a. jákli- classification and electro-optical properties of smectic phases of bent-shape molecules

8/3/2019 A. Jkli- Classification and electro-optical properties of smectic phases of bent-shape molecules

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Classification and electro-optical

properties of smectic phases of bent-

shape molecules

A. Jkli

Liquid Crystal Institute, Kent State University, Kent, OH44242

+ great number of coworkers listed later


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Light shutters

45

60

75

90

105

0 5 10 15 20

f

=20Hz

FE Sta

teAFE Sta

te

Tra

nsf

er to chir

a

l

Chir

al

Ra

cemic

Chira

l

Ra

cemic

E (V/m)

Transmittan

ce(%)

ChiralOFF: transparent

ON: opaque

RacemicOFF: opaque

ON: transparent

A. Jkli, D. Krerke, H. Sawade, L-C. Chien, G. Heppke ,Liq. Cryst., 29, 377-381 (2002)


3/28

Haze-free, sub-millisecond switching

Electrode area(chiral)

No electroderacemic

Scattering is based on spontaneous symmetry breaking:Chiral state: spontaneous breaking into left and right handed domains

Racemic state: spontaneous breaking into left and right tilted domains


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Racemic stateTilt Separation Mode (TSN-LCD)


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Chiral state from achiral moleculesChiral Separation Mode (CSM-LCD)


6/28

Chiral state from chiral moleculesNo scattering


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Scattering properties

40

60

80

100

0.15 0.17 0.19 0.21 0.23 0.25-10

-5

0

5

10

TransmittancePolarization current

Time (sec)

Transmittanc

e(%)

current(arb.unit)

10m

60

70

80

90

100

-0.03 -0.01 0.01 0.03

-0.5

0

0.5

1.0

-80

-40

0

40

80

Voltage (V)

TransmittancePolarization currentApplied Voltage (V)

Time (sec)

Transmittance(%)

curr

ent(ar.unit)

4m

Color: white(blueish)

400 500 600 700

40

60

80

100

120 53wt% sz157 in 3F10Bq

4 m DT-cell DC 80COFF (0 V)

ON (3.8 V)

%transm

ission

/ nm


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Thickness dependence:

d>5m: flow effects: domain size increases

scattering efficiency decreasing in time

50

60

70

80

90

100

0 2000 4000 6000 8000 10000

5 m

10m2 m

OFF

ONON

time (sec)

Tran

smittance(%)

d~2m: no flow effect scattering efficiency is stable

scattering in 2m cell is about twice as big as in 10mcells both in ON and OFF states ( thinner cells are

better)

Example

With G.G. Nair, material from Berlin TU


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Voltage dependence:scattering efficiency has a maximum(defect wall size decreases at high fields) optimum field: ~7-10V/m)

0 5 10 15

40

50

60

70

80

90

100

110

field dependency of the

scattering behaviour

for a 4m DT-cell

at 450 nm at different

temperatures for in-

creasing dc E-fields.

T / C

6070

80

90

scattering state

clear state (E=0) : 100% transmission

%transmiss

ion

V / m

with D. Krerke


10/28

Layer chirality may be altered

reversibly by electric fields!

Possible light shutters that use energy only duringretransformation between chiral and racemic states

G. Heppke, A. Jkli, S. Rauch, H. Sawade, Phys. Rev. E, 60, 5575-5579 (1999)


11/28

Most recent example (see S. Rauch for details)

Antiferroelectric racemic

E>20V/m, f>500Hz, t>30s E>20V/m, f=1Hz, t>30s

Ferroelectric chiral, bistablePh. Bault, et al. P.611 ILCC2002


12/28

Vitrified states

DSC curves in heating and cooling.

280 320 360 400-4

-2

0

2

4

P/mW

T / K

280 300 320

0,4

0,6

0,8

250 300

-0,8-0,6

-0,4

-0,2

I SmCP - Gl

144oC 17oC

See details at poster by S. Rauch


13/28

E > Eth

DC

E = 0

E < -Eth

DC

U

U

racemic homochiral

Polarizing micrographs of a 10m

cell without applied voltage at 283

K. The liquid crystal is forming

six states with either racemic (left,

SmCSPA, SmCAPF+/-) or

homochiral layer structure (right,

SmCAPA, SmCSPF+/-). An

interchange between states takesplace when heating the sample to

323 K and applying the

appropriate voltages: E > |Eth| or E

= 0. The chirality of domains may

be interchanged by heating thesample to 373 K and either

applying bipolar square electric

field, E = 300 Vpp and f = 1 KHz

(leading to homochiral texture), or

a triangular electric field, E = 200Vpp and f = 100 Hz (leading to a

racemic texture).

Optically 2-type of states x 3 electronic stateseach pixel hides 3 possible states


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Effect of chiral dopant on polarization and

chirality(with S. Rauch)

cryst. SmC SPA M1

heating T [C] 113.1 174 206.5

H [J/g] 21.6 0.3 21.7

cooling T [C] 105.4 164 207.0

H [J/g] -20.7 0.2 -17.7

N

O

O

O

O

C8H

17O

N OC8H17

F

F

+1.5wt% ZLI 811 (Merck)


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0

5

10

15

20

25

0 5 10 15 20 25E3E

2E

1

racemicchiral

AF pol.peaks.

pol. peakonlyunder

rect. field

no pol.peak

E (V/m)

apparenttiltangle(degree

s)

130oC (SmCP phase)

+15V/m

+15V/m

0V

on SmCsPA phase

+5V/m

-5V/m

0V


16/28

ModelMolecular chirality induces polarization (PS,MC) and a helix

short pitchsynclinic antiferroelectric

helical structure

anticlinic

ferroelectric

synclinic antiferroelectric,

deformed helix - uniform

O ti ll i t i t t


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Optically isotropic state

Material by K. Fodor-Csorba (RISPO, Budapest)

-0.1

0

0.1

0.2

-0.005 0.005

80oC

93oC

85oC

83oC

Time (sec)

Current(a

rb.unit)

0

0.5

1.0

1.5

-0.005

Current*20k

0 0.005

35V75V55V

Time (sec)


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0

0.2

0.4

0.6

0.8

1.0

-50 0 50

31Hz5Hz

Voltage (V)

Transmittan

ce(arb.unit)

Banana-nematics


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Banana nematicsUniaxial or biaxial, or something else?

Cl

O O

O O

O

O

O

O

ORRO

I N SmC - Cr125oC 67oC 60oC

DYNAMIC LIGHT SCATTERINGwith Sam Sprunt and Strahinja Stojadinovic

V

H

V

Hs

488nm

5mW

rub direction

i

n 2n+1

no electrode

electrodeE=2V/m,f=1kHz

R=C H

Material from H. SawadeE. Mtyus, K.Keser:J. Mol. Structures (Theochem), 543, 89 (2001)25m cellwith rubbed polyimide alignment layers homogeneous alignment

Variable i , s and polarization selection:VH, VV, HV, HH


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10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

1.0

1.2

1.4

1.6

1.8

2.0Planar Cell, VH geometry

(q I rub direction n0)

9-CPOB114.71

0C

82.740C

NormalizedCorrelationFunction[a.u.]

Time [s]

Model:nematic-like arrangements of smectic clustersViscoelastic (it forms fibers!!!)

Direct observation of flow in

nematic phase of BCM confirms highviscosity, Approximately 100 timesthat of ordinary nematic

Relaxation rates observed in planar

and homeotropic geometries are nearlydegenerate.

Mode is hydrodynamic likeconventional director fluctuation

modes but approximately 100 timesslower than in usual rod-likethermotropic.


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T>82oC: uniaxial

T


22/28

Nomenclature

n: layer normal;l: director (pointing from end-to-end);

P: polar axis (bow arrow)


23/28

SmAP

Pis along the layers and lis parallel to n

Double orthogonal smectic phase

The uniaxial (single) orthogonal phasewith fluid in layer structure

is called SmA

The biaxial (double) orthogonal phase

with fluid in-layer structuremaybe called SmAA


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SmCP

Pis along the layers and lis tilted with respect to n

Single orthogonal and single tilted smectic phase

The uniaxial (single) tilted phasewith fluid in layer structure

is called SmC

The single orthogonal and single tilted phase

with fluid in-layer structuremaybe called SmAC


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????

Pis tilted away the layers and lis parallel to n

Single tilted and single orthogonal smectic phase


is called SmC

The single tilted and single orthogonal phase

with fluid in-layer structuremaybe called SmCA


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SmCG

Pis tilted away the layers and lis tilted with respect to n

Double tilted smectic phase


is called SmC

The double tilted phase

with fluid in-layer structuremaybe called SmCC

P l h id i


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Polar phases considering

maximum two layer periodicity

AF: antiferroelectric; FE: ferroelectric

a:anticlinic orantileaning; s: synclinic or synleaning


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Switching options

Rotation around long axisOptical axis fixed

Chirality variesSmCA+SmCC+SmACSmCC-SmCA-

Rotation around layer normalOptical axis rotates by 2

Chirality fixedSmCA+ SmCA+

a. jákli- classification and electro-optical properties of smectic phases of bent-shape molecules

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