Emulsion rotor-stator systems

Colloid Mill Colloid mills are rotor-stator systems that can be used to reduce the particle size distribution of both liquid dispersions (emulsions) and solid dispersions (suspensions). The emulsion or suspension is pumped through a narrow gap that is formed by the rotating inner cone and the stationary outer cone. The width of the annulus can be adjusted by changing the relative position of the two cones. The principal size reduction in colloid mills is due to the high shear forces that are caused by the velocity difference between the rotor and the stator surfaces. To increase wall friction and reduce slip, surfaces are usually not smooth but are roughened or toothed, which, in turn, changes the flow conditions from laminar to turbulent, thereby increasing the shear forces in the annulus. 

Membrane emulsihcation has been recently proposed for the preparation of stable and uniform-sized microcapsules [27]. Membrane emulsihcation is a technology that allows to obtain uniform emulsions at low energy input compared to the emulsion prepared using high-pressure homogenizers and rotor/stator systems therefore, it is very useful for the preparation of emulsions containing labile compounds such as bioactive molecules sensihve to shear stress [28]. 

The stirrers are mainly of the flat-blade, disk, propeller, or turbine type [7.16]-[7.19]. Rotor-stator systems are also used as continuous mixers (Fig. 7.5). These machines are employed particularly if an emulsion or an emulsion-like product has to be produced (e.g., waterborne paints) [7.20]-[7.22]. 

Many types of emulsification equipment are widely appUed in industry, such as high pressure homogenizers and rotor-stator systems. In these machines the premix droplets are deformed and disrupted in the flow field of the emulsification device [1]. In addition to these techniques, alternative methods for the production of emulsions using microporous devices have been developed since the early 1990s. 

Figure 20.11 Photomicrographs of a fat-water cover plates. Each foil has a thickness of200 pm emulsion. Left, produced by a rotor-stator and is structured with 10 channels. The channels system right, produced by a micromixer. The have a width of 100pm and a depth of 70pm body of the mixer applied consists of five foils the channels are separated by walls with a stacked together, two foils forthe aqueous phase thickness of 100pm. and three for the fat phase, clamped between...

The cell has two concentric rotating and fixed cylinders fitted with a syringe pump containing the premixed polydisperse emulsion. The inner cylinder is connected to a motor of variable speed and acts as the rotor, while the fixed outer cylinder is the stator. At high shear rates, the pre-mix emulsion pushed through the system by the syringe pump is converted to narrow size distribution emulsions. 

---