Stability of Charged Colloids

Many colloidal systems and in particular biological systems contain oligomers and macromolecules that can carry a charge. A typical colloidal solution 

In practice, M or X are not evenly distributed but are influenced by the presence of P, the colloidal species and the more colloid or macroions present and the higher the charge they carry z, then the greater the unevenness of the distribution of the M ion. In practice, the membrane itself generally becomes polarized because of the macroions on one side and this is similar to the natural membranes in living systems. In dialysis, the Donnan equilibrium allows the removal of ions and traces of impurities. This is a fascinating topic that we do not have space to explore in detail in this monograph. 

---

In tills section we focus on tlie tlieory of stability of charged colloids. In section C2.6.5.1 it is shown how particles can be made to aggregate by adding sufficient electrolyte. The associated aggregation kinetics are discussed in section C2.6.5.2, and tlie stmcture of tlie aggregates in section C2.6.5.3. For more details, see tlie recent reviews [53, 54 and 55], or tlie colloid science textbooks [33, 39]. 

When two charged particles immersed in an electrolyte approach each other, the overlap of their ionic atmospheres (the double layers) generates a repulsive force. The traditional Derjaguin—Landau—Verwey—Overbeek (DLVO) theory assumes that the stability of charged colloids is a consequence of a balance between this double layer repulsion and the attractive van der Waals interactions.1... 

The concentration and nature of the electrolyte also has a significant impact on the stability of charged colloid dispersions. This was discussed in Section 3.3.2, where the concept of electric double layers was introduced. The electric double layer results from the atmosphere of counterions around a charged colloid particle. The decay of the potential in an electric double layer is governed by the Debye screening length, which is dependent on electrolyte concentration (Eq. 3.8). In the section that follows, the stability of charged colloids is analysed in terms of the balance between the electrostatic (repulsive) forces between double layers and the (predominantly attractive) van der Waals forces. 

---