Colloids, charged

The generation of colloidal charges in water.The theory of the diffuse electrical double-layer. The zeta potential. The flocculation of charged colloids. The interaction between two charged surfaces in water. Laboratory project on the use of microelectrophoresis to measure the zeta potential of a colloid. 

---

The influence of electrical charges on surfaces is very important to their physical chemistry. The Coulombic interaction between charged colloids is responsible for a myriad of behaviors from the formation of opals to the stability of biological cells. Although this is a broad subject involving both practical application and fundamental physics and chemistry, we must limit our discussion to those areas having direct implications for surface science. 

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

In electrophoresis, the motion of charged colloidal particles under the influence of an electric field is studied. For spherical particles, we can write... 

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]. 

For a more complete understanding of colloid stability, we need to address the kinetics of aggregation. The theory discussed here was developed to describe coagulation of charged colloids, but it does apply to other cases as well. First, we consider the case of so-called rapid coagulation, which means that two particles will aggregate as soon as they meet (at high salt concentration, for instance). This was considered by von Smoluchowski 1561 here we follow [39, 57]. 

Figure C2.6.9. Phase diagram of charged colloidal particles. The solid lines are predictions by Robbins et al [85]. Fluid phase (open circles), fee crystal (solid circles) and bee crystal (triangles). is tire interaction energy at tire...

Piazza R, Bellini T and Degiorgio V 1993 Equilibrium sedimentation profiles of screened charged colloids a test of the hard-sphere equation of state Rhys. Rev. Lett. 71 4267-70... 

Monovoukas Y and Cast A P 1989 The experimental phase diagram of charged colloidal suspensions J. Colloid Interface Sol. 128 533-48... 

Ueno, K. Kina, K. Colloid Titration—A Rapid Method for the Determination of Charged Colloid, /. Chem. Educ. 

Electrophoresis motion of charged colloidal particles immersed in a liquid driven by an electric field. 

An important reason for this lack of experimental work is that the zeta-potential cannot be easily determined independent of the electrophoretic mobility [284] however, in the case of proteins (as well as some other charged colloids), the intrinsic charge obtained by titration is a parameter that can be measured independent of the electrophoretic mobility. The charge obtained from electrophoretic measurements (i.e., the net charge) via the preceding theories is generally not the same as the charge obtained from titration (i.e., the in-... 

Stigter, D, The Charged Colloidal Cylinder with a Gouy Double Layer, Journal of Colloid and Interface Science 53, 296, 1975. 

Stigter, D, Electrophoresis of Highly Charged Colloidal Cylinders in Univalent Salt Solutions. 2. Random Orientation in External Field and Application to Polyelectrolytes, Journal of Physical Chemistry 82, 1424, 1978. 

The influence of interionic fores on ion mobilities is twofold. The electrophoretic effect (occurring also in the case of the electrophoretic motion of charged colloidal particles in an electric field, cf. p. 242) is caused by the simultaneous movement of the ion in the direction of the applied... 

This treatment process involves the use of chemical compounds to initiate a chemical reaction in the wastewater stream, which ends up neutralizing negatively charged colloids and thus, causing changes that would alter the nature of the wastewater, particularly to conform to the standard of wastewater discharge.4 The treatment process possesses an inherent disadvantage, especially net increase in the dissolved constituents of the wastewater, which can hinder reuse of the wastewater.2 Common chemical treatment processes are discussed below. 

The sorbents were hydrophobic Teflon, hydrophobic polystyrene (PS), and hydrophilic silica. These sorbents were negatively charged colloidal particles having smooth surfaces. In adition, PS particles at the surface of which oligomers (8-mers) of ethylene oxide ((EO)8) were grafted at a... 

Colloid stability in the Fe(III)(hydr)oxide-phosphate system. Surface complexation equilibria were used to calculate the concentration domains of positively charged and negatively charged colloids and of nearly uncharged phosphate surface complexes on FeOOH. 

C5. Cohen, E., Research on charged colloid generation, Wright-Patterson AFB, Aero Propulsion Lab. Final Rept. Contr. AF33(657)-10999. ASTIA Doc. AD 601, 390, NASA Rept. No. N64-27961 (1964). 

In the presence of colloidal solutions in contact with a liquid junction, anomalous liquid-junction potentials are often measured. This suspension or Palmarm effect [14] has not yet been satisfactorily explained. It is probably a Donnan-type potential with the electrically-charged colloidal species acting as indiffusible ions (cf. section 5.1.3). 

Stigter, D. (1977) Interactions of highly charged colloidal cylinders with applications to double stranded DNA. Biopolymers 16, 1435-1448. 

---