Electrical discharge in capillary breakup: controlling the charge of a droplet.

We studied the detachment of sessile droplets of conductive liquids from an immersed wire by reducing the contact angle using ac electrowetting. Upon detachment, the droplets acquire a certain amount of charge, which is shown to be controlled by a dimensionless parameter alpha. Alpha describes the interplay between the diverging Ohmic resistance of the breaking capillary neck and the ac frequency. In the specific configuration of the present experiment, discharging at high frequency leads to self-excited oscillations in which the droplets periodically detach from and reattach to the wire.

[1]  Leslie Y Yeo,et al.  A new ac electrospray mechanism by Maxwell-Wagner polarization and capillary resonance. , 2004, Physical review letters.

[2]  L. Rayleigh.  On the Capillary Phenomena of Jets , 1879 .

[3]  Andrew G. Glen,et al.  APPL , 2001 .

[4]  J. Sagiv,et al.  Organized monolayers by adsorption. 1. Formation and structure of oleophobic mixed monolayers on solid surfaces , 1980 .

[5]  I. Cohen,et al.  The two fluid drop snap-off problem: experiment and theory , 1999, physics/9902071.

[6]  Wendy W. Zhang,et al.  Similarity Solutions for Capillary Pinch-Off in Fluids of Differing Viscosity , 1999 .

[7]  H. Stone,et al.  CAPILLARY BREAKUP OF A VISCOUS THREAD SURROUNDED BY ANOTHER VISCOUS FLUID , 1998 .

[8]  Anke Klingner,et al.  Capillary bridges in electric fields. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[9]  J. Baret,et al.  Electrowetting: from basics to applications , 2005 .

[10]  J. Eggers.  Nonlinear dynamics and breakup of free-surface flows , 1997 .

[11]  P. Taborek,et al.  Fluid pinch-off dynamics at nanometer length scales. , 2004, Physical review letters.

[12]  M. Mann,et al.  Electrospray ionization for mass spectrometry of large biomolecules. , 1989, Science.

[13]  S. Herminghaus,et al.  Self-excited oscillatory dynamics of capillary bridges in electric fields , 2003 .

[14]  J. Eggers,et al.  Universal pinching of 3D axisymmetric free-surface flow. , 1993, Physical review letters.

[15]  Geoffrey Ingram Taylor,et al.  Disintegration of water drops in an electric field , 1964, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[16]  Aa Anton Darhuber,et al.  PRINCIPLES OF MICROFLUIDIC ACTUATION BY MODULATION OF SURFACE STRESSES , 2005 .