Ian Wark Research Institute,
University of South Australia, Mawson Lakes SA 5095 Australia.
Langmuir 16 ,1542-1552 (2000)
Abstract
The hypernetted chain (HNC) theory is used to compare
charge titration and zeta potential data for several colloids.
It is found that the HNC diffuse layer potential
is closer to the zeta potential than that calculated with the
traditional Poisson-Boltzmann (PB) approximation,
and hence the amount of counter-ion binding required
to bring the two into conformity is reduced.
Further improvement is obtained by using
an effective PB diffuse layer potential,
calculated from both the numerical HNC theory
and the analytic extended PB approximation.
The rationale for using the effective PB potential is that
the conversion from the measured electrophoretic mobility
to the zeta potential invokes the PB approximation.
In the case of silver iodide quantitative agreement
is obtained without any fitting parameters,
and it is concluded that no counter-ion binding occurs.
For the metal oxides analysed,
(titanium dioxide, aluminium oxide, and silicon dioxide),
the two measurements can only be reconciled by postulating
counter-ion binding or surface charge mobility.
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