This white paper presents four advanced rotor/stator technologies for ultra-high shear mixing of fine dispersions, emulsions and other applications beyond the capabilities of traditional single and multi-stage rotor/stator devices. These Ultra-High Shear Mixers are shown to effectively replace costly high pressure homogenization and colloid milling operations while delivering comparable levels of dispersion and particle size reduction.
Any high shear, high speed mixing operation — whether the process goal is straightforward dispersion, particle-size reduction or emulsification — generates a Gaussian distribution of results. The bottom-line objective is usually to produce the narrowest distribution possible with an equipment solution that meets both process and business needs. In some applications, engineers and scientists are more concerned with average particle size while others have strict standards pertaining to the largest particles that can be present in the suspension (for example, all particles must be under 2 microns). In reality, particle size profile is just one of many indicators of a good product. Depending on the end use, other properties like conductivity, stability, viscosity, thixotropy, yield stress, color, gloss, etc., whether directly or indirectly related to particle size, are also to be considered during equipment testing and selection.
The greatest extent of particle or droplet size reduction occurs within the first few passes through an inline rotor/stator mixer or the first few tank turnovers in a batch mixer set-up. This phenomenon is true for almost any dispersion or emulsion. Past this stage of sharp decrease in particle size, the distribution hovers at an equilibrium. Additional processing will gradually narrow the distribution curve, but extending the process for this purpose alone almost always amounts to a substantial waste of time and energy.