​The discoveries from this research and the novel technique used can help several industries including those involved in personal care products, cosmetics, fabric treatment and cleaning.

Image credit: Nanoscopic wetting behaviour of single oil droplets on a fibre -https://doi.org/10.1016/j.colsurfa.2024.134729.

Industries specialising in fabric washing and care need a good understanding of how oils interact with certain materials in order to formulate products that can clean and coat fabrics efficiently. In a recent paper published in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects, researchers from the University of Birmingham along with Dr Andy Ward from the Central Laser Facility (CLF) ran an experiment that will prove useful to industries involved in manufacturing fabric care and coating products. During the experiment, cotton and polyester fibres were made to approach a 10 µm droplet of silicone oil held in a focussed laser beam known as an Optical Tweezer, allowing interactions between oil and fibre in an aqueous environment to be studied.

While experiments of a similar nature have been performed previously, they have mostly involved larger droplets 20-200 µm in diameter. Furthermore, the tool of choice often used to study these droplets is an atomic force microscope (AFM), which can be challenging to use for pico-Newton force measurements on smaller droplets. Optical Tweezers utilise the forces exerted by lasers to hold tiny particles in place, allowing them to be precisely moved, manipulated, and observed. In this experiment, their highly precise nature presents several advantages. Firstly, it allows scientists to quantify the interactive forces to the order of pico-Newtons (10^-12 N). This is achieved using an Impetux Lunam force measurement module which has been integrated into the optical trapping apparatus. The force sensitivity gives them a deeper understanding of the mechanisms of interactions occurring at the droplet-fibre interface. Secondly, Optical Tweezers are contact-free and allow droplets to stay as a sphere. This supports careful controlling during the experiment and more realistically replicates the approach between droplet and fibre.

Image credit: Pexels.  This research is directly applicable to fabric care industries.

The insight gained from this study goes beyond the fabric care industry and can be applied across a whole range of industries where droplet-substrate interactions are involved. For instance, future experiments can use a similar methodology to study how respiratory aerosols stick onto the fibres of face masks. Water filtration techniques can also be optimised based on the attractive forces found between contaminant droplets and fibres within the filter. Similarly, industries specialising in personal products can use the same techniques to study interactions between oils and human hair in order to formulate better shampoo and hair oils. Besides the progress this research can bring to industry, this study is also testament to the diverse applicability and unique capability of the Optical Tweezer. This instrument will continue to prove useful in various areas of research.

Read the paper here: Nanoscopic wetting behaviour of single oil droplets on a fibre - ScienceDirect https://doi.org/10.1016/j.colsurfa.2024.134729

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