ISSN 0012-5008, Doklady Chemistry, 2009, Vol. 427, Part 1, pp. 179–182. © Pleiades Publishing, Ltd., 2009.Original Russian Text © R.F. Ganiev, V.N. Fomin, Yu.A. Belyaev, E.B. Malyukova, A.G. Chukaev, A.D. Vedenin, A.A. Berlin, 2009, published in Doklady Akademii Nauk, 2009,Vol. 427, No. 2, pp. 215–218.

179

Heterogeneity-dependent stability of disperse sys-tems is a significant challenge in many chemical engi-neering processes. The dynamic behavior of dispersesystems involves two simultaneous competing pro-cesses: breakup and coalescence of dispersed particles.These processes mainly underlie the practical applica-tion of disperse systems (production and use of paintand varnish materials, crude oil dehydration and desalt-ing in preparation for processing, etc.). Thus, thebehavior of disperse systems is controlled by surfacephenomena, including the formation of new surface,and also heat and mass transfer.

According to the Rehbinder equation, the work doneto form new surface is proportional to the increment inthe surface:

W

n

=

σ∆

S

, where

σ

is the energy of forma-tion of unit surface (surface tension) and

∆

S

is the form-ing surface area [1]. The surface tension is a surface

energy intensity factor and is caused by the uncompen-sated field of intermolecular forces at the interface.

In their classical works, Rehbinder [2] and Levich[3] considered methods for stabilizing disperse sys-tems, also taking into account adsorption on particlesurface. Vinokurov and Karpukhin [4] developed theRayleigh–Taylor–Tomotika model and proposed amathematical model of the dynamics of breakup of thedispersed phase on the basis of the energy conservationlaw and the dispersed-phase volume conservation law.Ur’ev and Kuchin [5] performed computer modeling ofthe properties of disperse systems under dynamic con-ditions and analyzed the effect of surfactants and vibra-tions on the rheological properties of dispersions. How-ever, it remains urgent to construct an adequate physi-cal model to determine the dependence of the stability

Stability of Disperse Systems

Academician

R. F. Ganiev, V. N. Fomin, Yu. A. Belyaev, E. B. Malyukova, A. G. Chukaev, A. D. Vedenin, and

Academician

A. A. Berlin

Received March 25, 2009

DOI:

10.1134/S001250080907009X

Scientific Center for Nonlinear Wave Mechanics and Technology, Russian Academy of Sciences, ul. Bardina 4, Moscow, 119991 RussiaKosygin Moscow State Textile University, Malaya Kaluzhskaya ul. 1, Moscow, 119071 RussiaSemenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia

CHEMICAL TECHNOLOGY

(a) (b)

Fig. 1.

Photomicrographs of samples of oil–water emulsions produced (a) by wave treatment and (b) using a paddle stirrer.

180

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GANIEV et al.

of a disperse system on the parameters of external(mechanical) action.

Previously [6], we obtained analytical expressionsfor decomposition criteria and breakup functions. Forthis purpose, we used expressions for decompositioncriterion and formation criterion for particles of the dis-persed phase of a multiphase flow, which were obtainedby methods of systems analysis and mechanics of het-erogeneous media. We also used expansions of a dissi-pative function representing the dispersion medium, thedispersed phase, and the mechanical field (induced byoperating members of processing equipment or bywave action). The expansion of the dissipative function(local entropy production) into driving forces andfluxes, which characterizes the energy consumption insuch a system, allows one to obtain analytical expres-sions for decomposition criteria and breakup functions,

i.e., decomposition probability

A

(

r

)

and distributionfunction

B

(

r

,

γ

)

, where

r

and

γ

are sizes of particles ofthe dispersed phase. The expressions obtained suggestthat the decomposition probability in case where it ismainly determined by the shear stress (wave effects canbe ignored) is lower than that in case where it is con-trolled by wave action. The distribution functions alsodiffer, which is confirmed by experimental particle sizedistributions in liquid-phase disperse systems undervarious actions.

In this work, we consider features of the wave actionon the stability of some disperse systems and comparethe wave action and the mechanical action of a labora-tory stirrer (1000 rpm) in production of an oil–wateremulsion. The objects of investigation were industrialoil emulsions (3, 5, 10, and 20 wt %). The water phasewas distilled water or a 0.2 wt % aqueous calciumhydroxide solution. A schematic of a wave treatmentsetup with a vortex-type hydrodynamic generator andan experimental procedure were published previously[7]. The wave treatment time was 10–30 min.

Figure 1 presents photomicrographs of samples of5% emulsions that were recorded with a LOMO Miko-med-2 microscope. The dispersity of the emulsion pre-pared on the wave treatment setup is seen to be higherthan that of the samples produced using the paddle stir-rer. The oil particle (drop) distribution histograms [8]showed that the most probable average particle size forthe emulsion obtained by wave treatment was smallerthan that for the emulsion prepared using the mechani-cal stirrer, with the specific energy consumption beingnoticeably lower [8]. The total breakdown times for theemulsions produced by wave and mechanical treatmentwere 15 and 1 days, respectively (Fig. 2). The relativelyhigh stability of the disperse system (water–oil emul-sion) even while mechanically stirring can probably beexplained by the presence of surface-active modifyingagents in the oil and also by high dispersity of the emul-

80

0 5

Emulsion volume, %

100

10 15

Time, days

90

70

60

50

40

30

20

10

1

2

Fig. 2.

Kinetics of breakdown of an oil–water emulsionunder the (

1

) wave and (

2

) mechanical actions.

(a) (b)

Fig. 3.

Photomicrographs of samples of an oil–aqueous calcium hydroxide solution emulsion under the (a) wave and (b) mechanicalactions.

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STABILITY OF DISPERSE SYSTEMS 181

sion and low concentration of the dispersed phase. Thiswas most clearly manifested by the emulsions sub-jected to wave treatment. These features of the effect ofthe emulsion preparation method were retained with anincrease in the oil content to 10–20%.

Emulsions are known [9] to be stabilized by addingsurfactants, polymers, and powders wettable by the dis-persion medium.

If the water phase was the calcium hydroxide solu-tion, the stability of the concentrated (10 and 20 wt %)emulsions was higher—by a factor of approximately1.5–2 for the emulsions prepared using the mechanicalstirrer and by more than an order of magnitude for theemulsions produced by wave treatment. The emulsiondispersity also increased (Fig. 3). This can be explainedby the action of several factors. It is not improbable thatthe oil contains carboxylic acids produced by oxidationof hydrocarbons; therefore, contact of the oil with theaqueous alkaline solution causes neutralization reac-tion to form fatty acid salts, which can exhibit surface-active properties. Moreover, it was shown [10] that theformation of surfactants at the interface favors interfaceinstability and efficient breakup of the monomer (oil

phase). The emulsifier forming at the interface is redis-tributed between the oil and water phases. The totalityof the occurring processes results in microemulsifica-tion at the interface and the formation of a highly dis-perse emulsion. The fact that a microemulsion can format the interface was confirmed by our data obtainedunder static conditions as the oil was layered onto theaqueous calcium hydroxide solution (table).

Studies of surfactant redistribution in the oil–watersystems showed [11, 12] that, at the interfaces, quasi-spontaneous monomer emulsification occurs to formmicroemulsion drops 0.04 to 0.2

µ

m (40–200 nm) insize at the interface. As the monomer in an aqueousemulsifier solution is mechanically stirred, there is anincrease in the number of monomer microdrops that arepassed to the bulk of the water phase in initiation ofpolymerization even at low monomer concentration.Because the microdrop surface is exposed on the side ofthe water phase, new monomer microdrops form untilmonomer macrodrops disappear completely and anequilibrium emulsifier distribution in the system isestablished.

Importantly, wave treatment under cavitation hydro-dynamic conditions can produce complex disperse sys-tems since stirring may give rise to three-phase struc-tures incorporating air bubbles. Figure 4 presents a pho-tomicrograph of an emulsion produced from theaqueous calcium hydroxide solution after 30-min wavetreatment. The emulsion is close in structure to foamand consists of air bubbles, oil microdrops, and waterphase, i.e., is a three-phase disperse system. Totalbreakdown of the emulsion was not observed for evena year. Similar phenomena were also detected previ-ously in producing a chalk dispersion in water by wavetreatment [8].

The formation of structures (called thermodynami-cally stable [13]) from direct and invert microemul-sions at the interface favors the stability of concentratedemulsions.

Thus, the increased aggregation stability of theemulsion prepared by wave treatment can be explainedby the presence of a microemulsion produced both byinterface neutralization and by surfactant mass transferat the enlarged interface as a result of enhancement ofheat- and mass-transfer processes by wave treatment.

REFERENCES

1. Frolov, Yu.G.,

Kurs kolloidnoi khimii

(A Course in Col-loid Chemistry), Moscow: Khimiya, 1982.

2. Kleiton, V.,

Emul’siii, ikh teoriya i tekhnicheskie prime-neniya

(Emulsions, Their Theory, and Technical Uses),Moscow: Inostrannaya Literatura, 1950.

3. Levich, V.G.,

Dokl. Akad. Nauk SSSR

, 1955, vol. 103,no. 3, pp. 453–456.

4. Vinokurov, V.A. and Karpukhin, A.A.,

Dokl. Akad.Nauk

, 2003, vol. 313, no. 6, pp. 766–769.5. Ur’ev, N.B. and Kuchin, I.V.,

Usp. Khim.

, 2006, vol. 75,no. 1, pp. 36–63.

Effect of the conditions of preparation of a disperse systemon its composition and its aggregation stability

Disperse system

Microemul-sion volume under static

conditions, %

Time of onset of emulsion breakdown

after action, h

mechani-cal action

waveaction

Oil–water Traces 1 24

Oil–aqueous calciumhydroxide solution

5–7 24 216

Fig. 4.

Photomicrograph of a sample of the three-phase oil–air–water system (foam).

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6. Fomin, V.N., Malyukova, E.B., and Berlin, A.A.,

Dokl.Chem.

, 2004, vol. 394, part 2, pp. 39–41 [

Dokl. Akad.Nauk

, 2004, vol. 394, no. 6, pp. 778–781].7. Ganiev, R.F.,

Volnovye mashiny i tekhnologii. Vvedeniev volnovuyu tekhnologiyu

(Wave Machines and Technol-ogies. Introduction to Wave Technology), Moscow:Nauch.-Izdat. Tsentr “Regulyarnaya i KhaoticheskayaDinamika,” 2008.

8. Ganiev, R.F., Fomin, V.N., Malyukova, E.B., Mezhi-kovskii, S.M., and Berlin, A.A.,

Dokl. Chem.

, 2004,vol.

399, part 1, pp. 232–236 [

Dokl. Akad. Nauk

, 2004,vol. 399, no. 1, pp. 85–89].

9. Volkov, V.A.,

Kolloidnaya khimiya

(Colloid Chemistry),Moscow: MGTU, 2001.

10. Simakova, G.A., Gritskova, I.A., Prokopov, N.I., andPravednikov, A.N.,

Kolloidn. Zh.

, 1985, vol. 47, no. 1,pp. 189–192.

11. Taubman, A.B. and Nikitina, S.A.,

Kolloidn. Zh.

, 1962,vol. 24, no. 5, pp. 633–635.

12. Gritskova, I.A., Malyukova, E.B., Simakova, G.A., andZubov, V.P.,

Vysokomol. Soedin., Ser. A,

1990, vol. 32,no. 1, pp. 14–19.

13. Mittel, K.

, Micellization, Solubilization, and Microemul-sions

, Mittel, K., Ed., New York: Plenum, 1977. Trans-lated under the title

Mitselloobrazovanie, solyubili-zatsiya i mikroemul’sii

, Moscow: Mir, 1980.