Electrophoretic displays using nanoparticles

• US 6,721,083 B2
• Filed: 11/04/2002
• Issued: 04/13/2004
• Est. Priority Date: 07/19/1996
• Status: Expired due to Fees

• Current Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Original Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Inventors: Pullen, Anthony E., Whitesides, Thomas H., Wang, Jianna, Gray, Caprice L., Drzaic, Paul S., Jacobson, Joseph M., Morrison, Ian D.
• Primary Examiner(s): Ben, Loha
• Application Number:
  US10/065,617
• Publication Number:
  US 20030096113A1
• Time in Patent Office: 526 Days
• Field of Search: 359/296, 345/108, 345/107, 345/85, 345/86, 264/4, 264/4.1, 264/4.3, 106/31.16, 106/31.32, 106/31.64
• US Class Current: 359/296
• CPC Class Codes: B41J 2/01 Ink jet
• CPC Class Codes: B41J 2/02 generating a continuous ink jet
• CPC Class Codes: B41J 3/4076 printing on rewritable, bistable "electronic paper" by a focused electric or magnetic field
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: C09D 11/30 Inkjet printing inks
• CPC Class Codes: C09D 11/50 Sympathetic, colour changing or similar inks
• CPC Class Codes: G02B 26/026 based on the rotation of particles under the influence of an external field, e.g. gyricons, twisting ball displays based on orientable dipolar particles G02F1/172; based on electrophoresis G02F1/167
• CPC Class Codes: G02F 1/133305 Flexible substrates, e.g. plastics, organic film
• CPC Class Codes: G02F 1/13336 Combining plural substrates to produce large-area displays, e.g. tiled displays
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13439 characterised by their electrical, optical, physical properties; materials therefor; method of making
• CPC Class Codes: G02F 1/1347 Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
• CPC Class Codes: G02F 1/167 by electrophoresis
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: G02F 2201/44 Arrangements combining different electro-active layers, e.g. electrochromic, liquid crystal or electroluminescent layers
• CPC Class Codes: G02F 2202/28 Adhesive materials or arrangements
• CPC Class Codes: G02F 2202/36 Micro- or nanomaterials
• CPC Class Codes: G04B 47/00 Time-pieces combined with other articles which do not interfere with the running or the time-keeping of the time-piece clockwork cases for special purposes G04B37/12; clocks with magnifying glass built in the face G04B39/00; time-pieces in which parts or cases produce special effects, e.g. aesthetic effects, G04B45/00, particularly with inscriptions or pictures moved by hand G04B45/003, with specially shaped cases or parts G04B45/0069; combination of writing or drawing implements with devices for indicating time B43K29/087; combined with cameras, projectors, or photographic printing apparatus G03B29/00
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field
• CPC Class Codes: H05K 1/097 Inks comprising nanoparticles and specially adapted for being sintered at low temperature H05K1/095 takes precedence
• CPC Class Codes: H05K 3/105 : by conversion of non-conductive material on or in the support into conductive material, e.g. by using an energy beam
• CPC Class Codes: H05K 3/1241 : by ink-jet printing or drawing by dispensing
• CPC Class Codes: H10K 10/46 : Field-effect transistors, e.g. organic thin-film transistors [OTFT] H10K10/43 takes precedence
• CPC Class Codes: H10K 10/462 : Insulated gate field-effect transistors [IGFETs]
• CPC Class Codes: H10K 85/30 : Coordination compounds
• CPC Class Codes: H10K 85/60 : Organic compounds having low molecular weight H10K85/10 - H10K85/50 take precedence
• CPC Class Codes: Y10T 428/25 : Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
• CPC Class Codes: Y10T 428/294 : including metal or compound thereof [excluding glass, ceramic and asbestos]

Abstract

An electrophoretic display comprises a fluid and a plurality of nanoparticles having diameters substantially less the wavelengths of visible light such that, when the nanoparticles are in a dispersed state and uniformly dispersed throughout the fluid, the fluid presents a first optical characteristic, but when the nanoparticles are in an aggregated state in which they are gathered into aggregates substantially larger than the individual nanoparticles, the fluid presents a second optical characteristic different from the first optical characteristic. The electrophoretic display further comprises at least one electrode arranged to apply an electric field to the nanoparticle-containing fluid and thereby move the nanoparticles between their dispersed and aggregated states. Various compound particles comprising multiple nanoparticles, alone or in combination with larger objects, and processes for the preparation of such compound particles, are also described.

Claims

1. A nanoparticle assembly comprising a nanoparticle, a second particle and a tether connecting the nanoparticle to the second particle, the tether having first and second states differing in electrical conductivity such that at least one optical characteristic of the nanoparticle assembly changes when the tether is varied from its first state to its second state.

2. A nanoparticle assembly according to claim 1 wherein the second particle is a second nanoparticle.

3. A nanoparticle assembly according to claim 2 wherein the two nanoparticles are formed of the same material.

4. A nanoparticle assembly according to claim 3 wherein the material is an electrically conductive metal.

5. A nanoparticle assembly according to claim 4 wherein the electrically conductive metal is one of silver, gold, platinum, palladium and an alloy of any of these metals.

6. A nanoparticle assembly according to claim 3 wherein the material is a semiconductor.

7. A nanoparticle assembly according to claim 6 wherein the semiconductor is cadmium selenide.

8. A nanoparticle assembly according to claim 2 wherein the tether has a length not greater than about 2 nm.

9. A nanoparticle assembly according to claim 1 wherein the tether comprises an electroactive polymer or oligomer capable of being switched between a conducting and a non-conducting state by a reversible redox reaction.

10. A nanoparticle assembly according to claim 9 wherein the electroactive polymer or oligomer comprises at least one thiophene, pyrrole, furan, aniline, phenyl, ethynyl or pyridyl repeating unit.

11. A nanoparticle assembly according to claim 9 wherein the electroactive polymer or oligomer comprises polythiophene.

12. A nanoparticle assembly according to claim 11 wherein the polythiophene contains from about 3 to about 5 repeating units.

13. A nanoparticle assembly according to claim 1 wherein the nanoparticle comprises an electrically conductive metal and is connected to the tether via a thiol linkage.

14. A nanoparticle assembly according to claim 1 wherein the second particle is larger than the nanoparticle and has a plurality of nanoparticles attached thereto, each nanoparticle being attached via a separate tether.

15. A nanoparticle assembly according to claim 14 wherein the second particle comprises an electrode.

16. A nanoparticle assembly according to claim 14 wherein the plurality of tethers have substantially the same length.

17. An electro-optic medium comprising a plurality of nanoparticle assemblies according to claim 1 and means for varying the electrical conductivity of the tethers of the nanoparticle assemblies.

18. An electro-optic medium according to claim 17 wherein the second particle is a second nanoparticle, the nanoparticle assemblies being dispersed in a solvent or gel, the solvent or gel containing an electrolyte.

19. An electro-optic display comprising an electro-optic medium according to claim 18 and a pair of electrodes on opposed sides of the electro-optic medium, at least one of the electrodes being substantially transparent.

20. An electro-optic medium comprising:

a suspending fluid;

a plurality of a first type of particles suspended in the suspending fluid, the first type of particles being light transmissive and bearing an electric charge; and

a plurality of a second type of particles suspended in the suspending fluid, the second type of particles being smaller than the first type of particles and bearing an electric charge of opposite polarity, the particles being such that when no electric field is applied to the medium and the second type of particles lie on the surfaces of the first type of particles, the medium presents a first optical characteristic, but when an electric field is applied to the medium and the second type of particles are removed from the surfaces of the first type of particles and dispersed through the suspending fluid, the medium presents a second optical characteristic different from the first optical characteristic.

21. An electro-optic medium according to claim 20 wherein the first type of particles comprise any one or more of silica, titania and a polymer.

22. An electro-optic medium according to claim 20 wherein the first type of particles have an average diameter of about 500 to about 2000 nm.

23. An electro-optic medium according to claim 20 wherein the second type of particles are formed from a metal.

24. An electro-optic medium according to claim 20 wherein the second type of particles have an average diameter of about 3 to about 60 nm.

25. A nanoparticle assembly comprising a plurality of nanoparticles dispersed in a polymeric medium or gel, the medium or gel having first and second states differing in electrical conductivity such that at least one optical characteristic of the nanoparticle assembly changes when the medium or gel is varied from its first to its second state.

26. An electrophoretic display comprising a fluid containing a plurality of nanoparticles and at least one electrode arranged to apply an electric field to the fluid and thereby move the nanoparticles through the fluid the nanoparticles having diameters substantially less than the wavelengths of visible light, the diameters of the nanoparticles being such that, when the nanoparticles are in a dispersed state and uniformly dispersed throughout the fluid they display a low level of light scattering so that the fluid presents a first optical characteristic, but when the nanoparticles are in an aggregated state in which they are gathered into aggregates substantially larger than the individual nanoparticles, the nanoparticles display a substantially increased level of light scattering so that the fluid presents a second optical characteristic different from the first optical characteristic, the electric field being effective to move the nanoparticles between their dispersed and aggregated states.