n16

Materials Chemistry and Physics 91 (2005) 205211

ehavilicaince

a -dong, Sb M rds and

ber 200

Abstract

The influe al behathis study, si ic amplDespite a hig logicalbut the rheo th. Nothat incorpo uperimpotential an sufficiesilica nanosols, without first taking into account the effects of particle crowding and the repulsive interactions on suspension structure. Therelatively low magnitude of van der Waals attractive forces between silica particles in water also plays an important role at high electrolyteconcentrations. A comparison is made between silica nanosols and silica microspheres, and also between nano-silica and nano-alumina. 2004 Published by Elsevier B.V.

Keywords: C

1. Introdu

Nanosizually beingvices andpackages, ucatalysts, mcases, the nvia a liquidused to botior of so-cadimensionsindicated thplain the cdifficultiesvelopmentnology.

CorresponE-mail ad

0254-0584/$doi:10.1016/jeramics; Oxides; Surface properties

ction

e inorganic particles (i.e., below 100 nm) are grad-incorporated into a broad range of advanced de-

applications; some examples include electronicltra-thin-film optical devices, advanced fuel cellolecular conductors, and biochips [17]. In mostanoparticle component is incorporated or utilizedsuspension. Classical colloid science is generallyh describe and predict the properties and behav-lled nanosols, in which the dispersed phase hasin the nanoscale regime. Recent evidence [8] hasat classical colloid principles might not fully ex-

omplex behavior of concentrated nanosols. Thuscan be anticipated in the course of research, de-and production of devices based on nanosol tech-

ding author. Tel.: +82 2 2290 0502; fax: +82 2 2281 0502.dress: [email protected] (U. Paik).

According to DerjaguinLandauVerweyOverbeek(DLVO) theory [9], a cornerstone of modern colloid sci-ence, two types of forces exist between colloidal particlessuspended in a dielectric medium: (1) electrostatic forces,which result from unscreened surface charge on the particle,and (2) Londonvan der Waals attractive forces, which areuniversal in nature. The colloidal stability and rheology ofoxide suspensions, in the absence of steric additives, canbe largely understood by combining these two forces (i.e.,assumption of additivity). However, the expressions of theelectrical forces are derived from the PoissonBoltzmannequation, which is based on two key approximations: (1) thesolvent is considered as a structureless dielectric continuumand (2) the field generated by the ions is a mean field.

There are several reports [1012] of the unique stabilityof nanosize silica hydrosols near the isoelectric point (IEP).Mahanty and Ninham [13] discovered experimentally the ex-istence of short-range forces that play an important role inthe interaction process and which must be added to those

see front matter 2004 Published by Elsevier B.V..matchemphys.2004.11.011Rheological and electrokinetic bconcentrated nanosize s

Ungyu Paika,, Jang Yul Kima, VDepartment of Ceramic Engineering, Hanyang University, 17 Haengdangaterial Science and Engineering Laboratory, National Institute of Standa

Received 21 July 2004; received in revised form 2 Novem

nce of solids loading and the electrical double layer on the rheologiclica suspensions were characterized by viscosity, electrokinetic sonh electrokinetic potential at pH 8, fumed silica not only exhibits rheo

logy does not have the expected DLVO dependence on ionic strengrates the influence of the electrical double layer, leads to partially sd viscosity indicates that classical DLVO calculations alone are inior associated withhydrosols

nt A. Hackleyb

eongdong-ku, Seoul 133-791, Republic of KoreaTechnology, Gaithersburg, MD 20899-8520, USA

4; accepted 15 November 2004

vior of concentrated silica nanosols was investigated. Initude measurements, and by theoretical considerations.behavior normally indicative of an unstable suspension,

rmalization of viscosity to an effective volume fractionposable curves. The positive correlation between zetant to predict the rheological behavior of concentrated

206 U. Paik et al. / Materials Chemistry and Physics 91 (2005) 205211

forces already accounted for by the original DLVO theory.These short-range interactions are referred to as structuralforces [1416]. Structural forces might explain some par-ticular aspects of the stability behavior of silica nanosols,but they are insufficient to account for the apparent cooper-ative effects of solids loading and electrostatics found in thepresent study. Contrary to suspensions based on colloidal-size (1001000 nm) silica [17] and other inorganic oxides[18] as replogical behsilica nanotions basedDespite a hica not onlmally indipseudoplasthe expecteperimentalgeometricence of solrheologicalcompare thcrospheresconditions.

2. Experim

2.1. Prepa

Aerosiloxide C ((Frankfurtarea and amanufacturfor A90; 1microspherameter of 5FL). The sor NaNO3intense ultraggregatesof the suspan equilibrat room temaging, the5 min.

1 Certain tror identified iprocedure andommendationnology, nor dofor the purpos

2.2. Characterization techniques

The electrokinetic behavior of silica suspensions at avolume fraction of 2% and a temperature of 25 0.1 Cwere characterized using the electrokinetic sonic amplitude(ESA) technique (Acoustosizer II, Colloidal Dynamics, Syd-ney, Australia). The basic theory and application of ESAhave been described in detail elsewhere [1921]. For ESA

urements, two identical suspensions were prepared foranalysis. Separate acid (1.0 N HCl) and base (1.0 N

H) titrations were then performed beginning at the nat-H, and subsequently combined to generate a completebase titration curve. Based on previous work, we esti-a measurement precision of 1 mV for zeta potential.

rheological behavior of suspensions was measured us-controlled-stress rheometer (MCR300, Paar Physica,

gart, Germany) with a concentric-cylinder tool geom-and an external temperature-controlled bath-circulatorting at 25 0.1 C. To obtain the rheological behavior

spensions at specific pH values (pH 3, 5, 7, 8, 9, 11, andth added NaNO ), the suspensions were prepared forsis inted prhear rof 30data a

cted foitions.

esults

y chanof th

lectrolrical dte con

elect

. The reica suspicrosph

le volumorted in the literature, we find that the rheo-avior of concentrated electrostatically stabilizedsols is counterintuitive with regards to predic-

on a standard interpretation of DLVO theory.igh electrokinetic potential at pH 8, fumed sil-y exhibits rheological behavior that would nor-cate an unstable or aggregated suspension (i.e.,tic-high viscosity), but the rheology does not haved dependence on ionic strength. In this study, ex-measurements, DLVO calculations, and simple

considerations are used to understand the influ-ids loading and the electrical double-layer on thebehavior of concentrated silica nanosols, and toeir behavior with that of much larger silica mi-

, as well as like-sized nano-alumina, under similar

ental

ration of suspensions

90 fumed silica (designated A90) and aluminum-alumina) were obtained from Degussa AGam Main, Germany)1. The specific surface

verage primary particle size, as provided by theer, was as follows: 90 15 m2 g1 and 20 nm00 15 m2 g1 and 13 nm for -alumina. Silicaes (designated Geltech) with a nominal median di-00 nm were obtained from Geltech Inc. (Alachua,ilica particles were dispersed in deionized water

solution. Each suspension was subjected toasonic treatment for 5 min in order to break down. An ice bath was used to control the temperatureension during ultrasonic treatment. To establishium dispersion, the suspension was aged for 12 h

perature using a wrist-action shaker. Followingsuspension was ultrasonicated for an additional

ade names and company products are mentioned in the textn illustrations in order to specify adequately the experimentalequipment used. In no case does such identification imply rec-or endorsement by National Institute of Standards and Tech-es it imply that the products are necessarily the best availablee.

meas

eachNaOural pacidmateTheing aStuttetryoperaof su8 wianalyadjusThe stimementexpecond

3. R

Bsign)ert eelecttrolyin an

Fig. 1for siltech mPartic3the manner previously described, but the pH wasior to ultrasonic treatment using HCl or NaOH.ate was increased from 1 to 1000 s1, with a pauses at each shear rate. Based on previous measure-nd experience, a reproducibility of 10% can ber viscosity measurements performed under these

and discussion

ging the pH, one can alter the magnitude (ande zeta potential (), while the addition of an in-yte will affect both the magnitude of and theouble-layer thickness. Thus, both pH and elec-centration will directly impact colloidal stabilityrostatically stabilized system. Fig. 1 compares

lationship between zeta potential (open) and viscosity (filled)ensions as a function of suspension pH: nanosize A90 vs. Gel-eres (G). Viscosity was determined at a shear rate of 26.4 s1.e fraction given in %.

U. Paik et al. / Materials Chemistry and Physics 91 (2005) 205211 207

Fig. 2. The efsilica at pH 8

and viscosifor the A90tration of 2stant and loA90 exhibi13.2%, wit300%. Fig.tion on visc13.2% A90

Fig. 1 incosity bothcal DLVO twhich is loity decreasthe expectaas , and bviscosity shcosity aredispersion.exhibit a mgation) whesimilarly, astant. Sincfrom DLVOsumption thgregation (valid. Viscobe influencters the struHence, facand electrotion to agg

In ordeFigs. 1 andsions of theticle centerdp/1/2, whparticle vosurface septhe system

. Diagram illustrating the relationship between average interparticlee-to-surface separation distance, ds, and other system dimensions, forcle diameter dp = 20 nm and = 13.2%.

le length (ds/dp1), which can lead to constrained mo-nd excluded volume effects. That is, other particles maycluded from the interparticle space once the average sep-n distance is of the order of the particle size, therebying the number of possible positions each particle is

to sample during Brownian motion. Furthermore, eachle witell. Fs as a

es, dsanosizo obtams. Tthe crirrespowevetic fole sizsepaforceles. Aogicalin stabge sepfect of electrolyte concentration on the viscosity of 13.2% A90as a function of shear rate.

ty (at a shear rate of 26.4 s1) as a function of pHand Geltech suspensions. Even at a solid concen-

0%, the Geltech microspheres exhibit a fairly con-w viscosity across the entire pH range, whereas

ts a strong pH dependence at a volume fraction ofh an increase in viscosity near pH 7 in excess of2 shows the effect of inert electrolyte concentra-osity as a function of shear rate for highly chargedat pH 8.dicates that for Geltech microspheres, and vis-follow the expected behavior predicted by classi-heory. That is, as the pH moves away from the IEP,cated near pH 2 for silica, increases and viscos-es. However, A90 exhibits a discrepancy betweention of DLVO theory and the experimental results:y inference colloidal stability, of A90 increases,arply increases. For suspensions, changes in vis-

often assumed to reflect changes in the state ofWith this assumption in mind, viscosity should

inimum (i.e., reflecting the least amount of aggre-n is at a maximum at constant ionic strength, or,t the lowest ionic strength when pH is held con-e A90 exhibits the reverse behavior, a deviation

appears to exist. However, the often-applied as-at viscosity is a direct reflection of the state of ag-

or, by inference, colloidal stability) is not strictlysity is a macroscopic property, and as such it will

Fig. 3surfaca parti

parabtion abe exaratioreducableparticical cand dcreas

for ncult tsystesince13%

Htrostaparticeragetheseparticrheolrema

averaed by any chemical or physical process that al-ctural or hydrodynamic conditions of the system.tors such as particle crowding, particle orderingviscous effects will also impact viscosity, in addi-regate or network formation.r to more properly analyze the results of2, it helps to first lay out the physical dimen-system as depicted in Fig. 3. The mean interpar-

-to-center separation distance (dc2c) is defined asere dp is the primary particle diameter and is the

lume fraction. The mean interparticle surface-to-aration distance (ds) is dc2cdp. As increases,dimensions, ds and dp, eventually become of com-

Fig. 4. Calcution distancesize for silicah a surrounding volume of liquid defines a spher-ig. 4 shows the average cell radius, rcell = dc2c/2,function of and dp. As dp decreases or in-

becomes smaller. This has important implicationse particles, and helps to explain why it is so diffi-in low-viscosity concentrated nanosols in aqueoushis explanation may not be immediately obvious,itical corresponding to ds/dp = 1 occurs at aboutective of particle size.r, the distance over which hydrodynamic and elec-rces act in solution is more or less independent ofe at first approximation. As a result, when the av-ration distance between particles is rather large,s dissipate before they can influence neighborings a result, particle motion is independent and thebehavior is Newtonian so long as the particles

le and do not aggregate. On the other hand, as thearation distance is reduced, these forces begin tolated average cell radius (open) and surface-to-surface separa-(filled) as a function of particle volume fraction and particle.


influence nearest neighbors, and the motion of nearby parti-cles becomes coupled. Coupling leads to an increase in sus-pension structure, which provides an additional mechanismfor viscousture refersparticles orfluid. In eithe application. In aquon structurthe length sare active.

For the cof 39 nm fotion distanthe particleelectrical danticipatevalue of simple harelectrostatiyond its acvalue of dstive hard-spcations [23can be esti1/, where

=(F2r

andNi andof the counThe doubleof ionic stforce will da simple 1:

= 3.288

where I is tthe suspensas representhe presencof particletrations, thof orderedanalogousAccordingthe range aminished.particle colAggregatioshear thinn

Based soobserved foand with in

the impression that the low ionic strength nanosol is less sta-ble than its high ionic strength counterpart. If we consider theinfluence of the double layer in crowded systems, as described

e, a different interpretation is then possible. Krieger andluz [25] working with polymer latices demonstrated thatg repulsive interactions can result in increased structure,ng to higher viscosities and a shear-dependent flow be-r, without impacting stability per se. For a concentratedm, compression of the double layer can have a substan-

pact on viscosity. Therefore, the higher suspension vis-y of A90 in the absence of added electrolyte is attributed

development of structure resulting from the reductioneffective average interparticle separation distance by a

r comparable to 1/. Shear flow alters this ordered struc-leadinrates,rate

ucturerolyteof struthinn

n theing atg. 2 w

spitehe incntradiwithi

ed thebarri[28]arativof the

m. Thonvaof a

um. Aon c

1. Cfor agmpar

rostatint rol

urface

1ker conlculated

ial

amorphO3O33 (averaveragelculated

ttivity [3dissipation [22]. In the present context, struc-to the formation of stable physical bonds between

to the ordering or alignment of particles in thether case, the structure is altered or disrupted bytion of shear forces, resulting in energy dissipa-eous nanosols, the effects of electrostatic forces

e can be particularly strong as dp and ds approachcale over which short-range repulsive interactions

ase of 20 nm A90 at= 13.2%, we obtain a valuer dc2c and 19 nm for ds. Hence, the mean separa-

ce between A90 particles is roughly the same asdiameter. If we consider also the impact of the

ouble layer surrounding the charged particles, wethe appearance of particle crowding effects at athat is lower than what would be predicted for a

d-sphere system. This is because the short-rangec forces extend the influence of each particle be-tual diameter, thereby effectively decreasing the. The contribution of the double layer in the effec-here model has been discussed in previous publi-

,24]. Briefly, the electrical double layer thicknessmated using the DebyeHuckel screening length,

iNiz2i

0kT

)1/2

zi are the number density and valence, respectively,terions of type i, and F is the Faraday constant.layer thickness is therefore primarily a function

rength, although the magnitude of the repulsiveepend on the surface charge density as well. For

1 electrolyte at 25 C in water

I (nm1)he ionic strength in mol L1. When salt is added toion, it results in compression of the double layerted by a decrease in 1/. At low ionic strengths,e of the double layer contributes to the effectscrowding. At sufficiently high particle concen-

e electrostatic interactions enhance the formationstructures and viscoelasticity in a manner that isto the secondary electroviscous effect [22,25,26].to DLVO theory, with the addition of electrolyte,nd magnitude of the repulsive interactions are di-This permits a higher sticking frequency duringlisions and leads to the formation of aggregates.n in turn is manifested by higher viscosities anding behavior.lely on a classical DLVO interpretation, the trendr the viscosity of A90 as a function of shear ratecreasing electrolyte concentration in Fig. 2 gives

abovEguistronleadihaviosystetial imcositto thein thefactoture,shearshearin strelectlossshear

Othinnin Fiity inlike tto costoodplainstericmontcomptancesysteLondticlesmedicomm

Tableforceica coelectnificathe s

TableHamater, ca

Mater

SiO2 (-Al2-Al2BaTiOTiO2 (

a Capermig to the observed shear thinning response. At higha limiting linear relation between shear stress and

was observed, indicating that additional changesdo not occur beyond a critical shear. Addition ofcauses the double layer to collapse, resulting incture, and a corresponding loss of viscosity anding behavior.other hand, the lower viscosity and lack of shearhigh electrolyte concentration (e.g., 0.5 mol L1)ould seem to indicate excellent colloidal stabil-of strong electrostatic screening. This behavior,rease in viscosity at low ionic strength, appears

ct DLVO predictions, but, in fact, it can be under-n the DLVO framework. Although Healy [10] ex-unusually stability of silica by invoking a surface

er containing polysilicates and bound cations, Du-approached this issue by consideration of silicasely low Hamaker constant and the relative impor-static (dielectric) term in the silicawatersilica

e Hamaker constant reflects the magnitude of then der Waals attractive forces between two par-given material separated by a vacuum or other

comparison of Hamaker constants for severaleramic materials across water (A131) is shown inlearly, the attractive force, and hence the drivinggregation, is an order of magnitude lower for sil-

ed with the other ceramic materials. Therefore, thec repulsive forces should continue to play a sig-e for silica stability, even under conditions wherepotential is well screened.

stants (non-retarded) for various ceramic materials across wa-using the Lifshitz theory [29]

A131 (1020 J)ous) 0.46

3.48a3.67

age) 8) 5.35

from Eq. (8) in [30] using a value of 8.7 for the relative1] and 1.7 for the refractive index [32].


Fig. 5. Calcualumina, baseand a Stern po

Fig. 5 shas a functiotion energystants for sing a spherameters, s(0.001 andchosen basculations instant. The Sof . The re(a) and (b)(d). At lowsive (positifrom the pastability. A(negative)beyond 1 ntion), withan unstablesilica exhibthat is actiand whichto preventtem. The raction curvstability. Inabout 32%0.001 to 0.the net reputo screeninwith respecpair interacinteractionand order oport for oursilica and a

For expand for com

. The effect of electrolyte concentration on the viscosity of 13.2%ina at pH 5 as a function of shear rate.

ilar sized and highly charged 13.2% -alumina nanosol5 (IEP is near pH 9) as a function of electrolyte con-

ation and shear rate. These results are shown in Fig. 6,houldshowhear

ws theincreathinn

ina naaggregLVOFig. 7tted ae fra

ctiveness,hard see, thhe inclated DLVO pair interaction energy curves for silica and -d on a spherical geometry with a particle diameter of 20 nmtential of 85 mV.

ows the DLVO pair interaction energy calculatedn of separation distance [27]. DLVO pair interac-curves were calculated using the Hamaker con-

ilica and -alumina listed in Table 1, and apply-rical particle geometry. Otherwise, material pa-uch as particle size (10 nm radius), ionic strength0.5 mol L1), and Stern potential (85 mV), wereed on A90 at pH 8 and used for both sets of cal-

order to stress the impact of the Hamaker con-tern potential was estimated from measurementssulting curves in Fig. 5 for A90 silica are marked, and those for alumina are identified as (c) andionic strength, both systems display large repul-

ve) energy barriers extending out more than 30 nmrticle surface, and representing a high degree oft 0.5 mol L1 calculations show a net attractiveinteraction for alumina at all separation distancesm (the net energy approaches zero in the bulk solu-a primary maximum barely above zero, indicatingsystem. In contrast, the corresponding curve forits a significant, albeit reduced, repulsive barrier

ve over short separation distances (below 2 nm),should be sufficient in magnitude (about 30 kT)

extensive aggregation from occurring in this sys-

Fig. 6-alum

a simat pHcentrand ssilicaand sfollowithshearalumsivethe D

Inis plovolumeffethickas a

can s

that telative heights of the maxima in the pair inter-es directly reflect the relative degree of colloidalthe case of silica, the maximum is reduced byupon raising the electrolyte concentration from

5 mol L1. Additionally, the distance over whichlsive interaction is felt is greatly compressed due

g. Although these calculations are not quantitativet to real systems, since they consider explicitlytions and do not take into account multi-particle

s in crowded systems, they do indicate clear trendsf magnitude differences, and therefore lend sup-interpretation of the experimental results for bothlumina.erimental confirmation of the DLVO calculations

parative purposes, we measured the viscosity of

Fig. 7. Viscovolume fractioViscosity is nthickness of tbe compared with the corresponding data for A90n in Fig. 2. For alumina, the change in viscositythinning behavior with increasing ionic strength

expected monotonic DLVO prediction. That is,sing ionic strength, viscosity continually rises anding becomes more prominent. At 0.5 mol L1, thenosol is highly shear thinning as a result of exten-ation in the unstable suspension as predicted bycalculations in Fig. 5., the normalized viscosity for the silica nanosol

s a function of electrolyte concentration and solidction. In this case, viscosity is normalized to thevolume fraction, which takes into account the

1/, of the electrical double layer, and treats thisphere extension to the particle diameter. As onee curves are partially superimposable, indicatingrease in viscosity at very low ionic strength can besity of A90 silica at pH 8 as a function of the actual particlen and electrolyte concentration and at a shear rate of 26.4 s1.

ormalized to an effective volume fraction that accounts for thehe electrical double layer, 1/.


Fig. 8. The eshear rate of13.2% and th

at least paring from thabove 13%the low iontions. Appacannot be sdiameter wreality, theneighborintance smalvolume fraviscosity isume effectsolids concappropriatetion experideionizedthen dilutethe viscosithough 1/pH 9. Oncetribute signtive deviatiings (>10%shown in Fresulting fr1/, combithe viscosidestabilizethe influenthe effectsionic streng

The precorrelationDLVO calcalone is inconcentrateing and ovstructure m

4. Conclusions

e observed influence of solids loading and ionic strengthe rheoationaverlapy con

of thee a stry worrimentn ans insufated slectronsideo som

reasef flows to cs wheion whmparae resu

le laye meted an

arily bilica. S

icwtive L

was des for sflow

owled

is woe of STEP)ffect of dilution on the viscosity of A90 silica measured at a26.4 s1. Particles were first dispersed in deionized water aten diluted to 2%.

tially attributed to exclude volume effects result-e influence of repulsive interactions, particularly. However, there is some overcompensation withic strength suspension at low solids concentra-rently, the influence of the electrical double layer

imply viewed as an extension of the hydrodynamicith the resultant increase in excluded volume. Ineffect of the repulsive interactions is only felt ifg particles approach to within a separation dis-ler than 2/ (which occurs more frequently as thection is increased). Otherwise, the influence oninsignificant, since at low solids an excluded vol-is not apparent. Thus normalization at very lowentrations (below about 10% in this case) is not. This is clearly demonstrated by a simple dilu-ment in which suspensions that were prepared inwater, without added electrolyte, at 13.2% wered to 2%. The results, shown in Fig. 8, show thatty is dramatically diminished upon dilution, evenremains large and relatively constant up to aboutdiluted, the repulsive interactions no longer con-

ificantly to viscosity. On the other hand, the posi-on from the normalized curves at high solid load-) and high electrolyte concentration (0.5 mol L1)

Thon thwas r

and oand bnentWhiltheorexpetweeself icentrand ebe coior. Tto inction ocurve

workfractis co

Thdoubtuitivchargprimfor sceram

attracfectcurve

sured

Ackn

Thstitut(KISig. 7 is consistent with an increase in aggregationom the lower repulsive barrier and compressed

ned with a higher collision frequency. In this case,ty is still lower than one would expect for a fullyd system with high solids concentrations. Clearly,ce of the electrical double layer is responsible forobserved near and above 13% solids under lowth conditions.

sent experimental results, particularly the positivebetween and viscosity in conjunction with theulations, demonstrate that classical DLVO theorysufficient to predict the rheological behavior ofd silica nanosols. The effects of particle crowd-erlapping electrical double layers on suspensionust also be taken into account.

program in

Reference

[1] J. Yang,[2] L.E. Cro[3] M. Rozm[4] P.G. Mc

13 (2001[5] R.K. Sin

B.M. M[6] B. Xia, I[7] L.L. Bee[8] S.R. Rag[9] P.C. Hie

Chemistlogical behavior of concentrated silica nanosolslized in terms of simple geometric considerationsping electrical double layers at low ionic strength,sideration of the relatively low attractive compo-DLVO pair interaction term at high ionic strength.aight forward interpretation of the classical DLVOks well for larger silica microspheres, the presental results, particularly the positive correlation be-d viscosity, demonstrates that DLVO theory by it-ficient to predict the rheological behavior of con-ilica nanosols. The effects of particle crowdingstatic interactions on suspension structure mustred for a full accounting of the observed behav-e extent these effects can be considered as actingthe excluded volume, and appropriate normaliza-curves to an effective volume fraction causes the

ollapse into a narrow range; normalization onlyn the solids loading reaches the critical volumeere the average interparticle separation distance

ble to the particle diameter.lts point to partial compression of the electrical

er by salt addition as a viable albeit counter in-hod for decreasing suspension viscosity in highlyd concentrated silica nanosols. This method worksecause of the particularly low Hamaker constantalt additions will not work well for most other

ater systems, due to the greater magnitude of theondonvan der Waals interaction force. This ef-monstrated by comparing the calculated DLVOilica and alumina, and by comparison of the mea-curves as a function of ionic strength.

gements

rk was financially supported by the Korean In-cience and Technology Evaluation and Planningthrough the National Research Laboratory (NRL)the year of 2004.

s

S. Mei, J.M.F. Ferreira, J. Am. Ceram. Soc. 83 (2000) 1361.ss, Ferroelectrics 76 (1987) 241.an, M. Drofenik, J. Am. Ceram. Soc. 81 (1998) 1757.

Cormick, T. Tsuzuki, J.S. Robinson, J. Ding, Adv. Mater.) 1008.gh, S.-M. Lee, K.-S. Choi, G.B. Basim, W. Choi, Z. Chen,

oudgil, J. Mater. Res. Bull. 27 (2002) 752..W. Lenggoro, K. Okuyama, Chem. Mater. 14 (2002) 2623.croft, C.K. Ober, Chem. Mater. 9 (1997) 1302.havan, H.J. Walls, S.A. Khan, Langmuir 16 (2000) 7920.menz, R. Rajagopalan, Principles of Colloid and Surfacery, Marcel Dekker, New York, 1997.


[10] T.W. Healy, in: H.E. Bergna (Ed.), The Colloid Chemistry of Silica,American Chemical Society, Washington, 1994, p. 147.

[11] J. Depasse, A. Watillon, J. Colloid Interf. Sci. 33 (1970) 430.[12] S.K. Milonjic, Colloids Surf. 63 (1992) 113.[13] J. Mahanty, B.W. Ninham, Dispersion Forces, Academic Press, New

York, 1979.[14] J.N. Israelachvili, Intermolecular and Surface Forces, Academic

Press, San Diego, 1987.[15] J.A. Lewis, J. Am. Ceram. Soc. 83 (2000) 2341.[16] R.G. Horn, J. Am. Ceram. Soc. 73 (1990) 1117.[17] A.A. Zaman, B.M. Moudgil, A.L. Fricke, H. El-Shall, J. Rheol. 40

(1996) 1191.[18] Z. Zhou, P.J. Scales, D.V. Boger, Chem. Eng. Sci. 56 (2001)

2901.[19] V.A. Hackley, J. Texter, Ultrasonic and Dielectric Characterization

Techniques for Suspended Particulates, The American Ceramic So-ciety, Westerville, 1998, p. 191.

[20] U. Paik, V.A. Hackley, H.W. Lee, J. Am. Ceram. Soc. 82 (1999)833.

[21] V.A. Hackley, U. Paik, B.H. Kim, S.G. Malghan, J. Am. Ceram.Soc. 80 (1997) 1781.

[22] W.B. Russel, J. Rheol. 24 (1980) 287.[23] T. Okubo, J. Chem. Phys. 87 (1987) 6733.[24] T. Matsumoto, J. Rheol. 33 (1989) 371.[25] I.M. Krieger, M. Eguiluz, Trans. Soc. Rheol. 20 (1976) 29.[26] R. Buscall, J.W. Goodwin, M.W. Hawkins, R.H. Ottewill, J. Chem.

Soc. Faraday Trans. I 78 (1982) 2873.[27] R.V. Linhart, J.H. Adair, STABIL ver. 4.5, University of Florida,

Department of Materials Science and Engineering, 1996;R.V. Linhart, J.H. Adair, in: J.H. Adair, J.A. Casey, S. Veni-galla (Eds.), Handbook on Characterization Techniques for theSolidSolution Interface, American Ceramic Society, Westerville,1993, p. 69.

[28] F. Dumont, in: H.E. Bergna (Ed.), The Colloid Chemistry of Silica,American Chemical Society, Washington, DC, 1994, p. 143.

[29] L. Bergstrom, Adv. Colloid Interf. Sci. 70 (1997) 125.[30] L. Bergstrom, N. Meurk, H. Arwin, D.J. Rowcliffe, J. Am. Ceram.

Soc. 79 (1996) 339.[31] G.P. Singh, M. von Schickfus, S. Hunklinger, K. Dransfeld, Solid

State Commun. 40 (1981) 951.[32] R.H. French, H. Mullejans, D.J. Jones, J. Am. Ceram. Soc. 81 (1998)

2549.

Rheological and electrokinetic behavior associated with concentrated nanosize silica hydrosolsIntroductionExperimentalPreparation of suspensionsCharacterization techniques

Results and discussionConclusionsAcknowledgementsReferences

Documents

n16