Page 229 - Introduction to Colloid and Surface Chemistry

218 Colloid stability

105
Table 8.3 Values of Hamaker constants
Material AH (microscopic) AH (macroscopic)

20
1(T J 10"
Water 3.3- 6.4 3.0- 6.1
Ionic crystals 15.8-41.8 5.8-11.8
Metals 7.6-15.9 22.1
Silica 50 8.6
Quartz 11.0-18.6 8.0- 8.8
Hydrocarbons 4.6-10 6.3
Polystyrene 6.2-16.8 5.6- 6.4

%
(a) (T)(T , (T
V_x < ».... / V^
|b|
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Figure 8,1

the interactions are particle-dispersion medium interactions, with
Hamaker constants A 13 and A 23. K particle 2 is brought close to
particle 1 (Figure 8.1b), dispersion medium must be displaced to the
position originally occupied by particle 2 and the above interactions
are replaced by particle-particle and dispersion medium-dispersion
medium interactions, with Hamaker constants A\ 2 and A 33. The
effective Hamaker constant is, therefore, given by

32 (8.11)

If the attractions between unlike phases is taken to be the geometric
mean of the attractions of each phase to itself (cf . equation 4.3) - i.e.

equation (8.11) becomes

^02 = (Aft - A£) (A£ - A&) (8.12)