1. Liquid Crystal Materials

2. Broad Classification Lyotropics Thermotropics + - hydrophobic
amphiphilic molecules, polar and non-polar
parts form liquid crystal phases over certain
concentration ranges when mixed with a
solvent
molecules consisting of a rigid core and
flexible tail(s) form liquid crystal phases
over certain temperature ranges.
hydrophobic
non-polar tail
flexible tail + -
hydrophilic
polar head
rigid core

3. The Lyotropic Phases micelle cross section reverse micelle

4. The molecule above (5CB) is ~2 nm × 0.5 nm
The Thermotropic Liquid Crystal Molecule
Chemist’s
View
Physicist’s
Engineer’s
View CN
Shape Anisotropy
Length > Width
The molecule above (5CB) is ~2 nm × 0.5 nm

5. ( ) ( ) Geometrical Structures of Mesogenic Molecules
Low Molecular Weight High Molecular Weight
(polymers)
( )
disk-like
rod-like n
( ) n
most practical applications

6. Crystal Nematic LC Isotropic Temperature
The Liquid Crystal Phase n
Crystal Nematic LC Isotropic
Temperature

7. The Nematic Director n n The local average axis
of the long molecular axis

8. Smectic C Smectic A Nematic Temperature
Other Liquid Crystal Phases n z n n q
Smectic C Smectic A Nematic
Temperature

9. Chirality left-handed right-handed mirror images H-C-C-C-C-C C N
The methyl group on the 2nd carbon atom
on the alkyl chain of the molecules extends
out of the plane of the paper and the hydro-
gen atom extends into the plane of the paper.
Therefore the 2nd carbon can be thought of
as a right or left handed coordinate system
left-handed right-handed H H H H H
mirror images
H-C-C-C-C-C
C N H H H H H
non-chiral H H H H H
H-C-C-C-C-C
C N
CH3
non-superimposable H H H H
chiral (RH)

10. The Chiral Nematic Ordinary Nematic Chiral Nematic n P CN CN director
pitch P

11. The Chiral Doped Nematic
You can create a cholesteric material by doping a conventional
nematic with a chiral dopant.
For dilute solutions
Chiral Dopant HTP (mm)-1 S IS
- indicates left twist sense
For a 10% doping of S-811

12. The Chiral Smectic C: Ferroelectricsq m
Eye- dipole moment m
fin - chiral
ferroelectric LC has a
dipole moment perp-
endicular to its long
axis, and is chiral.

13. The Chiral Smectic: TGB
Twisted Grain Boundary (TGB)
A twisted grain boundary smectic A phase (frustrated) - TGBA*

14. Discotic Liquid Crystal
example: R=OCOC11H23 C R O R

15. Discotics Liquid Crystalsn n
Nematic discotic phase
Columnar, columns of molecules
in hexagonal lattice

16. Polymer Liquid Crystals
Combining the properties of liquid crystals and polymers
Main Chain Side Chain
mesogenic moieties
attached as side chains
on the polymer backbone
mesogenic moieties are
connected head-to-tail
rigid
semi-flexible

17. Polymer Liquid Crystals
forming nematic liquid crystal phases n
side-chain
main-chain

18. Example of Side-Chain Polymer LCs
-(-CH2-C-)X- O
O C-O-(CH2)n-O
C-O R2
Too slow for display applications (switching times ~ s
Useful for other applications such as:
Optical filters
Optical memory
Alignment layers for low molecular weight LCs
Non-linear optic devices (optical computing)

19. The Order Parameter n q n no order perfect order perfect crystal
isotropic fluid

20. Maier-Saupe Theory - Mean Field Approach
Interactions between individual molecules are represented by a
potential of average force n y q
{V: minimum} when phase is ordered (-P2(cosq))
{V: V=0} when phase is disordered (<P2(cosq)>)
factor for intermolecular strength ( n) f
From Statistical Mechanics (Self Consistency)
b=(kT)-1

21. n n Temperature Maier-Saupe Theory - Mean Field Approach Isotropic
1.0
Isotropic
Fluid
Nematic
Liquid
Crystal
Order Parameter, S
0.0 n
-0.6
Temperature

22. Landau-de Gennes Theory
a=ao(T-T*), ao, b, c, T*, L are phenomenological constants
G is a surface interaction strength
Good near NI transition
surface
Order Parameter, S
Predicts order near
surface
Temperature

23. How does it affects display performance ?
The Order Parameter:
How does it affects display performance ?
The order parameter, S, is proportional to a number of important
parameters which dictate display performance.
proportional to
Parameter Nomenclature 
Elastic Constant Kii S2
Birefringence Dn S
Dielectric Anisotropy De S
Magnetic Anisotropy Dc S
Viscosity Anisotropy Dh S
Example: Does the threshold switching voltage for a TN increase
or decrease as the operating temperature increases.
Scales as the square root of S
therefore lowers with increasing temperature

24. Anisotropy: Dielectric Constant
Off-axis dipole moment, angle b with molecular axis b
N: number density
h,f: reaction field, reaction
cavity parameters
S: order parameter
Da: anisotropy in polarizability
m: molecular dipole moment
kB: Boltzman constant
T: Temperature
For values of the angle b<54.7o, the
dipolar term is positive, and for
values b>54.7o, the dipolar term is
negative, and may result in a
materials with an overall -De.

25. Anisotropy: Dielectric Constant++ e + ++
positive
- - -
- - e
De = e - e > 0 E + E -
negative
all angles in
the plane 
to E are
possible for the
-De materials
De = e - e < 0

26. Anisotropy: Duel Frequency
high frequency, De<0
low frequency, De>0
MLC-2048 (EM Industries), Duel Frequency Material
Frequency (kHz)
Dielectric Anisotropy (De)

27. Dielectric Constants (@20oC, 1kHz)
*Mixture Application De e e
BL038 PDLCs
MLC-6292 TN AMLCDs
ZLI-4792 TN AMLCDs
TL205 AM PDLCs
Fiber-Optics
De material
*EM Materials
Materials Dielectric Constant
Vacuum
Air
Polystyrene
Polyethylene
Nylon
Water

28. Dielectric Constants: Temperature Dependence
4’-pentyl-4-cyanobiphenyl
Temperature Dependence
Average Dielectric Anistropy

29. Magnetic Anisotropy: Diamagnetism
Diamagnetism: induction of a magnetic moment in opposition
to an applied magnetic field. LCs are diamagnetic due to the
dispersed electron distribution associated with the electron
structure.
Delocalized charge makes
the major contribution to
diamagnetism.
Ring currents associated with
aromatic units give a large
negative component to c for
directions  to aromatic ring
plane. Dc is usually positive since:

30. Magnetic Anisotropy: Diamagnetism
Compound

31. Optical Anisotropy: Birefringence
ordinary ray (no, ordinary index of refraction)
extraordinary ray (ne, extraordinary index
of refraction)

32. Optical Anisotropy: Birefringence
ordinary wave
extraordinary wave
optic
axis q
For propagation along the optic
axis, both modes are no

33. Optical Anisotropy: Phase Shift
f = 2pdno,e/l
Df = fe - fo=2pdDn/l
Dn = ne - no
0 < Dn < 0.2
depending on deformation
380 nm < l < 780 nm
visible light
analyzer
liquid
crystal
polarizer
light

34. Birefringence (20oC @ 589 nm)
EM Industry Dn ne no Application
Mixture
BL PDLC
TL PDLC
TL AM PDLC
ZLI STN
ZLI TN
ZLI AM TN LCDs
MLC AM TN LCDs
ZLI AN TN LCDs
MLC ECB
De devices
MLC IPS
MLC IPS
Fiber Optics
ZLI De device

35. Birefringence: Temperature Dependence
Average Index
Temperature
Dependence

36. Birefringence Example: 1/4 Wave Plate
circular polarized
What is minimum d for
liquid crystal 1/4 wave plate ?
linear polarized
Unpolarized d
LC: Dn=0.05
polarizer
Takes greater number of e-waves
than o-waves to span d, use
Dn=0.05

37. ò Nematic Elasticity: Frank Elastic Theory Splay, K Twist, K Bend, K FdV d V e o = Ñ × + - ò 1 2 11 22 33 24 13 { ( ) } )} n E B c D
Splay, K
Twist, K
Bend, K 22 33 11

38. Surface Anchoring
Alignment at surfaces propagates over macroscopic distances
microgrooved surface -
homogeneous alignment (//)
rubbed polyimide
ensemble of chains -
homeotropic alignment ()
surfactant or silane

39. Surface Anchoring q f N polar anchoring Wq n surface azimuthalWf
Wq,f is energy needed to
move director n from
its easy axis
Strong anchoring J/m2
Weak anchoring J/m2

40. E or B Creating Deformations with a
Field and Surface - Bend Deformation
E or B

41. E or B Creating Deformations with a
Field and Surface - Splay Deformation
E or B

42. E or B Creating Deformations with a
Field and Surface - Twist Deformation
E or B

43. Magnitudes of Elastic Constants
EM Industry K11 K22 K33
Mixture (pN) (pN) (pN) Application
BL PDLC
TL AM PDLC
ZLI TN AM LCD
ZLI TN
ZLI AM LCD
Order of magnitude estimate of elastic constant
U: intermolecular interaction energy
a: molecule distance

44. Elastic Constant K22:
Temperature Dependence

45. The Flexoelectric Effect- + - +
Undeformed
state of banana
and pear shaped
molecules
Polar structure
corresponds to
closer packing
of pear and
banana molecules
Bend
Polar Axis
Splay

46. Effects of an Electric Fieldy E x q e e
Electric Free Energy Density
Electric Torque Density
Using De = 5 and E=0.5 V/mm

47. Effects of an Magnetic Fieldy n B x q c c
Magnetic free energy density
Magnetic torque density
Using Dc = 10-7 m3kg-1 and B= 2 T = 20,000 G

48. Deformation Torque x q Surface Orientation of molecules obeys this eq.
Free energy density from elastic theory
Torque density

49. Deformation Torque x q Surface Material Shear Modulus Steel 100 GPa
Silica GPa
Nylon GPa
Shear modulus  Young’s modulus

50. x Coherence Length: Electric or Magnetic q E Surface Balance torqued x E
Balance torque
Find distance d
Coherence length x
Using E = 0.5 V/mm
and De = 20

51. n n  n  n  Viscosity: Shear Flow Viscosity Coefficient h11 h33
Typically h22 > h33 >h11

52. Viscosity: Flow Viscosity Coefficient
LC specification sheets give
kinematic viscosity in mm2/s
Kinematic Viscosity (n)
1 m2/s
Dynamic Viscosity (h)
1 kg/m·s = 1 Pa·s
0.1 kg/m·s = 1 poise
Approximate density

53. Viscosity: Flow Viscosity Coefficient
Typical Conversion Density Conversion
Flow r kg/ms = 1 poise
Viscosity
EM Industry Kinematic (n) Dynamic (h)
MIXTURE CONFIGURATION (mm2/s) (Poise)
ZLI-4792 TN AM LCDs
ZLI-2293 STN
MLC-6610 ECB
MLC-6292 TN AM LCDs (Tc=120oC)
Fiber Optics (no=1.4599)
TL205 PDLC AM LCD
BL038 PDLCs (Dn=0.28)

54. Viscosity: Temperature Dependence
C4H9
H3CO
For isotropic liquids
E is the activation energy for diffusion of molecular motion.

55. Viscosity: Rotational Viscosity Coefficient
Rotation of the director n bv external
fields (rotating fields or static).
Viscous torque's Gv are exerted on a liquid
crystal during rotation of the director n
and by shear flow. n
Time n
g1: rotational viscosity coefficient

56. Viscosity: Rotational Viscosity Coefficient
EM Industry Viscosity Viscosity
MIXTURE CONFIGURATION (mPas) (Poise)
ZLI-5400 TN LCDs
ZLI TN AM LCDs
ZLI-2293 STN
De Applications
MLC-6608 TN AM LCD

57. Viscosity: Comparisons
Material Viscosity (poise)
Air
Water
Light Oil
Glycerin 1.5
LC-Rotational (g1) 1< g1 < 2
LC-Flow (hii) 0.2< hii<1.0

58. Relaxation from Deformation
field on state
Surface x
Relaxation when field is turned off
Relaxation time t
Surface
zero field
state x

59. Relaxation from Deformation
Balance viscous/deformation torque
Assume small deformations
Solution
For 100 mm cell
For 5 mm cell

60. Freedericksz Transition - The Threshold Iy E n z E Ec q x y x d n
At some critical E
field, the director
rotates, before Ec
nothing happens

61. Freedericksz Transition - The Threshold II
E-field
free energy
total
free energy
Minimize free energy with
‘Euler’ Equation

62. Freedericksz Transition - The Threshold III
differential equation
soln.
small q
threshold
mid-layer tilt (deg)
E/Ec

63. Defects s=1/2 s=-1 s=-1/2 s=+1 s=+1 s=+1 s=+2 s=3/2 The singular line
(disclination) is pointing
out of the page, and director
orientation changes by
2ps on going around the
line (s is the strength)
s=+2
s=3/2

64. Estimate Defect Size
The simplest hypothesis is that the core or defect
or disclination is an isotropic liquid, therefore the
core energy is proportional to kBDTc. Let M be the
molecular mass, N Avogadadro’s number and r
the density of the liquid crystal.

65. Microscopic Fluttering and Fluctuations
Characteristic time t of
Fluctuations:
Can see fluctuations with
microscope:
Responsible for opaque
appearance of nematic LC
Thermally induced
Deformations

66. Z Z’ Y X A General Structure X & Y are terminal groups
Aromatic or saturated ring core
X & Y are terminal groups
A is linkage between ring systems
Z and Z’ are lateral substituents
CH3 - (CH2)4
C N
4-pentyl-4’-cyanobiphenyl (5CB)

67. Common Groups Mesogenic Core Linking Groups Ring Groups biphenyl
terphenyl
diphenylethane
stilbene
tolane
schiffs base
azobenzene
azoxyben-
zene
phenylbenzoate
(ester)
phenylthio-
benzoate
phenyl N
pyrimidine N
cyclohexane

68. Nomenclature Mesogenic Core terphenyl biphenyl phenyl benzyl benzene
phenylcyclohexane (PCH)
cyclohexane
cyclohexyl 3’ 2’ 2 3 1’ 1
Ring Numbering
Scheme 4’ 4 5’ 6’ 6 5

69. Terminal Groups CH2 CH2 straight chain CH2 CH3 branched chain (chiral)
(one terminal group is typically an alkyl chain)
CH2
CH2
straight chain
branched chain
(chiral)
CH2
CH3
CH2
CH2
C*H
CH3
CH3
Attachment to mesogenic ring structure
Direct alkyl (butyl)
Ether O- alkoxy (butoxy)

70. Terminal Groups CH3- methyl CH3-O- methoxy CH3-CH2- ethyl CH3-CH2-O-
propyl
CH3-(CH2)2-O-
propoxy
CH3-(CH2)3-
butyl
CH3-(CH2)3-O-
butoxy
CH3-(CH2)4-
pentyl
CH3-(CH2)4-O-
pentoxy
CH3-(CH2)5-
hexyl
CH3-(CH2)5-O-
hexoxy
CH3-(CH2)6-
heptyl
CH3-(CH2)6-O-
heptoxy
CH3-(CH2)7-
octyl
CH3-(CH2)7-O-
octoxy

71. Second Terminal Group and Lateral Substituents (Y & Z)H
F flouro
Cl chloro
Br bromo
I iodo
CH3 methyl
CH3(CH2)n alkyl
CN cyano
NH2 amino
N(CH3) dimethylamino
NO2 nitro
phenyl
cyclohexyl

72. Odd-Even Effect Clearing point versus alkyl chain length O
CH3-(CH2)n-O
C-O
O-(CH2)n-CH3 18 16 14 12 10
clearing point
carbons in alkyl chain (n)

73. Nomenclature Common molecules which exhibit a LC phase
CH3-(CH2)4
C N
4’-pentyl-4-cyanobiphenyl
CH3-(CH2)4-O
C N
4’-pentoxy-4-cyanobiphenyl

74. Structure - Property A vary mesogenic core A C-N (oC) N-I(oC) Dn De
CH3-(CH2)4
C N
A C-N (oC) N-I(oC) Dn De N

75. Structure - Property X C-N (oC) N-I (oC) H F Br CN CH3 C6H5 87.5 92.0
vary end group
CH3-(CH2)4
COO X
X C-N (oC) N-I (oC) H F Br CN
CH3
C6H5
87.5
92.0
115.5
111.0
106.0
155.0
114.0
156.0
193.0
226.0
176.0
266.0

76. Lateral Substituents (Z & Z’)X A Y
Z and Z’ are lateral substituents
Broadens the molecules
Lowers nematic stability
May introduce negative dielectric anisotropy

77. Why Liquid Crystal Mixtures
Melt Temperature:
Liquid Crystal-Solid
ln ci = DHi(Teu-1 - Tmi-1)/R
DH: enthalpies
Teu: eutectic temperature
Tmi: melt temperature
R: constant
Nematic-Isotropic
Temperature: TNI
TNI = S ciTNIi
Isotropic Liquid
Liquid
Crystal
Temperature
eutectic
point
Solid
Concentration (c2), %

78. EM Industry Mixtures
S-N <-40 C solid nematic transition (< means supercools)
Clearing C nematic-isotropic transition temperature
Viscosity (mm2 /s) flow viscosity, some materials may stipulate the
+20 C rotational viscosity also. May or may not give
0 C a few temperatures
K33/K ratio of the bend-to-splay elastic constant
De dielectric anisotropy
Dn optical birefringence (may or may not give ne, no)
dDn (mm) product of dDn (essentially the optical path length)
dV/dT (mV/oC) how drive voltage changes as temperature varies
V(10,0,20)
V(50,0,20) threshold voltage (% transmission, viewing angle,
V(90,0,20) temperature)

79. EM Industry Mixtures Property ZLI 4792 MLC 6292/000 MLC 6292/100
S-N <-40 C <-30 C <-40 C
Clearing C C C
Viscosity (mm2 /s)
+20 C
0 C
-20 C
-40 C
K33/K De Dn
dDn (mm)
dV/dT (mV/C)
V(10,0,20)
V(50,0,20)
V(90,0,20)

80. Summary of Fundamentals
Thermotropic Liquid Crystal
Anisotropy
Nematic phase
Chirality
Order parameters
Dielectric Anisotropy
Diamagnetism
Birefringence
Elastic constants
Surface Anchoring
Viscosity
Threshold
Defects
Eutectic Mixture