Structure, stability and feel
Creams, lotions and ointments are emulsions: one liquid finely dispersed in another. The size of the droplets and the mobility of the two phases decide how the product feels, how it spreads, how it releases its ingredients and how long it stays stable. Over time, droplets in a weak formulation merge and grow, long before the product visibly separates.
Where it is used
- Creams, lotions and ointments
- Topical pharmaceutical and dermatological products
- Cosmetic and sun-care emulsions
- Gels and other semi-solid formulations
Typical tasks are comparing batches, comparing recipes and stabilisers, optimising process settings, following the ageing of a product in storage and in temperature cycles, and finding the cause of a separation.
Movement held back by the droplet wall
Molecules inside a droplet can move only as far as the droplet wall. A pulse sequence with a magnetic field gradient measures how far they move in a set time. The smaller the droplet, the more the movement is held back, and the more slowly the signal fades as the gradient increases. From the shape of this decay, the droplet size distribution is calculated.
Relaxation times of the oil and water phases add information about their mobility and about how the structure builds up. The measurement needs a gradient option on the instrument and matching software.
What it adds
- The product is measured undiluted, so dilution cannot change the emulsion
- Opaque and thick products are no problem
- A small sample is enough, and the same sample can be measured again after storage
- The result is a size distribution, not only an average
Points that matter in practice
- The method works within a range of droplet sizes. Droplets that are very large or very small fall outside it
- Fill the tube carefully. Strong shear or trapped air can change a delicate cream
- Measure at a defined temperature
- Semi-solid structures, such as gel networks around the droplets, can make the interpretation more complex. Compare with microscopy or laser diffraction for your product type before relying on the numbers
From your formulation to a routine method
Send or bring representative samples. MSY Consulting runs feasibility measurements, checks which droplet sizes your product allows the method to resolve, compares the results with your own reference technique, and trains your team until the measurement is part of your routine.
Let's talk about your application
Send an email describing your instrument and your application, and you will get a reply.
contact@msyconsulting.euMSY CONSULTING SAS · Wissembourg, France · LinkedIn