B. Jachimska, Z Adamczyk /Joumal of the European Ceramic Society 27(2007)2209-2215 Analogous measurements of the viscosity of the anionic polyelectrolyte-PSS used to enhance the stability of zirconia suspensions showed that the slope of the intrinsic viscosity vs. volume fraction attained values as high as 50 for 1=5 X 10-M. This effect was interpreted in terms of the flexible rod model According to this model, for higher electrolyte concentration, the PSS molecule assumes the shape of a semi circle or sinusoidal curve rather than a random coil structure as often suggested. It was further confirmed experimentally that adsorption of PSS on zirconia decreased significantly the negative zeta poten- tial but did not influence too significantly the dispersion degree of zirconia particles. Also the viscosity of the zirconia suspen- sion in PSS solutions was found equal to the product of the viscosity of zirconia dispersed in PSS free solution of the same composition and the viscosity of Pss al Fig 8. The dependence of the intrinsic viscosity Inl=ns/n ZrO2 vS the volume raction v= wpssPp pH 10, 1=5x 10-3M. ()ZrO2, the line denotes the Acknowledgements near regression [nI=1+4.5dv21o, (curve 2):(O)ZrO2+PSS mixture, the solid line denoted the product of intrinsic viscosities [n]=[ o, +Inlpss (1+4.5V2o,)+(1+50vgs)( curve 1) This work was supported by MNiS W Grant 4T08B 03425 help of Ms K. Kusak in perfo ormins penitents conia did not increase too significantly the dispersion degree of kindly acknowledged. aggregates. This is evident from the particle size measurements showing that the average size of zirconia particles dispersed in References PSS(at pH 7.4)was 0.56 um, which does not differ much from the value observed in PSS free solutions. The limited influence of 1. Liu, D M, Ceram. Int, 2000, 26, 279 2. Baklouti, S. M., Romdhane, R. B, Boufi, Pagnoux, S C. Chartier, Tand PSS on the dispersion degree of zirconia also was confirmed by Baumard. J F. J. Eur. Ceram. Sci., 2003, 23, 905. the viscosity measurements whose results are shown in Fig 8. As 3. Ewais, E, Zaman, A. A and Sigmund, W, J. Eur Ceram. Sci., 2002, 22, can be seen, the dependence of the intrinsic viscosity of zirconia 2805 dispersed in PSS solution(variable polymer concentration from 4 Decher, G,Multilayer Thin Films.Wiley-VCH, 2002. 350 ppm to 2000 ppm, pH 10, 1=5 x 10-3 M)on the volume 5. Fengqiu, T, Xiaoxian, H, Yufeng, Z. and Jingkun, G, Ceram. Int, 2000, fraction solid can well be fitted by a line with the slope being the 6. Johnson, S. B. Franks, G. V, Scales, P. J, Boder, D. V and Healy, T.W. product of the viscosity of zirconia dispersed in PSS free solution IntJ. Miner: Process. 2000. 58. 267. of pss alone. henc 7. Picon, C. and Maccauro, G. Biomaterials, 1999, 20. 1 our results seem to confirm the effective medium hypothesis. 8. Adamczyk, Z, Jachimska, B and Kolasiniska, M, J. Colloid Interface Sci according to which the relative viscosity of a suspension having 9. Okada, K and Nagase, Y,. Chem. Eng. Jpn., 2000, 33, 168 the solid concentration v, v2(where v, is the volume 10. Atkins, A Physical Chemistry. Oxford University Press, Oxford, 1994, p fraction of zirconia and v, is the volume fraction of Pss) equals to the product of relative viscosities n(v)i(v,). 11. Adamczyk, Z, Zembala, M, Warszynski, P and Jachimska, B, Langmuir, 2004,20,10517 4. Concluding remarks 12. Hunter, R, Foundations of Colloid Science. Oxford, 2001 13. Crucean, E. Rand. B and Brit, T.J., Ceram. Soc., 1979. 78, 96. 14. Kosmulski, M, Che. Properties Mater: Surf: Surf. Sci. Ser, 2001, 102 It has been demonstrated experimentally that the relative vis- 15. Masiliyah, J H, Neale, G, Malysa, K and van de Ven, T.G.M, Chem. cosity of dilute zirconia suspensions increased more rapid Emg.Sci,1987,42,245 with the volume fraction that the Einstein formula predicted. 16. Honig, E P Punt, W.F. J and Offermans, P H.G.,J. Colloid Interface Sc This discrepancy could not be explained in terms of the pri- 17. Adamczyk, Z, Siwek, B. and Zembala, M, Bull. Pol. Acad. Chem., 2000, mary electroviscous effect because of small thickness of the electric double-layer. As a plausible explanation the presence of 18 Laven, J and Stein, H N, J. Colloid Interface Sci., 2001, 238.8 aggregates in the zirconia suspension was given, which were 19. Brenner, H, Int J Multiphase Flow, 1974,1, 195 composed of primary particles of the size ca. 200 nm. The 20. Greenwood, R, Luckham, P F and Gregory, T.J. Colloid Interface Sc hypothesis of the presence of aggregates was also confirmed 21. Stoll. s and chodanowski p Macromolecules, 2002. 35.9556 by the SEM. The viscosity measurements allowed one to deter- 22. Pal, R, Rheology of emulsions containing polymeric liquids In Encyclop mine the averaged solid content in these aggregates, which was dia of Emulsion Technology, Vol. 4, ed P. Becher. Marcel Dekker, Newyork, found close to 0.45 Basel, Hong Kong, 1996.B. Jachimska, Z. Adamczyk / Journal of the European Ceramic Society 27 (2007) 2209–2215 2215 Fig. 8. The dependence of the intrinsic viscosity [η] = ηs/η ZrO2 vs. the volume fraction ΦV = wρsus/ρp, pH 10, I = 5 × 10−3 M. () ZrO2, the line denotes the linear regression [η] = 1 + 4.5 ΦVZrO2 (curve 2); () ZrO2 + PSS mixture, the solid line denoted the product of intrinsic viscosities [η] = [η]ZrO2 + [η]PSS = (1 + 4.5 ΦVZrO2 ) + (1 + 50 ΦVPSS ) (curve 1). conia did not increase too significantly the dispersion degree of aggregates. This is evident from the particle size measurements showing that the average size of zirconia particles dispersed in PSS (at pH 7.4) was 0.56 m, which does not differ much from the value observed in PSS free solutions. The limited influence of PSS on the dispersion degree of zirconia also was confirmed by the viscosity measurements whose results are shown in Fig. 8. As can be seen, the dependence of the intrinsic viscosity of zirconia dispersed in PSS solution (variable polymer concentration from 350 ppm to 2000 ppm, pH 10, I = 5 × 10−3 M) on the volume fraction solid can well be fitted by a line with the slope being the product of the viscosity of zirconia dispersed in PSS free solution of the same composition and the viscosity of PSS alone. Hence, our results seem to confirm the effective medium hypothesis22 according to which the relative viscosity of a suspension having the solid concentration ΦV1 + ΦV2 (where ΦV1 is the volume fraction of zirconia and ΦV2 is the volume fraction of PSS) equals to the product of relative viscosities ¯η(ΦV1 )¯η(ΦV2 ). 4. Concluding remarks It has been demonstrated experimentally that the relative vis￾cosity of dilute zirconia suspensions increased more rapidly with the volume fraction that the Einstein formula predicted. This discrepancy could not be explained in terms of the pri￾mary electroviscous effect because of small thickness of the electric double-layer. As a plausible explanation the presence of aggregates in the zirconia suspension was given, which were composed of primary particles of the size ca. 200 nm. The hypothesis of the presence of aggregates was also confirmed by the SEM. The viscosity measurements allowed one to deter￾mine the averaged solid content in these aggregates, which was found close to 0.45. Analogous measurements of the viscosity of the anionic polyelectrolyte-PSS used to enhance the stability of zirconia suspensions showed that the slope of the intrinsic viscosity vs. volume fraction attained values as high as 50 for I = 5 × 10−3 M. This effect was interpreted in terms of the flexible rod model. According to this model, for higher electrolyte concentration, the PSS molecule assumes the shape of a semi circle or sinusoidal curve rather than a random coil structure as often suggested. It was further confirmed experimentally that adsorption of PSS on zirconia decreased significantly the negative zeta poten￾tial but did not influence too significantly the dispersion degree of zirconia particles. Also the viscosity of the zirconia suspen￾sion in PSS solutions was found equal to the product of the viscosity of zirconia dispersed in PSS free solution of the same composition and the viscosity of PSS alone. Acknowledgements This work was supported by MNiSW Grant 4T08B 03425. The help of Ms. K. Kusak in performing the experiments is kindly acknowledged. References 1. Liu, D. M., Ceram. Int., 2000, 26, 279. 2. Baklouti, S. M., Romdhane, R. B., Boufi, Pagnoux, S. C., Chartier, T. and Baumard, J. F., J. Eur. Ceram. Sci., 2003, 23, 905. 3. Ewais, E., Zaman, A. A. and Sigmund, W., J. Eur. Ceram. Sci., 2002, 22, 2805. 4. Decher, G., Multilayer Thin Films. Wiley-VCH, 2002. 5. Fengqiu, T., Xiaoxian, H., Yufeng, Z. and Jingkun, G., Ceram. Int., 2000, 26, 93. 6. Johnson, S. B., Franks, G. V., Scales, P. J., Boder, D. V. and Healy, T. W., Int. J. Miner. Process., 2000, 58, 267. 7. Piconi, C. and Maccauro, G., Biomaterials, 1999, 20, 1. 8. Adamczyk, Z., Jachimska, B. and Kolasinska, M., ´ J. Colloid Interface Sci., 2004, 273, 668. 9. Okada, K. and Nagase, Y., J. Chem. Eng. Jpn., 2000, 33, 168. 10. Atkins, A., Physical Chemistry. Oxford University Press, Oxford, 1994, p. C18. 11. Adamczyk, Z., Zembala, M., Warszynski, P. and Jachimska, B., ´ Langmuir, 2004, 20, 10517. 12. Hunter, R., Foundations of Colloid Science. Oxford, 2001. 13. Crucean, E., Rand, B. and Brit, T. J., Ceram. Soc., 1979, 78, 96. 14. Kosmulski, M., Chem. Properties Mater. Surf.: Surf. Sci. Ser., 2001, 102. 15. Masiliyah, J. H., Neale, G., Malysa, K. and van de Ven, T. G. M., Chem. Eng. Sci., 1987, 42, 245. 16. Honig, E. P., Punt, W. F. J. and Offermans, P. H. G., J. Colloid Interface Sci., 1990, 134, 169. 17. Adamczyk, Z., Siwek, B. and Zembala, M., Bull. Pol. Acad. Chem., 2000, 48, 231. 18. Laven, J. and Stein, H. N., J. Colloid Interface Sci., 2001, 238, 8. 19. Brenner, H., Int. J. Multiphase Flow, 1974, 1, 195. 20. Greenwood, R., Luckham, P. F. and Gregory, T., J. Colloid Interface Sci., 1997, 191, 11. 21. Stoll, S. and Chodanowski, P., Macromolecules, 2002, 35, 9556. 22. Pal, R., Rheology of emulsions containing polymeric liquids. In Encyclope￾dia of Emulsion Technology, Vol. 4, ed. P. Becher. Marcel Dekker, Newyork, Basel, Hong Kong, 1996.