and Microemulsions - American Chemical Society

24 Emulsion BreakinginElectrical Fields A. KRIECHBAUMER and R. MARR

Downloaded by CORNELL UNIV on September 7, 2016 | http://pubs.acs.org Publication Date: March 27, 1985 | doi: 10.1021/bk-1985-0272.ch024

Institute of Chemical Engineering, Technical University, Graz, Austria

The stability of disperse systems is controlled by interparticulary attraction and repulsion forces, and by the range of the free energy of the particle surface. Pure water/oil-systems are not stable. Addition of surfactants sometimes leads to high stability. Stability parameters and coalescence processes, especially when using electrical fields for emulsion breaking, are discussed in theory and compared to practical experimental data. The influence of parameters like applied field strength, contact time, surfactant concentration and type of surfactant, ionic strength of inner water phase, and droplet diameter on the breaking efficiency have been investigated. Advantages and technical applications of electrical emulsion breaking are discussed. The use of emulsions and their range of practical application has been expanded enormously. As a result, the field of the theory of emulsions and technical emulsion science, as a part of classical colloid chemistry, can use a lot of theory developed there. One of the greatest concerns for emulsions is the question of their stability. A very typical example of the different requirements on the stability of an emulsion is their application in Liquid-Membrane-Permeation (Figure 1) (1,2) . In this process, a water-in-oil emulsion is dispersed by stirring in a bulk water phase containing metal-ions. Under certain conditions these ions w i l l permeate through the oil-phase of the emulsion into the inner water phase of the emulsion. During this time, the emulsion should be very stable but after the permeation, the emulsion is to be separated from the bulk water and has to be broken; that mean that at this step the emulsion is required to be unstable. The stability of dispersed systems is influenced by an enormous number of parameters. Part of them can be predicted by considering the theory of stability, others can be obtained by experiments, but the influence of some parameters could not be explained until now. 0097-6156/85/0272-0381$06.00/0 © 1985 American Chemical Society

Shah; Macro- and Microemulsions ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

382

MACRO- AND MICROEMULSIONS


There are some important advantages of s p l i t t i n g emulsions by means of an e l e c t r i c a l f i e l d in contrast to the usual breaking processes (3). Thermal breaking does need a l o t of energy and cannot be applied to a l l emulsions, because of thermal i n s t a b i l i t y of some components. Centrifugation technique has the disadvantage of high mechanical work input and high investment costs; systems containing very small droplets and showing l i t t l e density difference between the dispersed and continuous phases are unable to be separated by this method. In contrast to the mentioned usual methods, the e l e c t r i c a l emulsion breaking workè at room temperature, has no moving parts, low energy input (only low condensator current between the electrodes because of low conductivity organic bulk phase) , and it is possible to separate small droplets from the continuous phase. Theory of S t a b i l i t y Thermodynamic View. Generally, there are three types of s t a b i l i t y for emulsions : 1. thermodynamic s t a b i l i t y 2. s t a b i l i t y by surface active agents (known as emulsifiers or surfactants) 3. s t a b i l i t y by adsorption of c o l l o i d s To s p l i t a l i q u i d droplet one has to spend surface energy dW by increasing the droplet surface O. dW = σ . dO = dG

dW ... changing of free energy (surface energy) σ ... surface tension dO ... changing of droplet surface dG ... free energy change This means that the smaller the droplet there is a greater ten dency for two droplets to coalesce into one larger droplet. There fore, a system of two l i q u i d s which exhibit a very low interface tension (σ = 0) is thermodynamically stable. Pure water/oil-emulsions are unstable. For this reason, sur face active agents (surfactants) are added, which adsorb at the interface between the two immiscible l i q u i d s and decreasing the i n t e r f a c i a l tension. In this way, the s t a b i l i t y of a water droplet in oil w i l l be increased. In addition, there is a second s t a b i l i z ing e f f e c t by s t e r i c hindrance which w i l l be explained l a t e r (4). There is another way to s t a b i l i z e colloids by addition of sub stances which cover the whole p a r t i c l e or droplet thus hindering the mutual approach of two p a r t i c l e s . DLVO-Theory. The mutual approach of two droplets is a requirement for the coalescence process. Larger droplets approach each other on account of g r a v i t a t i o n a l forces. Smaller droplets show i n t e r p a r t i c u l a r forces with short distance range, which are responsible for t h e i r mutual approach. Derjaguin, Landau, Overbeek and Verwey explained the s t a b i l i t y of dispersions by the superposition of i n t e r p a r t i c u l a r forces (5). The so called "DLVO-Theory" has been proved by experiments e l s e where (6-9). P r i n c i p a l l y , there are two forces: a t t r a c t i v e Van-der Waals forces (figure 2a) and repulsive forces (figure 2b).



24.

KRIECHBAUMER AND MARR

Emulsion BreakinginElectrical Fields

383

By superposition of these forces, a resulting force w i l l be obtained (Figure 2c). I f coalescence should occur, the thermal energy of the p a r t i c l e has to be greater than the energy b a r r i e r Ε (Figure 2) (10). When the thermal energy of the p a r t i c l e is lower, the dispersion only w i l l f l o c c u l a t e , which means that the p a r t i c l e s show a mutual approach u n t i l a c e r t a i n distance (between point 1 and 2 in Figure 2). Overcoming of the energy b a r r i e r can also occur by bringing additional energy (thermal energy; mechanical energy: centrifugat i o n , ultrasonic waves, etc.) to the emulsion (11-13). Water droplets in an organic continuous phase show very low e l e c t r i c repulsion potentials. This means that a pure w/o-emulsion cannot be stable, because the t o t a l p o t e n t i a l energy is only of the a t t r a c t i o n mode. By addition of surface active agents, a so called " s t e r i c hindrance" occurs. In this case, a mutual approach of two p a r t i c l e s w i l l be prevented by the l i p o p h i l i c t a i l s of the surfactants, which can be understood as a mechanical b a r r i e r with the same function as the adsorbed c o l l o i d s as described in the previous section (see Figure 3). Coalescence Process The coalescence process can be described by two steps. At f i r s t , there is a mutual approach of the drops which is controlled by the T h e o l o g i c a l properties of the continuous (organic) phase (see Figure 4a). Secondly, a f l a t t e n i n g of the droplets appears by the forma tion of a so c a l l e d "dimple" (see Figure 4b). The decrease in d i s tance d is determined by the rate of flow out of the continuous phase between the droplets (14,15). A t h i n f i l m is formed which decreases to a certain c r i t i c a l f i l m thickness, d i t > at which point approach stops (16). Coalescence of the droplets can only happen i f it is possible to break up the t h i n film. This occurs i f surface waves are formed or i f external forces are applied. At a certain point, the thick ness w i l l f a l l below the c r i t i c a l value and coalescence occurs (17, 18). The influence of this step is given by the i n t e r f a c i a l and surface rheological properties such as interface e l a s t i c i t y , i n t e r face v i s c o s i t y , type of surfactant, etc. (19-25). c r

Coalescence in E l e c t r i c a l Fields The theory of breaking emulsions in e l e c t r i c a l f i e l d s , e s p e c i a l l y in a.c. f i e l d s , has not been investigated much (26-31). But there are some e f f e c t s which mainly are responsible for coalescence phenomena (Figure 5; lower figures are microscopic photographs). I f a water droplet (containing ions) which is surrounded by an organic phase is exposed to an e l e c t r i c d.c. f i e l d , a dipole moment w i l l be in duced (Figure 5a). Two drops, therefore, show at t h e i r adjacent ends e l e c t r i c a l charges of opposite signs. This leads to an e l e c t r i c a l a t t r a c t i o n force Frj (see Figure 5b) (32) . On the other hand, it can be seen from the d i s t r i b u t i o n of the e l e c t r i c a l f i e l d l i n e s , that the density of the f i e l d lines is increased between two drop l e t s . For smaller droplets, this gives r i s e to a t t r a c t i v e forces between them.


384


Phase III Phase I Phase II


1+

Raffinate phase III Extract phase I

Emulsification step

Permeation step

Settling

Breaking of emulsion

Figure 1. Flow sheet of a l i q u i d membrane permeation process. •v

0

Van-der -Waal . attraction

a)

•v.,

elektr. repulsion

b)

superposition c)

Figure 2. DLVO-Theory; a t t r a c t i o n and repulsion forces of dispersed p a r t i c l e s ; d: Distance of the centers of two spherical particles.



24.


Figure 3 .

Figure 4 .


Steric hindrance; monolayer films of d i f f e r e n t surfactants between two flattened droplets.

Film thinning; approach of two droplets and development of a thin f i l m .


385

386

MACRO- AND

MICROEMULSIONS

As mentioned above, the application of e l e c t r i c a l f i e l d s deforms the spherical form of the droplets to an e l l i p s o i d thus decreasing the distance between two droplets. This deformation can also d i s turb the thin f i l m between droplet surfaces and lead to coalescence, especially when using a.c. f i e l d s where an o s c i l l a t i n g movement of the droplets also is induced.


Experimental

Section

Emulsion preparation: the emulsion was prepared in a s t i r r i n g vessel adding the discontinuous water phase dropwise to the continuous phase under s t i r r i n g with 5000 rpm. Total s t i r r i n g time 10 minutes. Volume fraction phase I (discontinuous phase) to phase II (continous phase) = 1:1. Emulsion breaking: an apparatus (see Figure 6 ) has been developed to s p l i t w/o-emulsion in e l e c t r i c a l f i e l d s (2). Immediately after preparation, the emulsion was pumped through the e l e c t r i c a l f i e l d in the s p l i t t e r . After s e t t l i n g down of the greater water droplets, the unspittëd emulsion was recycled through the s p l i t t e r again. After a d e f i n i t e c i r c u l a t i o n time, the emulsion was c e n t r i fugated at a low centrifugation number (rw2 = 2000) for two minutes to get a clear interface between oil-emulsion and emulsion-water interface. Materials Phase I was 5 η s u l f u r i c acid with 15 g CU / l . Phase II was a mixture of 60 wt % paraffine t h i n , 34 wt % S h e l l s o l T, 2 wt % ECA 4360 (EXXON) as surfactant and 4 wt % LIX64N as c a r r i e r . Table I shows the main parameters which influence emulsion s t a b i l i t y . In addition to the parameters above, there are s t i l l further process parameters. E f f e c t of E l e c t r i c a l F i e l d Strength. Emulsions with constant phase r a t i o were broken in e l e c t r i c a l f i e l d s of d i f f e r e n t f i e l d strengths. The applied f i e l d was varied from zero up to 1000 V/mm. Figure 7 shows the volume fraction of separated water in r e l a t i o n to the t o t a l emulsion volume. At f i e l d strengths lower than 90 V/mm there cannot be any emulsion breaking. Increasing the f i e l d strength leads to a steep r i s e in s p l i t t i n g e f f i c i e n c y . From 400 to 1000 V/mm only a small improvement of separation effect can be observed. E f f e c t of S p l i t t i n g Time. The s p l i t t i n g time of an emulsion is shown in Figure 8. There was an applied e l e c t r i c f i e l d strength of 1000 V/mm. Both the volume r a t i o of separated water and the s p l i t t i n g time scales are logarithmic. Up to a residence time of 30 seconds, 80% of the emulsion has been broken. With increased breaking time, there is a smooth change up to a saturation state. After 100 seconds about 98% of the distributed water is separated from the organic phase. An extension of s p l i t t i n g time has no more separation e f f e c t . Effect of Residence Time. The influence of varying the residence time by varying the electrode length on emulsion s t a b i l i t y is shown




Κ Ε α 2

F D

6

attractive force due to dipole ind.

Ε ... electr. field strength a... droplet


α)

induced

Figure 5.

dipole

K... constant

b) dipole-dipole attraction

Interaction forces in e l e c t r i c

t

yA

Ô

diameter

fields.

1

VA•Ά

F i g u r e 6. P r i n c i p a l f u n c t i o n of e l e c t r i c a l s p l i t t i n g apparatus Key: 1, pump; 2, e m u l s i o n i n l e t ; 3, e l e c t r o d e s ; 4, e m u l s i o n o u t l e t ; 5, e l e c t r o d e i n s u l a t i o n ; 6, h i g h v o l t a g e ; 7, s e t t l e r ; 8, c o a l e s c e n c e a i d ; 9, w a t e r - p h a s e V-j-; 10, oil-phase V - Q .


388



Table I.

Parameters That I n f l u e n c e

Emulsion S t a b i l i t y

Phase

Parameter I n f l u e n c i n g

All

Applied e l e c t r i c a l c o n t a c t time

Phases

Stability

field

strength

Phase I I Cont. phase

Viscosity Surfactant concentration Type o f s u r f a c t a n t (HLB-value, e t c . )

Phase I Discont.

Ionic

strength

phase

Interface

Surface f i l m p r o p e r t i e s Interface rheological properties Interface tension

Emulsion

Viscosity Phase r a t i o V j i V j j Droplet diameter Emulsion p r e p a r a t i o n Aging

0

Vol./. Phase I KX)i

Figure 7.

E f f e c t of e l e c t r i c a l f i e l d strength on emulsion breaking e f f i c i e n c y ; o...vol.% of phase I a f t e r s p l i t t i n g f o r 40 seconds.



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389

in Figure 9. Decreasing the electrode length means decreasing of the residence time of the emulsion in the e l e c t r i c a l f i e l d . When decreasing the electrode length from 160 mm to a few mm that means, that the contact "ime of the emulsion with the e l e c t r i c a l f i e l d decreases from about 10 seconds to less than 1 second - the emulsion breaking c o e f f i c i e n t does not decrease very steep. This experiment shows that there is nearly no influence of contact time on the breaking e f f i c i e n c y . This means, that the coalescence of the droplets occurs very rapidly in the f i r s t part of the e l e c t r i c f i e l d up to a certain magnitude of droplet diameter. In the next part of the e l e c t r i c a l f i e l d , nc further coalescence w i l l occur. The e f f e c t of electrode length on the e l e c t r i c a l current flow between the electrodes ((3), Figure 6) is also shown in Figure 9. When pumping a i r or homogeneous liquids through the s p l i t t e r , a low current flow was observed. In the case of pumping emulsion through the s p l i t t e r , there was obtained a much higher current flow between the electrodes. The current flow decreased l i n e a r l y with decreasing electrode length. E f f e c t of Surfactant Type and Concentration. Surfactant concentration and type is of great importance for the s t a b i l i t y of thin l i quid films and for emulsion s t a b i l i t y . Type and concentration of surfactants are responsible for the degree of lowering the i n t e r f a c i a l tension and for the v i s c o e l a s t i c properties of droplet surface, as well as for the f i l m thickness between two droplets. Figure 10 shows the volume f r a c t i o n of the s p l i t t e d emulsion a f t e r treating in the e l e c t r i c a l a.c. f i e l d for 30 seconds f o r various surfactant concentrations and surfactant types. I t is evident that in the absence of surfactants, there is no s t a b i l i t y and a l l the water droplets coagulate with coalescence. 50 v o l . % water phase s i g n i f i e s 100% s p l i t t i n g e f f i c i e n c y . With increasing surfactant concentration, the s t a b i l i t y of the emulsion increases continuously u n t i l a certain value. Increasing surfactant concentration above this point y i e l d s no more emulsion s t a b i l i t y . This means that there is a saturation concentration of adsorbed surfactant molecules at the droplet surfaces corresponding to the molecular size (12). An increase in bulk phase concentration has therefore no more e f f e c t on emulsion s t a b i l i t y . Span 20 is a S ORB ITAN-MONOLAURAT with a hydrophobic chain length of 11 carbon molecules. Span 80 is a SORBITAN-MONOOLEAT with 17 C-molecules at the hydrophobic chain length. Due to t h e i r molecule structures, Span 20 w i l l develop a more r i g i d and therefore more stable interface f i l m than Span 80. Because of the higher HLB-value of 816 of Span 20 than 4.3 of Span 80, the hydrophobic part and therefore the s t e r i c hindrance of Span 20 is of higher magnitude than that of Span 80, which fact means higher s t a b i l i t y against coalescence (9,33). With increasing molecular weight of a homologous series of surfactants, the emulsion s t a b i l i t y decreases (Figure 11). Viscosity measurements show that with increasing surfactant concentration even at high concentration the bulk phase v i s c o s i t y only increases very smoothly (Figure 12).



390

log. Vol°/o ο ph.I. total a ph.I clear

5fi 30]


20

10'I

F i g u r e 8.

F i g u r e 9.

—S' π

/•s Ci

X)

, 20

°

•

,

50

100 200 300 log.breaking time (s)

E f f e c t o f b r e a k i n g time on e m u l s i o n b r e a k i n g e l e c t r i c a l f i e l d s t r e n g t h 1000 V/mm.

efficiency;

E f f e c t o f e l e c t r o d e l e n g t h and t o t a l r e s i d e n c e time on s p l i t t i n g e f f i c i e n c y and c u r r e n t flow a t an e l e c t r i c a l f i e l d o f 1000 V/mm.


24. KRIECHBAUMER AND MARR


391

7 Downloaded by CORNELL UNIV on September 7, 2016 | http://pubs.acs.org Publication Date: March 27, 1985 | doi: 10.1021/bk-1985-0272.ch024

conz.-tenside lwt%)

Figure 10. Effect of surfactant type and surfactant concentration on emulsion s t a b i l i t y ; • Span 20; ο Span 80; V Span 85; breaking time 20's.

50 VoL%

375

460

1050

molecular weight

Figure 11. Comparison of surfactants with different molecular weight and molecular structures on their s t a b i l i z i n g e f f e c t ; o...phase I obtained after 20 s s p l i t t i n g by 1000 V/mm e l e c t r i c a l f i e l d strength; surfactant concentration 3 wt %. f

7c

[m Pas]

8— «-

0

1 2

3

4 5 6 cone- tensidelwt. %)

7

Figure 12. Effect of surfactant concentration on bulk phase viscos i t y ^ ECA 4360, • Span 20, Δ Span 80, ο Span 85.



392


E f f e c t of Continuous Phase V i s c o s i t y . Bulk phase v i s c o s i t y has a great influence on the approach of two droplets. Figure 13 shows the influence of continuous phase v i s c o s i t y as a function of the volume rate of S h e l l s o l Τ and paraffine oil as continuous phase. Increas ing concentration of Shellsol Τ decreases the continuous phase viscosity. The emulsions which were obtained with these organic phases showed an analogous decrease in emulsion v i s c o s i t y . A mathematical description of the experimental data even could be obtained from the organic phase v i s c o s i t y by an additive factor. E f f e c t of Continuous Phase Composition. With increasing concentra t i o n of S h e l l s o l Τ in the continuous phase and therefore decreasing bulk phase v i s c o s i t y (as shown in Figure 13), the emulsion breaking e f f i c i e n c y increases (Figure 14). As expected, the mutual approach of the water droplets w i l l be f a c i l i t a t e d in lower viscous continuous phases. E f f e c t of Phase Ratio. The effect of phase r a t i o of discontinuous phase over continuous phase on the v i s c o s i t y of the emulsion is shown in Figure 15. Continous and discontinuous phase composition and v i s c o s i t y are constant in each experiment. With increasing phase r a t i o , the v i s c o s i t y of the emulsion increases because of the increasing of the amount of water droplets. The emulsion breaking e f f i c i e n c y was obtained by pumping the emulsion one time through che s p l i t t e r and comparing the s p l i t t e d water with the o v e r a l l water coûtent in the unsplitted emulsion. The increase of emulsion breaking e f f i c i e n c y can be explained by the shorter distances between the droplets at higher phase ratios and therefore, the minor mutual approaching time. E f f e c t of Emulsion Preparation, There are a l o t of parameters in emulsion preparation which have effects on emulsion s t a b i l i t y (e.g. phase r a t i o , phase I, phase I I , s t i r r i n g time, s t i r r i n g speed). Some of them have been explained above, others have already been investigated (34,35) and others are s t i l l under discussion (Kriechbaumer, Thesis; Wacnter, Thesis). As an example, I would l i k e to mention the effect of s t i r r i n g speed on emulsion s t a b i l i t y . In Figure 16, it can be seen that with increasing s t i r r i n g speed in a homogenizer, the emulsion can be broken with less e f f i c i e n c y . This correlates with decreasing "Sauter diameter" D . The droplet diameter d i s t r i b u t i o n of the emulsiun becomes more and more uniform. The smaller the droplets, the smaller are the mutual a t t r a c t i v e forces and the smaller is the probability of a c o l l i s i o n of two p a r t i c l e s . p

E f f e c t of Aging. With increasing volume f r a c t i o n of the dispersed phase, increasing droplet diameter and wider diameter d i s t r i b u t i o n , the v i s c o s i t y of a dispersed system increases (36). Unstable emulsions show droplet coalescence by extending the diameter d i s t r i b u tion, accompanied by v i s c o s i t y increasing, an e f f e c t , which is c a l l e d "aging" ( 3 6 - 2 8 ) .



24.

K R I E C H B A U M E R

A N D


M A R R

0

20

AO

60

80

393

100

Vol.% SHELLSOL Τ

Figure 13. Effect of continuous phase composition on v i s c o s i t y and emulsion v i s c o s i t y . Experimental data: • emulsion, ο organic phase; f i t t e d data: — 1 η η = expi-Kj^(vol%)+K2] -.- Ιηη • = 1 η η + K 3 . 0

0

100

Vol.% PhaseI

50

10 « 0

20

40

60

80

100

Vol.% SHELLSOL Τ Figure 14. Effect of continuous phase composition on emulsion breaking e f f i c i e n c y .



394


phase ratio

V! :V

n

Figure 15. Effect of phase r a t i o Vj/νχχ on emuls ion v i s c o s i t y 17 eni and s p l i t t i n g e f f i c i e n c y T j ; V j . . . t o t a l water content; ^I>splitted«.-obtained continuous water phase after splitting. s

p


24.



395

,100


° phi: total * phi: clear a droplet diameter 50

3500

5000

6500

8000 9500 η (rpm) lU/minl

Em. nach Permeation

100 Vol. /. 0

50

Figure 16. Effect of s t i r r i n g speed on breaking e f f i c i e n c y and drop l e t diameter.



396


Technical Applications This method can be used to s p l i t w/o-emuIsions, to separate the smallest water droplets from motor oil, to clear a turbid organic phase after solvent extraction (containing water) and crude oil dewatering, etc. As an example of an a p p l i c a t i o n of the s p l i t t e r , the continuous breaking of an emulsion used in the liquid-membrane-permeation technology is shown in Figure 17. After the emulsification and permeation step the emulsion enters the f i r s t breaking apparatus. Leaving this step, the emulsion passes a s e t t l e r in which the greater water droplets coalesce with the bulk water phase. The unsplitted emulsion flows in the second s p l i t t e r from which it is pumped through the second breaking step, which contains a package of pairs of electrodes. The unsplitted emulsion w i l l also be recycled through the second breaking step. Clear organic phase can be obtained from the surface, while at the bottom, the outlet of the water phase is i n s t a l l e d . The breaking e f f i c i e n c y can be seen in the lower part of the figure. The fresh emulsion contains nearly 14 v o l . % of water in the organic phase. After the f i r s t step, it is already reduced to 5.4 vol.% and after the second step there is less than O.4 v o l . % water in the organic phase. A

ft

Figure 17. Continuous emulsion breaking; emulsion flow rate: 20 I . . . f i r s t breaking step, II...second breaking step.


1/h.

24.



397

Conclusions


It can be seen that there are a l o t of parameters influencing emul sion s t a b i l i t y . Some of them can be predicted by theory, while others are able to be explained by experimental r e s u l t s . An emulsion breaking device has been developed which enables the investigation of various parameters and d i f f e r e n t emulsion systems. Thus, on the one hand, emulsion s t a b i l i t y can be compared with theory, while on the other hand, conclusions about coalescence processes are obtained. The s c i e n t i f i c investigation w i l l lead to expanding the p r a c t i cal application of e l e c t r i c a l emulsion breaking in chemical engineer ing, chemistry, biology, etc.

Literature Cited 1. Florence, A . T . ; Whitehill, D. J. Coll. Int. Sci. 1981, 79, 243. 2. Marr, R.; Bouvier, Α.; Draxler, J . ; Protsch, M.; Kriechbaumer, A. Proc. PACHEC 83, 1983, p. 327. 3. Sharma, M.K. et a l . Ind. J. Techn. 1982, 20, 175. 4. Tadros, Th. F. Proc. Int. Symp., 1981. 5. Verwey, E . J . ; Overbeek, J. Th. G. Ph.D. Thesis, Elsevier, Am sterdam, 1948. 6. Derjaguin, B.V. Farad. Disc. Chem. Soc. 1978, 65, 306. 7. Frens, G. Farad. Disc. Chem. Soc. 1978, 65, 146. 8. Goswami, A.K.; Bahadur, P. Progr. Coll. Polym. S c i . , 1978, p. 27. 9. Srivastava, S.N.; Haydon, D.A. Proc. Int. Congr. Surf. Act. 4th, 1967, p. 1221. 10. Sonntag, H . ; Strenge, K. "Koagulation und Stabilitat disperser Systeme"; VEB Deutschei Verlag Jer Wissenschaften: Berlin, 1960. 11. Rehfeld, S.J. J. Coll. Int. Sci. 1974, 46, 448. 12. Rehfeld, S.J. J. Phys. Chem. 1962, 66, 1966. 13. Vold, R.D.; Groot, R.C. J. Phys. Chem. 1962, 66, 1969. 14. Schulze, H.J. Coll. Polym. Sci. 1975, 253, 730. 15. Sherman, P. "Emulsion Science"; Academic Press: London-New York, 1968. 16. Scheludko, Α.; Exerowa, D. Coll. Polym. Sci. 1974, 252, 586. 17. Ivanov, I.B. et al. Proc. Sect. 52nd Coll. Surf. Sci. Symp., 1979, p. 817. 18. Gershfeld, N.L. Molecular Association in Biological and Re lated Systems, 1965. 19. Prins, A. et a l . J. Coll. Int. Sci., 1967, 24, 84. 20. Mysels, K.J. J. Phys. Chem. 1964, 68, 3441. 21. Scheludko, A. Adv. Coll. Interf. Sci. 1967, 1, 392. 22. V r i j , A. Disc. Farad. Soc. 1966, 42, 23. 23. Lucassen, J.; Luc.-Reynders, E. J. Coll. Int. Sci. 1967, 25, 496. 24. Matsumoto, S.; Sherman, P. J. Coll. Int. Sci. 1970, 33, 294. 25. Wasan, D.T. et a l . AIChE Symp. Series No. 192, 1980, p. 93. 26. Stauff, J. "Kolloidchemie"; Springer Verlag: Berlin, 1960. 27. Cho, A.Y.H. J. Appl. Pnysics 1964, 35, 2561. 28. Hendricks, Ch. D. et a l . IEEE Transac. Industry Appl., 1977, p. 489. 29. Simonova, T.S.; Dukhin, S.S. Coll. J. USSR (USA) 1973, 35, 952. 30. Waterman, L.C. Chem. Eng. Progr. 1965, 61, 51. 31. Waterman, L.C. Hydrocarbon P r o c , 1965. p. 133.


398

32. 33. 34. 35. 36. 37. 38.


Kriechbaumer, Α.; Marr, R. Chem. Ing. Techn. 1983, 9, 700. Kriechbaumer, A. Ph.D. Thesis, Technical University, GrazAustria, 1984. Kopp, G. Ph.D. Thesis, Technical University, Graz-Austria, 1978. Draxler, J. Ph.D. Thesis, Technical University, Graz-Austria, 1983. Gillespie, T. Proc. Symp. Brit. Soc. of Rheology, 1962, p. 115. Reddy, S.R.; Folger, H.S. J. Coll. Int. Sci. 1981, 82, 128. Boyd, J.; Sherman, P. J. Coll. Int. Sci. 1970, 34, 76. 1984


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