Polymerization-encapsulated cholesteric liquid crystal for bistable reflective displays
View Patent ↗A liquid crystal polymer dispersion is formed where liquid crystal encapsulation is produced by a process in which a reactive additive formulation is mixed and photo-polymerized. The polymerizable additive formulation includes monofunctional, multifunctional and photoinitiator compounds in specific composition. The polymerizable additive formulation enhances the control of deformed globule or droplet size, structure integrity, electro-optical properties, and prohibits flow of the liquid crystal as it is encapsulated. A simple process and a controllable system for encapsulating cholesteric materials that provides rugged low-power flexible passively-driven displays. Such displays offer the possibility of lower cost roll-to-roll manufacturing in addition to lighter weight, more rugged and conformable displays.
1. A bistable polymer dispersed liquid crystal display comprising:
at least one substrate;
a polymerized liquid crystal dispersion disposed on said at least one substrate, said dispersion comprising a plurality of domains, wherein said liquid crystal dispersion comprises at least a non-polymerizable liquid crystal material, a mixture of polymerizable monomers, and a polymerization initiator, wherein said polymerizable monomers comprise one or more polymerizable groups; and
wherein a size of each said domain is controlled by a functionality of said polymerizable monomers defined by
F
=
∑
x
=
1
n
f
x
*
M
x
/
∑
x
=
1
n
M
x
,
wherein F is functionality,
f x is the number of polymerizable groups,
M x is a mass fraction of the dispersion material, and
n is the number of polymerizable monomers in said dispersion.
2. The display according to claim 1 , wherein each said domain has a polymeric boundary wall adjoined to an adjacent domain.
3. The display according to claim 2 , wherein said non-polymerizable liquid crystal material comprises a cholesteric liquid crystal.
4. The display according to claim 2 , further comprising:
a pair of opposed substrates having said liquid crystal dispersion received between said substrates, each said substrate having a facing surface with an electrode disposed thereon.
5. The display according to claim 4 , wherein said substrates are made from a flexible plastic material.
6. The display according to claim 4 , wherein said substrates are made from a glass material.
7. The display according to claim 4 , wherein said electrodes are made from a transparent conductive metal.
8. The display according to claim 4 , wherein said electrodes are made from a conducting polymer.
9. The display according to claim 4 , wherein said electrodes are made from a conductive blend of carbon nanotubes.
10. The display according to claim 2 , wherein said liquid crystal dispersion is formed from at least a non-polymerizable liquid crystal material, a mixture of polymerizable monomers, and a polymerization initiator, and wherein a size of said domain is controlled by a ratio of non-polymerizable liquid crystal material to said polymerizable monomers and said polymerizable initiator.
11. The display according to claim 1 , wherein said mixture of polymerizable monomers comprises mono- and multi-functional monomers.
12. The display according to claim 11 , wherein said liquid crystal dispersion further comprises one or more surfactants and block co-polymers.
13. The display according to claim 1 , wherein said polymerizable monomers comprise a thio-ene, epoxy, divinyl, vinyl ether, oxetane, acrylate, or methacrylate monomer, or mixture thereof.
14. The display according to claim 1 , wherein said mixture of polymerizable monomers comprises at least one monomer with a single polymerizable group and at least one monomer with multiple polymerizable groups.
15. The display according to claim 14 , wherein said single polymerizable group and said multiple polymerizable groups each independently are selected from thio-ene, epoxy, divinyl, vinyl ether, oxetane, acrylate, and methacrylate groups.
16. The display according to claim 14 , wherein said single polymerizable group can be represented by the formula
wherein R 1 is H, CH 3 , CF 3 , or halogen, and W is O or a COO group.
17. The display according to claim 14 , wherein one or more of said multiple polymerizable groups can be represented by the formula
wherein R 1 is H, CH 3 , CF 3 , or halogen, and W is O or a COO group.
18. A method of preparing a polymer dispersed liquid crystal display, comprising:
mixing a liquid crystal dispersion comprising a non-polymerizable liquid crystal material, a mixture of polymerizable monomers, and a polymerization initiator;
phase separating said liquid crystal dispersion into a plurality of domains; and
controlling a size of each said domain by selecting the functionality of said polymerizable monomers, wherein said polymerizable monomers comprise one or more polymerizable groups, and wherein the functionality of said polymerizable monomers is defined by
F
=
∑
x
=
1
n
f
x
*
M
x
/
∑
x
=
1
n
M
x
,
wherein F is functionality,
f x is the number of polymerizable groups,
M x is a mass fraction of the dispersion material, and
n is the number of polymerizable monomers in said dispersion.
19. The method according to claim 18 , wherein said phase separating step comprises:
phase separating by polymerizing said liquid crystal dispersion.
20. The method according to claim 18 , further comprising:
disposing said liquid crystal dispersion on a substrate.
21. The method according to claim 18 , further comprising:
disposing said liquid crystal dispersion between a pair of opposed substrates.
22. The method according to claim 18 , further comprising:
disposing said liquid crystal dispersion between a pair of opposed flexible plastic substrates having at least one electrode disposed on each facing surface.
23. The method of claim 18 , wherein said polymerizable groups are selected from thio-ene, epoxy, divinyl, vinyl ether, oxetane, acrylate, and methacrylate groups.
24. The method of claim 18 , further comprising:
disposing said liquid crystal dispersion between a pair of opposed flexible plastic substrates having at least one electrode disposed on each facing surface; and
selecting said functionality so that a switched focal conic state is substantially indistinguishable from an unswitched focal conic state.
25. The method of claim 18 , further comprising:
disposing said liquid crystal dispersion between a pair of opposed flexible plastic substrates having at least one electrode disposed on each facing surface; and
selecting a weight ratio of liquid crystal and polymer so that a switched focal conic state is substantially indistinguishable from an unswitched focal conic state.
26. The method according to claim 18 , further comprising:
controlling a size of each said domain by adjusting a ratio of said non-polymerizable liquid crystal material to said polymerizable monomers and said polymerizable initiator.
27. The method of claim 18 , wherein said mixture of polymerizable monomers includes mono- and multi-functional monomers.