1 research outputs found
Probing the Surface Properties of Gold at Low Electrolyte Concentration
Using
the surface force balance (SFB), we studied the surface properties
of gold in aqueous solution with low electrolyte concentration (∼10<sup>–5</sup> M and pH = 5.8), i.e., water with no added salt,
by directly measuring the interaction between an ultrasmooth gold
surface (ca. 0.2 nm rms roughness) and a mica surface. Under these
conditions, specific adsorption of ions is minimized and its influence
on the surface charge and surface potential of gold is markedly reduced.
At open circuit potential, the electrostatic interaction between gold
and mica was purely attractive and gold was found to be positively
charged. This was further confirmed by force measurements against
a positively charged surface, poly-l-lysine coated mica.
Successive force measurements unambiguously showed that once gold
and mica reach contact all counterions are expelled from the gap,
confirming that at contact the surface charge of gold is equal and
opposite in charge to that of mica. Further analysis of adhesion energy
between the surfaces indicated that adhesion is mostly governed by
vdW dispersion force and to a lesser extent by electrostatic interaction.
Force measurements under external applied potentials showed that the
gold–mica interaction can be regulated as a function of applied
potential even at low electrolyte concentration. The gold–mica
interaction was described very precisely by the nonlinearized Poisson–Boltzmann
(PB) equation, where one of the surfaces is at constant charge, i.e.,
mica, and the other, i.e., gold, is at constant potential. Consequently,
the gold surface potential could be determined accurately both at
open circuit potential (OCP) and under different applied potentials.
Using the obtained surface potentials, we were able to derive fundamental
characteristics of the gold surface, e.g., its surface charge density
and potential of zero charge (PZC), at very low electrolyte concentration