Empirical study and prediction of contact angle and surface free energy of commonly used plastics with pillar-like structure
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Copyright 2014 John Wiley & Sons, Ltd. An effective approach is proposed to estimate liquids' contact angles on five commonly used plastics, polyethylene terephthalate, polypropylene, high-density polyethylene, low-density polyethylene, and polyvinyl chloride, with pillar-like structures. A change in liquid droplets' three-phase contact line due to surface roughness has been proposed in literatures. In this article, contact length ratio, , was used as a parameter corresponding to a specific dimension of the pillar-like structure. Wettability of these rough plastics and their surface free energy were investigated by liquids with various polarities-de-ionized water (polar), ethylene glycol (monopolar), and a-bromonaphthalene (apolar). The effects of pillar-like structures on liquids' contact angles and plastics' surface free energy were studied, and the results reveal that both effects are linear in the range of = 1.0 to 1.96. Linear regression models are hence proposed to predict liquids' contact angles, and accuracies are confirmed by less than 6% error for most plastic-liquid combinations. Plastics' surface free energy is also predicted by linear regression models, and the results agree with existing experimental data. Plastic-liquid interactions were also studied, and the results further validate predictions of plastics' surface free energy. In addition, plastics' polarity alteration due to effects of pillar-like structure were analyzed and reported in this article.
