Harden, J. P. Palffy-Muhoray, P. via LC Materials Facility
Near Room temperature (~30 oC) bent-core nematic materials
See presentation this Saturday by John Harden for flexoelectric
measurements of this material (RA3, 11:05 on Saturday)
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110℃ 90℃70℃ 50℃
Pure bent-core elastomer exhibits four-peak pattern with marked temperature dependence
I N107 oC
Samples aligned by stretching
Orientation angle of peaks increases
from 35o near the TNI to 45o near
room temperature
85 oC
T
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Route 3: Controlled polymerization of bent-core LC macromonomer leads to end-functionalized polymers
Initiator CTA [M] Conversion Mp PDI
AIBN None 0.20 88 %
(40 h)
29.1K
(DP = 30)
1.5
AIBN
(5:1 ratio)
4-Cyano-4-
(dodecylsulfanylthiocarbonyl)
sulfanylpentanoic acid
0.40 80%
(20 h)
15.2 K
(DP = 15)
1.2
Phase behavior: Polymer is rubbery and nematic at room temperature. It shows
a nematic-isotropic transition at ~ 145 oC and Tg at ~ 25 oC.
Cl Cl
OO
O O
O OO CH37 7
O
Cl Cl
OO
O O
O OO CH37 7
O
AIBN, THF, 65 oC
S
SSCH3
CNHOOCH2CH2C CH2(CH2)10CH3
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X-ray scattering of bent-core polymer in 5CB reveals cooperative alignment of LC and polymer
62 OC 40 OC 34 OC
Solution of 10 % LC polymer in 5CB:
60 OC 50 OC 46 OC
Solution of 30 % LC polymer in 5CB:
Low-angle peak
( > 8 nm)
Polymer Backbone
Bent Core LC
(42 Angstroms)
wide-angle peak
( 25 Angstroms)
5CB
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Acknowledgements
General
Martin Chambers
Seung Hong
Sam Sprunt
Jim Gleeson
Antal Jakli
Jon Harden
Paul Luchette and P. Palffy-Muhoray
Elaine DiMasi and Ron Pindak (BNL)
K. Fodor-Csorba
Funding
CNMS
NSF (DMR 0606160)
Office of Naval Research
(N00014-07-1-0440)
Facilities
CNMS User Facilities
Liquid Crystal Materials Facility
(http://nlcmf.lci.kent.edu/)
Brookhaven National Lab Beamline X6B
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Pure BCLC polymer (polyBCLC_rv187)
122 OC 106 OC
At 126oC the halo becomes anisotropic, and on further cooling in the nematic phase more intense low-angle peaks appear. The d-spacing of the broad halo that first appears is roughly 42 Angstroms. The d-spacing of the additional, sharper low-angle peak is roughly 78 Angstroms. As the samples is cooled below 100 oC, these two peaks at 42 and 78 Angstroms become sharper and more intense. A third broad peak at higher angles also emerges, and this peak has a d-spacing of roughly 25 Angstroms
Below 65oC, the low-angle peak at 78 Angstroms becomes very sharp and intense, suggesting smectic-like order
76OC 45OC
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85 90 95 100 105 110 115
-10
0
10
20
30
40
50
60
70
0
10
20
30
40
An
gle
(d
eg
ree
s)
Peak Intensity
Inte
nsity (
a. u
.)
Temperature (oC)
Peak Angle
Fig. 3. Temperature dependent changes in scattering profiles of BC1 and BC2. a) Scattered intensity averaged over a rectangular area centered around low-angle scattering peak (Qx = 0.15 Å). b) Plot of the temperature dependence of the peak intensity normalized by the maximum scattered intensity at Qy=0.
-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20450
500
550
600
650
85 oC
95 oC
100 oC
103 oC
107 oC
Inte
nsity (
a.
u.)
Qy (Å
-1)
113 oC
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-60 -40 -20 0 201.0
1.1
1.2
1.3
1.4
1.5
1.6
0.00
0.04
0.08
0.12
0.16
L/L
0
T-TNI
(K)
n
Length Change in Bent-Core Swollen Elastomers
-40 -30 -20 -10 0 101.0
1.2
1.4
1.6
0.00
0.04
0.08
0.12
0.16
L/L
0
T-TNI
(K)
n
Unswollen Elastomer
-40 -20 01.0
1.1
1.2
1.3
1.4
1.5
1.6
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
L/L
0
T-TNI
(K)
n
BC1-ss
BC2-su
http://www.tcm.phy.cam.ac.u
k/~mw141/
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POM and XRD reveals phase behavior of bent-core LCs (BC2-ss)
Isotropiccrystal 1
crystal 2
Polarized optical
microscopy
118 oC102 oC
cooling:
heating:
Nematic
IsotropicNematic crystal 1
115 oC75 oC
105 oC
10 20 30 400
10000
20000
30000
40000
50000
60000
70000
80000
90000
140 - 117.5 oC, isotropic
Sca
tte
red
In
ten
sity (
arb
. u
nits)
2 (degrees)
4.2
Å
23
.7 Å
10 20 30 400
10000
20000
30000
40000
50000
60000
70000
80000
90000 140 - 117.5
oC, isotropic
115.0 oC, nematic
112.5 oC, nematic
110.0 oC, nematic
90.0 oC, nematic
Sca
tte
red
In
ten
sity (
arb
. u
nits)
2 (degrees)
4.2
Å
23
.7 Å
10 20 30 400
50000
100000
150000
200000 140 - 117.5
oC, isotropic
90.0 oC, nematic
87.5 oC, crystal 2
85.0 oC, crystal 2
72.5 oC, crystal 2
Sca
tte
red
In
ten
sity (
arb
. u
nits)
2 (degrees)
21
.5 Å
3.8
Å
Wide-angle x-ray
diffraction
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Liquid
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org/pr
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Liquid crystal networks enable functional devices
Palffy-Muhoray et al. http://www.tcm.phy.cam.ac.uk/~mw141/mw_talk/index.html
Mark Warner et al.
Ikeda et al.
Liquid Crystal Elastomer Gel
Liquid Crystal Elastomers, Terentjev E. and Warner, M.
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onic-
Liquid
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org/pr
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http://www.tcm.phy.cam.ac.uk/~mw141/mw_talk/index.htmlhttp://www.tcm.phy.cam.ac.uk/~mw141/mw_talk/index.htmlhttp://www.tcm.phy.cam.ac.uk/~mw141/mw_talk/index.html
-
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 50 100 150 200
Strain
Vis
co
sit
y (
Pa
s)
5 wt % polymer
5 CB
Bent-core LC shows an oblate conformation in calamitic liquid crystal
n v
5 wt. % polymer
solution shows
director tumbling
behavior
Electro-optic
experiments show
K3 >> K1
prolateoblate
Jamieson, Kornfield, et al.
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Liquid
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Measurement of Flexoelectric Coupling in Liquid Crystal Materials
0
20
40
60
-50 -25 0
BCN1+BCN3BCN3+6008BCN1
T-TN-I
e 3 (
nC
/m)
BC1-uu + BC2-uu
BC2-uu + 6008
BC1-uu
Harden, et al., Phys. Rev. Lett. 2006, 157802
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Converse Flexoelectric Effect
0
20
40
60
80
100
-30 -20 -10 0 10 20
converse
direct
Adjusted temperature T-TNI
(oC )
e3 (
nC
/m)
Figure : The set-up (left) and the temperature dependence of the bend flexoelectric constant measured by the converse (red) and direct (blue) effects
(right).
Harden, et al., Phys. Rev. E 2008, 78, 031702
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Conclusions
Bent-core elastomers can be prepared by swelling polysiloxane
networks, and they exhibit properties characteristic of unswollen LC
elastomers
RAFT affords well-defined LC homopolymers, and these can be used
as building blocks for complex polymeric architectures
Bent-core molecules exhibit an enhanced flexoelectricity, and this can
be measured using a direct flexing device and by studing the converse
flexing effect
Future work includes investigating block copolymers to form self-
assembled gels and elastomers and investigating the
supramolecular clustering of bent-core molecules
Lubensky, T. C.;
Radsihovsky, L. Phys.
Rev. E., 2002 , 66,
031704.(Phase
Behavior)
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0 10 20 30 40
1
2
3
4
5
K3/K
1
%wt BCLC polymer in 5CB
Electro-optic measurements indicate an oblate polymer conformation in solution
0 1 2 3 4
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
n
Voltage (V/m)
Red – 0% polyBCLC in 5CB
Blue – 20% polyBCLC in 5CB
Green – 40% polyBCLC in 5CB
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Swollen LC Elastomers
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0
20
40
60
-50 -25 0
BCN1+BCN3BCN3+6008BCN1
T-TN-I
e 3 (
nC
/m)
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onic-
Liquid
Crys
tal Pr
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tation
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Length Change in Bent-Core Swollen Elastomers
http://www.tcm.phy.cam.ac.u
k/~mw141/
-40 -30 -20 -10 0 101.0
1.2
1.4
1.6
0.00
0.04
0.08
0.12
0.16
L/L
0
T-TNI
(K)
n
Unswollen Elastomer
OO
OO
OOC
OR
C
RO
O O
Cl
-40 -20 01.0
1.1
1.2
1.3
1.4
1.5
1.6
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
L/L
0
T-TNI
(K)
n
-60 -40 -20 0 201.0
1.1
1.2
1.3
1.4
1.5
1.6
0.00
0.04
0.08
0.12
0.16
L/L
0
T-TNI
(K)
n
OO
OO
OR2R1O
Cl Clele
ctron
ic-Liq
uid C
rystal
Pres
entat
ions
electr
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Liquid
Crys
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