Polymer dispersed ferroelectric smectic liquid crystal formed by inducing a force during phase separation

• US 5,530,566 A
• Filed: 02/25/1994
• Issued: 06/25/1996
• Est. Priority Date: 09/24/1992
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Kumar, Satyendra
• Primary Examiner(s): Pellman Gross, Anita
• Assistant Examiner(s): TRICE, RONALD
• Application Number:
  US08/201,902
• Time in Patent Office: 851 Days
• Field of Search: 359/100, 359/51, 359/52, 359/43, 359/46
• US Class Current: 349/86
• CPC Class Codes: C09K 19/0225 Ferroelectric
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals

Abstract

Disclosed is a class of light modulating materials comprising microdomains of ferroelectric smectic liquid crystal dispersed in a light-transmissive polymer medium. The microdomains are formed by phase separation of the liquid crystal from solution with the polymer as the polymer is solidified. The switching of the liquid crystal may be either monostable or multistable (e.g., bistable), depending on the liquid crystal and polymer. The material modulates light in either a scattering-transmissive mode or a birefringence mode. Materials operating in the scattering-transmissive mode do not require polarizers, Advantages of the materials include switching times down to the order of microseconds or less, multistable optical states, wide viewing angles and high contrast.

Claims

1. A method for forming a light modulating material comprising the steps of:

a) forming a solution having a mesogenic component capable of forming a ferroelectric smectic liquid crystal phase and a medium-forming component capable of forming a light transmissive polymer medium;

b) inducing a force in the solution to promote alignment of molecules of the mesogenic component along a direction relative to a surface of the solution; and

c) solidifying the medium-forming component while the force is induced to promote phase separation of microdomains of the ferro-electric smectic phase from the polymeric medium.

2. A method according to claim 1 wherein the step of inducing a force in the solution is performed by imposing an electromagnetic field in the solution while the medium-forming component is being solidified.

3. The method of claim 2 wherein the step of imposing an electromagnetic field includes imposing an electromagnetic field having a electric field component perpendicular to the surface of the solution.

4. The method of claim 2 wherein the step of imposing an electromagnetic field includes imposing an electromagnetic field having a magnetic field component parallel to the surface of the solution.

5. The method of claim 4 wherein the step of imposing an electromagnetic field includes imposing an electromagnetic field having a magnetic field component parallel to the surface of the solution and a DC electric field component perpendicular to the surface;

and

wherein the method includes the additional steps of positioning optical polarizers adjacent the material and adjusting the polarization directions of the polarizers to maximize or minimize light transmission.

6. A method according to claim 1 wherein the step of inducing a force in the solution is performed by imposing a thermal gradient along a direction parallel to the surface of the solution while the medium-forming component is being solidified.

7. A method according to claim 1 wherein said step of inducing said force is performed by shearing said material to promote elongation of droplets of the ferroelectric smectic phase.

8. A method according to claim 7 wherein the mesogenic material is selected to have positive dielectric anisotropy.

9. A method according to claim 7 wherein the step of shearing the material is performed while heating the material to a temperature in which the liquid crystal is in the smectic A or smectic C phase.