turbidity ratio for emulsion stability

5/20/2018 Turbidity Ratio for Emulsion Stability

1/6

Korean J. C hem. Eng.,

19(3), 425-43 0 (2002)

No ve l Evalu at ion M eth od for th e W ater - in -Oi l W /O) Em u ls ion S tab i li ty b y

Tu rb id i ty Rat io M easu remen ts

M y u n g - G e u n S o n g , S u n g - H o C h o , J o n g - Y u n K i m a n d 3 o n g - D u k K im

D e p a l - ~ e n t o f C h e m i c a l E n g i n e e r i n g , K o r e a A d v a n c e d I n stit~ _~ te o f S c i e n c e a n d T e c h n o l o g y ,

3 7 3 -1 G u s e o n g - d o n g , Y u s e o n g - g u , D a e j e o n 3 0 5 - 7 0 1 , K o r e a

* L G H o u s e h o l d & H e a l t h C a r e R e s e a r c h P a rk , # 8 4 Ja n g - d o n g , Y u s u n g - g u , D a e j e o n 3 0 5 - 3 4 3 , K o r e a

( R e c e i v e d 1 4 J u n e 2 0 0 1 9 a c c e p t e d 1 5 F e b r u a r y 2 0 0 2 )

A bs l r a c t - Th e tu rb id i ty r a t io me th od o f eva lua t ing the st a bi li ti e s o f w a ter -in -o i l e muls ions ha s be e n e s t a bl ishe d w i th

t w o w a v e l e n g t h s ( 4 5 0 a n d 8 5 0 z m ~ ) b y t a ! d n g t h e i n t e n s i ty r a t i o o f t w o b e a n s . T h e s l o p e s o f t u rb i d i t y r a ti o o f s e v e ra l

w a te r - in -o i l e muls ions w i th t ime w e re c a lc u la te d to e va lua te the e muls ion s t a b i l i t i e s a t d i f f e r e n t H LB (H ydrophi l i e -

L ipop hi l e Ba la nc e ) , t he a m oun ts o f e muls i f i e r s , a nd w a te r c on te n t s . The r e st il ts o f the tu rb id i ty r a t io t e c hnique w e re

c o n s i s t e n t w i t h t h e a m o u n t o f p h a s e s e p a r a t i o n o f e m u l s i o n s i n c u b a t e d f o r 3 0 d a y s a t r o o m t e m p e r at m - e . F r o m t h e

turb id i ty r a t io me a sm -e me nts , w e de te m a me d tha t the r e qui r e d H LB of d ie se l o il w a s a b out 6 . 0 , a nd tha t the s t a b i l i ty

of e m uls ion inc re a se d w i th the a mou nt o f emuls if ie r . Th e inc re a s ing a m oun t o f the w a te r show e d a ne ga t ive e f f e c t on

e mu ls ion s t a b il ity . F ina l ly , th i s me tho d pro~4des a use fu l too l fo r the qu ic k e va lua t ion o f the r e qui r e d H LB a nd the

c o n d i t i o n o f e m u l s i f ic a t i o n t h r o u g h o u t t h i s s t u d y .

K e y w o r d s : S t a b i li t y o f E m u l s i o n , W / O E m u l s i o n , T u r b i d i t y R a t io , R e q u i r e d H L B , D r o p l e t S i z e D i sh J b u t io n

I N T R O D U C T I O N

T h e s t a b il i ti e s o f e m u l s i o n s a r e v e r y i m p o r t a n t f o r v a r i o u s i n -

dusN a l p roc e s se s a nd e mu ls ion prc duc t s , bu t the e va lua t ion of e m ul -

s ion s tabi l i ty is not easy. Genemlly, the kine t ics of the emuls ion-

bre a k ing p roc e s se s i s go ve rne d by t t~-e e d i ff e re n t pa r t ic le los s me c ha -

nisms: Bro wn ian f loccula t ion, sedimen ta t ion f lcccula tion, an d cream -

i n g [ R e d @ a n d F o g l e i ; 1 9 8 1 ] . P a r t i c l e s u n d e r B r o w n i a n m o t i o n

c ol l ide a nd th e n c o a le sc e to fo rm la rge r iz a rt ic l es . A t the s a me t ime ,

pa r t i c l e s a r e c r e a ming ou t due to the d i f f e r e nc e be tw e e n the de ns i -

t i es o f p a r ti c le s a n d c o n g r u o u s m e d i u m . S e d i m e n t a t io n f l o c c u l a ,

t ion i s due to d ikTe re n ti al c r e a m ing r a te s o fpa r t i c l e s a n d c re a m s ou t

a t a fas te r ra te th a i the sm alle r ones ; therefore , la rger par t ic les col l ide

w i t h s l o w l y - m o v i n g s m a l l e r pa r ti c le s a s t h e y c r e a m o u t.

Suc h e muls ion-bre a k ing proc e s se s ha ve be e n s tud ie d e x te ns ive ly

by m a l y i tw e s tigators , ma d va iou s m e thods o f de te rmin ing the e mul -

s ion s t a b il ity ha v e be e n pro pose d suc h a s d rop le t s i ze a na lyse s [Tre i-

ne t e t a l ., 1989; Ta&o s, 1994] , mea suring phy sica l i :~werties o f em ul-

s ion [ Ta nb e a n d Sha n~a a , 1994; D re h e r e t a l ., 1999] , a nd a c c e le r -

a te d t e s t s [For s t e r e t a l ., 1992; L a t r e i l le a nd Pa q uin , 1990]. Turb id -

i t y m e a s u r e m e i ~ h a v e a l s o b e e n u s e d to d e te m ~ in e t h e e m u l s i o n

s ta b i li ty [K im a nd K im , 1988; Song e t a l. , 2000; L e e e t a l ., 1999] ,

a n d a t e c h n i q u e u t i l i~ n g t h e s p e c t ra l a b s o r b a n c e a t s e v e ra l w a v e -

Ie ig t tz s w a s prop ose d to a l low the de te nn ina t ion w i th in a r e l a t ive ly

shor t pe r iod of t ime [Fre nke l e t al ., 1982; K a t f i -na n a nd G a rb , 1981;

Gu nji e t al . , 1992] . T he tu rbidi ty "c is def ined in ten ,a s o f the a t -

t e nua t ion of e l e c t roma gn e t i c r ac li a tion a t a s c a t t e ring a a g le o f 0 ~

= } i n ( I / I ) ( I )

~To w ho m c one spond e nc e should be a ddre s se d .

E-mail: [email protected]

4 2 5

wh ere l ks the pa th length, a nd I0 and I a re the inte t~s i t ies of the in-

c ident and ~aansmit ted bea~as , respec t ive ly. Expe~-hnentaI 0m-bidi-

t ie s c o u l d b e m e a s u r e d w i t h a c o n v e n t i o n a l U V / V I S s p ec ~ -o p h o-

t o m e t e r , w h i c h r e a d s a b s o r b a n c e . I f t h e r e i s n o m o l e c u l a r a b s o r p -

t io n , t h e t u r b i ~ t y i s re l a t ed t o t h e s a m p l e a b s o r b a n c e m e a s u r e d a t a

w a v e l e n g t h ,

9 =2.303 x (absorbance) (2)

F o r a m o n c ~ i s p e r s e s y s t e m o f n o u a b s o r b i n g i s o ~r o pi c s p h e r e s i n

the a bse nc e o f mu l t ip le a nd de pe nd e nt s ca t te r ing , the ~b i c l i ty i s

g i v e n b y [ M e l i k a n d F o g l ei \ 1 9 8 3 ; K e r k e i \ 1 9 6 9 ]

9 -~Nr~Q (r, 9~, m ) (3)

w he re " c de pe nds

o

the par t ic le concenh-a t ion, N, the c ross sec-

t iona I a r e a o f pa r t lc I e s , m 2 , a nd th e s c a t te r ing c oe f f i c i e n t, Q , w h ic h

i s de f ine d a s the r at io o f the s ca t te z mg to g e o m ~i c a l c ros s se c tions.

Th e s c a t t e r ing c ros s s e c t io n i s the to ta l r a d ia t ion a re a s c a t t e r e d by a

s ing le sphe re f lo ra a n inc ide n t b e a n of un i t in t ens ity . Thi s s c a t t e r -

ing c oe f t i c i e n t i s, i n tu rn , a fv i l c t ion of the pa r t i c l e s i z e , the r a t io o f

the r e f r a c t ive inde x of the pa rhc le g~ to the r e fi -a c tive inde x o f the

m e d i u m ~ ,, , d en o t e d b y m , a n d t h e w a v e l e n g t h o f t h e i n c id e n t w a v e

in the d i spe i~ ing me dium, ~ . Th e w a v e le ng th 9~ i s e qu a l to kJ /. t, ,,

w h e re ~0 i s the w a v e le n gth in a5 i~ Th e s c at te a -ing c oe f f ic i e n t i s c a l -

c u la te d by us ing the M ie the ory of l igh t sc a t t e ma g S inc e the tu rb id-

i t y o f a p o l y d i s p e r s i o n i s th e s u m o f a l l t h e c o n t t i b u ti o n s o v e r t h e

var io us par t ic le s izes , the turbic li ty of the tota l dis tr ibut ion exp ressed

in in te gra l fon~a i s [K e rke r , 1969]

N ~ ~

= -~ -~ c~ f( c~)Q (c ~,m)dc~ (4)

wh ere cz(=2 nr~) is dimension less par t ic le size , and f(cZ) s the dis tri -

bu t ion funct io i1 The re fore , the tu rb id i ty o f e muls io n c a n be e va lu -


2/6

426

M.-G. Song et al.

ated with particIe size distribution (P SI)).

The changes in PSI)

~der

conditions of simultaneous floccula-

don and creaming for vaz-ious times s howed that the PSI) shifts to

large particle sizes, owing to flocculation of the small particles ihi-

tally. Since the stability to flocculation increases exponentially with

increasing particle size, the smaller particles flocculate quickly to

form relatively stabIe larger parttcles [Becher, 1988]. Rathermore,

the la ger particles cream out at a much faster rate than the smaller

ones, thereby resulting in an observable shift of tile PSD back to

the smaller after long brae. Finally, the PSD becomes increasingly

na~xower for longer times because the total particle concentration

is now exlremely low, thereby resulting only in tile slow creaming

out of the sm aller particles. If the prepared emul siom were stable

relatively, thes e cyclic changes or shit~ in PSI ) woul d occu r slowly.

From this point of view, it is possible to evaluate the em ulsion sta-

bility by measurement of the change of PSD with time and the ~r -

bidity method can be a useful one, because the ~bi~ty measure-

ments are rapid and simple.

It is we ll established that the intemity of light scatteiqmg increases

with decreastng droplet diameter, and therefore we can estimate

the relative size dis~-ibution by measuring tile ratio of turbidity at

two widely separated wavelengths. In fact, the change of IJarbidity

ratio as a function of time exhibits the rel atve emulsion brealdng

process by simultaneous flocculation and coalescence more exactly

compared with turbidity at single wavelength.

In order to appraise the turbidity ratio technique, several water-

in-oil emul siom were tested by using co~m-nerdaUy available e~-nuI-

sifters. Th e results of this technique were co mpared with other meth-

ods such as -oplet size dis~-ibution and the m'nount of phase separ a-

tion of emulsion.

E X P E R J M E N T A L

1. M at er i a l s an d M et h od s

The oil phase w as res~icted to dieseI (com posed of C12-C20 hydro-

carbon mLxture) and was obtained from H anw ha Enelgy Co. The re-

fiactive index of oil meas~-ed with Abb6 reffactometer is 1.469 at 20

~ No a -iitiveswere contained in oil and deioi/zed water was us ed

For emulsifiers, sorbitan moncoleate (Sp an 80), polyoxyeth ylene

sorbitan monooleate (Tween 80), polyoxyethylene 2-cetyl ether

(Brij 52), and polyoxyethylene 2- and 12-nonylphenyl ethers (NP2

and NP12) flora Sigma C hemicals were used without ftather puri-

fication. Emulsio ns were prepa red by dissolving the hy opho bic

emulsifiers in oil phase and mixed thoro~@aly with slowly adding

the water phase contmned with hydrophilic emulsifier. L abor atoly

homogenizer (Heidolph DIA X 900) was used at 10,000 rpm for

8 minutes. All the emulsions were aJiowed to age for 24 hours at

room tem perature and diluted 500 ~'nes in oil within 1 minute. Spec-

tral absorbance was measured after dilv~on by using the Jasco V -

570 UV/V-LS speclrophotometei: Tile IJarbidity ratio was desigilated

as R(='cJ'cs, L: long wavelength, S: short wavelength).

Droplet size distributions were analyzed by means o f dynamic

light scattering technique with a Zetaplus instrument (Brookhaven

Instruments Co.) aider dilv~on with 500 ames. Multlmodal size dis-

tribution was calculated based on Non-Negatively Comtrained Least

Square (NNLS) method and the results were plotted as Iognon-naI

size distributions. The droplet size variation was monitored with time.

The emulsions were incubated in order to measure the amount

of phase separation of the water phase from the oil phase. T he fleshly

prepared emulsions were replaced into 25 ml-cylindticaI test tubes

and incubated at room tempera~e. After 30 days, tile sepa-ation

heights were measured and compared with ~trbidity ratio measure-

m

ent.

R E S U L T S A N D D I S C U S S I O N

Fig. 1 shows the speclru m o f typical optical densities w ith wav e-

1.0

06

_E 6o

40

0 500 1000 1500 2000

D i a m e t e r / nm

Fig. 10. Time dependence of the droplet size distribution of an

emulsion prepared with Span 80 and Tween 80 (HLB=6.0,

2.5 wt of emulsifie~; and 10 wt of wate r) after 500

times dilution measm'ed by using a dyn amic light scatter-

ing technique.

e 0 mini

9 -o- 10 min :

100 ~ n n n n n . --~ 30 min [

? . ~ ~ = . -o_ 50mn I

t. # ~ ~ 9 . o 7o_mm]

.o N xrR

It'/ ...9 \ \ \ . -.

. . . . i t _ . , __ . _ 9

0 500 1000 ]500 2000 250o 3000 3500

D i a m e t e r / n m

Fig. 11. Time dependence of the droplet size distribution of an

emulsion prepared with Span 80 (2.5 wt of emulsifie~;

and 10 wt of wate r) after 500 times dilution measured

by using a dynam ic l ight scattering technique.

Since tile tw-bidity ratio method provides indirect size distn"ou

tioil, we obse rved tile ddroplet size distribution in diluted emul sion

system wi th time. It is woithwh ile to com t:are two methods. There-

fore, tile ~n e dependence of tile droplet size dish-ibution was mon i-

tored by using dynamic light scattering tectmique.

Figs. 10 and 11 show tile time dependencies of the size di~i bu -

tion of enm lsion di-oplets diluted with 500 ~n es in oil phase. EmuI-

sion with Span 80 and Tween 80 at HL B= 6.0 was us ed in Fig. 10,

and with Span 80 only (HLB=4.3) in Fig. 11. From Fig. 4, enml-

sion at 6.0 of HLB ks more stable than at 4.3. Both emuls iom con-

tam 2.5 wt% of emulsifier and 10 wt% of water. In Fig. 10, the water

droplets are small and the size distribLaon is initially narrow, but

the size distribution shifts toward lager partMe sizes and becomes

broader, o wing to simultaneons flocculation or coales cence of the

smaller particles w ith time. In Fig. 11, the di-oplet size distribution

also shifts toward la ge r size, but muc h faster and broader than in

Fig. 10. Generally, the turbidity decreases with time at any wave-

length, because the nu mber of droplets decreases b y the emulsion-

breaking process. Furthermore, tile turbidity at longer wavel ength

decreases much faster thai at shorter wavelength, since tile larger

par~cles cream out at a much faster rate than the smaller ones. The

mo re unstable tile enmls ion is, the faster the turbiclity ratio decreases.

Therefore, it is a usefi, I, rapid, and relatively simple me tho d fo r the

evaluation of tile emu lsion stability.

C O N C L U S I O N S

Tile validity of the ~-bidity ratio measurement to evaluate water-

in-diesel oil emulsion stability has been examined tt~-oughout tt~

study. Tile turbidity ratios were measured with fine after dilution

of emulsion, and the slot:es of the tarbi~ty ratio were compared.

Vaiious fa~oz~ affecting emuIsion stability, such as HLB of emuI-

sifiez; tile amoun t of emuIsifier an d wate r concentration were tested

by using this method. The turbidity technique has been comp ared

with sepaation ano unt of emulsion after 30 days incubation at room

temperatare.

As tile results of tile turbidity ratio measurements, the required

HL B of diesel oil was 6.0 and the stability o f emulsion was increased

with the am ount o f emulsifier. T he increasing amou nt of the water

showed a negative effect on emuIsion stability. These results were

well in accord with those of inner phase setx~ation meas urem e:~.

Thr oug hou t this study, turbidity ratio techniq ue prov ed to be a

simple, rapid, an d relatively accurate metho d for the evaluation of

the emulsion stability.

A C K N O W L E D G E M E N T

This investigation was canied out in collaboration with In chon

Oil Refinery Co. and was financially supported by tim company

and BK21 project.

R E F E R E N C E S

B~&er, t~, ~%ncyclopedia of Emulsion Tectmolog,f,,' Marcel Deld


6/6

43

M.-G. Song e t a l.

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K O N G H A K ,

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79(1),

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May 2002

turbidity ratio for emulsion stability

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