154

Formation of a Liquid C stalline Phase Between Aqueous Suffactant Solutions and Oily Substances M. Yatagai ",o, M. Komaki b, T. N a k a j i m a b, and T. Hashimoto c aDoctoral Research Course in Human Culture, Ochanomizu University, 2-I-I Otsuka, Bunkyo-ku, Tokyo 112, Japan, bDepartment of Clothing, Faculty of Home Economics, Ochanomizu University, and CDepartment of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-I 2-I O-okayama, Meguro-ku, Tokyo 152, Japan

The p r o c e s s in w h i c h a t e r n a r y liquid crystalline (LC) p h a s e c o n t a i n i n g surfactant, w a t e r and oily s u b s t a n c e is f o r m e d after c o n t a c t o f a q u e o u s s u r f a c t a n t s o l u t i o n and oily s u b s t a n c e w a s i n v e s t i g a t e d by a c o m b i n a t i o n o f ( i ) m i c r o s c o p i c o b s e r v a t i o n in p o l a r i z e d light and ( i i ) p e n e t r a t i o n o f w a t e r - s o l u b l e or oil-soluble dye into LC p h a s e . The s t r u c t u r e o f LC p h a s e and t h e p r o c e s s o f its f o r m a t i o n w e r e f o u n d to be a f f e c t e d by m a n y factors, s u c h as k i n d s o f s u r f a c t a n t , s u r f a c t a n t concentration, alkyl c h a i n l e n g t h o f oil and s o on. Oil is s u p p o s e d to be gradually i n c o r p o r a t e d into LC p h a s e w i t h time. The fact that parts o f LC p h a s e are p r o j e c t e d into t h e e x t e r i o r s u r f a c t a n t s o l u t i o n , and that t h e c o n t i n u o u s p h a s e w i t h i n LC p h a s e is w a t e r , s u g g e s t t h e p o s s i b i l i t y o f t h e d i s p e r s i o n o f LC p h a s e into t h e e x t e r i o r solution. T h e p r o c e s s o f t h e f o r m a t i o n o f LC p h a s e i m p l i e s s o m e c o n t r i b u t i o n to oily dirt removal.

Several workers have noted that a t e r n a r y liquid crystalline (LC) phase containing surfactant, water and oily substance is formed between aqueous surfactant solution and oily substance when they come into contact with each other in various systems (1-4). Such a formation of LC phase has been discussed with respect to the mechanism of oily dirt removal, and the results of m a n y washing experiments (performed under conditions where LC phases were present) have suggested some contribution of LC phase to detergency (3-7). We have also described elsewhere (8) the detergency performance for cotton and polyester fabrics in both conditions where LC phase is formed and where it is not. There is a large recent literature on the structure of LC phase appearing in various systems containing surfactants. For example, Friberg and his co-workers (9-11) have described the structure of LC phases formed in various emulsions and foams. Miller, et al. (12-17) have described the phase behavior and the structure of LC phase, microemulsion and other phases, especially with respect to oil recovery and to detergency. For investigation of the correlation between the LC phase formation and the oily dirt removal, the structure of LC phase formed between s u r f a c t a n t solution and oil after contact is more important than that formed in mixed systems such as emulsions. Miller and his coworkers have also observed the diffusion process of oily substance into aqueous surfactant solution through microemulsion and LC phase (15,18,19). In this paper we describe the process in which LC phase is formed between surfactant solution and oily substance from the standpoint of the structure of LC phase, especially molecular orientation of surfactant. The dynamic *To whom correspondence should be addressed. JAOCS, VoL 67, no. 3 (March 1990)

phenomena, which occur after bringing s u r f a c t a n t solution into contact with oil, were observed with a polarizing microscope in various systems. The structure of LC phase in each system was investigated from its optical properties found in polarized light, and also from penetration of water-soluble or oil-soluble dye into LC phase.

EXPERIMENTAL M a t e r i a l s . Sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (DBS), with linear alkyl chains, were obtained from Wako Junyaku Kogyo Co. Sodium dodecylbenzene sulfonate, with a branched alkyl chain, was obtained from Kanto Kagaku Kogyo Co. Various oily substances in a liquid state at room t e m p e r a t u r e were used as simple models of oily dirt. n-Alkanes, n-fatty alcohols and n-fatty acids with various alkyl chain lengths were obtained form Tokyo Kasei Kogyo Co. (Tokyo, Japan). All surfactants and oily substances were used without further purification of the commercial e x t r a pure grade samples, having purities of at least 95%. Deionized and distilled water was used to prepare the surfactant solutions. Water-soluble and oil-soluble dyes used were Benzopurprine 4B (C.I. Direct Red 2) and Sudan I (C.I. Solvent Yellow 14), obtained from Tokyo Kasei Kogyo Co. and Sigma Chemical Co. (St. Louis, MO), respectively. O b s e r v a t i o n s w i t h a p o l a r i z i n g microscope. Sample was prepared in a vertical orientation within a glass cell, which has rectangular windows and path length of 1 mm. After pouring aqueous surfactant solution into the cell by haft, oily substance was gently added to make the cell filled out. When these two liquids were brought into contact with each other, care was taken to control the disturbance near the solution/oil interface as little as possible. Immediately after contact, the cell was set in a horizontal orientation on the stage of a polarizing microscope (Nikon, OPTIPHOTO-POL), and dynamic phenomena, which occurred in the vicinity of the solution/oil interface, were observed. Similar techniques have been used by Benton et al. (20) to study the dynamic contacting of aqueous surfactant solutions with hydrocarbons. Sample preparations and observations were performed at 200C. In case LC phase was formed as a layer, the increase of its thickness with time was measured using a micrometer. The structure of LC phase was investigated by examining the molecular orientation using a sensitive color plate (R=530 nm) inserted between a sample and an analyzer in the crossed-nicols. A birefrigent sample shows a higher order interference color (blue), or a lower order interference color (yellow), depending upon the direction in which the sample is set against the axes of the sensitive color plate (21). In linear hydrocarbon chain surfactants, the refractive index is larger in the direction of long chain axis (22), so t h a t the different interference color can be observed whether hydrocarbon chains are oriented parallel or perpendicular to the one axis of the sensitive color plate. Therefore, molecular orientation of surfactant in

155 FORMATIONOF LIQUIDCRYSTALLINEPHASE LC phase can be examined by the color observed using the plate. Textures found in polarized light were also used for classification of liquid crystal (23). Observation of textures was performed for a small a m o u n t taken from LC phase on a slide glass.

Penetration of water-soluble or oil-soluble dye into LC phase. The penetration p h e n o m e n a of water-soluble or oil-soluble dye into LC phase in the process of its formation were also examined in order to investigate the structure of LC phase. Sample preparations were as follows: 0.2 mol/1 SDS solution colored with Benzopurprine 4B (0.01%) was gentlybrought into contact with the colorless oil in avial (System A). On the other hand, oil colored with Sudan I (0.01%) was brought into contact with the colorless 0.2 mol/1 SDS solution (System B). Whether the LC phase formed between SDS solution and oil became dyed or not was examined with time for both systems at 20~C.

z o W~ z

i J

0.2

i

',' (.9

z o O1 ~ E ~ m o 0.0

LC

N N

N

6 t

alkane

fatty alcohol

i

iatty acid'

CARBON NUMBER FIG. 2. Conditions w h e r e a liquid crystalline phase is either formed (LC) or not ( N ) in the s y s t e m s o f DBS solutions and various oily s u b s t a n c e s (20~C).

RESULTS AND DISCUSSION

ing both SDS molecules and oil molecules is formed or not at the interface. Polar oils, having some surface activity, not. Prior to investigation of the structure of LC phase, the are supposed to be adsorbed at the interface and form a conditions determining its formation were defined. Var- mixed film with SDS molecules. The mixed adsorbed film ious combinations of surfactant solutions and oils were might grow to multi-layer, and then successively to LC brought into contact with each other. The sample was left phase above the critical concentration. for 30 min, and then the vicinity of the solution/oil interThe lowest SDS concentration, at which LC phase forface was observed with a polarizing microscope (X 100). mation can be detected between SDS solution and fatty When a birefrigent phase was found between dark solu- alcohols or fatty acids, is dependent upon the alkyl chain tion phase and dark oily phase in the crossed-nicols LC length or carbon number of these oils. The critical concenphase formation was recognized. tration is lowered with increasing the carbon number of Results are shown in Figure 1 for the systems of SDS them. There is no remarkable difference between the sysand in Figure 2 for the systems of DBS, respectively. Con- tem of fatty alcohols and that of fatty acids with respect ditions where LC phase is formed (LC) and not (N), were to the critical concentration. defined. LC phase is also formed between DBS solutions and In Figure 1, no change is detected in the vicinity of the polar oils above a certain concentration of DBS, as shown interface between SDS solution and n-alkanes having var- in Figure 2. The critical DBS concentration, however, beious alkyl chain lengths. On the other hand, LC phase is comes higher with increasing the carbon number of oils, formed above a certain SDS concentration between aque- as opposed to the systems of SDS. ous SDS solutions and polar oily substances, n-fatty alcoWhether an alkyl chain of surfactant is linear or hols and n-fatty acids. branched also affected the results. In the case of DBS with It is supposed that whether or not LC phase is formed a branched dodecyl group, LC phase was not formed bebetween SDS solutions and oils after contact is primarily tween aqueous solutions and all kinds of oils examined. In dependent upon whether a mixed adsorbed film contain- both systems of linear and branched DBS, spontaneous emulsification often occurred in the vicinity of the interface, whether or not LC phase was formed. The structure of emulsion was not examined. z 0.3 From these results, it is found that whether LC phase is O I.-formed or not between surfactant solutions and oily sub< stances is dependent upon m a n y factors, such as polarity LC ~- 0-2 N and alkyl chain length of oils, kinds and concentration of Z ~ surfactants, and so on. It is supposed that the interaction 9, zo 0 E in a ternary system (which contains surfactant, water .1 and oil) is affected by such factors, and that the complicated p h e n o m e n a (including the formation of LC phase C~ L ~ L and spontaneous emulsification) result from the interacL tn O0 6 7 8 9 tion in each system. 6 Microscopic observation of LC phase formation: SDS 'fatty acid' fatty alcohol alkane

Conditions d~t~rmining whetl~r LC phase is formed or

,

I

CARBON NUMBER FIG. 1. Conditions w h e r e a liquid crystalline phase is either formed (LC) or not ( N ) in the s y s t e m s o f SDS solutions and various oily s u b s t a n c e s (20~C).

solution/fatty alcohol systems and the effect of SDS cancentration. Figure 3 shows a micrograph of the interface

between 0.05 mol/1 SDS solution (left side) and octanol (right side). Formation of LC phase is found in the vicinity of the interface. Because of the vigorous convection in the vicinity of the interface, the LC phase dispersed into the JAOCS, Vol. 67, no. 3 (March 1990)

156 M. YATAGAIETAL.

FIG. 3. Microscopic observation o f the interface b e t w e e n 0.05 m o l / 1 SDS solution and octanol (25 rain after contact, crosseduicols, X 40).

exterior SDS solution, and then disappeared without growing. At the higher SDS concentrations, the LC phase was formed as a thin layer between SDS solution and octanol as soon as they were brought into contact. Figure 4a shows a typical micrograph of the LC phase formed between 0.25 mol/1 SDS solution (left side) and octanol (right side). By using a sensitive color plate, as mentioned above, the hydrocarbon chains in LC phase were found to be oriented parallel to the interface at first contact in almost all parts of LC phase. Partially different molecular orientations were found in some parts of it. Such partial disorder of the molecular orientation is supposed to be caused by a disturbance which occurs at the time of contact. After about 10 min m a n y free drops appeared near the b o u n d a r y between the LC phase and the exterior SDS solution. From the heterogeneity of the color of the LC phase, the molecular orientation in the LC phase was

FIG. 4. Microscopic observation in the s y s t e m o f 0.25 m o l / 1 SDS solution and octanol ( c r o s s e d - u i c o l s ) . a) 1 min after contact (X 40); b) after 4 hr, the boundary b e t w e e n a liquid crystalline phase and SDS solution (X 100); and c) after 4 hr, the boundary b e t w e e n a liquid crystalline phase and octanol p h a s e (• 100).

JAOCS, Vol. 67, no. 3 (March 1990)

157 FORMATION OF LIQUID CRYSTALLINE PHASE

SDS CONCENTRATION( mol/I ) o 0.25 "0-2 l, 0.15 A0.1

600

O O

400

00

~

~J z

o

O

A A~

0 o

200

u

@~A4

9

-r-

,~

Oo'

'

i

'

;

JTIME(min) FIG. 5. Oily streak and mosaic textures found in the SDS solut i o n / o c t a n o l system (crossed-nicols, X 100).

found to become gradually disordered, probably due to the diffusion of the molecules. As shown in Figure 4b, m a n y spherulites projecting into the exterior solution a p p e a r near the b o u n d a r y between the LC phase and the solution after 4 hr of contact. From the color of the spherulites, the hydrocarbon chains in them were found to be oriented from the center to the surface. Tube-like structures called myeline figures were also observed. Stevenson (2) has already discussed the formation of myeline figures and anisotropic droplets or spherulites. The structure near the b o u n d a r y between LC phase and the exterior octanol phase (Fig. 4c) is obviously different from the other side, shown in Figure 4b, which has been in contact with the aqueous solution. These features were observed more clearly after 24 hr of contact. Figure 5 shows the texture observed in the crossednicols in both samples, which are taken from the LC phases left for 4 and 24 hr. Oily streak and mosaic textures, characteristic of the lyotropic liquid crystal of lamellar structure (neat soap) (23), were found. SDS CONCENTRATION ( mo[/L ) 00.25

" 0.2

o0.15

" 0.1

600

FIG. 7. Replotting of the data in Figure 6. The t h i c k n e s s of a liquid cystailine p h a s e vs square root o f time.

When LC phase was formed as a layer, it thickened gradually toward the aqueous phase from the interface of first contact. Figure 6 shows the increase of its thickness with time after contact for the representative case of SDS solution and octanol. LC phase becomes thicker with increasing SDS concentration. These d a t a are replotted against square root of time in Figure 7. Diffusion p a t h theory predicts a linear relationship between the thickness of LC phase and square root of time (18,24). In Figure 7, however, a p p a r e n t deviations are observed from the linearity. Many complicated factors, such as the effect of convection, are supposed to cause the nonlinearity in this system. The effect of alkyl chain length offatty alcohol. Various p h e n o m e n a were observed in the systems of 0.25 mol/1 SDS solution and fatty alcohols of various alkyl chain lengths. As shown in Figure 8, when pentanol is brought into contact with 0.25 mol/1 SDS solution, m a n y spherulites are formed near the interface of solution (left side) and pentanol (right side). From the color of the spherulites, the molecular orientation within them was found to be the same as those observed in the octanol system. The

O 0

E 400 :L

0

0 0

A

z~

A

O U3 u"1 1,1 Z U "II--

@AA

O

200

i

0

0

i

10 20 TIME(min )

i

30

FIG. 6. Effect of SDS concentration on the t h i c k n e s s of a liquid crystalline p h a s e (20"C).

FIG. 8. Spherulites formed in the s y s t e m of 0.25 m o l / 1 SDS solution and pentanol (al~er I rain, crossed-uicols, X 40).

JAOCS, Vol. 67, no. 3 (March 1990)

158 M. YATAGAIETAL. In the case of decanol (Figure 10), LC phase is formed in entangled layers between SDS solution (left side) and oil (right side) with vigorous disturbance immediately after contact. Spherulites were observed near the b o u n d a r y between the LC phase and the exterior solution, same as in the case of octanol. Oily streak and mosaic textures were also observed. It is found that LC phases formed in the SDS solution/ fatty alcohol systems contain lamellar structures from the characteristic textures; but their whole features are determined by the alkyl chain length of fatty alcohol.

Other systems: Effect of polar group of oily substance.

FIG. 9. A liquid crystalline p h a s e formed in the s y s t e m o f 0.25 m o l / 1 SDS solution and h e x a n o l (after 1 hr, crossed-nicols, X 100).

spherulites moved about near the interface, dispersed into the aqueous solution, and then disappeared. This means that LC phase is broken and dissolved in the surfactant solution. In the case of hexanol, LC phase is formed as a thin layer between SDS solution (left side) and hexanol (right side) (Figure 9). Striation pattern parallel to the interface is observed in it. The distance between striations is in the range of about 20-30pm. A region of fme drops is also observed on the side of the b o u n d a r y in contact with the aqueous solution. The region was gradually spread over a wide range in time. From the color of the LC phase, the molecular orientation was found to be parallel to the interface in the region with striation pattern, but perpendicular to the interface in the region of fine drops. It is supposed that the striation pattern observed in the crossed-nicols suggests the existence of a kind of longrange ordered structure. Furthermore, the LC phase was found to contain lamellar structure from the oily streak and mosaic textures similar to those shown in Figure 5. The detailed discussion of its structure needs further investigations. Similar behaviors were observed in the system of heptanol.

FIG. 10. A liquid crystalline p h a s e formed in the s y s t e m o f 0.25 m o l / 1 SDS solution and decanol ( a f t e r 2.5 min, crossed nicols, X 40).

JAOCS, Vol. 67, no. 3 (March 1990)

The system of fatty acid was c o m p a r e d with that of fatty alcohol in order to examine the effect of polar group of oil on the process of LC phase formation. In the system of octanoic acid and 0.25 mol/1 SDS solution, similar pheno m e n a were observed to the systems of octanol. Spherulites and myeline figures were observed near the aqueous solution, and textures showed the features of lamellar structure. Effect of molecular structure of surfactant. When 0.25 mol/1 DBS solution was brought into contact with octanol, disturbance near the interface was more vigorous than t h a t of the SDS systems. It was about 10 min after contact that a stable LC phase was formed. By the color of the LC phase, molecules in the LC phase were found to be oriented parallel to the interface, as in the SDS systems, at the initial stage. At the latter stage, however, the molecular orientation was found to invert from parallel to perpendicular to the interface, from the change of the color. As shown in Figure 11, fan-like texture, which is characteristic of the lyotropic liquid crystal of hexagonal structure (middle soap) (23), is found in both samples left for 4 and 24 hr. These results suggest that the hexagonal structures become dominant at the latter stage in this system. Molecular shape generally affects the way that molecules pack into hexagonal or lamellar structure (25). Molecular structure of surfactants is supposed to be one of the i m p o r t a n t factors determining the liquid crystalline structure. The difference of LC structure between SDS and DBS systems might be explained by the poor molecular packing of DBS molecules, as c o m p a r e d with SDS, owing to a benzene ring.

FIG. 11. Fan-like t e x t u r e found in the DBS s o l u t i o n / o c t a n o l syst e m (crossed-nicols, • 100).

159 FORMATIONOF LIQUIDCRYSTALLINEPHASE o-- SOS ,,.- ]-Octanol W Aqueous SDS Solution

.o

o~ ~;-

0 : ]-Octanol

~ a d s o r p t i o n of SDS and 1-octonol at the interface

w

FIG. 12. Coloring o f the liquid crystalline phase 24 hr after contact in the s y s t e m s o f ( A ) 0.2 m o l / 1 SDS solution = Benzopurprine 4 B / o c t a n o l , and ( B ) 0.2 m o l / l SDS s o l u t i o n / o c t a n o l = Sudan I.

Penetration of water-soluble or oil-soluble dye into LC phase. Ekwall et al. (1) revealed t h a t the LC p h a s e formed between laurate solution and decanol was hydrophilic from the fact t h a t the LC p h a s e was dyed when watersoluble dye was added in laurate solution, but not dyed when oil-soluble dye was a d d e d in decanol. However, it is supposed t h a t the hydrophilicity or lipophilicity of the LC p h a s e will change according to the change of its s t r u c t u r e in the process of the formation. In order to obtain some information on the s t r u c t u r e of LC phase, penetration of water-soluble or oil-soluble dye into LC p h a s e was e x a m ined in the systems of SDS solution and fatty alcohol or fatty acid. The formed LC p h a s e was dyed in the system of SDS solution colored with Benzopurprine 4B and octanol (System A), but not dyed in the system of SDS solution and octanol colored with Sudan I (System B) at the initial stage of its formation. It shows t h a t only water-soluble dye can be dissolved in the LC p h a s e at this stage; namely, the continuous p h a s e within the LC p h a s e is s u p p o s e d to be water. In other words, the LC p h a s e is supposed to be hydrophilic. This result is consistent with t h a t r e p o r t e d by Ekwall et al. (1). However, it was found t h a t r e m a r k a b l e changes occur in both systems left for longer periods. Figure 12 shows the samples left for 24 hr after contact. In System B, the LC p h a s e becomes gradually dyed f r o m the b o u n d a r y contact with the colored octanol phase. Penetration of oil-soluble dye into the LC p h a s e occurs. This suggests t h a t incorporation ofoil into the LC p h a s e is e n h a n c e d as the LC p h a s e is formed, a n d s e p a r a t e d phases of oil, in which oil-soluble dye can be dissolved, a p p e a r within the LC phase. On the contrary, at the initial stage of the formation of the LC p h a s e oil is incorporated only as monomolecules to form the liquid crystalline structure, because oil-soluble dye c a n n o t be dissolved in the LC phase. Moreover, in System A, the octanol p h a s e becomes dyed with time from the b o u n d a r y c o n t a c t with the dyed LC phase. This m e a n s t h a t the penetration of water-soluble dye into the oily p h a s e occurs. This change is s u p p o s e d to be caused by the solubilization of w a t e r and water-soluble dye in the reversed micelles of SDS, or the W/O emulsification of them, in the oily phase.

~'/" ~'~T~

o

b) diffusion of 1-octono[ into the aqueous solution

w

F

LC L~quid crystalline phase r

formation of a liquid crystalline phase I - - L C %

d W

~o~

d) incorporation of oil as dusters

w

LC

,'7t~7

,gNU, e] spheruhte and myeline figure

FIG. 13. Schematic illustration o f the process o f a liquid crystalline phase formation in the s y s t e m o f SDS solution and o c t a n o l - a ) a d s o r p t i o n o f SDS and octanol at the interface; b) diffusion o f octanol into the aqueous solution; c) formation o f a liquid crystalline phase; d) incorporation o f off into a liquid crystalline p h a s e and e m u l s i f i c a t i o n or solubilization o f off; and e ) spherulite and myeline figure.

JAOCS, Vol. 67, no. 3 (March t990)

160 M. YATAGAIETAL. In the systems of o t h e r oily s u b s t a n c e s - - h e x a n o l , hexanoic acid a n d o c t a n o i c a c i d - - s i m i l a r results were obtained. Process o f L C p h a s e f o r m a t i o n . F r o m the results obt a i n e d above, the process of f o r m a t i o n of LC p h a s e is s p e c u l a t e d with r e s p e c t to its s t r u c t u r e for t h e representative case of SDS solution a n d octanol. Figure 13 shows the s c h e m a t i c illustration of the process of LC p h a s e formation. When SDS solution c o m e s into c o n t a c t with o c t a n o l initially, t h e m i x e d a d s o r b e d film which consists of SDS molecules a n d o c t a n o l molecules is f o r m e d (Figure 13a). Diffusion of o c t a n o l molecules into the a q u e o u s solution causes the orientation of SDS molecules (Figure 13b). Above a certain SDS c o n c e n t r a t i o n a stable layer of LC phase, thick e n o u g h to be observed, is f o r m e d b e t w e e n solution a n d oil. At the initial stage of its f o r m a t i o n (Figure 13c), the m o l e c u l a r orientation is mainly parallel to t h e interface of first c o n t a c t , a n d w a t e r layers exist between the hydrophilic g r o u p s o f l a m e l l a r layers. LC p h a s e at the p r o c e e d i n g stage (Figure 13d) consists of stacks of lamellar layers of SDS a n d octanol, with the w a t e r layers i n t e r p o s e d between the hydrophilic g r o u p s of t h e lamellar layers, a n d s e p a r a t e d p h a s e s of octanol. At the s a m e time, n e a r the b o u n d a r y between the LC p h a s e a n d t h e a q u e o u s solution, o c t a n o l is emulsified or solubilized. As the f o r m a t i o n of LC p h a s e is advanced, the m o l e c u l a r a r r a n g e m e n t of the lamellar s t r u c t u r e b e c o m e s disord e r e d b e c a u s e of the diffusion of the molecules. N e a r the b o u n d a r y c o n t a c t with the a q u e o u s solution, p a r t s o f LC p h a s e are p r o j e c t e d into the solution (Figure 13e), which are t h e spherulites and t h e myeline figures. It is s u p p o s e d t h a t t h e basic s t r u c t u r e o f the LC p h a s e f o r m e d b e t w e e n SDS solution a n d f a t t y alcohol or f a t t y acid is similar to t h a t described above. As m e n t i o n e d above, the p r o c e s s of LC p h a s e f o r m a t i o n includes the i n c o r p o r a t i o n of oil into it a n d the projection of spherulites a n d myeline figures into the exterior solution. The latter suggests t h a t since t h e c o n t i n u o u s p h a s e within LC p h a s e is water, LC p h a s e will be dispersed into t h e solution. Therefore, t h e p r o c e s s describes t h e incorp o r a t i o n of oil into the LC p h a s e a n d the s u b s e q u e n t release of oil into the e x t e r i o r solution. Kielman et al. (24) have claimed the c o n t r i b u t i o n of LC p h a s e f o r m a t i o n to oil r e m o v a l b a s e d on a series of studies which involve diffusion p a t h in s u r f a c t a n t - w a t e r - o i l systems a n d d e t e r g e n c y p e r f o r m a n c e in t h e p r e s e n c e of LC p h a s e (26). Detailed discussion on the correlation between the LC p h a s e f o r m a t i o n a n d the m e c h a n i s m of oily

JAOCS, VoL 67, no. 3 (March 1990)

dirt removal needs f u r t h e r investigation, including cont a c t experiments, p h a s e behavior studies a n d w a s h i n g experiments. However, o u r results of the microscopic observations suggest s o m e c o n t r i b u t i o n o f the LC p h a s e to detergency.

REFERENCES 1. Ekwall, P., M. Salonen, I. Krokfors and I. Danielsson, Acta. Chem. Stand. 1~.1146 (1956). 2. Stevenson, D.G.,in Surface Activity and Detergency, K. Durh um

3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

23. 24. 25. 26.

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[Received March 7, 1988, Accepted September 10, 1989.] [J5421]