Chemo-Sensitive Running Droplet.pdf

a r X i v : n l i n / 0 5 0 5 0 0 6 v 3 [ n l i n .A O ] 2 3 A u g 2 0 0 5 Chemo-Sensitive Running Droplet Yutaka Sumino, Hiroyuki Kitahata, and Kenichi Yoshikawa? Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan Masaharu Nagayama Graduate School of Natural Science Technology, Kanazawa University, Ishikawa 920-1192, Japan Shin-ichiro M. Nomura Department of Organic Materials, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo 101-0062, Japan Nobuyuki Magome Department of Food and Nutrition, Nagoya Bunri College, Aichi 451-0077, Japan Yoshihito Mori Department of Chemistry, Ochanomizu University, Tokyo 112-8610, Japan (Dated: February 8, 2008) Chemical control of the spontaneous motion of a reactive oil droplet moving on a glass substrate under an aqueous phase is reported. Experimental results show that the self-motion of an oil droplet is confined on an acid-treated glass surface. The transient behavior of oil-droplet motion is also observed with a high-speed video camera. A mathematical model that incorporates the effect of the glass surface charge is built based on the experimental observation of oil-droplet motion. A numerical simulation of this mathematical model reproduced the essential features concerning confinement of oil droplet motion within a certain chemical territory, and also its transient behavior. Our results may shed light on physical aspects of reactive spreading and a chemotaxis in living things. PACS numbers: 68.05.-n, 83.80.Jx, 47.70.Fw ?To whom correspondance should be addressed. Tel:+81-75-753-3812. Fax:+81-75-753-3779. Email:yoshikaw@scphys.kyoto-u.ac.jp 2I. INTRODUCTION The spontaneous motion of reactive droplets has attracted considerable attention in relation to energy transduc- tion by living organisms, i.e. chemomechanical energy transduction. In 1978, the motion of a droplet driven by a surface-tension gradient was predicted by Greenspan to explain