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Combining Polymers and Liquid Crystals for Flexible Photonic Devices. John West Kent State University April 22, 2004. Outline. Why Flexible Printed Flexible Cholesteric Displays Printing techniques Polymer walls Stressed Liquid Crystals

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Combining Polymers

and Liquid Crystals


Flexible Photonic Devices

John West

Kent State University

April 22, 2004



  • Why Flexible
  • Printed Flexible Cholesteric Displays
    • Printing techniques
    • Polymer walls
  • Stressed Liquid Crystals
  • Flexible Optical and Electronic Device Manufacturing Facility

Mike Fisch

David Heineman

Greg R. Novotny

Anatoliy Glushenko

Ke Zhang

Guoqiang(Matt) Zhang

Toshihio Aoki

Ebru Aylin Buyuktanir



Why Flexible??








Approaches to Flexible Displays

  • Conventional LCD’s and OLED/PLEDS require expensive substrates and development of organic TFT’s
    • Conventional LCD’s
      • Use polarized light (non birefringent substrates)
      • Active matrix (organic TFT’s)
      • Surface alignment (high temperature and solvent stability)
      • Oxygen sensitive (barrier layers)
      • Active matrix (organic TFT’s)
  • Unconventional LC Conventional SubstrateApproaches
    • Polymer Dispersed Liquid Crystals
    • Bistable Chosterics
    • Bistable Smectics
    • Dichroic Dye LCDs

PDLCs: The first flexible display??

Manufactured in a continuous roll-to-roll process

Conventional ITO coated polyester substrates (no barrier coatings, no alignment layers)

Single pixel.

bistable cholesterics
Bistable Cholesterics
  • Bright, high contrast images
  • High resolution with passive matrix
  • No polarizers required (can use birefringent substrates)
  • Polymers added for mechanical stability
reflective cholesteric displays


focal conic

Reflective Cholesteric Displays

Switch between reflecting planar texture and weakly scattering focal conic texture


Switching Mechanism




Electric Field

transient planar


focal conic

focal conic


flexible plastic bistable cholesteric display

Figure 1: A four inch square, 320 by 320 pixel bistable cholesteric display made using flexible polyester substrates

Flexible Plastic Bistable Cholesteric Display
  • 4 inch square
  • 320 x 320 pixel
  • bistable cholesteric with polymer
  • flexible polyester substrate

West Rouberol, Francl, Ji, Doane and Pfeiffer

Asia Display, 1995

  • Photolithography makes roll-to-roll processing difficult (expensive)
  • High polymer content formulation produces light scattering
    • Reduces reflection in planar state
    • Increases back scatter in focal conic state
    • Lowers brightness and contrast
preliminary solution
Preliminary Solution
  • Print resist for etching of electrodes:(roll-to-roll processing)
  • Segregate polymer into the inter-pixel region: Polymer Walls (bright display)
wax transfer printing of resist
Wax Transfer Printing of Resist

Thermal Print Head

Wax Transfer Sheet

ITO Coated Polyester Film

Tektronix Phaser 240 Wax Transfer Printer

resist pattern 30 pixels inch
Resist Pattern30 pixels/inch

Close-up of the wax pattern printed onto the ITO coated Mylar. The dark lines are the wax pattern.

A replica of the wax resist pattern.

etching and stripping
Etching and Stripping
  • Standard etch bath of nitric-sulfuric acid
  • Strip using warmed (50 C) tetrahydrofuran or toluene
cell assembly
Cell Assembly

Top Substrate

Bottom Substrate

Cholesteric Polymer Mixture

BL 094 92%

NOA 65 8%


Form Polymer Walls

  • Improve contrast
  • Provide rugged displays
  • Improve the pressure resistance of displays
  • -- PM-STN-LCDs by Sharp*
  • Make possible large area, flexible plastic displays
  • -- adhere the top and bottom substrates
  • -- maintain uniform thickness

* T. Shinomiya, K. Fujimori, S. Yamagishi, K. Nishiguchi, S. Kohzaki, Y. Ishii,

F. Funada, and K. Awane, Asia Display, 255 (1995).


Polymer Wall Formation Methods

  • Photo-mask
  • -- patterned UV exposure of homogeneous mixtures
  • of UV-curable monomers and liquid crystals
  • N. Yamada, S. Kohzaki, F. Funada, and K. Awane, SID Digest of Technical
  • Papers, 575 (1995).
  • T. Shinomiya, K. Fujimori, S. Yamagishi, K. Nishiguchi, S. Kohzaki, Y. Ishii,
  • F. Funada, and K. Awane, Asia Display, 255 (1995).
  • Y. Ji, J. Francl, W. J. Fritz, P. J. Bos, and J. L. West, SID Digest of Technical
  • Papers, 611 (1996).
  • Patterned Electric Field
  • -- blanket UV exposure after phase separation
field formed polymer walls
Field Formed Polymer Walls
  • Apply an electric field while solution is warmed aboveclearing/phase separation temperature

2) Cool to RT with field applied to induce polymer segregation

3) UV expose to form polymer walls

Kim, Francl, Taheri, West,

Appl. Phys. Lett., 72, 2253 (1998).

field induced phase separation
Field Induced Phase Separation
  • A patterned electric field is applied to a mixture of liquid crystal and UV curable monomer
  • Due to a larger dielectric constant, liquid crystal migrates to the high field pixel region while the monomer moves to the low field inter-pixel region
  • When phase separation is complete, exposure to UV light polymerizes the monomer locking in the wall structure

Electric Field Distribution

SEM Image of Polymer Walls

measure rate of field induced phase separation
Measure Rate of Field Induced Phase Separation

Diagram of Test Cell

  • One side of cell has aluminum electrodes which block incoming UV light.
  • Only light passing through inter-pixel makes it to the detector
  • This allows study of change in concentration of E44 in inter-pixel over time
absorbance vs time
Absorbance vs Time

Mixture of E44 and Trimethylolpropane tris(3-mercaptopropionate)

at 40 °C

how t and v affect the rate
How T and V Affect the Rate
  • With the same voltage applied, increasing temperature decreases change observed in absorbance between field on and field off states
rate of phase separation
Rate of Phase Separation
  • Occurs in several seconds.
  • Increasing temperature decreases the magnitude of the effectbut has little effect on the rate.
  • Increasing the voltage increases the rate and extent of phase separation
flexible plastic display
Flexible Plastic Display
  • Compatible with roll-to-roll processing
  • Uses commercially available materials.
stressed liquid crystals
Stressed Liquid Crystals
  • Developed for beam steering applications
    • Decouple thickness and speed
    • Eliminate alignment layers
  • Fastest nematic devices




Unidirectionally Oriented Micro-Domains of Liquid Crystal Separated by Polymer Network

our results

AFM image

  • Middle range of concentration of the polymer: between those for traditional polymer network structures and PDLC.
  • Well-developed interpenetrating structure of polymer chains and connected liquid crystal domains.
  • The active area may be of any size
  • Application of shearing deformation in order to orient the liquid crystal domains

SEM image


Effect of Shearing

  • Reduces the relaxation time of the material.
  • Decrease the scattering in visible region of spectrum.
  • The liquid crystal domains become oriented in the direction of shearing
  • By adjusting the degree of shearing one can control the total phase shift.

Phase retardation shift vs an applied electric field

For a 22 m film almost all change of the phase retardation occurs below 130V.

The change of phase retardation depends linearly on the applied voltage – simple driving devices


Dynamics of the Relaxation

A phase retardation shift of 2 m occurs within 1 ms.

Phase retardation of 0.15 m occurred just in40 microseconds





Possible applications: basic design of an OPA device

  • Beam steering: a tilted LC director will yield an index of refraction gradient
  • Industrial application (laser cutting of metals or glass)
  • Free space communications
  • Fiber-optics connectors
  • Military applications
  • Laser displays
  • Imaging applications



SLCs for display applications

  • 30 volt offset
  • 10 volt pulse
  • 20 sec turn on time
  • 40 sec turn off time
  • Stressed LC films produce ferroelectric speeds in a nematic film
  • No alignment layer
  • No light scattering
  • No hysteresis
  • Linear response
the next step flexible optical and electronic device manufacturing facility
The Next StepFlexible Optical and Electronic Device Manufacturing Facility
  • Wright Capital Grant, $1.6M (State of Ohio)
  • $1.6M match from industry and KSU
  • Add to existing Resource Facility
  • Provide centralized facility for development and prototyping of flexible devices.
  • Develop materials required for flexible displays
    • optimized liquid crystals
    • organic semiconductors
    • conducting polymers
    • optimized substrates
  • Develop fabrications techniques
    • printing electrodes
    • applying thin films
    • lamination
    • cutting

Establish a facility for the research and development of flexible electronic devices

  • Printing
  • Coating
  • Lamination
  • Cutting
  • Electronics
  • Materials Synthesis
Planned Research
  • Evaluation of available substrates
  • Development of printing techniques for electrodes
  • Fabrication of printed flexible VGA display using only commercial materials.

Built on an Effective Academic Industrial Collaboration

Start-Ups bring Innovation and Jobs






Poly Displays

LXD, Inc.



Utilize the unique skills in the region in polymers/liquid crystals and printing to spawn a new industry in flexible displays and related electronic devices.