Slide 11 of 12
Notes:
We know that cationic starch electrosterically stabilizes most, if not all, anionic surfaces to aggregation or coalescence, even in high concentrations of salt. But an unusual thing that we observed was a long-range attractive snap-in only at high salt without engulfment of the probe. Much more work is needed to understand this phenomenon, but it suggests a depletion mechanism of the free polymer. The interfaces are now hydrophilic, so we don’t expect a hydrophobic effect, and the adlayers are both positive.
It is possible that there was a net charge reversal of only one interface as it is seen by the opposing adlayer which causes an electrostatic attraction. But in order to say anything with certainty, the adlayers still need to be characterized thoroughly. The future holds promising experiments that could determine what the minimum adlayer conditions for colloidal stability are, or why cationic starch seems not to inhibit air flotation while it is disastrous for oil-assisted agglomeration?