Dispersion characteristics of fine particles in water, ethanol and kerosene

NOTES .Dispersion characteristics of fine particles in water, ethanoland keroseneREN Jun', LU Shouci?, SHEN Jian' & HU Boxing 11. Center of Research on Surface and Interface Chemical Engineering and Technology, Nanjing University, Nanjing 210093,China; .2. College of Resources Engineering, University of Science and Technology Beijig, Bejing 100083, ChinaAbstractDispersion behavior of hydrophilic calcium carbonate particles and hydrophobic talcumparticles in water, ethanol and kerosene media has been studied by sedimentation analysis. It isfound that the dispersion of fine particles complies with the principle of polarity compatibility. That isto say, the dispersion effect will be improved when surface polarity of particles is similar to that ofliquid media. The adsorption models of oleic acid on the surface of particles in water and ethanolare proposed.Keywords: fine particles, aqueous medium, dispersion behavior, adsorption model.Dispersion of fine particles in liquid phase is a common but important problem in bothfundamental research and industrial technology. Medium, the property of which affects the stability ofdispersion system to some extent, is an important part in a dispersion system. Among dispersion media,water, ethanol and kerosene are typical polar or nonpolar ones. Dispersion behavior of mineral particlesin water or organic dyes in polar or nonpolar media have been reported in literature beforell“6,， but thatof natural particles in ethanol or kerosene and dispersion characteristics of fine particles in differentmedia with different polarities have rarely been investigated.In this note, the dispersion behavior of natural hydrophilic and hydrophobic particles in differentmedia with different polarities are studied to recognize their general and individual characteristics andessence, and to supply the foundation for resolving practical problems on dispersion.1 Experimental(- ) Samples and reagents. Samples for experiment were natural hydrophilic calcium carbonate(CaCO3) taken from Lintao, Gansu Province and hydrophobic talcum from Haicheng, LiaoningProvince. The samples were purified, ground, sieved, washed and dried in the air at low temperature.The characteristics of the samples are given in table 1. Water was deionized, with pH equal to 6.5.Ethanol was absolute ethanol, a product of the Beijing Chemical Reagents Factory. Kerosene wasobtained by distilling the industrial product used in aviation at 170.. 7; oleic acid (Cc.p.) was purchasedfrom the Shanghai Chemical Reagents Factory.Table 1 Characteristics of samplesSamplesPurity (%)Density1 g“cm3P.Z.C./ pHVolume diameter /umCalcium carbonate98.572.7611.02.522Talcum91.172.611.400(. i) Experimental methods. The dispersion- aggregation of solid particle -liquid systems wasexamined using sedimentation analysis. The suspension of solid particles was agitated at 550 r/m for 5min, and then moved to a cylinder for sedimentation. A refitted electronic balance was used to measurethe change of the weight of settled particles on the balance pan with the sedimentation time. Thesediment weight at a given sedimentation duration ( W) was also obtained. From the difference betweenthe total weight Wo and W, the dispersion extent of pasticlefr hs 11*:d by the expression中国煤化工Fs =-TYHCNMHG(1)where Wo is the total weight of sample particles in the suspension, and W is the cumulative weight ofsettled particles at a given time of settling. The bigger the dispersion extent, the better the dispersioncondition of the particle suspension.1376Chinese Science BulletinVol.45 No. 15August 2000NOTES2 Results and discussion(- ) Characteristics of particles natural dispersion. The dispersion behavior of particles in liquidphase is affected by not only mutual interaction of particles but also the interaction between particlesand dispersion media. The dispersion behavior of particles is different obviously in different media.Dispersion characteristics of hydrophilic calcium carbonate particles in water, ethanol and kerosene areillustrated in fig. 1(a). It is shown that calcium carbonate particles can be dispersed well in water andethanol. Dispersion extent decreased slowly with extending of settling time. The tendency of decreasingwas weakened 100 s later. Calcium carbonate particles can hardly be dispersed in kerosene. In the first20 s, particles settled almost completely and were aggregated obviously. The dispersion extents ofcalcium carbonate particles in water, ethanol and kerosene rank in ethanol > water > kerosene. Thedispersion behavior of hydrophobic talcum in water, ethanol and kerosene is illustrated in fig.1(b). It isshown from fig. 1(b) that particles of talcum aggregate closely in water. Compared with that of calciumcarbonate in kerosene, the aggregation speed decreases and the intensity is weakened. Both calciumcarbonate and talcum particles are dispersed well in ethanol. The dispersion extents of talcum particlesin water, ethanol and kerosene rank in ethanol > kerosene > water. Although talcum particles arehydrophobic (the wetting contact angle in water is 56“), it is dispersed undesirably in kerosene. This is .due to the structure of talcum. Talcum belongs to laminated silicate, in which cleavage planes consist ofinert oxygen atoms only. But in rupture plane, polar valent bonds exist between silicon and ox ygen1005100--0-280▲360 F、600t★▲20↑20(a)一▲ ▲★★▲★▲本b)010120160 200401201602001/min/minFig. 1. The dispersion of dfferent particles in water, ethanol and kerosene. (a) Calcium carbonate. (b) Talcum.1, Water; 2, ethanol; 3, kerosene.atoms 7, which leads to automatic aggregation of particles.The wetting contact angles and dispersion characteristics of calcium and talcum in water, ethanoland kerosene are given in table 2. It shows that the better the wettability of particles in liquid media, thebigger the dispersion extent.Table 2 Wetting contact angle and dispersion characteristics of calcium and talcum particles in water, ethanol and keroseneWetting contact angle e( °)Dispersion characteristicsParticleswateethanolkerosenewaterCalcium carbonate10.00.086.0..0“Talcum56.045.0.LDispersed well; 4 dispersed ordinarily; “disperse中国煤化工(_. i) Effect of oleic acid on dispersion of partiMHCNMHGvtheeffectofoleicacidon dispersion and wetting contact angles of calcium carbonate and talcum particles in water, ethanoland kerosene. It is obtained that low concentration oleic acid accelerates aggregation of calciumcarbonate and talcum particles in water. The two kinds of particles aggregate almost completely and theChinesej数蟈BulletinVol.45 No. 15August 20001377NOTES8080 r(a)b)a、o60口40: 40之20●00<0✧一o-2-7lgC /mol.1.Ig( /mo1+L.1Fig. 2. Efect of oleic acid on dispersion extent (F) and wetting contact angles ( θ of calcium carbonate (a) andtalcum (b) particles in water, ethanol and kerosene. 1, Water- Fs; 2, ethanol-Fs; 3 kerosene-F; 4, water- θ;5, ethanol-θ; 6, keroseneθ .particle size becomes greater when the concentration of oleic acid is between 1.0x10-3 mol/L and1.8x103 mol/L However, the aggregation is weakened when the concentration is above 1.0x103 mol/L“1.8x103 mol/L. The dispersion of particles will become better and better above this concentration. Inethanol, oleic acid can hardly affect the dispersion of calcium carbonate and talcum particles. Inkerosene, oleic acid will improve the dispersion of calcium carbonate greatly with the increase ofconcentration of oleic acid. But the increasing will no longer accelerate dispersion of particles once it isabove a certain value. It is obvious that oleic acid has completely different effects on the dispersion ofcalcium carbonate in water and kerosene. It is special that oleic acid makes the dispersion of talcum inkerosene change periodically with the increase of concentration of oleic acid.From comparing the effects of oleic acid on dispersion of the two kinds of particles in differentmedia, it is known that sufficient oleic acid will improve the lipophilicity of calcium carbonate. Inwater and kerosene, its effect on dispersion of calcium carbonate is just opposite. Calcium carbonateparticles would be dispersed well in water if they were dispersed badly in kerosene, and vice versa.That is to say, they have the relation of growth and decline. However, its effect on dispersion of talcumin water and kerosene has no corresponding relation. In ethanol, oleic acid has no distinct effect on thedispersion of the two kinds of particles.Oleic acid influences dispersion-aggregation of particles mainly by surface properties, mediumproperties and the form of interaction between particle surface and oleic acid. The effect of oleic acidon dispersion and aggregation of particles can be explained by the following structural models ofadsorption layer (fig. 3). In water, randomly-moved oleic acid molecules at low concentration formpartial monomolecular layer in which hydrophobic groups face aqueous phase through physical OIchemical adsorption on the surface of particles (fig. 3(b))， which leads to the increasing ofhydrophobicity on the surface of particles. The water molecules around the particles are liable to pushaside those molecules different from them. To minimize the interface between solid and liquid and to场中国煤化工FHCNMHG(b)(C)(d)心(1)Fig.3. Adsorption models of oleic acid on the surface of particles in water and kerosene. (a), Natural state;(b) single-layer adsorption; (c) double layer adsorption; (d) lttle micelles; (e) micelles; (f) reversal micelles.1378Chinese Science BulletinVol.45 No. 15August 2000NOTESdiminish free energy of system, hydrophobic particles have to get nearer, which results in aggregation.When the concentration surpasses a certain value, the second adsorption layer or lttle micellesl8] (fig.3(d)) will form because of hydrophobic interaction between molecules. In this layer, the hydrophilicgroups face to aqueous phase (fig. 3(c)), so the surfaces of particles become hydrophilic again and theparticles could be dispersed. When the concentration becomes further bigger, the molecules of oleicacid will form micelles in water, too. Hydrophilic groups facing aqueous phase interact with watermolecules, which leads to polar surface. However, hydrophobic groups avoid contacting with water andthus form nonpolar core (fig. 3(e)). In this condition, oleic acid no longer contributes to dispersion-aggregation of particles. The free energy of forming standard oleic acid micelles in water can brepresented as follows:△G= 2.303 RT log(CMC/W),where CMC is the critical micelle concentration, W is the number of mole per liter pure water at thetemperature of T.Ethanol molecules have both polar hydroxy and nonpolar alkyl, so oleic acid has good intermisci-bility with ethanol. No matter how particles interact with oleic acid (either nonpolar or polar groups ofoleic acid facing ethanol), the particle surfaces have little difference for ethanol around them. That iswhy oleic acid has no obvious influence on wettability and dispersion-aggregation of particles.In kerosene, polar groups of oleic acid form a monomolecular layer in which hydrophobic groupsface kerosene phase on the surface of particles of calcium carbonate (fig. 3(b)), which makes thesurface of particles hydrophobic and the particles can be dispersed. When the concentration of oleicacid is further increased, reversal micelles with cores of polar groups come into being (fig. 3(f)) and theoleic acid will no longer affect the dispersion of calcium carbonate. The shape and size of reversalmicelles are mainly decided by concentration of oleic acid, solvent properties and temperature. Thenumber of reversal micelles is far less than that of micelles in water. The free energy of formingstandard oleic acid reversal micelles can be represented by△G=-2.303RT log Bβ,(3)where β, is the total average constant of forming micelles.In kerosene, oleic acid contributes little to the change of wetting contact angle of talcum particles,but it does affect dispersion-aggregation of the particles periodically. The special phenomenon cannotbe explained reasonably, so further research remains to be done.3 ConclusionThe dispersion of fine particles in water, ethanol and kerosene complies with the principle ofcompatibility of polarity. The particles will be dispersed well when the polarity of particle surface issimilar to that of liquid media. Instead, in ethanol, the concept of hydrophobic interaction seemsinvalid.Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No.59374031).References1. Ren, J., The dispersing action of Na2SiO3 in the selective aggregation of fine hematite and silicate mineral, Mining andMetallurgical Engineering (in Chinese), 1991, 11(3): 29.Kobayashi, T.. Paint appearance and pigment dispersion, Surface Science (in Japanese), 1995, 16(11): 705.3. Ikeda, S., Recent development in pigment dispersion, Journal of the Japan Society of Color Material (in Japanese), 1995,68(1):2.Kobayashi, T, Pigment dispersion in water borne paints, Journal of the Japan Society of Color Material (in Japanese),1995, 68(6): 362.5. Kitahara, A.. Stability of dispersion in polar media, Adv. inCrllaid.1992, 38: 1.6. Napper, P. L. L, Polyer Stabilization of Colliodal Dispers中国煤化工1983, 98“-10.7. Cheng, C. x., Surface Physical Chemistry (in Chinese)| YHCNM HGLiterature Press, 1995, 216”8. Koopal,L. K., Gu Xiren, Lu, S. C, Some Advancements in Theory of Physical Chemistry on Floatation, ChemistryCircular (in Chinese), 1995( 10): 19.(Received January 19, 2000)Chinese'i BlletinVol.45 No. 15August 20001379