Silverson Machines has recently tested their High Shear Laboratory mixer against a standard overhead stirrer for creating a cleansing lotion product, demonstrating the difference in the resulting emulsion under the microscope
In one of the latest videos on their YouTube channel, Silverson Machines were welcomed to Holiferm’s R&D laboratory in Manchester, where their team formulates personal care products around their own naturally derived biosurfactants and sophorolipids. Application Scientist Clarissa Clark talked Silverson Technical Sales Engineer James Cardus through her cleansing lotion formulation.
The cleansing lotion formulation was developed using Holiferm’s LF and HF sophorolipids. Beyond providing emulsion stability and effective cleansing, the naturally derived biosurfactants also contribute microbiome-friendly and skin barrier-supporting properties.
After combining the water phase with the oil phase, the mixture was split into beakers and processed under both a Silverson L5M-A High Shear Laboratory mixer and a standard overhead stirrer.
Initially, the overhead stirrer looked to have incorporated the water phase into the oil phase, but there was a contrast in the colour of the mixture compared to the emulsion produced by the Silverson. Processing the same formulation with the Silverson high shear mixer the emulsion almost instantly developed a brighter, whiter appearance, an indication that particle size had been significantly reduced.
Although both mixing methods appeared to the naked eye to have combined the phases and created an emulsion, the differences in the quality of these emulsions would become apparent once the samples were looked at under the microscope.
The results from the Silverson Laboratory mixer showed a tightly compact, homogeneous mix of oil and water with small and uniform droplet size. This even droplet size distribution throughout the sample confirmed it was a stable emulsion.
The overhead-stirred sample told a very different story. Under the microscope the stirrer sample showed a broad range of droplet sizes, with much larger droplets dispersed among smaller ones. This sample lacked the fine dispersion needed for long-term stability. Larger oil droplets remain more prone to coalescence, increasing the likelihood of separation during storage and reducing product consistency over time.
The stability of the emulsion in products like cleansing lotions and other personal care items is not only important for the subsequent processing steps, but for the consumer once they take the product home. A stable emulsion will allow the product to remain on a consumer’s shelf for a prolonged period of time, performing as it did on day one, without the emulsion separating.
In order to form a stable emulsion, whether you are producing an oil-in-water or water-in-oil emulsion, the mixing equipment needs to impart a large amount of energy into the mix to ensure the globule, or droplet size of both phases is reduced finely enough that the phases are completely and uniformly dispersed into one another.
Conventional mixers and agitators, which are suitable for basic liquid/liquid blending, are unable to form a stable emulsion because they do not have the necessary means to impart large amounts of energy into the mix. This type of mixing equipment simply moves the two liquid phases around the vessel, so although it may appear as though the phases have blended, the droplet size hasn’t been significantly reduced, as shown under the microscope. So once the agitation stops the emulsion will soon separate into the two distinct phases once more.
High shear mixing subjects the liquids to intense high-energy which reduces the droplet size sufficiently and allows the two phases to combine, resulting in a stable emulsion which will not separate once the shear energy has been removed.
Successfully manufacturing emulsions requires the right balance of ingredients, processing techniques and equipment to get it right. With a Silverson mixer you can take one of these factors out of the equation. Silverson High Shear mixers are able to rapidly produce a fine, uniform emulsion with a droplet size of 2 to 5 microns. Finer emulsions down to 0.5 microns can be obtained, depending on the formulation.
The microscope comparison illustrates why high shear mixers are superior to conventional methods of mixing when it comes to create fine, stable emulsions.
As demonstrated in the video, for making emulsions at a Laboratory scale, the Silverson L5M-A is ideal. The advantage of a Silverson mixer over simple agitators and stirrers stems from the specially designed rotor/stator workhead; the high speed rotation of the rotor blades draws materials into the workhead where they are intensively mixed, before being projected back into the body of the mix at high velocity. With this method, droplet sizes are significantly reduced, resulting in a fine, stable emulsion.
For research and development, QA analysis and small scale production in all industries the L5M-A offers efficiency and flexibility unmatched by other machines. With a capacity from 1ml up to 12 litres and the ability to mix in-line, the L5M-A offers excellent reproducibility when scaling up to full-scale production and provide an accurate and easy means of forecasting the performance of larger Silverson machines under full-scale working conditions.
You can watch the video on the Silverson website.
To trial a Silverson Laboratory mixer for yourself, please get in touch with: sales@silverson.co.uk
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