Page 198 - Introduction to Colloid and Surface Chemistry

Charged interfaces 187

(5.3 -pAg) x 59 mV
•s
\
+50
\ \

I ° 4 \6 8 10 12 14
2
jg v>
"c \
£ \ pAg
£ -50
\\
'
\ X^ t ,•*
\ ^•»-. •^l .iro..!! — -"-
V
-100
90
Figure 7.4 Zeta potentials for silver iodide sols prepared by simple mixing . £
calculated from Smoluchowski equation (By courtesy ofElsevier Publishing Company)

identified with i/r d and making the assumptions outlined in the last
paragraph,

d(pAg)
f-»0
= -59- mV (7.20)
C,+C 2
Values of calculated from double-layer capacities

using the above expression seem to be, at least semiquantitatively, in
accord with the experimental values (from electrophoretic measure-
91
ments) , which suggests that the assumptions involved may be valid.
However, this is a topic which has not yet been subjected to sufficient
systematic investigation for firm conclusions to be drawn.
From the discussion so far it can be appreciated that the Stern
model of the electric double layer presents only a rough picture of
what is undoubtedly a most complex situation. Nevertheless, it
provides a good basis for interpretating, at least semiquantitatively,
most experimental observations connected with electric double layer
phenomena. In particular, it helps to account for the magnitude of