W. Richard Bowen and Nidal Hilal 4

3.6 EFFECT OF LOADINg FORCE ON PARTICLE–BUBBLE INTERACTIONs 97
using SDS and DTAB. In both cases probes became attached to the CGA
surfaces. However, when approaching SDS CGAs, a repulsive force was
observed prior to contact. This force was not observed with the DTAB
aphrons. The difference is most likely due to charge repulsion effects,
which is due to the interaction between the negatively charged glass surface
and the negatively charged SDS. In the case of DTAB, which contains
a positive charge in solution, only attractive forces are observed prior to
contact. When silica was allowed to interact with CGAs in bulk flotation
experiments, the silica was found to separate with the CGA fraction
when using DTAB to create the CGAs, but a much smaller fraction was
recovered when using SDS. The attachment of silica to CGAs in solution
was modulated by the charge interactions between silica and the CGAs
in solution, with repulsive charges preventing the attachment of the particles
to SDS CGAs in solution.
3.6 EFFECt oF LoADInG ForCE on
PArtICLE–BuBBLE IntErACtIonS
As has been seen above in the work by Preuss and Butt, in the presence
of surfactants [36, 39, 48], sometimes a threshold force is required to form a
TPC contact, but there are likely to be other effects of the loading force on
particle–bubble interactions. As the loading force is increased, deformation
of the bubble would be expected to increase, particularly if the TPC line
does not move over the particle surface. For other deformable surfaces,
such as soft polymer interfaces, the maximum loading force reached has
been observed to have a positive effect on the adhesion force [64]. This is
not surprising, as the area of contact between the probe and the surface
will increase as the surface becomes increasingly deformed. At small loading
forces, where the force F