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Col loid & Polymer Science Colloid & Polymer Sci 263:156-159 (1985)

A system with non-aqueous birefr ingent microemuls ions

S. E . F r ibe rg and C . S . W ohn

Chem is t ry Depa r tmen t , UM R, Ro l la , MO 65401

Abstract:No n-aqu eous birefringent microemulsions were fou nd in a sys tem ofp-xylene,glycerol , t rie thanolam mo nium oleate and ole ic acid. The microemulsions show ed long

term s tabi li ty once formed , but fai led to form sp ontaneo us ly when the com ponen ts werecontacted. A fter partial separation by centrifugation, no signs of spontaneous refor ma -t ion were found.

Key words:N on -aq ueo us microemulsions, birefringent microemulsions, lyo trop ic liquidcrystals, glyceroMn-p-xylene microemulsions, glycerol inverse micelles.

Introduct ion

Co l lo ida l a ssoc ia t ion s truc tu res in wa te r - f lee sys-tems have recen t ly a t t rac ted cons ide rab le in te res t .Evans and co l labora to rs [1, 2] have inves t iga ted mice l -la r fo rm at ion o f su r fac tan ts in e thy lam m oniu m n i t ra tea n d h y d r a z in e a n d I o n e s c u [ 3] f o u n d m ic e l l iz a t io n o facy lca rn i t ine in g lyce ro l . L yo t rop ic l iqu id c rys ta l wi thn o n - a q u e o u s s o lv e n t s h av e b e e n i n t r o d u c e d b y F r i-be rg and co l labora to rs [4 -7 ] an d s tud ied by Evans [8 ].M cIn tosh e t a l. [9] have ana lyzed assoc ia t ion s t ruc -tu res o f lec ith in and g lyce ro l emphas iz ing the i r b io lo -g ica l impor tance .

M ic r o e m u l s io n s i n w h ic h a n o n - a q u e o u s p o l a rc o m p o u n d r e p la ce s w a t e r h a v e i n d e p e n d e n t l y b e e nin t roduce d by F r ibe rg [10] and b y La t te s [11].

A no t her n ove l ty in the a rea a re b i re fr ingen t mice l la rso lu t ions [12 ,13] o r m ic roemu ls ions [14,15] . The y

w e r e i n t r o d u c e d b y H o f f m a n i n 1 9 7 8 [1 2 ] , w h o a t tr i -bu ted the i r p roper t ie s to the p resence o f g ian t mice lles ,whi le Taup in and co l labora to rs [14 ,15] di scussed thes t ruc tu re o f b i re f r ingen t m ic roemu ls ions . The ques-t ion o f s tab i l i ty o f such sys tems has recen t ly beenra ised by Fo n te l l [16 ] w ho expressed dou b t a s to theb i re f r ingen t so lu t ions possessing the rm od yna m ic s ta -b i l i ty . Wi th regard to the fac t tha t the compos i t ionswere foun d a t the l imi t o f the so lub i l i ty a rea , Fon te l l[16] cau t ioned aga ins t an inadver ten t pa th in to thetwo-ph ase reg ion co n ta in ing a l iqu id c rys ta l line phase .Bi re f r ingen t phases have a lso been o bse rved by M i l le rand co l labora to rs [17] in the i r inves t iga tions on te r t i-

M870

ary o i l recovery . The ques t ion o f the s t ruc tu re and s ta -b i l i ty O such sys tems i s a fa sc ina ting p rob lem .

W e h a v e r e c e n t l y fo u n d a s y s t e m c o n t a in in g non-

aqueous b i re f r ingen t m ic roem uls ions and we cons id -ered o ur resul ts con cern ing their s tabi l i ty to be o f suf-f ic ien t in te res t to m er i t pu b l ica t ion o f a re sea rch no te .

The sys tem inves t iga ted was g lyce ro l , t r i e thano lam-m on ium o lea te , o le ic ac id and p -xy lene .

Experimental

Th e p-xylen e was Aldrich, 99 %, the glycerol was Aldrich G oldLabel, 99.5 % and the t r ie thanolam mon ium oleate (TEA O) wasmade by contacting equimolar amounts of oteic acid, Fisher puri-fied, and triethanolamine, Fisher certified. All chemicals were usedas received.

The solubi liza tion of glycerol in the p-x ylen e/TE AO solut ionwas determined by titration with mixing, using a vibromixer at

30 ~ The viscos i ty of the solut ions was measured us ing Can non -Fenske capillary viscometers at 30 ~ covering the range of viscosi-ties encountered.

Th e stability of he microemulsions p art of he system was inves-t igated b y long term s torage a t 30 ~ and by examinat ion of thetransp ort direction of layers in partially separated o r incompletelyhom ogen ized samples a t the same temperature .

Results and discussion

O ur ea r l ie r re su l ts in aqueous sys tems [18] havein t roduced the re la t ion be tween l iqu id c rys ta l s andmicroemuls ions ; hence , ou r p r imary e f fo r t s werel imi ted to f ind ing the lamel la r l iqu id c rys ta l l ine phase

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Friberg and Wohn, A system w ith non-aqueous birefringent microemulsions 157

OLEIC ACID

G L Y C E R O L T E A O L

Fig. 1. The liquidcrystallinephase n the systemglycerol, riethanolammonium oleate (TEAOL ) and oleicacid (OLA)

i n th e s y s t e m o f th e t h r e e s t r u c t u re - f o r m i n g c o m p o -

n e n t s : t h e g ly c e r o l , t h e tr i e t h a n o l a m m o n i u m o l e a t e

a n d t h e o l e i c a c i d. T h e l a m e l l a r l iq u i d c r y s t a l li n e p h a s e

r e a c h e d i n a l a r g e c r e s c e n t - f o r m e d a r e a f r o m t h e t r i -

e t h a n o l a m m o n i u m o l e a te c o r n e r t o w a r d s t h e g l y c e ro l

c o r n e r r e a c h i n g t o 7 5 % b y w e i g h t o f g l y c e r o l ( fi g. 1 ).

T h e b a si s f o r t h e m i c r o e m u l s i o n s y s t e m w a s c h o s e n

w i t h a t r ie t h a n o l a m m o n i u m o l e a te / o l ei c ac i d r a ti o o f

2 , 5 7 i n o r d e r t o o b t a i n t h e l a r g e s t p o s s i b le e x t e n s i o n o f

th e l i q u id c r y s t a l l i n e a r ea ( mar k ed in f i g . 1 ) . Th i s

c h o i c e w a s m a d e a g a i n st o u r e a r l ie r o b s e r v a t i o n [ 1 8] o f

t h e c l o s e r e l a t i o n b e t w e e n W / O m i c r o e m u l s io n s a n dth e l ame l l a r l i q u id c r y s t a l s .

C o m b i n i n g t h e c o m p o s i t io n s a l o n g t h e l in e in f ig u r e

1 w i t h p - x y l e n e g a v e th e p - x y l e n e / s u r f a c t a n t i s o t r o p i c

s o l u t i o n a r e a w i t h s o l u b i l i z e d g l y c e r o l a c c o r d i n g t o

f i g u re 2 . T h e m a r k e d p a r t t o t h e l e ft o f t h e r e g i o n is n o t

4 0 -

3 0 -

ILl

o o ~ ~

I--

~ 2 oI.-zW('~ RINGENT(,I)

1 0

I ~ ~ BIREFRINGENT(X)BIREFRIN(ENT(O)

I i J

0 5 . 0 1 0 . 0 1 5 . 0 2 0 . 0

G L Y C E R O L , W E I G H T 96

Fig. 3. The viscosityversus glycerolcontentfor solutions with dif-ferent tr iethanol am mo nium oleate/p-xylene we ight ratios.

TEA OL/p-xylene O 0 . 1 1 ; X 0.18; 9 0.25

a s e p a r a t e p h a s e . I n s t e a d , t h e s t r i p e d p a r t s h o w s t h e

e x t e n t o f b l u is h s o l u t i o n s a n d t h e z i g - z a g m a r k i n g i n d i -

ca t e s t h e b i r e f r in g en t so lu t io n s .

T h e v i s c o si ty o f s o l u ti o n s w i t h a T E A O / p - x y l e n e

r a t io o f 0 .11 , 0 .1 8 an d 0 .2 5 v e r su s t h e g ly ce r o l f r ac t io n

a r e g i v e n in f i g u re 3 . T h e s u d d e n i n c r e a s e o f v i s c o s it y

w h e n t h e c o m p o s i t i o n e n t e r e d t h e b i r e fr i ng e n t re g i o n

i s a co n sp icu o u s f ea tu r e .

T h e s t a b il i ty o f w e l l m i x e d s a m p l e s i s i ll u s t ra t e d i nf ig u r e 4 . A l l t h r e e s a m p l e s a p p e a r e d a s a h o m o g e n o u s

b i r e f r i n g e n t s o l u t i o n a t t h e b e g i n n i n g o f t h e s t o r a g e

t i m e , f i g u re 5 . A f t e r 3 0 d a y s , a n u p p e r t r a n s p a r e n t l a y -

e r s t a r t e d s e p a r a t i n g in s a m p l e 3 a n d t h e b i r e f ri n g e n t

p a r t r e t r a c t e d a c c o r d i n g t o t h e d i a g r a m i n f i g u r e 4 .

P - X Y L E N E

SAMPLE

/

G L Y C E R O L T E A O L

Fig. 2. The area for hydrocarboncontinuousmicroem ulsions n thesystem g lycerol, p-xylene and triethanol am mo nium oleate at30 ~ The striped areama rks bluish sotropicsolutions, he zig-zagmarkings show birefringent olutions. The co mp ositions ndicatedby 1,2,3 refer to figure 3

1 . 0

z

0 0 . 8

I -

O

e v 0 . 6

I.-.-" r

o 0 . 4

LU

7-

0 . 2

t t I I I

0 2 8 5 6 8 4 1 1 2 1 4 0

T I M E , D A Y S

Fig. 4. The relative heigh t of the birefringent aye r versus tim e forthree samples marked in figure 1

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158 Colloid and P olymer Science, Vol. 263 9No. 2 (1985)

Fig. 5. The birefringent microe mulsio ns were easily detected betw een crossed polarize rs

Similar behavior was observed in sample 1 after 71

days. Sample 2 remained identical during the 4 m ont hperiod. The separated phase in sample 3 was identified

as a liquid crystalline phase with lamellar structure

from its optical pattern (fig. 6).In order to obtain further information about the

potential thermodynamic stability of sample 2, twosamples of this composition were carefully mixed toobtain th e single birefringe nt liquid and parti ally sepa-rated by centrifugation to form two layers with thebirefringent one at the bottom . The height of the bire-

fringe nt layers in the two samples was different. Stor-age at 30 ~ for a two m on th period gave no changes in

layer thickness to indicate a spontaneous reformation

of the birefringent microemulsion. A fu rther test wasmade in the following manner. Samples of composi-

tion 2 were less thor ough ly mixed so that the birefrin-gent layer did not occupy the entire sample at the

beginning of the experiment. The changes in height of

the layers with time was observed at 30~ No

increase of the thickness of the birefringent wasobserved.

Conclusions

Birefringent microemulsions were observed in anon-aqueous system and showed excellent long termstability once formed. For th e sample which separated

spontaneously with time, the rate of separation wasaccelerated. It sudden ly stopped at the format ion of a

lamellar liquid crystal (fig. 3).

No case of spontaneous formation from compo-nents was found and awaiting further experimental

information, a conclusion of therm odyn amic instabil-ity of the microemulsions investigated appears most

Fig. 6. The op tical pattern in polarize d light of the s eparated phase fro m samples 1 and 3 was typic al of a lamellar liquid crystalline p hase

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Friberg and Woh n, A system with non-aqueous birefringent microemulsions 159

r e a s o n a b l e . T h e b i r e f ri n g e n t s o l u t i o n s m a y , u n t i l f u r -

t h e r e v i d e n c e , b e c o n s i d e r e d a s a k i n e t i c a l l y s ta b l e s ta te

o f a l a m e l la r li q u i d c r ys ta l a n d a p - x y l e n e / T E A O s o l u -

t i o n w i t h s o l u b i l i z e d g l y c e r o l . S u c h a c o n c l u s i o n b y

n o m e a n s i m p l ie s t h e st r u ct u r e o f th e s e m i c r o e m u l -

s i o n s w i t h a l o n g t e r m s t a b il it y to b e w i t h o u t i n t e r e s t.

References

1. Evans DF, Chen S-H, Schriver GW , Arnett EM (1981) J A mCh em Soc 103:481

2. Evans DF, Yam auchi A, Ro ma n R, Casassa EZ (1982)J ColloidInterface Sci 88:89

3. Ionescu L G, Fu ng DS (1981) J C hem Soc Faraday Trans I77:2907-2912

4. Mou charafieh N , Friberg SE (1979) Mol C ryst Liq Cry st 49:2315. L arsen DW, Friberg SE, Christenson H (1980) J Am er Che m

Soc 102:65656. El Nokaly M A, Ford L D, Friberg SE, Larsen DW (1981)J Col-

loid Interface Sci 84:2287. G anzuo L, El Nok aly MA , Friberg SE (1982) Mol Cryst Liq

Cry st 72:1838. E vans DF, Kaler EW, Benton WJ (1983) J Phys C hem 87:5339. Mclntosh TJ, McDaniel RV, Simon SA (1983) Biochim Biophys

Acta 731:109-114

10. Friberg SE, Podzimek M (1984) Colloid Polym Sci 262:25211. Rico I, Lattes A, N ouv eau Journal D e Ch imie (in press)12. Ho ffm an H, Ulbricht W, Tagesson B (1978)J Phys Ch em 113:1713. Ho ffm an H , Tagesson B (1978) Ibid 113:11014. Dvolaitzky M, Ob er R, B illar J, Taupin C, Charvolin J,

Hendricks Y (1981) C R A cad Sc Paris 292:45

15. di Meglio JM, Dv olaitzky M, Ob er R, T aupin C (1983) C RAcad Sc Paris 296:405

16. Fontell K, Lindman B (1983) J Phys Ch em 87:328917. Benton W J, Miller CA, F ort Jr T (1982)J Dispersion Sci Tech-

nol 3:118. Fribe rg S, Buraczew ska I (1978) Progr Colloid Po lym Sci 63:1

Received July 30, 1984;accepted Septem ber 21, 1984

Autho rs ' address:

Prof. S. FribergCu rators ' Distinguished ProfessorUniversity of M issouri-Rola142 Schrenk HallRolla, Missouri 65401, USA