Withdrawal of a conical pin from a pool of liquid

A. B. Wang, Y. S. Chen, Y. J. Wu, J. Y. Sung, A. L. Yarin

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


The development of biochips leads to a straightforward, fast and cost effective method to obtain valuable genetic information. A key element of the emerging biochip technology is a microarray system, which fabricates high-density samples on solid materials of a microscopic area. In particular, dots of test liquid are printed on solids by a system of pins constituting a microarray. At present, however, the technique cannot make dots of arbitrary equivalent and controllable size. On the other hand, printing pins in microarrays represent themselves as a particular example of dip coating. In the experiments of the present work, a model of tapered stainless steel needle was withdrawn from different glycerine-water mixtures. Thicknesses and volumes of the withdrawn liquid films were measured as a function of the needle geometry, immersion depth, withdrawal rate, and physical parameters of the liquid. The experimental data are analyzed as a function of the capillary number Ca based on the withdrawal speed and compared to the predictions of the modified Landau-Levich-Deryagin (LLD) theory. The results show that for Ca < 10 -2 the thickness and the volume of the liquid follow the Ca 2/3-scaling, while for Ca > 10-2 - the Ca 1/2-scaling, as it is expected from the LLD theory. Flow visualization is utilized to resolve the detail flow structure. The results put the key element of the pin-printing technology exploited in microarrays into a familiar hydrodynamic context of dip coating. This allows one to expect that under appropriate operational conditions, high-precision sampling could be attainable.

Original languageEnglish
Pages (from-to)219-232
Number of pages14
JournalJournal of Mechanics
Issue number3
Publication statusPublished - 2004 Sept

Bibliographical note

Funding Information:
We gratefully acknowledge the support by the National Science Council of Taiwan (NSC 89-2323-B-002-008). ALY acknowledges the National Science Council of Taiwan, and the hospitality of the Institute of Applied Mechanics, National Taiwan University, during his visit in May 2000. The computer graphics from Y.-C. Chang is also acknowledged.


  • Conical pin
  • Flow visualization
  • Withdrawn liquid

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanical Engineering
  • Applied Mathematics


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