What is it?
The Malvern Mastersizer uses laser diffraction techniques to measure the size of particles. These could be suspensions of solid particles, emulsion droplets, or even dry powders.
Why do we use it?
The size of particles in a lubricant can have a significant impact on the performance. A commonly encountered example is the size of emulsion droplets in an emulsion-based metal working fluid (MWF).
In a rolling oil, the emulsion droplets (oil-in-water) need to plate out at the roll bite and their size is an important contribution to how well they do this. If the droplets are too large they will not be able to enter the roll bite; if they are too small they will enter but pass straight through and not plate out. In either case the lubricant contained in the droplet will not be delivered. The ideal case is a narrow distribution centred on a desired mean radius as shown in the diagram below.
How does it work?
The Malvern Mastersizer uses the principles of static light scattering (SLS) and Mie theory to calculate the size of particles in a sample. The basic principle is that small particles will scatter light at large angles and large particles will scatter light at small angles, as shown in the diagram on the right.
The scattering pattern produced by the sample is recorded and by applying Mie scattering theory the distribution of particle sizes can be calculated.
The technique of laser diffraction particle sizing enables us to measure the size distribution of emulsion droplets. This data obtained aids in the selection of appropriate emulsifiers to control droplet size and distribution.
The graph to the left shows the size distribution of two emulsion samples. Both have the same mean size; however one sample (red) has a much broader size distribution than the other (blue). For a rolling fluid, blue is the preferred size distribution.
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