I would like to know if there are any works describing the variation of ionic strength for alkali silicate solutions at high solid concentration (i.e. >50%) i.e. when the suspension turns from liquid like to honey like consistence. If I have a suspension of colloidal particles in a diluted waterglass solution, the the zeta potential and Debye length can be calculated by the DLVO theory in diluted state, but what happens when the viscosity of the system increase from liquid to honey-like state? I suppose the mobility of ionic species drops due ionic crowding (electroviscous effects)? how can I quantify this phenomenon? how does the ionic double layer change?
You work with concentrated suspensions. In other words, with pastes. As you yourself write there does not work the theory of DLFO, the ionic strength does not change. It depends on the ion concentration and the ion charge. According to the DLFO theory, there are two minima on the potential curve of the interaction of the particles of the disperse phase. The condensation-crystallization structure formation, corresponding to coagulation in the first minimum, occurs by direct chemical interaction between the particles. You have a structure that corresponds to the second minimum on the potential curve of the interaction of the particles of the disperse phase through the interlayers of the dispersion medium. Your systems are better researched by methods of rheology. Electrophoresis in such systems will occur, but there is no theory for such systems. Hence, it is impossible to determine exactly the zeta potential. The theory of a double electric layer is also complicated.
Dear Luca,
Strictly, the ionic strength is not going to change with the solid fraction, as it is rigorously defined through the ion concentrations unperturbed by the surfaces. Yet, of course, the ion concentration per unit volume of liquid will increase.
The apparent viscosity change shouldn’t affect directly the ion mobility. In such a suspension, what matters the most is the surface conductivity (and respectively, the surface mobility).
I would recommend the works of Dukhin and Shilov (they are great!):
doi/abs/10.1021/la991305y,
doi/abs/10.1021/la981382d,
and check also for their books. You may also consider a description of your system as a porous medium.
The final question (how does the EDL change) - when the distance between the particles becomes comparable to the Debye length, the surface conductivity changes a lot due to the overlap between the EDLs of the particles; how precisely it changes depends on the adsorption isotherm of the ions (the classical two regimes are constant potential and constant charge, but generally you have to consider charge regulation, you can google that out).
Dear Radomir,
Sorry for the late reply, Thank you very much for your suggestions and for the two works you recommended.
Best regards
Luca
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry