© 2018 Phys.org Cleans better than the leading brand. Rinsing soapy, stained cotton with fresh water (right) works far better than rinsing with detergent-filled water (left). The difference is that fresh water produces detergent gradients that draw out dirt particles. Credit: Physical Review Applied (2018). DOI: 10.1103/PhysRevApplied.9.034012 Panning for silver in laundry wastewater Humans have probably been washing their clothes for as long as they have been wearing them. The typical process generally involves swishing the clothes in water containing some type of detergent, followed by rinsing with clean water. Interestingly, despite this long history, it is unclear how, exactly, clothes become clean from this regimen. In this new effort, the research team conducted experiments in the lab to figure it out.Stains, the researchers note, are usually due to staining agents infiltrating into small pores in fabric via capillary action. In order to clean them, a liquid must be able to make its way into the pore and then somehow pull out the staining agent. To learn more about how this process works, the researchers created material with tiny tubes 10 microns in diameter to serve as a sort of fabric—tiny polystyrene balls served as the staining agent. The researchers then “stained” their fabric and filmed the action with a microscope as the material was cleaned.The team reports that the water with the detergent was unable to infiltrate all the way into the pore, but because the detergent contained ingredients that prevented the material from repelling water while also attracting the staining agent, the stain was primed for removal. When the water containing detergent was replaced with clean water, the staining agent was pulled from the pores due to chemophoresis. Interestingly, they found that if they tried rinsing the material with detergent-bearing water, chemophoresis did not occur and the stain remained in place. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.