TITANIA NANOPARTICLES: A PROPOSED MECHANISM FOR THE COLLOIDAL SYSTEM PEPTIZATION
ABSTRACT:
When titania particles are created via sol-gel method, large particles that are visible to the naked eye are formed. In the presence of acid, in this case nitric acid, the large particles are peptized over time. This paper proposes a mechanism for this peptization process. The mechanism is: during peptization, small 10 to 20 nm "primary particles" break off from the large agglomerates in the system, creating smaller average particle sizes within the system. To test this hypothesis, size distribution measurements are taken of the solution using a light scattering machine that has four different methods for obtaining size distributions: CONTIN, double exponential, exponential sampling, and least squares mean multipass. The presence of two modes, one large and one small (within the primary particle range), in each of the methods during peptization would be consistent with the proposed mechanism. Measurements were initially taken during the peptization process at a measurement angle of 90 degrees. Bimodal distributions were present at this angle for all methods. Yet, this bimodality was not observed for all times during peptization. It was found, by measuring peptized solutions that are known to have two modes, that this bimodality can be seen by light scattering at measurement angles greater than or equal to 120 degrees.