#EBSstories Looking for the perfect squeak

10-06-2021

Manufacturers tailor consumer products in order to satisfy the customer wishes while making their products environmentally friendly. At the ESRF’s BM28/XMaS, scientists from the University of Bristol (UK) and Procter and Gamble have studied an unusual sample: a noise.

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In the case of dishwashing liquid, manufacturers want to minimize the water and energy usage and, at the same time, make a squeaky noise appear, as some consumers link the concept of cleanliness with a squeaky noise while washing the dishes. This perception is prevalent in Japan, where there is even a term to define this noise: ‘kyu-kyu’. This sound appears when there is physical contact of the human fingertip across a wet lubricated surface (or dish).

Charlotte Kenton, from the University of Bristol and sponsored by Procter and Gamble, is studying how this sound can appear earlier in the process of washing the dishes, reducing the amount of water used in the process.

This ‘kyu-kyu’ sound has its origin in a physical phenomenon known as stick-slip friction. “We want to find out how this friction occurs and how we can control it. So we came to the ESRF to use X-ray reflectivity (XRR) on BM28 to study the self-assembled structures formed at interfaces by two surfactants under various temperature, pH and water conditions”, explains Kenton. The surfactants used  are analogues of the surfactants used commonly in P&G domestic cleaning formulations and are widely reported to exhibit significant synergy, forming mixed micelles of compositionally dependent structures in bulk and displaying improved adsorption to silica substrates.

The experience of doing a remote experiment was painless for Kenton: “It is a fairly simple set-up, so we just had to prepare the sample, where we put together silica, to simulate the dish, the surfactant and the skin”. Then the team on BM28 scanned the samples on the beamline. BM28 has undergone a huge renovation in the last two years.  As Laurence Bouchenoire, scientist on the beamline, explains: “The beamline was completely redesigned to make full use of the EBS. For example, we are now on a 0.86 T dipole magnet, producing more flux at higher energies.”

Kenton is now analyzing the data from the experiment. It will hopefully provide her with some clues as to how to monitor the sound to make it appear with a lower concentration of dishwashing liquid and at an earlier stage of the process of washing dishes.

Text by Montserrat Capellas Espuny.

Video by Montserrat Capellas Espuny and Mark McGee.