Controlling negative and positive photothermal migration of centimeter-sized droplets.
The photoinduced motion of an oil droplet on an aqueous solution under local irradiation by a green laser is reported. The results showed that a repulsive force is generated on pure water, while an attractive force is observed with an aqueous solution containing a surfactant. The driving force is discussed in terms of a thermal Marangoni effect. The switching on the photothermal effect is interpreted by taking into account the advection caused by the spatial gradient of the surface tension under local heating by a laser. A numerical model revealed that the geometrical profile of the surface tension around the droplet determines the mode of advection around the droplet and causes switching in the direction of migrations.
Department of Physics, Kyoto University, Kyoto 606-8502, Japan. ichi@scphys.kyoto-u.ac.jp
Masatoshi
M
Ichikawa
Fumi
F
Takabatake
Keitaro
K
Miura
Takafumi
T
Iwaki
Nobuyuki
N
Magome
Kenichi
K
Yoshikawa