Critical coagulation concentration DLVO theory

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

In summary High surface potentials stabilize colloidal systems. The addition of inert salt leads to stronger screening and destabilizes the system. The point at which rapid coagulation (case b) sets in is defined as the critical coagulation concentration (ccc). One key result of DLVO theory is the explanation of the Schultze-Hardy rule, which states that the ccc depends on the counterion valency z like 1/z . 

This expression is the principal result of DLVO theory. The steep r dependence of the critical coagulation concentration has been observed experimentally for strongly charged surfaces and is commonly known as the Schulze-Hardy rule. In the case of weakly charged surfaces, a less steep dependence of the critical coagulation concentration on the valence (z" ) is observed. In fact, it was the empirical dependence of the c.c.c. on the valence established in the course of experimental studies on coagulation that inspired the development of DLVO theory. 

Critical coagulation concentration Yes (series of experiments adding salts in colloidal dispersions until coagulation occurs) Yes (DLVO theory) Stability of colloids... 

The SH rule states that the critical coagulation concentration (CCC) is strongly dependent on the valency of the counter-ion and, in combination with the DLVO theory, it is found that CCC is inversely proportional to the sixth power of the valency of the counter-ion. 

The critical coagulation concentration can be obtained by the DLVO theory and is found to be inversely proportional to the sixth power of the counterion valency, in agreement with the Schulze-Hardy rale. 

According to the DLVO theory, the critical concentration of a coagulating ion should be independent of the particle size of the colloid, but Wiese and Healy (279) have shown that by further reflnement of the theory, taking into account both primary and secondary minima, colloid stability increases with particle size and reaches a maximum and then decreases. Such behavior has never been noted in the case of colloidal silicas with particle sizes in the usual range of 5-100 nm. 

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