ABSTRACT
K, α, and β ....................................................................................................99 2.4 Hofmeister Effect on cmc of Ionic Surfactants and Disjoining Pressure in Foam Films .... 100
2.4.1 Effect of Counterion on the cmc of Ionic Surfactants .............................................. 100 2.4.2 Ion-Specic Effect on the Disjoining Pressure of Foam Films Stabilized with
Ionic Surfactants ....................................................................................................... 106
In 1887, F. Hofmeister published an article [1] in which the precipitation efciency of different salts on proteins was investigated. Hofmeister found that the critical electrolyte concentration for protein precipitation exhibited regularity and ordered the ions by their efciency; nowadays, this ordering is called the Hofmeister series. For a series of salts with the same cation and different anions, the precipitation efciency increases (i.e., the precipitation concentration decreases) in the following sequence [2] (“Ac−” is acetate ion; F− was added by us):
Ac F OH Cl Br NO BF I ClO− − − − − − − − −> > > > > > > >3 4 4 (2.1)
Similarly, for salts sharing the same anion, the Hofmeister series for the cations reads [2]:
Li Na K Rb Cs NH NMe+ + + + + + +< < < < < <4 4 (2.2)
(“Me” stands for methyl group). These ion sequences in series (Equations 2.1 and 2.2) were found to be approximately independent of the protein, although the direction of the effect depends [3,4], among other factors, on the sign of the protein’s net charge (in Hofmeister experiments, proteins were negatively charged). Since the work of Hofmeister, a large number of experimental studies have demonstrated similar regularities in various phenomena. The interested reader can nd a collection of articles on the Hofmeister effect and related phenomena in two special issues of Current Opinion in Colloid and Interface Science in 2004 [5] and in perhaps the only book dedicated to this topic, Specific Ion Effects [2].
