conduct research on the properties and applications of polymer
cholesteric liquid crystal (pCLC) flakes. Developed and characterized
in our laboratory in the mid '90's, pCLC's retain the optical
property of wavelength-selective reflection found in low molecular
weight mesogens, but in a robust form that is environmentally
stable. Thin films of pCLC material are freeze-fractured into
small, flat particles of arbitrary size (20-80 µm) with
a thickness of ~5 µm.
may be added to an adhesive and coated onto a surface, or they may
be suspended in a host liquid medium and confined within a cell
with transparent, conductive coatings. Particles that are fixed
in a binder find applications as decorative paints, or as polarizing
pigments for document security. In a low viscosity fluid confined
between substrates, flake rotation with an external electric field
may some day form the basis for electronic paper color displays.
normally incident on a flake surface is circularly polarized and
selectively reflected. The application of a small electric field
causes the particles to tilt away from normal, causing the intensity
of reflected light of a given wavelength to change. Under moderate
dc and ac fields, pCLC flakes exhibit motion that results in large
intensity changes with response times under a second. Our work has
shown that, by using host fluids with moderately large dielectric
constants, controlled flake motion from 0 to 90 degrees of tilt
may be observed with applied ac voltages less than 50 mv rms/µm
and response times less than 500 ms. There are significant opportunities
for these flakes in particle display technology and electronic paper,
where they would offer both polarization for 3-D and variable color.
However, significant materials and process issues need to be addressed.
models for flake motion indicate that there are several variables
that might be exploited to reduce response time and improve control
of particle tilt. Among these are particle dielectric properties,
shape anisotropy, host viscosity, host dielectric properties, and
confinement geometry. These are subjects for our research.
and shaped flakes manufactured with soft lithography; on the cover
of Advanced Functional Materials, Feb. 2004
recently succeeded in manufacturing shaped flakes by soft lithography.
When driven with 50 Hz AC fields in dielectric fluid-filled, ITO
coated cells, these flakes exhibited very uniform reorientation
behavior with response times below 300 ms.
shaped PCLC flakes encapsulated in a PVA binder. The fluid host
was doped with a red dye to distinguish microcapsules from air voids.
also recently succeeded in encapsulating flakes in flexible binders.
This work may open up the possibility for bistable, flexible, electronic
display applications. Earlier papers are listed here. More recent
papers are listed elsewhere on this site.
A. Trajkovska-Petkoska and S. D. Jacobs, “Effect of Different Dopants on Polymer Cholesteric Liquid Crystal Flakes,” Molecular Crystals and Liquid Crystals, 495, pp. 334-347 (2008)
A. Trajkovska-Petkoska, T. Z. Kosc, K. L. Marshall, K. Hasman, and S. D. Jacobs, “Motion of Doped-Cholesteric Liquid Crystal Flakes in a Direct-Current Electric Field,” , J. Appl. Phys., 103, pp. 094907 (2008)
T. Z. Kosc, K. L. Marshall, S. D. Jacobs, and J. C. Lambropoulos, "Polymer Cholesteric Liquid Crystal Flake Reorientation in an AC Electric Field," J. Appl. Phys., 98, 013509 (2005)
A. Trajkovska-Petkoska, R. Varshneya, T. Z. Kosc, K. L. Marshall, and S. D. Jacobs, "Enhanced Electro-optic Behavior for Shaped Polymer Cholesteric Liquid Crystal (PCLC) Flakes Made by Soft Lithography," Adv. Funct. Mater., 15(2), 217-222 (2005)
Z. Kosc, K. L.Marshall, A. Trajkovska-Petkoska, R. Varshneya and
S. D. Jacobs, "Development of Polymer Cholesteric Liquid Crystal
Flakes for Electro- Optic Applications," Optics & Photonics
News, p. 33 (Dec., 2004).
T. Z. Kosc, K. L. Marshall, and S. D.Jacobs, "Electrically
Addressable Optical Devices Using a System of Composite Layered
Flakes Suspended in a Fluid Host to Obtain Angularly Dependent Optical
Effects," U.S. Patent No. 6,829,075 (7 Dec., 2004).
L. Marshall, E. Kimball, S. McNamara, T. Z. Kosc, A. Trajkovska-Petkoska,
S. D. Jacobs, "Electro-optical behavior of polymer cholesteric
liquid crystal flake/fluid suspensions in a microencapsulation matrix,"
Liquid Crystals VIII, edited by I.-C. Khoo, (SPIE, Bellingham, WA,
2004), Vol. 5518, pp. 170-180.
K. Marshall, T. Kosc, S. Jacobs, S. Faris, L. Li. “Electrically
Switchable Polymer Liquid Crystal and Polymer Birefringent Flake/Fluid
Host Systems and Optical Devices Utilizing Same.” U.S. Patent
6,650,042 issued on December 16, 2003.
Z. Kosc, K. L. Marshall, and S. D. Jacobs“
Polymer Cholesteric Liquid Crystal Flake Particle Displays Utilizing
Maxwell-Wagner Polarization Effects for Switching,” , presented
at the SID 23rd Annual International Display Research Conference,
Phoenix, AZ, 8 September 2003, pp. 237–239.
Z. Kosc, K. L. Marshall, and S. D. Jacobs ,“Polymer
Cholesteric Liquid Crystal Flakes for Particle Displays,” in 2003
SID International Symposium, Digest of Technical Papers , 1st
ed., edited by J. Morreale (Society for Information Display, San
Jose, CA, 2003), Vol. 34, Book 1, pp. 581 - 583.
Z. Kosc, K. L. Marshall, S. D. Jacobs, J. C. Lambropoulos, and S.
Faris, "Electric-Field-Induced Motion of Polymer Cholesteric
Liquid Crystal Flakes in a Moderately Conductive Fluid,"
Appl. Opt. 41, 5362-5366 (2002).
Z. Kosc, K. L. Marshall, and S. D. Jacobs, "Electric Field
Induced Rotation of Polymer Cholesteric Liquid Crystal Flakes: Mechanisms
and Applications," in Liquid Crystals IV, edited by
I. C. Khoo (SPIE, Bellingham, WA, 2002), Vol. 4799, pp. 96-101 (invited).
Z. Kosc, S. D. Jacobs, K. L. Marshall, and B. Klehn, "Polymer
Cholesteric Liquid Crystal Flakes for Display and Other Electro-Optic
Applications," presented at the Novel Optical Materials and
Applications Meeting (NOMA), Cetraro, Italy, 20-27 May 2001.