Advancing and Receding Sessile Droplet Contact Angles

ADVANCING AND RECEDING SESSILE DROPLET CONTACT ANGLES 

Similar to (TMS -f O2) plasma-treated PP, many of the (TMS -f O2) plasma-treated polymers showed that the three-phase contact line hardly recedes on the wet surface. Specifically, (TMS + O2) plasma-treated PTFE, UHMWPE, PP, HDPE, PVDF, and nylon showed hardly any change in contact area during the receding process. This is due to the strong specific attractive forces formed at the surface underneath the bulk droplet, i.e., the interfacial tension (underneath the droplet) changed due to the interaction of water with the surface. 

PTFEHMWPE PP LDPE HOPE PC PET PMMA PVDF NYLON 

The Wilhelmy balance apparatus is composed of an electronic balance interfaced with a PC computer. The tensiometer measures the force exerted by a partially immersed thin-sample plate in water. A beaker containing water is moved up (increasing the immersion) and down (emerging the sample) by a constant speed, and the corresponding force change is recorded. 

The total force exerted to the microbalance may be given by the following force balance equation  

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Figure 23.8 Advancing and receding sessile droplet contact angle of water on a dry ethylene/vinyl alcohol film.

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