ISSN 0012-5008, Doklady Chemistry, 2008, Vol. 423, Part 1, pp. 305–308. © Pleiades Publishing, Ltd., 2008.Original Russian Text © R.F. Ganiev, N.A. Bulychev, V.N. Fomin, I.A. Arutyunov, S.D. Eisenbach, V.P. Zubov, E.B. Malyukova, 2008, published in Doklady Akademii Nauk, 2008,Vol. 423, No. 2, pp. 218–221.

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In the context of the wide use of disperse systems, itis important to develop new methods for improvingtheir quality and controllably changing their properties,including the production of aqueous suspensions ofhighly stable finely dispersed pigments used as compo-nents of paints and varnishes, oil and fuel additives, etc.Among the problems involved are surface phenomena;polymer adsorption on surfaces of different nature,especially in mechanical activation; and interfacialinteractions.

A study of the dynamic behavior of multiphase mul-ticomponent systems on excitation nonlinear vibrationsrevealed phenomena related to enhancement of masstransfer processes and phase and relaxation transitions,and to chemical transformations [1, 2]. The multilevelinhomogeneity and instability of such systems result intheir increased sensitivity to external factors. For poly-mer dispersions, which are, in essence, models or com-ponents of polymer composite materials, the effect of awave field can be considered as a method for affectingthe structure of a disperse system. Polymer dispersions,which, according to P.A. Rehbinder’s classification, arelyophobic colloids, are of interest as the object of wavetreatment in the context of the possibility of evaluating

such an effect at various structural levels: in the disper-sion medium, in the dispersed phase, and at the inter-face. Some aspects of the relationship between thestructure and properties of a number of polymer com-posites and the effect of nonlinear vibrations in a reso-nant mode were considered previously [3–5].

The interface and the interfacial interaction play afundamental role in the formation and manifestation ofthe set of properties of disperse systems; therefore, inthis article, we focus on studying specific features ofthe interaction of polymers with the surface of inor-ganic pigments under mechanical activation over awide range of wave field frequencies. Disperse systemsbased on inorganic pigments and polymers can be usedas model systems for revealing laws of interaction ofpolymers with a solid surface. At the same time, hydro-philic and hydrophobic polymers are of interest as sta-bilizers of disperse systems in aqueous media. Polymerstabilizers are also known to perform one more impor-tant function as film-forming components of paints,varnishes, and coatings: polymer stabilizers improvethe properties and quality of the end products.

Aqueous disperse systems based on pigments withhigh- and low-molecular-weight surfactants were mod-ified by various mechanical activation methods, includ-ing wave technology [6–11]. No noticeable differencewas found in stability of dispersions obtained by differ-ent methods for enhancing mechanical activation (dis-integrator, wave treatment in an ultrasonic field). An IRspectroscopic study showed that mechanical treatmentincreases the concentration of the polymer ethylhy-droxyethylcellulose (EHEC) adsorbed on the surface ofthe pigments TiO

2

and Fe

2

O

3

[6]. EHEC has a molecu-lar weight of about 60 000 and is well soluble in waterwithout forming aggregates [6]. The pigment concen-tration in the experiments was 1 wt %; the polymer con-centration was determined by the dynamics of adsorp-tion and saturation of the adsorbed layer and varied

Effect of Mechanical Activation on the Structure of Adsorbed Polymer Layers on the Surface

of Pigment Particles in Aqueous Disperse Systems

Academician

R. F. Ganiev

a

, N. A. Bulychev

b

, V. N. Fomin

a

, I. A. Arutyunov

c

, S. D. Eisenbach

d

, V. P. Zubov

c

, and E. B. Malyukova

e

Received April 28, 2008

DOI:

10.1134/S0012500808110104

a

Scientific Center for Nonlinear Wave Mechanics and Technology, Russian Academy of Sciences, ul. Bardina 4, Moscow, 119334 Russia

b

Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119991 Russia

c

Lomonosov State Academy of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 117571 Russia

d

Institut für Angewandte Makromolekulare Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany

e

Kosygin Moscow State Textile University, Malaya Kaluzhskaya ul. 1, Moscow, 119071 Russia

CHEMICAL TECHNOLOGY

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GANIEV et al.

from 1% (samples before mechanical treatment) to15% (samples after mechanical treatment) with respectto pigment weight [12]. The ultrasonic treatment timeand intensity were 2 min and 1.5 W/cm

3

, respectively.Earlier, by the example of EHEC, it was shown thattreatment at such parameters does not lead to polymerdegradation [10]. The particle size was determined bylight scattering, and the found values agree with thedata obtained by the electrokinetic sound amplitudemethod [12]. By this method in EHEC-modified aque-ous TiO

2

and Fe

2

O

3

disperse systems, the concentra-tions at which the adsorbed layer is saturated with thepolymer were determined and it was shown that thepolymer is almost completely deposited on the surfaceof the pigments [12]. The data obtained were used tocalculate the adsorbed polymer layer thicknesses and toprove that there occurs activated polymer adsorptionaccompanied by an increase in the adsorbed layerthickness and by the formation of a more stable morefinely dispersed system. However, the question of thestructure of adsorbed polymer layers on a pigment sur-face and the effect of mechanical activation on theirstructure remained open.

Investigation of disperse systems by the electroki-netic sound amplitude method gives not only the valuesof diameter,

ζ

potential, and dynamic mobility of dis-persed-phase particles, but also the changes in theseparameters as functions of the frequency of the alternat-ing electric field acting on the disperse system [13, 14].An example of such a function is presented in Fig. 1.The

ζ

potential and dynamic mobility versus frequencycurves can be used to obtain quantitative information

on the structure of adsorbed polymer layers forming onthe surface of particles according to a published proce-dure [13]. We assume that the adsorbed polymer layeron the surface of solid-phase particles is not homoge-neous but consists of two sublayers, inner (of thickness

d

) and outer (of thickness

∆

). A model of an adsorbedlayer is shown in Fig. 2 [15]. The inner layer layingdirectly on the particle surface is denser; it forms by thedirect adsorption interaction between the pigment andthe polymer. The outer layer is loose; it is produced byintermolecular interactions and consists of more swol-len polymer. The boundary between these layers israther arbitrary (the density is likely to change gradu-ally) but can be defined as the boundary between thelayer of polymer molecules involved in the adsorptioninteraction with the pigment surface and the layer ofmolecules interacting with one another. Analysis of the

ζ

potential and the dynamic mobility as functions offrequency for particles of the disperse system as deter-mined by the electrokinetic sound amplitude methodallows one to calculate the thicknesses of the outer andinner polymer layers [14]. The calculation formula isthe following:

(1)

where

(2)

(3)

µµ0----- l κ∆–

iωαγ

---------- k2–

k2 κ2–--------------------- l κd– 1

κk--- kdtanh+⎝ ⎠

⎛ ⎞–

⎩⎪⎨⎪⎧

=

------–

κ2

k2 kdcosh----------------------- iωα

γ k2----------–

⎭⎪⎬⎪⎫

,

k2 αη--- 1 iωη

γ----------+⎝ ⎠

⎛ ⎞ ,=

γ ω0η,=

0.5

50 10 15 20

Frequency, MHz

1.0

1.5

2.0

2.5

3.0

Dynamic mobility, m

2

/

(V

s

)

Dispersed-phase particle surface

ζ∆

,

d

ζ∆ζ

0

d

∆

Fig. 1.

Example of the dependence of dynamic mobility oftitanium dioxide particles on alternating electric field fre-quency.

Fig. 2.

Model of an adsorbed polymer layer:

ζ

0

,

ζ∆

, and

ζ∆

,

d

are the

ζ

potential values on the initial particle sur-face, the boundary between the layers, and the boundary ofthe outer layer, respectively.

DOKLADY CHEMISTRY

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EFFECT OF MECHANICAL ACTIVATION 307

is the ratio of the dynamic mobility of a particle

coated with a polymer layer to the dynamic mobility ofthe initial particle,

∆

is the thickness of the inneradsorbed layer,

d

is the thickness of the outer adsorbedlayer,

ω

is the frequency of the alternating electric field,

η

is the dynamic viscosity of the system,

κ

is theDebye–Hückel parameter,

α

is the macromolecule coil-ing coefficient, and

ω

0

is the relaxation frequency.

It is also necessary to take into account the changein the dispersion particle size after addition of a poly-mer stabilizer since, as we showed previously, the dis-persion particle size in the presence of polymer isnoticeably smaller than that in the absence of it. Afterintense mechanical treatment of the system, the differ-ence in particle size between the initial pigment and thepigment modified by the surface-active polymer is stillhigher. In measurements of the

ζ

potential and thedynamic mobility by the electrokinetic sound ampli-tude method at low frequencies, the particle weight andsize can be ignored; however, when using data obtainedat higher frequencies, it is necessary to introduce a par-ticle inertia coefficient into calculations. The inertiacoefficient is calculated as

(4)

where

r

is the particle radius,

ρ

m

is the density of themedium, and

∆ρ

is the difference of the densities of theparticles and the medium.

The calculation procedure was described before[13–15]. According to this procedure, we calculated thethicknesses of the inner and outer adsorbed EHEC lay-ers for the TiO

2

and Fe

2

O

3

disperse systems obtained byultrasonic treatment (table). Figure 3 shows the relativedynamic mobility of particles of 1% aqueous TiO

2

dis-persions modified by EHEC at the adsorbed layer satu-ration concentration versus the alternating electric fieldfrequency before and after ultrasonic treatment. Therelative dynamic mobility of particles of aqueous Fe

2

O

3

dispersions as a function of alternating electric field fre-quency is similar.

Figures 1 and 3 show that the theoretical and exper-imental results are in good agreement in all cases, i.e.,the thicknesses of the inner and outer adsorbed layersare calculated accurately.

Comparison of the adsorbed polymer layer thick-nesses demonstrates that, in both systems studied,ultrasonic treatment mainly affects the inner adsorbed

µµ0-----

G r( )1 1 i+( ) r

2---+

1 1 i+( ) r2--- i

r9---⎝ ⎠

⎛ ⎞ 3 2∆ρρm

-------⎝ ⎠⎛ ⎞+⎝ ⎠

⎛ ⎞+ +

---------------------------------------------------------------------------------,=

layer forming by the polymer interaction with the pig-ment surface and the thickness of this layer after treat-ment considerably increases. The outer layer thicknessafter ultrasonic treatment changes not so significantly.This supports the conclusion on the activation of thepigment surface by mechanical treatment and the emer-gence of new active adsorption sites on the pigment sur-face, which leads to activated polymer adsorption toform rather a thick and dense adsorbed layer.

Thus, the calculations performed showed thatintense wave treatment is an efficient method for mod-ifying the surface in disperse systems of pigments andactivating pigment–polymer interaction with subse-quent formation of adsorbed layers of large thicknessand high strength. This allows one to obtain a highlystable finely dispersed system with a modified surfaceof the dispersed phase.

The data on obtaining stable disperse systems bymechanical activation in a wave field in the presence ofa polymer stabilizer confirmed the relationship betweentwo factors of aggregation and phase stability, namely,the electrostatic and adsorption–solvation barriers. The

0.2

50 10 15 20Frequency, MHz

0.4

0.6

0.7

0.5

0.3

0.1

Relative dynamic mobility

1

2

Thicknesses of the inner and outer adsorbed polymer layerson the surfaces of the pigments

System

Adsorbed polymer layer thickness, nm

without mechanical activation

after ultrasonic treatment

∆ d ∆ d

TiO2–EHEC 1.2 4.7 8.7 6.5

Fe2O3–EHEC 2.4 7.3 3.8 7.7

Fig. 3. Relative dynamic mobility of particles versus alter-nating electric field frequency without mechanical treat-ment in (1) 1 and (2) 15% aqueous titanium dioxide disper-sions modified by EHEC at saturation concentration. Thepoints represent experimental data; the curves, theoreticalresults.

308

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GANIEV et al.

electrokinetic sound amplitude method was used toestimate the ζ potential, a characteristic of the electricalproperties of the interface. Developing the concepts ofadsorbed and diffusion layers in the structure of colloidparticles, we used this method to calculate and justify amodel of an adsorbed layer. In this case, the role of thestructural–mechanical factor of stabilization shouldalso be taken into account.

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