Hostname: page-component-78c5997874-j824f Total loading time: 0 Render date: 2024-11-19T08:30:17.252Z Has data issue: false hasContentIssue false

Scanning Probe Characterization of Localized pH Changes on a Sapphire Surface in the Presence of an Applied Field

Published online by Cambridge University Press:  01 February 2011

Joseph W. Bullard
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 12–011 Cambridge, MA 02139
Ryan J. Kershner
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 12–011 Cambridge, MA 02139
Michael J. Cima
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 12–011 Cambridge, MA 02139
Get access

Abstract

Single crystal sapphire substrates were lithographically patterned with a system of parallel platinum electrodes, which were used to manipulate 1.58μm silica particles inplane, in the presence of an aqueous solution. Observation of the motion of these particles revealed the adhesion of some of them to the sapphire surface near the platinum working electrode, even in the range of pH where the zeta potentials of silica and sapphire are of the same sign. This phenomenon suggests the existence of localized differences in pH, attributable to the presence of potential determining ions produced in the faradaic processes occurring at the electrodes during the electrophoretic manipulation of silica particles. Atomic force microscopy (AFM) was used to corroborate this hypothesis, measuring the forces between a silica particle and a sapphire substrate in the presence of an applied field. The resultant force-distance curves demonstrate a change in the interaction forces between particle and substrate as a function of distance from the electrode. Variations in this interaction correspond to localized differences in the zeta potential of the substrate, which, in turn, are related to localized differences in pH. Quantification of these spatial variations in pH as a function of time yields further information about the diffusion of these faradaically produced potential determining ions across the substrate.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1) Hermanson, K.D., Lumsdon, S.O., Williams, J.P., Kaler, E.W., and Velev, O.D., Science, 294 1082, 2001 Google Scholar
2) Hayward, R.C., Saville, D.A., and Aksay, I.A., Nature, 404 56, 2000 Google Scholar
3) Velev, O.D., Kaler, E.W., Langmuir, 15 3693, 1999 Google Scholar
4) Boccaccini, A.R. and Zhitomirsky, I., Curr. Opin. Solid St. M. 6 251 (2002)Google Scholar
5) Van der Biest, O.O. and Vandeperre, L.J., Annu. Rev. Mater. Sci. 29 327 (1999)Google Scholar
6) Verwey, E.J.W. and Overbeek, J.T.G., Trans. Faraday Soc., 36 180, 1940 Google Scholar
7) Sarkar, P. and Nicholson, P.S., J. Am. Ceram. Soc., 79 1987, 1996 Google Scholar
8) Hunter, R.J., Foundations of Colloid Science, pp 581637, Oxford University Press, Oxford (2001)Google Scholar
9) Kershner, R.J. and Cima, M.J., Proc. Electrochem Soc., 2002–21 1 (2002)Google Scholar
10) Kershner, R.J., Bullard, J.W., and Cima, M.J., Submitted to J Colloid Interf Sci (December, 2003)Google Scholar