The constitution of aqueous liquid crystalline solutions of amphiphiles

J O U R N A L Off COLLOID AND I N T E R F A C E SCIENCE 9'5, 4 0 9 - 4 2 0

(1967)

The Constitution of Aqueous Liquid Crystalline Solutions of Amphiphiles i:

C. A. GILCHRIST, J. ROGERS, G. STEEL, E. G. VAAL, ANn P. A. WINSOR "Shell" Research Ltd., Thornton Research Centre, P.O. Box 1, Chester, England Received February 6, 1967; revised June 21, 1967 INTRODUCTION in composition between M1 and G, an array In amphiphile/water systems, in addition of fluid spherical micelles with external to mobile isotropic solutions (S), more or polar groups, and with the micelles disless viscous liquid crystalline phases are posed at the points of a face-centered cubic frequently encountered. Of these the follow- lattice with intervening water, was suging have been definitively characterized as gested (1, 2, 7). For the inverse middle individual thermodynamically stable phases phase Ms, an inverse MI model was proposed --"Middle" (M1), "viscous isotropic" (V0, (2) and, by implication, an inverse V1 "neat" (G), "inverse viscous isotropie" model should be assigned to the V~ phase, (V~), and "inverse middle" (Ms) (1-10). found intermediate in composition between Certain other liquid crystalline phases have G and Ms (@ reference 4). A difficulty pointed out by Clunie, Corkbeen reported (1, 2, 5) but seem less cerhill, and Goodman with respect to the M1, tainly authenticated. Although not all these liquid crystalline phases may appear V1, and G models is that, as calculated from in a given amphiphile/water system, the these models and the measured X-ray interorder of succession of the phases, with in- micellar spacings of the phases, the availcreasing concentration, is always the same, able area per polar group on the surface of viz., M1, V1, G, V~, M~. Intermediate con- the VI mieelles is greater than the available jugate two-phase systems, e.g., M~ + V1 area on either the M1 or G mieelles although, (7), M1 + G (1), or G + Ms (2) are found on the basis of composition, it would be in accordance with the phase rule. The expected to show an intermediate value (3, intermediate ranges of composition may be 7). This apparent anomaly led Clunie, Corkhill, and Goodman to suggest, as an very narrow (1). The constitution of the liquid crystalline alternative model for the M~ phase, linear neat G solution phase as fluid, parallel, aggregates of identical spheres arranged in lamellae consisting of bimolecular layers of a two-dimensional hexagonal array. This amphiphile molecules with water inter- model gave an area per polar group in the vening between adjacent layers of polar V1 phase of the N,N,N-trimethylaminogroups is generally accepted (1-10). There dodeeanoimide/water system intermediate is still discussion, however, concerning the between the areas for the G and M1 phases. Cogent objections to this "string-ofstructures of the M1, VI, V~, and 3/2 phases (3, 4, 7). spheres" model for the M1 phase have, According to the earlier suggestions of however, been raised by Luzzati and ReissLuzzati and his collaborators the micellar Husson, who prefer to retain their original units of the MI phase consist of amphiphile cylindrical model for the M~ phase while molecules associated in fluid form into revising their "Cubic I" model for the V1 parallel Cylindrical fibers in two-dimensional phase (7). In place of the Cubic I model hexagonal array, with external polar groups containing spherical hydrophilie tIartley and surrounded by water. For the micellar or $1 mieelles dispersed in water at the units of the V1 phase, found intermediate points of a face-centered cubic lattice, they 409

410

GILCHRIST, ET AL.

propose an inverse "Cubic I I " model in which the water and polar groups provide the spherical diffracting centers lying at the points of a face-centered cubic lattice and the hydrocarbon chains fill the gaps between the spheres. On this model, acceptable area/concentration relationships are obtained with some amphiphiles, though not with all (7). Certain objections to the Cubic II model, however, arise. Thus, Luzzati and ReissHusson state: "The very high viscosity of the cubic phase can be explained by the presence, in Cubic II, of a paraffin matrix; this matrix is likely to determine the rheological properties of the whole structure." It must be remembered, however, that the micellized hydrocarbon chains in aqueous amphiphile solutions take up a disordered liquid-like conformation, as Luzzati and Reiss-Husson, in common with other authors (I-9), have emphasized. On this basis a matrix of C~-C~s hydrocarbon chains would be expected to be mobile rathe r than viscous, and the high viscosity of the Vi phase would remain unexplained. A further objection to the Cubic II model is that it represents a water-discontinuous Vi phase intermediate in composition between the water-continuous Mi phase and the G phase. This seems anomalous,. Such an inverse Cubic II constitution, if it occurred, might be more likely to apply to the inverse viscous isotropic V~ phase found intermediate between the G phase and the hydrocarbon continuous inverse middle phase Ms in the "Aerosol OT"I/ water system (4). For the inverse middle phase in this system, Balmbra, Clunie, and Goodman implicitly consider an inverse string-of-spheres structure. On the other hand, Luzzati and Husson assign an inverse fibrous structure to the inverse middle phase which they encountered in a phospholipid/water system (2). The present paper provides experimental evidence from the optical properties and from the NMR spectra of certain liquid crystalline solutions of amphiphiles that favors

the fibrous structures (1, 2) for the M1 and M2 phases rather than the string-of-spheres constitution (3, 4). In addition experimental evidence from electrical conductivity measurements with the N,N,N-trimethylaminododecanoimide/ water system is given that opposes the Cubic II structure for the V1 phase. Suggested alternative structures for the V1 and V~ phases are outlined. EXPERIMENTAL 1. Materials. Unless otherwise stated the amphiphiles used have been commercial samples of the best available quality. Sodium caprylate solution (20% w) was prepared by neutralization Of caprylic acid (B.D.H. "pure" grade) with sodium hydroxide. N,N,N-Trimethylaminododecanoimide was prepared according to the method of Berry and Brocklehurst (11) (N found 10.9%; theory 10.9%). 2. Observations with the Polarizing Microscope. Relatively concentrated Solutions of a number of amphiphiles held between slide and cover slip were allowed to undergo slow peripheral evaporation, a concentration gradient being thereby established between the periphery and the Center :of the slide (1, 8, 10). In this way various phase sequences were produced which were examined with a Zeiss Photo-Microscope. The G and M~ phases were identified by their distinctive microscopic "textures" as described by Rosevear (10). The Ms phase was identified by its very close textural similarity to the M1 phase (5). The V1 and V2 phases were identified by their isotropic character and by their very high Viscosity. The optical properties of the Mi and Ms phases were studied and these phases, as considered further in the Discussion, were characterized (12) as negative uniaxial, in contrast to the G phase, which in accordance with the literature (10) was readily characterized as positive uniaxial. 3. N M R spectra. For the examination of N M R spectra the N,N,N-trimethylaminododecanoimide/water and the Aerosol OT/

i CH2. CO- O. CH2. CH (C2H~)- CH2- GI{2. CH~. CH8 l CH (SO~Na) CO. O- Ctt2. CH (C~Hs) •CH2. CH~. CH~. CHs.

CONSTITUTION OF LIQUID CRYSTALLINE SOLUTIONS water systems, recently characterized by X-ray methods by Goodman and his collaborators (3, 4), were used. The NMR spectra were obtained on an AEI RS2 spectrometer at 60 megacycles per second under high-resolution conditions. Samples of various compositions were sealed in 4.6 mm. tubes and a sealed capillary tube containing tetramethylsilane (TMS) was used as an external reference, and chemical shifts measured by use of a 360 e.p.s, side band of the TMS signal. The spectrum of each sample was recorded over the temperature range 25 ° to 100°C. using the AEI variable temperature probe; the temperatures at which the spectra were recorded were controlled to =t=2°C. A 8-scale in parts per million with TMS reference peak at 0 is shown in Figs. 1 and 2; the 8 values are accurate to about 4-0.05 p.p.m. No facilities were avalable for investigating broad band spectra. A phase diagram for the N , N , N - t r i methylaminododecanoimide/water system, drawn on the basis of NMR spectra, is given in Fig. 3. 4. Electrical Conductivity Measurements. In the electrical conductivity measurements the N,N,N-trimethylaminododecanoimide/water system was again employed. Laboratory distilled water was used (specific conductivity 5.2 ~ mho cm-I at 20°C.).. The apparatus used is shown diagrammatically in Fig. 4. Values of conductivity were recorded at different temperatures and also the accompanying appearances of the sample (65% w imide) when viewed between crossed polaroids. Heating or cooling rates were 0.2 ° to 0.4°C. per minute. The experimental results are presented in Fig. 5. The specific conductivity of the liquid imide was very low (0.45 ~ mho cm. -1 at 25°C., supercooled). DISCUSSION

1. Observations with the Polarizing Microscope. The model of the M~ phase as fibrous cylindrical micelles in two-dimensional hexagonal array (1, 2) and the model as strings of spherical micelles with the strings again in hexagonal array (3, 4) both represent the phase as forming uniaxial crystals

411

(12), the optic axis lying along the cylinders or strings, respectively. For n-alkyl amphiphiles on the cylindrical model the proportion of --C--C-- hydrocarbon chain bonds directed along the optic axis would be expected to be statistically less than the number directed across it. On the string-of-spheres model the numbers of bonds directed along and across the optic axis would be statistically equal. The "intrinsic" birefringence of the MI phase on the cylindrical model should therefore be negative (12) whereas it should be zero on the string-of-spheres model. Both models should, in addition, possess a small positive "form birefringenee" (13). With the cylindrical model this would be expected to be outweighed by the negative intrinsic birefringenee just as the negative form component (13) of the birefringence of the lamellar neat phase is outweighed by the positive intrinsic component. In practice, although the positive sign of the birefringenee of neat phase is readily established (10), the optic sign of middle phase does not previously seem to have been determined. This is because, although many samples of neat phase held between slide and cover slip spontaneously orientate to yield accurately basal textures with lamellae parallel to slide and cover slip, basal sections of middle phase with cylinders accurately normal to slide and cover slip are, as might be expected, much less easily obtained. We have now found, however, that approximately basal textures in the M1 phase in the sodium caprylate/water system (5) are rather readily formed when an isotropic 20 % aqueous solution between slide and cover slip is allowed to undergo peripheral evaporation for several days at room temperature (Fig. 6). Accompanying fanlike textures (i0) are also produced. By careful selection of the most accurately basal of the approximately basal sections it is possible to observe conoscopically a well-defined uniaxial interference cross which may be characterized as negative using the Red I compensator (12). This characterizes the middle phase from sodium caprylate as having a negative optic sign and is thus in favor of the cylindrical model for this phase.

m

6ppm from

TMS

TMS

6p~m T $

14 - Z

6ppm

LLL'i S(77°C)

S (77°C1

LIQUID WATER ( 7 7 ° C )

6ppm from

from T S

TMS

v1(7~°C)

S(77°C)

TMS 16ppmfrom

ILIQUID WATER 160~1

TMS

ppm

ppm

6ppm

6ppm from

TMS

v,(6ooc)

S(60°C1

S(60°C)

S(60°C1

Vt ( 5 0 % )

TMS

)pm

TMS

6ppm

TMS H TMS

LIQUID WATER (4O°C)

MI ( 4 0 % )

S (40°C)

S(40"C1

TMS

Ts

i X_ [

Mt+S(25°C)

0

20

40

6 ppm from TMS

TMS

f%~

60

ML(25°C)

65

Fro. 1. Block diagram showing typical NMR spectra of the various phase regions of the N,N,Ntrimethylaminododecanoimide/water system. (The phases and temperatures corresponding to each spectrum are indicated by subscripts.) 412

6ppm

$(93%)

TMS

~ $ f r o m

6ppm TMS ~f

J S(77°C)

TMS

S(93°C)

6ppm from TM$

6ppm from TMS

TMS 1~

_~%t.

I

/

f.~4ff~

L112 S(77*C)

G (77°C1

G{ 77°C)

6pl~

TMS I ]

i

TMS R

I

6ppm

LIQUID IMIDE (77=C) o II - + :%-(c,z~-~=-c-s- N-(CHlsH~

6ppm from TMS

I

--'4

G(66°C)

TMS TMS

6ppm from TM$

6ppm from TMS

6 ppm from TMS

TMS

J v~(sooc)

j

6ppm

L G(60°C)

G(6O°C)

G{6O°C)

TMS J

I , , , , ,el IlppmO ~ 2 3 4 5 ~t09

8

7

6

54

LIQUID IMIDE {60°C )

I s

6ppm from TMS

J

~(4ooc)

Vl(40°C)

TMS

6ppm from TMS

-1

L

I

G (50°C1

TMS

6ppm from TMS

I r'-"

Lr !

TMS I

G (40°C1

G (40°C)

LIQUID IMIDE (4O°C)

6p~

TMS TMS

from

~

[6pprr

SOLID IMIDE (30°C)

VI (25°C)

70

75

80 413

90

I00

414

G I L C H R I S T , E T AL.

J, (CH3)4

6ppm FROM TMS

TMS

CH2)II H20

,Ms

ggg2

~

' ~pom

]

G (TO°C,)

M2{70°C)

/, r I0 9 8 7 6 5 a

V2{70°C )

6ppm FROM TMS

TMS

I

t j 7 FRO~ 6ppm

T S

~G (40°C) i,

60

TMS $

6pprn

v~(35oc1

Ma(35°C}

75

85

COMPOSITION, AEROSOL OT, % w

FIG. 2. Block diagram showing typical NMI% spectra in the G, V~, and Ms phases of the Aerosol O T / w a t e r system.

Although neat phase readily forms extended basal ("homeotropic neat") textures (10), it apparently does not give rise to optic normal textures, i.e., to textures with the optic axis lying in the plane of slide and cover slip and with the lamellae normal to them. On the other hand, middle, M1, and inverse middle, M2, phases readily give rise to extended textures which, we find, characteristically give negative optic normal interference figures (12) when observed conoscopically. These textures, which frequently appear when the peripheral evaporation method is used, when viewed with parallel light, show a number of fine parallel striations (Fig. 6) and may be regamed as examples of the "fanlike texture" of Rosevear, the fans being here of infinite radius. Extinction occurs when the striations are parallel to the planes of either polarizer or analyzer. The optic axis, as determined (12) by the movement of the isogyres on rotation of the sample when observed conoscopically, is normal to the striations and corresponds to the vibration direction of the fast ray, as established by use of the Red I plate. Textures having these parallel striations and showing similar optic normal negative interference figures when observed conoscopically are readily obtained with the M1 phase produced by the peripheral evaporation method from mobile isotropic solutions of sodium caprylate, Triton X 100,s N,N,N-trimethylaminododecanoimide, laurylpyridinium chloride, etc. Textures which behave qualitatively entirely similarly are shown by the M2 phases obtained from "Aerosol MA ''3 or Aerosol OT on peripheral evaporation of S, G, or V2 solutions. With S solutions the succession of phases S-G-V~-M2 is produced (Fig. 7). Textures giving optic normal interference figures are also obtained by uniformly shearing samples of middle, M1, or inverse middle, Ms, phases between slide and cover 2 A C8 phenol condensed w i t h 8-10 ethylene oxide units. CH~. CO-O. C H (Ctt~) • CH2- C H (CHs)~

L

C H (SO~Na) CO- O- C H (CH3) - C H v C H (CH3)2.

CONSTITUTION OF LIQUID CRYSTALLINE SOLUTIONS

415

x SPECTRA SHOWINGHYDROCARBONGROUPPEAKS 0 SPECTRANOT SHOWINGHYDROCARBONGROUPPEAKS ® POINTS SHOWINGTRANSITIONOF SPECTRALTYPES

xx x

95 t,D

w" e

85 n,I-- 75

x

x

x

x

i,i

x

x

x

x

bJ 55 J ft. 45

x

x

/.~

0

0

0

0

(a)

\

rr

bJ

65

S

Co

x

/MI\ ///'~

0

\

x x~ V I ,,

0 ~1

o

o G

k¢'~x, Xx "',,~ o

o t

35

C 25

0

I0

20

30

40 50 60 70 IMIDE IN WATER, %w

80

90

I00

90

I00

I00 POINTS FROM o OPTICAL X DENSITY • X-RAY DIFFRACTION

90 o

80

,~-Weo7°so ,'~_~<= (b)

MEASUREMENTS

/v

\

~~ ~

,

60

70

J

I0

20

30

IMIDE IN

40

50

WATER,%specific

80

volume

FIG. 3. Phase diagrams for N,N,N-trimethylaminododeeanoimide/water spectra; (b) after Clunie, Corkhill, and Goodman (3). slip. The optic axis, which, as before, corresponds to the fast direction, lies along the direction of shear. Further, striations, less well marked than those formed by the evaporation technique, develop at right angles to the direction of shear. These striations in both types of samples would seem to indicate that the sections are predominantly, rather than uniformly and entirely, in an optic normal orientation. However, the close similarity of tile optie normal

system: (a) from N M R

textures of all the above M1 and M2 phases apparently indicates that they possess the same optical character as the middle phase from sodium caprylate and likewise are negative uniaxial. 2. N M R Spectra. NMR spectra showing certain of the features of Figs. 1 and 3 have been obtained by Macdonald (14), Zlochower and Schulman (15), and particularly by Lawson and Flautt (8) with the system N-dimethyldodecylamine oxide/water which

GILCHRIST, ET AL.

416

~

T

O

MULLARD CONDUCTIVITY BRIDGE

THERMOMETER SMALL TEST-TUBE (75mm xlOmm o.d)

TEMPERATURE CONTROL-BATH

I

i ......

( approx.2 ml)

CELL( BRIGHT PLATINUM WlRESET IN GLASS)

CROSSED POLAROIDS/~/v

CELL CONSTANTI'5

Fro. 4. Conductivity apparatus gives a phase diagram (16) closely similar to that of the N,N,N-trimethylaminododeeanoimide/water system (3) (Fig. 3). The most important features of Fig. 1 are:

a) The absence of sharp line NMR spectra corresponding to the imide molecules in the M1, G and solid phases. b) The absence of a sharp NMR spectral line corresponding to the water protons at high concentrations in the G phase, and the reduction in intensity of the sharp NMR spectral line corresponding to the water protons at lower concentrations in the G and M~ phases as compared with the intensity for the isotropic V~ and S phases. c) The production of sharp NMR spectra corresponding to both the imide and water protons in the mobile isotropie (S), viscous isotropie (g0, and molten imide phases. In Fig. 2 a significant feature is the absence of a sharp spectrum corresponding to the Aerosol OT molecules with the G and Nq phases, in contrast to the production of the sharp spectrum with the V~ phase. These results apparently indicate (cf. references 8, 14) that 1) Rotary Brownian movement of the

amphiphile molecules is restricted in the G, M1, and M~ phases. 2) Rotary Brownian movement of the amphiphile molecules (probably as relatively small mieellar aggregates) occurs in the isotropie phases, both mobile (S) and viscous (cubic) (V1, V2). 3) In the G and M1 phases of the imide system the rotary Brownian motion of the water molecules close to the hydrophilie surface of the G and M1 mieelles is restricted whereas that of the water molecules further from the micellar surface is relatively free. When the results given in Fig. 1 are taken in conjunction with the available X-ray measurements (3) it may be estimated that the immobilized water layer is about 3 thick and corresponds to about 3 molecules of water per molecule of imide. 4) The mieellar structures of the V and M phases differ fundamentally, i.e., the M phases can hardly be derived from the V phases by a redisposition of spherical micellar units (cf. references 3, 4).

3. Electrical Conductivity Measurements. Noteworthy features of the electrical conductivity measurements (Fig. 5) are: i) When the general effect of tempera-

CONSTITUTION OF LIQUID CRYSTALLINE SOLUTIONS

417

90 e O.'v

80

PHASE

-- . .._-:.:=.._.::::="~. l "~ .,.V"~-PHASE TRANSITION (TEM PERATURE ....'" "" S~ G RISING) ..-'" .'"'" ( TEMPERATURE FALLING) ~, .." ®" ...'" '"" G~ S

70

~:'.. ~.o"" e"

.~. ........... v "''"~ " REORIENTATION

,~

(TEMPERATURE FALLING)

~' v, G . _ J - - - - J - : ,

PHASE TRANSITION 60

(TEMPERATURE RLSING)

?

~,'~:~4~ O/ ,/ ffz?.~

PHASE G~v,TRANSITION (TEMPERATURE FALLING)

50 0<~" / F" 4O 4\ e / zz / 50 # O ~ 4 - - - P H A S E TRANSITION M~ ~ V, • •

Ternperefure rising Tempereture falling .......... System birefringent . . . . . . System isotropic •~===='= System in frensition

20

I0

0 75

I 150

I 225

I 500

SPECIFIC CONDUCTIVITY,

575

F m h o cm -E

FIG. 5. Phase changes and accompanying changes in electrical conductivity shown by an aqueous solution of N,AT,~V-trimethylaminododecanoimide (65%w) with changes in temperature.

ture in increasing ionic conductivity is allowed for, there is no change in the order of electrical conductivity due to the phase changes M I -----~ V I --~ G ---~ S

with rise of temperature. ii) Although the eonductivities of the M~, V~, and S phases at different temperatures, within the limits of accuracy of the experiment, all lie on a single curve and are reversible with temperature, the curve for the G phase is separate and shows marked

hysteresis effects with a rising and falling temperature cycle. The occurrence of the transitions ~ M 1 - + Vt--~ G without marked change in electrical conductivity apparently excludes Luzzati's proposed Cubic II structure for the V1 phase. Such a hydrocarbon continuous structure might be expected to show a relatively low electrical conductivity. The supercooling of the G phase over 4 The intermediate two-phase zones are very n a r r o w .

418

GILCHRIST, ET AL.

FIG. 6. Basal texture and accompanying fanlike textures of the MI phase produced by peripheral evaporation between slide and coverslip of an isotropic aqueous solution of sodium caprylate. The basal texture appears dark at all orientations of the slide between the crossed polars. The difference in orientation of the slide between photographs (a) and (b) was 45 °.

about 5°C. so that the system remains in the G condition when the V1 phase is the stable form, is remarkable. At the termination of the supercooling the translucent birefringent G phase transforms rapidly into the glassclear VI phase, growth spreading outwards from some center of initiation. The electrical conductivity of a uniformly oriented region of G phase would be expected to be less across than along the lamellae since, in the former case, conduction would have to occur across the hydrocarbon regions of the bimolecular layers. An ordinary sample of G phase will, however, be made up of many regions in various orientations and an averaging of directional conductivities would be expected. The accentuated decrease in the electrical conductivity towards the middle of the descending branch of the conductivity-temperature curve for the G phase (Fig. 5) may well be

due to a spontaneous change in average orientation. Lamellar regions formed in many orientations on precipitation from the isotropic S phase may, at the inflexion, locally be taking up an orientation with lamellae parallel to the electrode surfaces. 4. General Remarks. Although the results collectively considered above accord with the fibrous and lamellar structures for the middle (MI and Ms) and neat (G) phases, respectively, they do not accord with the string-of-spheres structures for the MI or M2 phases or with the Cubic II structure for the VI phase. The Cubic I structure having been reiected by Luzzati (7), there is therefore now no remaining accepted structure for the VI phase, nor, by implication, for the V~ phase. It may be suggested, in outline, that the VI phase is constituted as a thermodynamically stable microinterdispersion of

CONSTITUTION

OF LIQUID

CRYSTALLINE

SOLUTIONS

419

FIG. 7. The phase succession G--~V2--M2produced on peripheral evaporation of the aqueous G phase from Aerosol MA (50%w). small units partaking of the character of the M~ and G phases, arranged in a facecentered cubic lattice. Although the details of such a mierointerdispersion structure cannot at present be suggested, the idea of a phase constituted as a thermodynamically stable dispersion of two parts is well established. Thus, isotropie solutions of amphiphiles at temperatures slightly above the critical mieelle concentration (e.m.e.) are generally believed to be constituted as thermodynamically stable mieroemulsions of Hartley mieelles in intermieellar solutions at a concentration close to the e.m.e., a ready interchange of amphiphile molecules between the two parts taking place (17). In a similar manner it seems possible that the VI phase consists of a molecularly mobile mierointerdispersion of units partaking, respectively, of the characters of the Mt and G phases. It is also suggested that the units, though disposed according to a face-

centered cubic lattice, are capable of rotary Brownian motion in a manner analogous to the free rotation of the ammonium and nitrate ions in the cubic crystalline form of ammonium nitrate (12) or of the molecules in cubic "plastic crystals," such as those of camphor (18). This structure would confer isotropie character on the V1 dispersion and would account for the absence from its X-ray diffraction diagram of lines derived from the bulk MI and G phases. The V~ phase similarly might be derived from units of the G and M2 phases. Such mobile microstruetures would accord with the observation of the sharp NMR spectra from the V1 and V2 phases in contrast to the absence of sharp spectra with the M~, G, and M2 phases, where the mieellar units are stable, capable of persistent orientation, and of virtually infinite extension (1, 2). Further, the high viscosities of the Vt and V~ phases, when these phases

420

GILCHRIST, ET AL.

are considered as types of plastic crystal, would be expected. I n conclusion, it m a y be mentioned t h a t the V1 phase of the imide/water system when viewed between crossed polaroids and pressed with a glass rod, shows marked shear birefringence which rapidly relaxes on removal of the shearing force. This suggests t h a t the building units of the V1 phase are not necessarily inherently iso~ tropic but m a y show statistically isotropie properties because of their free rotary Brownian m o v e m e n t in the phase at rest, Such statistical isotropy might well be upset b y shear. REFERENCES 1. LUZZATI,¥., MUSTACCHI,H., SKOULIOS,A. E., AND HUSSON, F., Acta Cryst. 13, 660 (1960). 2. LUZZATI,V., AND HUSSON, F., jr. Cell Biol. 12,

207 (1962).

6. MANDELL, L., AND ]~K~VALL,P., Proc. Intern. Congr. Surface Activity, 4th Brussels I964.

Preprint No. B IV 6. 7. LUZZATI, V., AND REIss-HussoN, F., Nature

210, 1350 (1966). 8. LAWSON, K. D., AND FLAUTT, T. J., Molecular Crystals 1, 241 (1966).

9. WlNSOR, P. A., "Solvent Properties of Amphiphilic Compounds." Butterworths, London, 1954. 10. cf. ROSEVEAR, J. B., J. Am. Oil Chemists' Soc. 31, 628 (1954). 11. BERRY, R. W. I-~., AND BROCKLEHURST, P., J. Chem. Soc. 1984, 2264. 12. cf. HARSTSHORNE, :N. I~., AND STUART, A.,

13. 14. 15.

3. CLUNIE, J. S., CORKHILL, J. M., AND GOODMAN, J. F., Proc. Roy. Soc. (London) A285,

16. 520 (1965). 4. BALMI~RA,]:~. R., CLUNIE, J. S., AND GOODMAN, J. F., Proc. Roy. Soc. (London) A285, 17. 534 (1965). 5. EKWALL, P., DANIELSSON, I., AND MANDELL, 18. L., KoUoid Z. 169, 113 (1960).

"Crystals and the Polarising Microscope," 3rd ed., Arnold, London, 1960. cf. PARTINGTON,J. R., "Advanced Treatise on Physical Chemistry," Vol. IV, p. 275. Longmans Green, London, 1953. MACDONALD,M. P., Arch. Sci. Geneva. 12, 141 (1959). ZLOCHOWER,I. A., AND SCHULMAN,J. H., Div. Colloid and Surface Chem. of the Am. Chem. Soc. Abstr. of 152nd Meeting, 1966. LUTTON, E. S., J. Am. Oil Chemists' Soc. 43, 28 (1966). cf. e.g., MIJNLIEFF, P. F., AND DITMARSCH, R., Nature 208, 889 (1965). SMITH,G. W., Intern. Sci. and Technol. 61, 72 (1967).