Polymer-doped vertically-aligned nematic liquid crystals

Abstract

A system having a vertically-aligned negative delta E nematic liquid crystal host material and a small amount of liquid crystal polymer is provided. The liquid crystal polymer improves the switching speed of a vertically aligned nematic system without sacrificing contrast or viewing angle.

We claim: 
     
         1 . A nematic liquid crystal composition, comprising:
 a negative delta epsilon liquid crystal host; and between 0.01 and 5 wt % of a liquid crystal polymer wherein the liquid crystal polymer has the structure (FX1):   
       
         
           
           
               
               
           
         
         wherein PX is a polymer backbone selected from, 
       
       
         
           
           
               
               
           
         
       
       [—(CH 2 —CH—S) n —], [—(NH—CH—C(═O)) n —], [—(—C(═O)—N—C(═O)) n —], [—(Si(CH 3 )—O) n —], [—(CH 2 —CH(C(O)═O)) n —], [—(CH 2 —C(CH 3 )(C(O)═O)) n —], [—(CH 2 CH) n —], [—(CH(CH 2 CH 2 )) n —] and [—(CH 2 —CH(CH 2 CH 2 )) n —] where, in each PX, n is independently an integer between 30 to 10000;
 W is a straight-chain or branched hydrocarbon group spacer having between 1 to 40 carbon atoms, wherein one or more adjacent or nonadjacent —CH 2 — groups in the hydrocarbon group can be independently replaced with —S—, —S(═O)—, —O—, —C(═O)—, —O—C(═O)—, —(Si—R 40 R 41 )—, —[OSiR 40 R 41 ] d —, —[Si(R 40 R 41 )O] d —, —[Si(R 40 R 41 )—(OSiR 40 R 41 ) d ]—, —OSiR 40 R 41 O—, —CF 2 —, and —GeR 40 R 41 —, where R 40  and R 41  are each independently a hydrogen or a C1-C5 straight chain or branched alkyl group wherein any hydrogen may be replaced with fluorine, and wherein d is independently an integer from 1 to 6; 
 M is a mesogen. 
 
     
     
         2 . The nematic liquid crystal composition of  claim 1  wherein M is: 
       
         
           
           
               
               
           
         
         wherein b and e are independently 0 or 1; bb is an integer from 0 to 10; aa is an integer from 0 to 10; and each A, R 1  and R 2  is independently a cycloalkane ring having from 3 to 8 carbons, independently a cycloalkene ring having from 3 to 8 carbons, an aromatic ring, or a fused two or three ring structure; where there may be from 1 to 6 cycloalkane rings and from 0 to 5 aromatic rings in M; 
         each L is independently selected from a direct bond, —O—, —O—C(═O)—, —C(═O)—O—, —C═C—, —C≡C—, —(CH 2 ) u —; where u is an integer from 1 to 10; 
         wherein one or more ring carbon atoms in one or more of A, R 1  and R 2  may be replaced with —N—, —S—, and —O—; 
         one or more hydrogens on any of A, R 1  and R 2  can be independently replaced with fluorine, chlorine, bromine, —CF 3 , —OCF 3 , —OCF 2 H and —OCFH 2 ; and 
         wherein each T is a terminating group independently selected from hydrogen, —CN, or a one- to fifteen-carbon alkyl, alkoxy or alkenyl chain wherein one or more hydrogen atoms may be independently replaced with fluorine and one or more —CH 2 — groups may be independently replaced with —O— or —O(C═O)—. 
       
     
     
         3 . The nematic liquid crystal composition of  claim 1  wherein the negative delta epsilon liquid crystal host is selected from nematic liquid crystal compositions comprising compounds having 4′-alkylbicyclohexyl-2,3-difluoro-4-alkyloxyphenyl and 4′-cyclohexyl-2,3-difluoro-4-alkyloxyphenylbenzene groups. 
     
     
         4 . The nematic liquid crystal composition of  claim 1  wherein the negative delta epsilon liquid crystal host has a delta epsilon of less than 0. 
     
     
         5 . The nematic liquid crystal composition of  claim 1  wherein the liquid crystal polymer has a delta epsilon value of between −5 and −10. 
     
     
         6 . The nematic liquid crystal composition of  claim 1  wherein the liquid crystal polymer has a delta epsilon value of greater than 0. 
     
     
         7 . The nematic liquid crystal composition of  claim 1  wherein the liquid crystal polymer has a delta epsilon value of less than 0. 
     
     
         8 . The nematic liquid crystal composition of  claim 1 , wherein W is —(CR 15 R 16 ) y —, where y is an integer from 1 to 40; wherein R 15  and R 16  are each independently hydrogen or halogen;
 wherein any adjacent or nonadjacent —(CR 15 R 16 )— group can be independently replaced with 
 —S—, —S(═O)—, —O—, —C(═O)—, —O—C(═O)—, —(Si—R 40 R 41 )—, —[OSiR 40 R 41 ] d —, —[Si (R 40 R 41 )O] d —, —[Si (R 40 R 41 )—[OSiR 40 R 41 ] d ]—, —OSiR 40 R 41 O—, —CF 2 —, and —GeR 40 R 41 —, where R 40  and R 41  are each independently a hydrogen or a C1-C5 straight chain or branched alkyl group wherein any hydrogen can be replaced with fluorine, and wherein d is independently an integer from 1 to 6. 
 
     
     
         9 . The nematic liquid crystal composition of  claim 1 , wherein W is —(CH 2 ) r —[Si(CH 3 ) 2 ] m —(CH 2 ) nn —[Si(CH 3 ) 2 ] m —(CH 2 ) r —O—[(C═O)] z —, wherein each r and nn is independently an integer from 0 to 6, each m is independently an integer from 0 to 6; z is 0 or 1. 
     
     
         10 . The nematic liquid crystal composition of  claim 1  wherein M is selected from: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
         11 . The nematic liquid crystal composition of  claim 1 , wherein in the liquid crystal polymer, M is a fused three ring structure having the formula: 
       
         
           
           
               
               
           
         
         where each R is independently C1-C6 alkyl. 
       
     
     
         12 . The nematic liquid crystal composition of  claim 1 , wherein in the liquid crystal polymer, M has the structure 
       
         
           
           
               
               
           
         
         where R is a C1-C6 alkyl or alkoxy or is CN. 
       
     
     
         13 . The nematic liquid crystal composition of  claim 2 , wherein each A, R 1  and R 2  is independently selected from: 
       
         
           
           
               
               
           
         
         where each X 5 , X 6 , X 7 , X 8 , X 9 , X 10  and X 11  can be independently replaced with —N—, —S— or —O—; 
         each X 1 , X 2 , X 3 , X 4 , X 12 , X 13 , X 14 , X 15 , X 16 , X 17 , and X 18  is independently hydrogen, —F, or —CF 3 . 
       
     
     
         14 . The nematic liquid crystal composition of  claim 1 , wherein M is selected from: 
       
         
           
           
               
               
           
         
         where R 25  is C1-C6 alkyl or C1-C6 alkoxy. 
       
     
     
         15 . The nematic liquid crystal composition of  claim 1 , wherein the liquid crystal polymer has the structure (FX9), (FX10) or (FX9A): 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         where n is an integer from 500 to 1,000 and a is an integer from 5 to 9. 
       
     
     
         16 . A nematic liquid crystal composition, comprising:
 a negative delta epsilon nematic liquid crystal host; and between 0.01 and 5 wt % of a liquid crystal polymer, wherein the liquid crystal polymer has the structure (FX11):   
       
         
           
           
               
               
           
         
         wherein PX is a polymer backbone; W is a thiol or siloxy-containing spacer; M is a mesogen, EG is a polystyrene end group, and each i is independently 0 or 1. 
       
     
     
         17 . The liquid crystal composition of  claim 16 , wherein one i is 1 and one i is 0. 
     
     
         18 . The liquid crystal composition of  claim 16 , wherein the liquid crystal polymer has the structure (FX12A): 
       
         
           
           
               
               
           
         
         where i is 1; 
         EG is 
       
       
         
           
           
               
               
           
         
       
       where d is independently an integer from 100 to 1000 and each R 10 , R 11  and R 12  is independently hydrogen, halogen or —CN;
 PX is 
 
       
         
           
           
               
               
           
         
       
       [—(CH 2 —CH—S) n —], [—(NH—CH—C(═O)) n —], [—(—C(═O)—N—C(═O)) n —], [—(Si(CH 3 )—O) n —], [—(CH 2 —CH(C(O)═O) n —], [—(CH 2 —C(CH 3 )(C(O)═O) n —], [—(CH 2 CH) n —], [—(CH(CH 2 CH 2 ))— n ] or [—(CH 2 —CH(CH 2 CH 2 )) n —] where in each PX n is independently an integer between 50 to 10000;
 W is a spacer selected from —S—, —S(═O)—, —O—, —C(═O)—, 
 
       
         
           
           
               
               
           
         
         where q is an integer from 0 to 10; 
         t is an integer from 1 to 10; 
         R 3 , R 4 , R 5  and R 6  are each independently selected from optionally substituted C 1 -C 6  alkyl, where the optional substituents are one or more halogens; 
         each L is independently selected from: —O—C(═O)—, —C(═O)—O—, —C═C—, —C≡C—, —(CH 2 ) u —; and a single bond; where u is an integer from 1 to 10; 
         R 1  and R 2  are each independently selected from: 
       
       
         
           
           
               
               
           
         
         where X 1 , X 2 , X 3  and X 4  are independently hydrogen, halogen, methoxy, C1-C 3  alkyl or —CN; where (a) each Z and each Y is CH, or (b) each Z is N and each Y is CH, or (c) each Y is N and each Z is CH; 
         R 7  and R 8  are each independently hydrogen, halogen, and —(O) v —(CH 2 ) p —CH 3  where p is an integer from 0 to 20 and v is 0 or 1 and where 
         R 30  and R 31  are each independently hydrogen or halogen. 
       
     
     
         19 . An optical device comprising:
 two opposing electrode surfaces;   the nematic liquid crystal composition of  claim 1  disposed therebetween.   
     
     
         20 . A method of preparing a nematic liquid crystal composition, comprising:
 contacting a nematic liquid crystal host; and   between 0.01 and 5 wt % of a liquid crystal polymer which is soluble in the nematic liquid crystal host.