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Cleaning by Surfactant Gradients: Particulate Removal from Porous Materials and the Significance of Rinsing in Laundry Detergency

Sangwoo Shin, Patrick B. Warren, and Howard A. Stone
Phys. Rev. Applied 9, 034012 – Published 16 March 2018
Physics logo See Focus story: Rinsing is Key to Removing Stains
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Abstract

Removing particles from fibrous materials involves loosening via surfactants followed by particle transfer in a flow. While flow advection is commonly believed to be the major driver for pore-scale transport, small pores within the fabric do not allow any significant fluid flow inside them, thus significantly reducing the role of advection. However, rinsing the fabric with fresh water naturally establishes a surfactant gradient within the pore space, providing a suitable environment for particles to undergo diffusiophoresis. We demonstrate that this mechanism can remove particles from deep within fabric pores at an accelerated rate. The nonlinear aspect of diffusiophoresis significantly prolongs the lifetime of the phoretic motion beyond the naive solute diffusion time scale during rinsing, allowing long-lasting, continuous removal of particles. Moreover, owing to the fine balance between chemiphoresis and electrophoresis for particles in anionic surfactant concentration gradients, we show that the particle removal is sensitive to the counterion mobility, suggesting a simple route to control the effect. We thus claim to have resolved the “stagnant core problem”—a long-standing mystery in laundry detergency—and have identified a physicochemical approach to particle transport in fibrous media with broad applicability.

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  • Received 15 August 2017
  • Revised 17 January 2018

DOI:https://doi.org/10.1103/PhysRevApplied.9.034012

© 2018 American Physical Society

Physics Subject Headings (PhySH)

Fluid DynamicsPolymers & Soft Matter

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Rinsing is Key to Removing Stains

Published 16 March 2018

Experiments show that rinsing clothes after washing can create imbalances in detergent concentration that pulls dirt out of the fabric.

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Authors & Affiliations

Sangwoo Shin1,*, Patrick B. Warren2,†, and Howard A. Stone3,‡

  • 1Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
  • 2Unilever R&D Port Sunlight, Bebington, Wirral CH63 3JW, United Kingdom
  • 3Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA

  • *sangwoos@hawaii.edu
  • patrick.warren@unilever.com
  • hastone@princeton.edu

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Vol. 9, Iss. 3 — March 2018

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