Stabilisation of an amphoteric latex by hydration forces
The colloidal stability of an amphoteric polystyrene latex has been studied using a low-angle light scattering technique (nephelometry). Measurements were carried out at different pH values and NaCl concentrations. The results show a behaviour in agreement with DLVO theory when the pH of the medium is below the isoelectric point of the latex. However, at a pH above the isoelectric point, the latex is completely stable even at high electrolyte concentrations. Electrophoretic mobility measurements indicate that the stability at basic pH values is not due to electrostatic repulsion. This stability could be explained by means of repulsive interactions due to the structure of water molecules (that accompany hydrated cations) around the hydrophilic latex surface. These interactions are the so-called hydration forces, which have been observed in some other systems like proteins, lipids, DNA, etc.
KeywordsAmphoteric latex Stability ratio Hydration forces Electrophoretic mobility
Unable to display preview. Download preview PDF.