Dendritic Pattern Formation and Contact Line Forces during Dewetting of Dilute Polymer Solutions on a Hydrophobic Surface

The micro-scale morphology of the receding contact line of dilute polyethylene oxide solution drops (c ∼ 100 ppm) after impact and inertial spreading on a fluorinated hydrophobic surface is investigated. One can observe the formation of transient liquid filaments and dendritic structures that evolve into a bead-on-a-string structure similar to the well-known capillary breakup mechanism of dilute polymer solutions, which confirm the interaction between stetched polymer coils and the receding three-phase contact line. The estimation of the average polymer force per unit contact line lenght provides a quantitative explanation for the reduction of the contact line retraction velocity reduction observed experimentally.

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Surface Topography Induced Ultrahydrophobic Behavior: Effect of Three-Phase Contact Line Topology

Microelectromechanical Systems ◽

10.1115/imece2006-15266 ◽

2006 ◽

Author(s):

Neeharika Anantharaju ◽

Mahesh Panchagnula ◽

Wayne Kimsey ◽

Sudhakar Neti ◽

Svetlana Tatic-Lucic

Keyword(s):

Contact Angle ◽

Contact Line ◽

Anomalous Behavior ◽

Contact Angles ◽

Wet Etching ◽

Surface Geometry ◽

Wetting Behavior ◽

Void Fractions ◽

Three Phase ◽

Receding Contact

The wettability of silicon surface hydrophobized using silanization reagents was studied. The advancing and receding contact angles were measured with the captive needle approach. In this approach, a drop under study was held on the hydrophobized surface with a fine needle immersed in it. The asymptotic advancing and receding angles were obtained by incrementally increasing the volume added and removed, respectively, until no change in angles was observed. The values were compared with the previously published results. Further, the wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The surfaces were prepared with the wet etching process and contain posts and holes of different sizes and void fractions. The surface geometry brought up a scope to study the Wenzel (filling of surface grooves) and Cassie (non filling of the surface grooves) theories and effects of surface geometry and roughness on the contact angle. Experimental data point to an anomalous behavior where the data does not obey either Wenzel or Cassie type phenomenology. This behavior is explained by an understanding of the contact line topography. The effect of contact line topography on the contact angle was thus parametrically studied. It was also inferred that, the contact angle increased with the increase in void fraction. The observations may serve as guidelines in designing surfaces with the desired wetting behavior.

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Study of the Morphology of the Three-Phase Contact Line and Its Evolution by Morphological Examination after Droplet Evaporation of Aqueous Polymer Solutions

Langmuir ◽

10.1021/la800452w ◽

2008 ◽

Vol 24 (15) ◽

pp. 7923-7930 ◽

Cited By ~ 10

Author(s):

Gang Liu ◽

Cunfu Zhang ◽

Jiang Zhao ◽

Yingxi Zhu

Keyword(s):

Contact Line ◽

Polymer Solutions ◽

Droplet Evaporation ◽

Phase Contact ◽

Morphological Examination ◽

Aqueous Polymer ◽

Three Phase

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Behavior of Dilute Polymer Solutions in the Inlet Region of a Pipe

Journal of Applied Mechanics ◽

10.1115/1.3422991 ◽

1973 ◽

Vol 40 (2) ◽

pp. 381-387 ◽

Cited By ~ 4

Author(s):

E. Bilgen

Keyword(s):

Polyethylene Oxide ◽

Polymer Solutions ◽

Round Tube ◽

Pressure Drops ◽

Fluid Elasticity ◽

Dilute Polymer Solutions ◽

Inlet Region ◽

Fluid Properties ◽

Inlet Length ◽

Increased Pressure

The behavior of dilute polymer solutions in the inlet region of a round tube has been analyzed with a Rivlin-Ericksen approximation to describe the fluid properties. It is shown that for dilute polymer solutions, shorter inlet length and increased pressure drop in the inlet region are predicted and that those changes are due to fluid elasticity. Available experimental evidence showed some qualitative support for the inlet-length predicted by the theory. Further, the pressure drops in the inlet region of various tubes have been measured for water and dilute solutions of polyethylene oxide; the results show fair agreement with the predictions.

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