Letters to Nature

Nature 405, 772-775 (15 June 2000) | doi:10.1038/35015525; Received 30 September 1999; Accepted 27 April 2000

Controlling droplet deposition with polymer additives

Vance Bergeron2, Daniel Bonn3, Jean Yves Martin2 & Louis Vovelle2

  1. Rhodia Recherches, Centre de Recherches Lyon, 85 Av. Des Freres Perret-BP62, 69192 Saint-Fons Cedex, France
  2. Ecole Normale Superieure, Laboratoire de Physique Statistique, 24 rue Lhomond, 75231 Paris Cedex 05, France

Correspondence to: Vance Bergeron2 Correspondence and requests for materials should be addressed to V.B. (e-mail: Email: vance.bergeron@rhone-poulenc.com).

Controlling the impact of drops onto solid surfaces is important for a wide variey of coating and deposition processes—for example, the treatment of plants with herbicides and pesticides requires precise targeting in order to meet stringent toxicological regulations. However, the outer wax-like layer of the leaves is a non-wetting substrate that causes sprayed droplets to rebound; often less than 50% of the initial spray is retained by the plant1. Although the impact and subsequent retraction of non-wetting aqueous drops on a hydrophobic surface have been the subjects of extensive experimental and theoretical work2, 3, 4, 5, 6, 7, non-newtonian rheological effects have not been considered in any detail. Here we report that, by adding very small amounts of a flexible polymer to the aqueous phase, we can inhibit droplet rebound on a hydrophobic surface and markedly improve deposition without significantly altering the shear viscosity of the solutions. Our results can be understood by taking into account the non-newtonian elongational viscosity, which provides a large resistance to drop retraction after impact, thereby suppressing droplet rebound.