Izlaganje sa skupa

Specific Chemical Interaction Affecting the Stability of Dispersed Systems

W. Stumm ; Laboratory of Applied Chemistry, Harvard University, Cambridge, Massachusetts, 02138, U.S.A.
C. P. Huang ; Laboratory of Applied Chemistry, Harvard University, Cambridge, Massachusetts, 02138, U.S.A.
S. R. Jenkins ; Laboratory of Applied Chemistry, Harvard University, Cambridge, Massachusetts, 02138, U.S.A.

Sažetak

1) Sorbable species may destabilize colloids at much lower
concentrations than nonsorbable ions. The VODL double layer
model neglects the dominating role that chemical forces play in
causing adsorption and is restricted in its application to lyophilic
colloids and simple electrolytes.
2) The distribution of ions in an oxide-electrolyte interface
can be evaluated from alkalimetric and acidimetric titration curves
of aqueous dispersions of these oxides.
3) A comparison of the differential capacity of the interface
at an oxide-electrolyte interface with that of Hg or Ag! shows
much larger capacitance values for the hydrophilic strongly
aquated oxide surface than for the more hydrophobic surface of
Hg and Ag!. The difference is caused primarily by the strongly
structured, extensively hydrogen-bonded and chemisorbed water
layer immediately adjacent to the solid oxide surface. Ions tend
strongly to penetrate (specific sorption) into the compact part of
the double layer adjoining the oxide surface, and may thus exert
a marked effect on the surface chemical properties beyond those
observed by a mere compaction of the diffuse part of the double
layer.
4) Association of oxide surfaces with H+, and other cations
can, similar as with polyelectrolytes, be characterized by acidity
and stability constants. The latter constants can be expressed as
intrinsic constants if they are corrected to a hypothetically
chargeless surface. The specificity of the interaction with H+ and
cations can be understood by considering simple electrostatic
models. This association of oxide surfaces with cations can be
used to explain the effect of cations such as Ca2+ on the stability
of hydrous oxide colloids, and on the deposition of Mn02 particles
on sand surfa ces.
The extent to which a coagulant species is specifically
adsorbed is reflected in the c. c. c. necessary to produce a ggregation.
When the specifically adsorbed species and the colloid are of
opposite charge, the sorbed species act to reduce the surface charge
of the colloid. The destabilizing agent can, in some cases, even
reverse the colloid charge and restabilization will occur.
5) Specific cation interactions as described here represent a
basis of related ion specific processes, such as the behavior of
ion selective glass or membrane electrodes; the selective ion
permeability of cell membranes and potential generating mechanisms
in the living cell.

Ključne riječi

Hrčak ID:

197549

URI

https://hrcak.srce.hr/197549

Datum izdavanja:

20.8.1970.

Posjeta: 1.678 *