Combining Polymers
Download
1 / 40

West - University of Akron - PowerPoint PPT Presentation


  • 121 Views
  • Uploaded on

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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'West - University of Akron' - liam


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

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

  • 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

Collaborators


Why Flexible??

Rugged

Lightweight

Roll-to-Roll

Manufacturing

Cheap

Conformable


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)

    • OLED/PLEDS

      • 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

planar

focal conic

Reflective Cholesteric Displays

Switch between reflecting planar texture and weakly scattering focal conic texture


Switching Mechanism

fast

homeotropic

slow

Electric Field

transient planar

fast

focal conic

focal conic

planar


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


Problems
Problems cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

Thermal Print Head

Wax Transfer Sheet

ITO Coated Polyester Film

Tektronix Phaser 240 Wax Transfer Printer


Resist pattern 30 pixels inch
Resist Pattern cholesteric display made using flexible polyester substrates30 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 cholesteric display made using flexible polyester substrates

  • Standard etch bath of nitric-sulfuric acid

  • Strip using warmed (50 C) tetrahydrofuran or toluene


Cell assembly
Cell Assembly cholesteric display made using flexible polyester substrates

Top Substrate

Bottom Substrate

Cholesteric Polymer Mixture

BL 094 92%

NOA 65 8%


Form Polymer Walls cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

SEM Image of Polymer Walls


Measure rate of field induced phase separation
Measure Rate of Field Induced Phase Separation cholesteric display made using flexible polyester substrates

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 cholesteric display made using flexible polyester substrates

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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

  • Compatible with roll-to-roll processing

  • Uses commercially available materials.


Stressed liquid crystals
Stressed Liquid Crystals cholesteric display made using flexible polyester substrates

  • Developed for beam steering applications

    • Decouple thickness and speed

    • Eliminate alignment layers

  • Fastest nematic devices


F cholesteric display made using flexible polyester substrates

LC

polymer

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 cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substratesvs 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 cholesteric display made using flexible polyester substrates

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

Phase retardation of 0.15 m occurred just in40 microseconds


millimeters cholesteric display made using flexible polyester substrates

mm

l=l0/nL

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

l=l0/nH


SLCs for display applications cholesteric display made using flexible polyester substrates

  • 30 volt offset

  • 10 volt pulse

  • 20 sec turn on time

  • 40 sec turn off time


Conclusion
Conclusion cholesteric display made using flexible polyester substrates

  • 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 Step cholesteric display made using flexible polyester substratesFlexible 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.


Goal cholesteric display made using flexible polyester substrates

  • 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


Plan cholesteric display made using flexible polyester substrates

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

  • Printing

  • Coating

  • Lamination

  • Cutting

  • Electronics

  • Materials Synthesis


Planned Research cholesteric display made using flexible polyester substrates

  • 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 cholesteric display made using flexible polyester substrates

Start-Ups bring Innovation and Jobs

HANA

Akron

Polymer

Systems

KSU/UA

Poly Displays

LXD, Inc.


Vision cholesteric display made using flexible polyester substrates

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.


ad