Study On The Zeta Potential And Stability Of Several Typical Dispersion Systems

Colloid is a highly distributed multiphase system and belongs to thermodynamical unstable system. Urea-formaldehyde resin adhesive(UF), silica sol and the "cement-superplasticizers" were three typical colloidal dispersion systems and have a wide use for application. This thesis has studied the electrical properties, micellar structure and rheological behavior of the above systems in terms of colloid chemistry, and discussed the relationship between the electrochemical properties and dispersion stability of the systems.The gel of UF is the aggregation of colloidal particles and the development to the aggregate structure. The phenomenon of UF become turbid during storage is the process of particles from small to big. According to the study, The average Zeta potential of UF colloidal particles is about-32.5mV at a pH value of 8.0 and they exist in monodisperse state. Electrolyte and pH values have a significant effect on the stability of the UF. The Zeta potential decreased rapidly with the addition of ferrous ions or hydrogen peroxide, which causes a decrease of expulsion potential, the aggregating of colloidal particles, the viscosity increases and eventually gel. However, the influence of hydrogen peroxide on Zeta potential and the viscosityηof UF colloidal particles are much less than those of the ferrous ion. pH value plays an important role in keeping the stability of the colloidal particles. The system has the highest Zeta potential at pH≈9. when pH>9 the absolute values of Zeta potential decrease more significantly. Combined with the gel properties and electrical properties of UF adhesive, the double-layer structure model and the stability mechanism of UF adhesive have been discussed by double-layer theory.In silica sol system the relationship between Zeta potential and dispersion stability are similar to UF system. Mutual exclusion of charged particles increase the stability of the dispersion, and the stability is proportional to the value of Zeta potential. The results show that, the Zeta potential of silica sol is 0 when pH= 1.8, the gel time is shorter, the viscosity is very high; when pH<1.8, Zeta potential is positive, the gel time is longer, the viscosity is low; while pH between 1.8 and 4, Zeta potential is negative, the viscosity decreased gradually. In addition, the temperature, water amount, etc. also have important impact on its stability. The temperature is higher, the gel time of silicon sol is shorter under the same pH.In the system of the "cement-water reducer", the law of Zeta potential affect its stability is different to the two system referred above. The saturation adsorption spot and the saturated adsorption capacity of the naphthalene superplasticizer and Calcium lingosulfonate superplasticizer are larger than those of the polycarboxylate superplasticizer. The absolute value of Zeta potential on cement particles surface is larger at beginning than naphthalene superplasticizer and Calcium lingosulfonate superplasticizer, and the values decline obviously with time, the fluidity loss of cement paste is larger. While the absolute value of zeta potential of the poly carboxylate superplasticizer is small, but the system is stable, the fluidity loss of cement paste was lower than the other superplasticizers referred above.