Co-deposition of fine particles on glass surfaces

Co-Deposition of Fine Particles on Glass Surfaces T. DABROS, H. BUCZAK, 1 AND J. KOSACZ Department of Chemistry, Jagiellonian University, Karasia 3, 30 060 Krakow, Poland Received October 17, 1990; accepted April 11, 1991 The deposition of latex particles on glass surfaces in the presence ofa CaF2 precipitant has been studied in the impinging jet cell. The initial flux of latex particles in 5 X 10 -4 M CaCIz solution was increased by a factor of thirty when the glass collector surface was modified by contact with CaF2 precipitant. However, after a period of time necessary to dissolve the positively charged CaF2, the flux had declined and eventually the previously deposited particles were washed out. Small amounts of the CaF2 precipitant added to the latex solution also promoted deposition, although in this case the flux increase was not as large as it was previously. Significant influence of the CaF2 precipitant on the latex particles flux to the glass collector was noted even for quantities of CaF2 which should have dissolved after being added to the latex suspension. For very small amounts of CaFa precipitant, the initially constant flux declined sharply after some period of time. However, one could not see the escape of the deposited particles. The experimental data presented herein indicate a great number of possible interactions during the deposition process from binary mixtures of chemically dissimilar colloid particles. This paper also briefly presents a theory of the phenomenon. © 1992AcademicPress,lnc. INTRODUCTION

The deposition of latex particles on glass surfaces in the presence of a CaF~ precipitant has been studied in the impinging jet cell ( 13). For dilute suspensions and well defined hydrodynamic conditions the particle flux to the solid surface can be predicted quite accurately, provided that particle-collector interaction forces are known (4, 5). Also, effects related to the distribution of the particle size can be easily accounted for (4, 6). In the case of moderate and high energy barriers, and even for monodisperse systems, a distribution of surface properties of the individual particles (such as ~"potentials) can have a significant influence on the mean value of the particle flux to the collector surface, as discussed in Refs. (4, 6). The kinetics of coating by colloidal particles from flowing suspensions has been described using adsorption (7, 8) or phenomenological models (9, 10). However, as long as the eleTo whom correspondence should be addressed.

mentary interaction between flowing and deposited particles is not described quantitatively, the effects of blocking, which are important for the coating formation, cannot be accounted for in an exact manner. It has been found experimentally that for stable colloids and low coating densities the deposited particles are distributed randomly over the uniform collector surface. As the coating increases, some degree of ordering is observed and significant deviations from the Poisson distribution law are noted (4, 11 ). These effects exemplify the importance of interparticle interactions in the wall region for deposition kinetics. Clint et al. (12) and Dabros (13) studied the influence of colloid stability on the coating. In the analysis it was assumed that the halftime of coagulation is much longer than the characteristic time necessary to develop the diffusion boundary layer. Thus, the process could be considered as a stationary one. At any instant, the flux of particles and aggregates to the collector surface was a linear function of their bulk concentration. On the other hand,

63 0021-9797/92 $3.00 Journal orColloid and lnteJJhce Science. VoL 148, No. 1, January 1992

Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved.

64

DABROS, BUCZAK, A N D K O S A C Z

the bulk concentrations were expressed by the Smoluchowski kinetic equation. The influence of fluid velocity gradients on the coagulation process was neglected. It has been noted ( 13, 14) that for unstable systems so-called surface aggregates grew due to collisions between deposited and flowing particles. In such a case, after a sufficiently long time, a complex coating structure was formed with disturbances in symmetry which reflected the geometry of the flow field ( 13, 14). There are a number of parameters which govern kinetics of the deposition process such as: the maximum energy of interactions between particle and collector, the maximum energy of interaction between particles, Ka (K is the Debye parameter of the electrical double layer, a is the particle radius), the fluid flow parameters, etc. Furthermore, in many practical situations the colloidal solution consists of a number of dissimilar particles. Even in the simple case of a mixture of two dispersed species of radii al and a2, the number of parameters which are necessary to describe the system increases dramatically, reflecting a variety of possible interparticle and particle-collector interactions. The aim of this paper is to present some experimental results on deposition of latex particles onto glass collector surfaces in the presence of the CaF2 precipitant. The experiments were done in the impinging jet cell described elsewhere ( 1, 2). The variety of conditions which can exist at the collector surface makes the analysis of the process quite complex. In principle, however, for sufficiently dilute solutions the effective flux of particles, defined as a derivative d S J d t , can be expressed as a function of time, t, and instantaneous coating densities Si ( i = I, 2 . • • N , where N is a number of classes of particles), dSi _ j o (t) + Z aoSj dt j=l N

N

+ Z Z 0/ijksj& + - . . , j=l k=l Journal o./'C~lloid and lnterjbce 5k'iemv,, Vol. 148, No. I. January 1992

[11

where J ° ( t ) is usually a well-defined flux of particles of kind i to the uncoated collector surface ( j 0 = [ - O × (Oc/On)colLsurf.[, D is the local diffusion coefficient), and 0/ij, 0/ijk are constant coefficients which account for the influence o f the deposited particles on the effective flux. Values o f the coefficients 0/can be estimated on the basis of various models of the deposition phenomenon. In some practical cases, when only a small fraction of the collector surface is coated by the particles, the nonlinear terms in Eq. [ 1] can be neglected. If only two species are present in the solutions ( N = 2), the formal solution o f E q . [1] takes a form S(t) =

eA(t-')J(r)dr,

[2]

where S = [ & , $2],

A

= [~ 0/110/12 1 \

} / 0/21 0/22 and

J = [J1, J2].

When the nonlinearity is caused by the blocking effect, the coefficients can be expressed as ( 1 ) 0/ ij =

- - "l~a 2 "Yj J °i .

[3

]

The dimensionless coefficient 2/j gives information on how m a n y times larger the area effectively blocked by the particle is than its geometrical cross section ~ra 2. It was experimentally found that for stable colloids its value was approximately equal to 20. The minus sign in the formula corresponds to the case when the already deposited particles inhibit the deposition of more particles. This is the usual case during deposition from a one-component stable colloidal dispersion. A positive value of the a coefficient would correspond to a situation when particles immobilized at the collector surface promote the deposition of the flowing ones. If the deposited particles are able to escape from the collector surface, the coefficient also depends on particle-collector interaction parameters ( 1 ). This problem is not considered here.

DEPOSITION EXPERIMENTAL

T h e experiments were done using the impinging jet cell described in detail elsewhere ( 1, 2). The jet was formed by a fluid flowing out o f a hole in a thin platinum plate at the end of the wider tube directed against the collector plane surface. The set up was designed to assure a smooth and steady flow of the colloidal dispersion. The hole had a diameter of 0.255 c m and the separation between the inner tube and the collector plate was 0.166 cm. The experiments reported in this paper were performed on latex particles with a m e a n radius of 0.55 t~m. The latex suspensions were prepared by adding to a CaC12 solution a small a m o u n t of concentrated latex sample, which just before each experiment was dispersed ultrasonically using a Labsonic 1510 generator. Finally, the proper a m o u n t of water was added to get the required concentration of latex and salt. A freshly prepared dispersion was used in the experiments. The final concentration of CaC12 was equal to 5 × 10 -4 M . In all experiments the latex concentration was 0.75 X l 0 7 particles/cm 3. The diffusion coefficient of latex particles was equal to 3.9 × 10-9 cm2/sec. The total volume of the suspension solution used in a single experiment was equal to 200 c m 3. The zeta potential o f the particles was determined by microelectrophoresis. The coating formation process was studied using the Amplival pol-u Carl Zeiss Jena microscope with dark field illumination from above. The microscope was coupled, via a T V camera, to a video recorder. During each experiment the microscopic image of the collector surface was recorded and subsequently analyzed by counting particles in 52 rectangular areas of the T V screen at a given time. The total area under observation was 240 × 360 ~ m z. The total magnification of the micros c o p e - c a m e r a system was equal to 800. Usually a single experiment lasted 20 rain and the coating was determined every 2 rain. The volumetric flow rate o f the fluid was deterrnined by measuring the weight of the solution flowing out of the cell in a given time

65

OF PARTICLES

period. The flow rate, equal to 0.409 ___0.02 g/s, was controlled at the beginning and end of an experiment. Calcium fluoride precipitant was obtained by adding 49 cm 3 of 0.1 M N a F solution to 50 cm 3 of 0.05 M CaC12. Subsequently, 1 c m 3 of water was added to obtain 100 cm 3 of CaF2 dispersion. The quality of the dispersion was controlled by a nephelometric method using a solid opalescent glass as a standard. Potentiometric titrations were carried out using a Coming digital electrometer model 101 with the Crytur fluoride electrode. Potential of the ion selective electrode was measured with respect to the saturated calomel electrode connected to the circuit through a 1 M N a N O 3 liquid junction. All experiments were done at a r o o m temperature, T --- 292 _+ 1 K. RESULTS

Zeta Potentials The zeta potential o f the latex particle in 5 × 10 -4 M CaC12 solution was equal to - 3 8 inV. Under the same conditions the glass surface is negatively charged as well. Thus the flux of the latex particles to the glass collector should be small compared to the flux calculated for the system when the energy barrier is absent. W h e n 2 cm 3 of the CaF2 precipitant was added to the latex solution, in a manner similar to the deposition experiments, it caused a rise of the zeta potential to - 2 1 inV. When 10 cm 3 of the CaF2 precipitant was added, the potential increased to +36 inV. It can be assumed that when excess of the CaF2 suspension is added, the latex particles are coated by the precipitant and the measured value is the zeta potential of CaF2 itself.

Deposition Experiments (a) The glass surface covered by CaFe. In a system composed of the glass collector and two disperse systems there exists a number of possible relative relations. Two of them can be easily realized experimentally. The CaF2 particles can be present on the collector surface Journal ¢fColloid and Inter[hce Science, Vol. 148, No. 1, January 1992

66

DABROS, BUCZAK, A N D KOSACZ

and absent in the solution and at the latex surface. In second case, the CaF2 precipitant can be added to the latex solution. Then positively charged CaF2 particles adsorb both on the negatively charged latex and glass surfaces. This part of the paper describes deposition experiments for the former case. The CaF2 precipitant was obtained, as described above, immediately before the deposition experiment. The clean glass plate was immersed in the precipitant for 5 min. After this, excess of the solution was removed and the wet plate was put on the impinging cell. At this moment the flow was switched on and the deposition started. The results of the experiment are shown in Fig. 1. As can be seen, for almost 4 rain the coating degree S(t) increases with the time. After 5 rain S passes through a maximum and drops to a small value. At a longer time the deposition again starts to go up with a rate characteristic for a clean glass surface. Figure 1 also shows the time dependence of the instantaneous fluxes of the particles de-

2.0

--

positing on the collector surface (positive J ) , and escaping from the surface (negative J). Escape o f the particles can be caused by dissolution of the CaF2 coating on the glass collector. As one can see, the characteristic time of dissolution is on the order of 5 min. For a uniform layer o f precipitant it is possible to estimate the rate of this process under the experimental conditions, assuming that the dissolving is diffusion controlled. The estimation gives 0.2 nm/s, which would suggest that the CaF2 particles are 0.06 t~m in diameter. Such a particle in water can hardly be visible under a microscope in an intensive dark field illumination. In fact, direct microscopic observations o f the glass surface, previously contacted with CaF2 precipitant, show only a light precipitant which disappears when contacted with 5 × 10-4 M CaC12. This indicates that the CaF2 particles are not larger than predicted and that the relatively long time necessary to wash out the coating can be attributed to the necessity of removal of adsorbed traces of the

I

--

I

I

1.5

~? o

1.0

0.5

0.0 800

_ ~_~v,v v ~ v _ v

v -- t h e d e p o s i t i o n flux zx - the escaping flux :

40O Io

v

0

~hNA _ - - 2 x ~_ ~- .-

. . . . . . . . . . . . .

' kS~:~x " " " "

~

"

" ' ~z x ~ Z x -

-400

-800 4 0' 0

0

8 0' 0

•

t i m e [scc]

12 o 0

FIG. 1. Dependence of the coating density S and the latex particle flux J o n the time for the glass collector surface coated with the CaF2 precipitant. Journal q/Col[oid and lntet'/ace Science,

Vol,

148, No.

I, January

1992

DEPOSITION

precipitant in a chemical sense and to rejuvenation of the electrical double layer of the glass. Since the hydrodynamic conditions are k n o w n it is possible, by solving the mass transfer equation in the vicinity of a stagnation point, to calculate the flux of the latex particles. T h e m e t h o d of the calculation is discussed in detail by Dabros and van de Ven ( l, 2). The dimensionless flux of the particles, given in the f o r m of Sherwood number, Sh = Ja/D°c °, where D o is the diffusion coefficient in an unb o u n d e d fluid of particles with the radius a and c o is the n u m b e r concentration of the particles, can be expressed as a function of dimensionless parameters:

OF

67

PARTICLES

dielectric constant of the m e d i u m was assumed to be equal to 80. The electric-double layer interaction shows up when the particlewall separation is a small fraction of the particle radius. The sign and magnitude of the electrical interaction is given by the double layer parameter D1, DI =

47r~o'~t'~2a/kT,

[6]

where e and eo are dielectric constants of the m e d i u m and the permittivity of the vacuum, respectively, and ~ and XI/2 a r e the surface potentials of the particle and the collector, respectively. For the glass surface coated by the CaF2 precipitant it is reasonable to assume that the zeta potential of the collector is positive and equal to 38 mV. The value of the D1 paSh = Sh(Pe, Ad, Gr, ra, Dl). [4] rameter for these parameters is on the order In this equation Pe is the Peclet n u m b e r o f - 2 0 0 0 . It should be noted that for Ka = 70, the flux is not a strong function of the D1 pagiven by rameter, as long as D1 < - 1 0 0 0 . In fact, if D1 Pe = 2Aa3/D °, [5] varies from - 1 0 0 0 to - 4 0 0 0 , the flux varies by less than 5% only. As was shown (1) the where A is the flow intensity parameter (1). flux is more sensitive to the position of the In the experimental conditions A = 3300 s -1 layer where the boundary conditions are specc m -1 and the Pe n u m b e r was equal to 0.3. ified. It should be noted that the CaF2 precipT h e adhesion number, itant on the glass surface m a y have some degree of permeability due to its loose structure. Ad = AI23/6kT, In such a case the latex particles are captured depends on the H a m a k e r constant A123for in- at some distances from the collector without teractions between latex particles with the glass squeezing out the fluid, which happens when collector through the water medium. In cal- approaching a smooth surface. Calculations culations it was assumed that Ad = 0.8 (A123 show that for experimental conditions the flux 2 X 10-2°J, (1)). of the latex particles to the collector can be The gravity n u m b e r is changed from 510 particles/s cm 2 to 640 particles/ s cm 2, if it is assumed that the particles G r = 2Apga3/9~D °, are captured at separations less than 10% and where A0 is the apparent density of the latex equal to 30% of the latex particle radius, reparticles equal to 0.05 g / c m 3, g is the gravi- spectively. The lower and upper values are tational acceleration, and n is the viscosity of shown on Fig. lb by arrows. Furthermore, the deposition flux can be inthe fluid being equal to 0.010 g / c m s. In the experimental conditions the gravity slightly fluenced by diffusiophoresis in the salt gradient prevented the deposition. The dimensionless caused by dissolution of the CaF2 ( 16, 17). A diffusion potential near the interface can arise value of G r was equal to 0.048. The dimensionless product of the Debye electrical double as a result of differences in mobilities of Ca z+ layer parameter r and the particle radius a ( o f and F - ions. For the considered system one the latex particles) for the experimental con- can expect enhancement of the deposition rate ditions was equal to 70. In the calculations the due to this effect. Journal o[Colloid and Inte~-/itce Science, Vol. 148, No. 1, January 1992

68

DABROS,

BUCZAK,

AND

KOSACZ

the fluid, deposited for a short period of time in another place. As is shown in Fig. 1, after 12 min a steady flux of depositing and escaping particles is established. At such a state the CaF2 precipitant has dissolved and the glass surface has had time to relax while being in contact with the solution. The presented m e t h o d allows one to determine the complete dynamics o f the deposition process. However, to do this it would be necessary to trace the full history o f a very large number of particles.

The mean experimental value of the flux, calculated from the slope of the S vs t curve (Fig. 1), is equal to 610 particles/s cm 2, as compared to 20 + 5 particles/era 2 s to the uncoated surface. Thus, a good agreement between the theoretical and experimental fluxes is found. The highest flux of the escaping particles was equal to 810 particles/s cm 2. In this case the maximum flux was not controlled by the bulk concentration. It rather depends on the surface concentration or surface flux of the particles released from the collector surface. The flux was determined by tracing the history of the particles on the collector surface. It should be noted that this is the only reliable way of determining the flux, which raises no doubts about what really happens on the surface; e.g., it was noted that most of the particles which escaped in large numbers from their deposition sites in the eighth minute did so in one step. However, a small percent of them, after leaving their sites and being carried by

(b) CaF2 precipitant present in the solution. Figure 2 shows the experimental values of the coating degree S as a function of time for various volumes of the CaFz suspension added to the latex solution. As one m a y see, the presence of the CaF2 precipitant has a significant influence on the kinetics of deposition. In order to explain the results, an estimate o f the order of magnitude of the characteristic parameters will be made. According to literature data (15), the solubility product o f CaF2 equals 3.4 X 10 -1~ at 18°C and 3.95 × 10 -1~

vc~,~[era"] • - 0.05 v - 0.I0 ,-0.15 o - 0,25

--.~ 2 o

•

~'~

-

~__

o

./.--"

1

7

-0.

VCaF2 [ e r n " ]

i

0 i

•

-

1.0

~

-

1.5

•

- 2.5

~

_

~

_"

~

400

r BOO

time [see]

z 1200

FIG. 2. Dependence of the coating density S on the time for various volumes of the CaF2 precipitant added to the latex solution. Jo trnal ¢f Co/Ioid and Interlace Science Vol. 148, No. I, January 1992

DEPOSITION OF PARTICLES at 26°C. Assuming a value of 3.4 × 10 - ~ one is able to calculate the volume v~F2 of the precipitant which is necessary to saturate the latex dispersion with respect to CaF2. The calculations show that under experimental conditions V~aV2 "~ 1 c m 3. Below this value the added precipitant should dissolve. The second import.ant parameter is the time of dissolution. The characteristic time, ra, of the process can be estimated, assuming that the dissolution is controlled by diffusion of the ions from the region near the crystal surface where the solution is saturated. The time depends on the particle radius. For acar2 = 10-6 cm ra ~ 10-2 s. If the CaF2 particles are adsorbed at the latex particles, the dissolution time is longer by a factor a/acaF~. But even then the characteristic time of dissolution is of the order of 1 s. F r o m the above discussion, it follows that if the volu m e o f the CaF2 precipitant solution VCaF~is smaller than V~F2 after about 1 s the deposit should disappear. The ionic strength of the solution is not changed by the process in a significant manner. Therefore, one could expect that the addition should not influence the deposition rate. Results of the experiments, shown in Fig. 1, contradict the prediction in

Io

69

two points. First, the deposition rate becomes significant for volume of CaF2 suspension below V~CaV2.The second effect can be related to m a x i m a at curves corresponding to Vcav~ 0.25. As one can see, the time at which the m a x i m u m occurs and the deposition becomes negligible is of the order of 5 to 10 rain. This time, which can be related to the dissolution time of the CaF2 precipitant, is 2 to 4 orders o f magnitude longer than previously estimated. The slopes of the curves for t ~ 0 give the initial flux of the latex particles to the collector j o . Figure 3 gives the dependence of the j o vs volume of the added CaF2 precipitant. It is possible to distinguish three regions on the volume axis. For Vc~F~ < 0.25 cm 3, a sharp increase of the initial flux is seen. For 0.25 < VCaF2< 1.85 crn 3, the flux is almost constant and reaches the m a x i m u m value 420 particles/ c m 2 s. For Vcav2 > 2 cm 3, a monotonic decrease of the flux is observed. This part of the curve can be easily explained by assuming that the excess of the CaF2 precipitant is adsorbed at the particle and collector surface causing repulsion of positively charged surfaces. Because in the experiments a fresh precip-

to-O "O

400

0

O \ O.._

200

O

0

I

I

5

10

V c ~ Iota~] FIG. 3. Dependence of the initial flux of latex particles J on the volume Vcav2of the CaF2 precipitant added to the latex solution. Journal (fColloid and lnterace Science, Vol. 148, No. I. January 1992

70

DABROS, BUCZAK, AND KOSACZ in the latex dispersion a systematic drop of the initial flux is noted. However, it should be realized that the kinetics of deposition is a composite function of the added volume, since the CaF2 influences not only interactions between latex and the collector surface, but also interactions between particles. For VCaF2 equal to about 3.5 cm 3 the latex colloid becomes unstable. The half-life time of fast coagulation is of the order of 200 min. But even during experiments depositions of aggregates and formarion of the surface aggregates is seen. One important conclusion can be drawn from the experimental data. It is possible toactivate the deposition o f negatively charged particles on the negatively charged collector surface by adding small a m o u n t s of a simple salt, which at higher concentrations would produce a positively charged deposit. However, the m a x i m u m activation occurs just before the solubility product is reached. The adsorbed species can influence the interaction between particles and the collector surface influencing the deposition kinetics. Because the surface o f the latex particles is small ( ~ 0 . 6 c m 2 per c m 3 of the solution) the adsorption has no significant influence on the titration results. As

itant of CaF2 was used, there is a possibility that its chemical potential is higher than that of the aged deposit. This supposition was verified experimentally by a potentiometric titration of the 5 × 10-4 CaC12 solution with and without latex by the CaF2 precipitant. The a m o u n t of CaC12 and latex solutions were exactly the same as in deposition experiments. The concentration of F - ions increased during titration until the saturation point was reached for VCaF2= V~av2.Figure 4 shows the results of the titrations. Filled circles show experimental results for the 5 × 10-4 M CaC12 solution while e m p t y squares show the same solution with latex. As one can see the differences are negligible. The solid and dotted lines were calculated assuming the solubility products were equal to 3.4 × 10 -1~ and 3.0 × 10 -~°, respectively. Without any doubt, the second value fits the experimental points m u c h better than the first one. Thus one can say that the fresh CaF2 precipitant has a m u c h higher solubility than the aged one. In reference to the deposition experiments, it is evident that the latex solution is saturated with respect to the CaF2 precipitant for Vcav2 higher than ~ 2 cm 3. When there is excess of the CaF2 precipitant

-

IO0

[]

.

-

without latex with latex

ICaF~

IcaF=

~.4x10

-11

3.0xlO

-1°

",,,

..

_

50

I

1

_ ,

t

Vc,,r~ iota ~1

I

1o

FIG. 4. Dependence of the potential of the fluoride electrode on the volume of the CaF2 precipitant VC~F2.The dotted and solid lines were calculated assuming the solubility product equal to 3.4 X 10-11 and 3 X 10-j°, respectively. Jom-t~al ~fCotloid and Interlace Sciem'e Vol. 148, No. 1, January 1992

DEPOSITION OF PARTICLES shown in Fig. 3 the m a x i m u m flux of the particles, in discussed experiments, is smaller than the flux obtained in experiments when the collector plate was covered by the CaF2 deposit. This is what can be expected because, when the CaF2 is added to the latex dispersion, both latex and the glass surface are modified in the same m a n n e r so there is only a specified range where the activation is effective. Using Eqs. [ 3 ] and [ 4 ] it is possible to estimate an order of magnitude of the blocking parameters aii and cross-interaction parameters a o. Assuming 3 / = 20, the blocking parameter a o-for deposition of the latex particles is o f the order of - 10-4 s - I , the blocking coefficient a22 for deposition of the CaF2 particles is of the order o f - 0 . 0 2 s -I and the cross-interaction coefficient a12 "~ 50 s -1 . These values explain why the coating is only slightly nonlinear in the region o f good deposition where only the latex particles are modified by the presence o f the CaF2 deposit. The time necessary to saturate the collector surface by the CaF2 is of the order of 1 rain. This is consistent with the character o f the experimental coating vs time curve where the expected " S " shape of curves was not found. On the basis o f present theory it is not possible to discuss details of the coating kinetics in all regions studied experimentally. CONCLUSIONS 1. There are a n u m b e r of possible interactions during the deposition process from mult i c o m p o n e n t colloidal dispersions. Studies of such processes, although more complicated, are, however, interesting due to an analogy to m a n y real systems encountered in industry. 2. Deposition of negatively charged particles on a glass collector surface covered b y positively charged CaF2 precipitant is not limited by an energy barrier. After a time period which is necessary to dissolve the CaF2 coating, the latex particles are washed out by the fluid. The experimentally found flux of the latex particles is slightly higher than the theoretical one, presumably due to the porous character o f the CaF2 precipitant at the glass surface. Porosity

71

of the adsorbed layer enhances the deposition as c o m p a r e d to a solid smooth surface. 3. The presence of the positively charged CaF2 precipitant in the latex dispersion has a significant influence on the kinetics of the latex deposition on the negatively charged glass surface. The m a x i m u m flux is observed when the solubility constant is not yet reached. Presumably, adsorbed forms of the precipitant at the latex particles are responsible for the activation. 4. Excess of the CaF2 precipitant slows down the deposition of the latex particles. The m e c h a n i s m of the stabilization is similar to the polymer stabilization (18). REFERENCES 1. Dabros, T., and van de Ven, T. G. M., ColloidPolym. Sci. 261, 694 (1983). 2. Dabros, T., and van de Ven,T. G. M., Phys. Chem. Hydrodyn. 8, 161 (1987). 3. Adamczyk,Z., Zembala,M., Siwek,B., and Czarnecki, J., J. Colloid Interface Sci. 110, 188 (1985). 4. Adamczyk, Z., Dabros, T., Czarnecki, J, and van de Ven, T. G. M., Adv. Colloid Interface Sci. 19, 183 (1983). 5. Adamczyk, Z., Colloids Surf. 39, 1 (1989). 6. Prieve, D. C., and Lin, M. J., J. Colloidlnterface Sci. 76, 32 (1980). 7. Adamczyk, Z., and van de Ven, T. G. M., J. Colloid Interface Sci. 97, 68 (1984). 8. Adamczyk,Z., Dabros, T., Czamecki, J., and van de Ven, T. G. M., J. Colloid Interface Sci. 97, 91 (1984). 9. van de Ven, T. G. M., Colloids Surf. 39, 107 (1989). 10. Dabros, T., and van de Ven, T. G. M., J. Colloid Interface Sci. 93, 576 (t983). 11. Dabros, T., and van de Ven, T. G. M., J. Colloid Interface Sci. 91, 298 (1983). 12. Clint, G. E., Clint, J. H, Corkill, J. M., and Walker, T., J. Colloid Interface Sci. 44, 121 (1973). 13. Dabros, T., PhD Thesis, Jagiellonian University, Krakow, 1976. 14. Marshal, J. K., and Kitchener, J. A., J. Colloid Sci. 22, 342 (1966). 15. Weast, R. C. (Ed.), "CRC Handbook of Chemistry and Physics," 58th ed. CRC Press, Boca Raton, FL, 1978. 16. Lin, M. M.-J., and Prieve, D. C., J. Colloid Interface Sci. 95, 327 (1983). 17. Ebel, J. P., Anderson, J. L., and Prieve, D. C., Langmuir 4, 396 (t988). 18. Boluk, M. Y., and van de Ven, T. G. M., Colloids Surf 46, 157 (1990). Journal q/ColtoM and lnter[&ce Sciemx,, Vol. 148, No. 1, January 1992