Lyotropic Liquid Crystals

1 Generic Relationships between Non -Amphiphilic and Amphiphilic Mesophases

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of the "Fused" Type Relationship of Cubic Mesophases ("Plastic Crystals") Formed by Non-Amphiphilic Globular Molecules to Cubic Mesophases of the Amphiphilic Series G. W . GRAY Department of Chemistry, The University, Hull, HU6 7 R X , England P. A . WINSOR Shell Research, Ltd., Thornton Research Centre, Chester, CH1 3SH, England

A generic relationship exists between lamellar mesophases (smectics A and C), formed by non-amphiphilic

mesogens

with lath-like molecules and "fused" lamellar mesophases, G (with or without solvents), formed by amphiphilic mesogens. A second generic relationship

occurs between

non-amphi-

philic nematic mesophases and two-dimensionally hexagonal "middle" mesophases (M

1,

M2), formed by fibrous amphi-

philic micelles. A third generic relationship is now proposed between

three-dimensionally

periodic

cubic

mesophases ("plastic crystals"), formed by

"rotational"

non-amphiphilic

mesogens with globular molecules, and cubic mesophases (S

1c,

V

1,

V ), 2

formed

by globular

amphiphilic

micelles.

Finally it is suggested that the cubic mesophase, "smectic D," formed by a few non-amphiphilic

mesogens with lath-

-likemolecules, is a rotational mesophase based on globular groupings (of parallel molecules) that arise in the transition between smectics A and C.

> " p h e p u r p o s e of this a c c o u n t is t o p o i n t o u t c e r t a i n g e n e r i c r e l a t i o n s h i p s between

t h e mesophases o f t h e n o n - a m p h i p h i l i c

series—nematic,

1 Friberg; Lyotropic Liquid Crystals Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

2

L Y O T R O P I C LIQUID

CRYSTALS

smectic, a n d plastic c r y s t a l — a n d the fused mesophases—middle

(M iand

M ) , smectic ( G ) , a n d c u b i c ( S i , V i , a n d V ) — o f t h e a m p h i p h i l i c series. 2

c

The

2

c u b i c a m p h i p h i l i c mesophases

( S i , V i , and V ) from c

2

their

i n t e r p o s i t i o n i n t h e succession o f mesophases S i , M i , V i , G , V , a n d M , c

2

2

h a v e g e n e r a l l y b e e n t e r m e d ' l i q u i d c r y s t a l l i n e " l i k e t h e o p t i c a l l y anisot r o p i c a m p h i p h i l i c mesophases M i , G , a n d M . T h e c u b i c mesophases 2

f o r m e d b y n o n - a m p h i p h i l i c globular molecules

have however

usually

b e e n t e r m e d " p l a s t i c c r y s t a l s / ' T h i s n o m e n c l a t u r e has o b s c u r e d t h e f a c t t h a t these " p l a s t i c crystals" are f u n d a m e n t a l l y l i q u i d crystals r a t h e r t h a n s o l i d cyrstals a n d b e a r a r e l a t i o n s h i p to t h e o p t i c a l l y a n i s o t r o p i c n o n a m p h i p h i l i c s m e c t i c a n d n e m a t i c l i q u i d crystals s i m i l a r to that b o r n b y


the a m p h i p h i l i c c u b i c mesophases to t h e o p t i c a l l y a n i s o t r o p i c " n e a t " ( G ) a n d m i d d l e ( M i a n d M ) l i q u i d c r y s t a l l i n e phases. 2

Mesophases of Nematic

Type

T h e intermicellar e q u i l i b r i u m w h i c h , according to the R theory ( I , 2, 3 ) is r e s p o n s i b l e f o r the succession of m i c e l l a r a m p h i p h i l i c s o l u t i o n phases, b o t h a m o r p h o u s a n d l i q u i d c r y s t a l l i n e , is s h o w n i n F i g u r e 1. A n a l o g o u s l y to the formation of the nematic mesophase i n t h e n o n a m p h i p h i l i c series b y t h e p a r a l l e l a r r a n g e m e n t

of lath-like

molecules

w i t h o u t other l o n g r a n g e p o s i t i o n a l o r o r i e n t a t i o n a l o r d e r ( F i g u r e 2 a ) , i n t h e a m p h i p h i l i c series t h e m i d d l e mesophases M i a n d M b y the parallel arrangement celles,

of c y l i n d r i c a l fibrous m i c e l l e s .

b e c a u s e o f t h e i r i n d e f i n i t e extension,

are arranged

2

are formed These m i in a two-

d i m e n s i o n a l h e x a g o n a l l a t t i c e ( F i g u r e 3 ) w h i c h confers a h i g h v i s c o s i t y o n these M phases t h a t is n o t f o u n d w i t h n o n - a m p h i p h i l i c n e m a t i c phases. Mesophases of Smectic

Type

I n t h e n o n - a m p h i p h i l i c series t h e s m e c t i c A m e s o p h a s e is c o n s t i t u t e d b y a n extension of t h e p a r a l l e l m o l e c u l a r o r d e r i n g i n t h e n e m a t i c p h a s e so that t h e p a r a l l e l l a t h - l i k e m o l e c u l e s a r e g r o u p e d i n p a r a l l e l i n d e f i n i t e l y extended

sheets

(Figure

2b).

I n t h e a m p h i p h i l i c series,

the smectic

m e s o p h a s e G ( F i g u r e 4 ) is f o r m e d b y t h e p a r a l l e l a r r a n g e m e n t of i n d e f i nitely extended lamellar " s a n d w i c h " micelles i n w h i c h the a m p h i p h i l i c molecules

have

a polar head-to-polar

head position a n d hydrocarbon

t a i l - t o - h y d r o c a r b o n t a i l a r r a n g e m e n t w i t h solvents, i f present, p a r t i t i o n e d b e t w e e n t h e O , C , a n d W regions

( R e f . 3, p . 273) according to their

polarity. I n the n o n - a m p h i p h i l i c smectic A mesophase ( F i g u r e 2 b ) , the p a r a l lel, f a i r l y r i g i d , lath-like molecules are g r o u p e d w i t h orientational disorder (at right angles t o t h e i r l o n g axes) a n d e n d - t o - e n d so t h a t t h e m o l e c u l e s l i e s t a t i s t i c a l l y n o r m a l to t h e sheets, c o n s t i t u t i n g a n o p t i c a l l y u n i a x i a l

Friberg; Lyotropic Liquid Crystals Advances in Chemistry; American Chemical Society: Washington, DC, 1976.


1.

v

x

R -1

R 1

R x

and

R y

mesophases of the fused type in refotion to the underlying (1,2).

Chang* of

tendency of C to be convex towards W

tendency of C to be convex towards Ο

Nature of the succession of amphiphilic

y

miceïlar

equilibria

2

Sc

Legend: Si and S2 Sic and S Vi and Ve Mi and M (2 W C Ο (a) (b) (c) (d)

= = = s= = == = t= = = = = 2e

rotational and positional disorder rotational disorder; units in three-dimensional cubic lattice; S is not yet definitely identified rotational disorder, units in three dimensional cubic lattice two-dimensional hexagonal lattice of indefinitely extended parallel cylindrical micelles lamellar lattice of indefinitely extended parallel lamellar micelles aqueous zone amphiphilic zone hydrocarbon zone breakdown of long rods caused by tendency to develop convexities longitudinally breakdown of indefinite extension of long rods caused by tendency to develop planar regions circumferentially breakdown of indefinite lamellae caused by tendency to develop convexities towards W breakdown of lamellae caused by development of convexities towards Ο

When the polar groups are ordered on the micellar face in two-dimensional nematic order, χ and y correspond to the directions on the miceliar face corresponding to the minimum and maximum values of R respectively (3).

Figure

and ic

Model Structures

for

V

z

A n u m b e r of c o n t i n u o u s n e t w o r k , j o i n t e d - r o d m o d e l s f o r the structures of the Sic, V i , a n d V h i s collaborators (10, ments.

2

11, 12)

phases h a v e b e e n p r o p o s e d b y L u z z a t i a n d o n the basis of x - r a y d i f f r a c t i o n measure-

I n these m o d e l s , the i n d i v i d u a l r o d s are close to i s o d i m e n s i o n a l

a n d thus represent

g l o b u l a r m i c e l l e s , b u t these are p i c t u r e d , n o t

r o t a t i n g at the lattice p o i n t s b u t as j o i n t e d i n t o c o n t i n u o u s t r a t i n g n e t w o r k s so as to c o n f e r

rigidity

o n the structure.

as

interpene-

Perhaps

the

m a i n o b j e c t i o n to these m o d e l s is that, i n contrast to r o t a t i o n a l p l a s t i c


10

LYOTROPIC

LIQUID

CRYSTALS

c r y s t a l structures ( 1 3 ) , t h e y w o u l d n o t l e a d one to expect these phases to s h o w t h e i r c h a r a c t e r i s t i c h i g h r e s o l u t i o n N M R s p e c t r a b u t to b e h a v e s i m i l a r l y to the m i d d l e a n d neat mesophases

w h i c h do not give such

spectra. I t seems to t h e present authors that to a c c o u n t f o r the x - r a y m e a s u r e ments i t m a y b e p o s s i b l e to r e p l a c e L u z z a t i ' s j o i n t e d rods b y r o t a t i o n a l g l o b u l a r m i c e l l e s g e o m e t r i c a l l y a r r a n g e d i n a m a n n e r r e l a t e d to

that

p o s t u l a t e d f o r the j o i n t e d r o d s . T h e s t a b i l i t y a n d r i g i d i t y of t h e p h a s e w o u l d t h e n b e a t t r i b u t e d to lattice forces ( v a n d e r W a a l s attractions a n d r e p u l s i o n s , forces o p p o s i n g the interpénétration of e l e c t r i c a l d o u b l e l a y ers)

s i m i l a r to those t h a t c o n f e r

s t a b i l i t y a n d some

m i c e l l a r lattices of M i , M , a n d G mesophases. Downloaded by 91.200.80.158 on May 28, 2016 | http://pubs.acs.org Publication Date: September 1, 1976 | doi: 10.1021/ba-1976-0152.ch001

rigidity on

A c c o r d i n g to L u z z a t i

2

a n d also a c c o r d i n g to the R t h e o r y (1, 2, 3, 15),

the (14)

the m i c e l l e s themselves

are a l m o s t d e v o i d o f i n t e r n a l r i g i d i t y . I t w i l l therefore b e t h e i n t e r m i c e l l a r forces—i.e., the lattice f o r c e s — r a t h e r t h a n forces f r o m j o i n t i n g o r close p a c k i n g (16)

w h i c h c o n f e r the viscosities a n d stabilities of the

meso-

phases Conditions for

the Formation of Amphiphilic

Mesophases

F r o m this p o i n t of v i e w , the f o l l o w i n g c o n d i t i o n s m u s t b e satisfied f o r a n a m p h i p h i l i c mesophase to f o r m : ( 1 ) M i c e l l e s of a p p r o p r i a t e c o n f o r m a t i o n — i . e . , m u s t b e present.

size a n d

shape—

( 2 ) T h e m i c e l l e s of this s i z e a n d shape (i.e., i n sufficient close p r o x i m i t y ) m u s t b e c o n c e n t r a t e d sufficiently to r e s u l t i n the f o r m a t i o n of the mesophase lattice at the p r e v a i l i n g t e m p e r a t u r e . A t some h i g h e r t e m p e r a t u r e , this lattice w i l l b r e a k d o w n to g i v e the a m o r p h o u s l i q u i d b y the d i s i n t e g r a t i n g effect of t h e i n c r e a s e d t h e r m a l m o t i o n . Formation of the S i

c

Phase in Binary Aqueous Alkyltrimethylam-

monium Halide Solutions. T h e s e considerations are w e l l i l l u s t r a t e d b y t h e f o r m a t i o n of t h e S solutions (17)

i c

phase i n aqueous a l k y l t r i m e t h y l a m m o n i u m h a l i d e

(Figure 7).

T h i s phase is a p p a r e n t l y c o m p o s e d of S i

micelles—probably on balance prolate—arranged i n a primitive, cubic l a t t i c e a n d r o t a t i n g f a i r l y f r e e l y at the lattice points. T h e lattice is f o r m e d b y d o d e c y l - a n d t e t r a d e c y l t r i m e t h y l a m m o n i u m c h l o r i d e s b u t n o t b y the hexadecyl

or

octadecyl

chlorides

nor

by

any

of

the

corresponding

b r o m i d e s . T h i s m a y b e expressed as f o l l o w s . I n F i g u r e 1, w i t h i n a series of h o m o l o g o u s a m p h i p h i l e s , a g i v e n stage i n t h e m i c e l l a r p r o g r e s s i o n is r e a c h e d at a l o w e r c o n c e n t r a t i o n the h i g h e r the h y d r o c a r b o n c h a i n l e n g t h of the a m p h i p h i l e is. W i t h the h e x a d e c y l a n d o c t a d e c y l t r i m e t h y l a m m o n i u m c h l o r i d e s c o n v e r s i o n of g l o b u l a r

(Si)

t o fibrous ( M i ) m i c e l l e s a p p a r e n t l y occurs at too l o w a c o n c e n t r a t i o n — i.e., at too great a n i n t e r m i c e l l a r d i s t a n c e — f o r S i lattice to f o r m . R e p l a c e c


1.

GRAY A N D WINSOR

Non- and Amphiphilic

Mesophases

11

200

160


120 Ο ο

| 80

40 0 20

40

60

80

100

NC Me Cl(%w) 12

3

Figure 7. Phase diagram for the dodecyltrimethyl ammonium chloride (NC Me Cl)/water system (17) 12

3

m e n t o f C l " b y B r " a g a i n results i n d i s p l a c e m e n t o f t h e i n t e r m i c e l l a r equilibrium i n F i g u r e 1 to t h e right. Thus, L u z z a t i a n d Reiss-Husson (18)

f o u n d b y x-ray diffraction methods that i n dodecyltrimethylammo

n i u m c h l o r i d e solutions at 2 7 ° C , S i g l o b u l a r m i c e l l e s p e r s i s t e d u p t o a concentration of about 40 w t % , w h i l e w i t h t h e corresponding bromide the t r a n s f o r m a t i o n to fibrous M i m i c e l l e s o c c u r r e d at a c o n c e n t r a t i o n o f o n l y 5%—i.e., a t a n i n t e r m i c e l l a r s e p a r a t i o n d i s t a n c e t o o great f o r t h e formation of the S

i c

lattice.

Formation of the V i and V Mesophases and of the Non-Amphiphilic 2

Cubic Mesophase "Smectic D " . I n F i g u r e s 1 a n d 5 , t h e f o r m a t i o n o f t h e a m p h i p h i l i c c u b i c mesophases V i a n d V

2

is a t t r i b u t e d to t r a n s i t i o n a l

g l o b u l a r m i c e l l a r f o r m s w h i c h arise i n t e r m e d i a t e b e t w e e n t h e i n d e f i n i t e l y extended

fibrous

( M ) a n d lamellar ( G ) forms w h i c h

constitute t h e

m i d d l e a n d neat mesophases, r e s p e c t i v e l y . W i t h a f e w n o n - a m p h i p h i l i c mesogens (19, 20, 21, 22) a c u b i c m e s o p h a s e " s m e c t i c D " i s f o u n d i n t e r m e d i a t e i n t h e t h e r m a l succession o f mesophases b e t w e e n

smectic A


12

LYOTROPIC LIQUID

CRYSTALS

( F i g u r e 2 b ) a n d smectic C ( F i g u r e 2 c ) . I t is n o w suggested that this may b e caused b y the formation of a rotational c u b i c lattice b y globular t r a n s i t i o n a l g r o u p i n g s of essentially p a r a l l e l m o l e c u l e s p r o d u c e d as t r a n s i tional intermediates, somewhat analogously to t h e transitional globular m i c e l l e s o f t h e V i a n d V mesophases, b e t w e e n t h e i n d e f i n i t e l y e x t e n d e d 2

sheets o f s m e c t i c A a n d s m e c t i c C t y p e s , r e s p e c t i v e l y ( F i g u r e 2 ) .


Literature

Cited

1. Winsor, P.A.,Chem. Rev. (1968) 68, 1. 2. Winsor, P.A.,Mol. Cryst. Liquid Cryst. (1971) 12, 141. 3. "Liquid Crystals and Plastic Crystals," G. W. Gray, P. A. Winsor, Eds., Vol. 1, Chap. 5, Ellis Horwood Publishers, Chichester, England, 1974. 4. Luzzati, V., Mustacchi, H., Skoulios, A. E., Discuss. Faraday Soc. (1958) 25, 43. 5. Mustacchi, H., Luzzati, V., Husson, F., Acta Cryst. (1960) 13, 660. 6. Luzzati, V., Husson, F., J. Cell. Biol. (1962) 12, 207. 7. Timmermanns, J., Bull. Soc. Chim. Belg. (1935) 44, 17. 8. Timmermanns, J., J. Phys. Chem. Solids (1961) 18, 1. 9. Gray, G. W., Winsor, P.A.,Mol. Cryst. Liquid Cryst. (1974) 26, 305. 10. Luzzati, V., Gulik-Krzywicki, T., Tardieu, Α., Nature (1968) 218, 1031. 11. Luzzati, V., Tardieu, Α., Gulik-Krzywicki, T., Rivas, E., Reiss-Husson, F., Nature (1968) 220, 485. 12. Tardieu, Α., Luzzati, V., Biochim. Biophys. Acta (1972) 219, 11. 13. Lawson, K. D., Mabis, A. J., Flautt, J., J. Phys. Chem. (1968) 72, 2058. 14. Luzzati, V., Reiss-Husson, F., Nature (1966) 210, 1351. 15. Winsor, P. Α., "Solvent Properties of Amphiphilic Compounds," Butter worths, London, 1954. 16. Ekwall, P., Mandell, L., Fontell, K., J. Colloid Interface Sci. (1970) 33, 215. 17. Balmbra, R. R., Clunie, J. S., Goodman, J. F., Nature (1969) 222, 1159. 18. Reiss-Husson, F., Luzzati, V., J. Colloid Interface Sci. (1966) 21, 534. 19. Gray, G. W., Jones, B., Marson, F., J. Chem. Soc. (1957) 393. 20. Demus, D., Kunicke, J., Neelson, J., Sackmann, Η., Z. Naturforsch. (1968) 23a, 84. 21. Diele, S., Brand, P., Sackmann, H., Mol. Cryst. Liquid Cryst. (1972) 17, 163. 22. Gray, G. W., Symp. Faraday Soc. (1971) 5, 94. 23. Aston, J. G., "Physics and Chemistry of the Organic Solid State," p. 543, Interscience Publishers, London, 1963. 24. Dunning, W. J., J. Phys. Chem. Solids (1961) 18, 21. RECEIVED November 19,

1974.


Lyotropic Liquid Crystals

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