Tension Between Polymer Surface and Liquid Water

INTERFACIAL TENSION BETWEEN POLYMER SURFACE AND LIQUID WATER 

In the classical treatment of the interfacial tension, the force balance at the three-phase contact line (liquid-surface-air) is considered, and the interfacial tension, 7sl, is given by the surface tension of the solid, 7s, and the surface tension of the liquid, Yl, as 

In the classical treatment of surface tensions, it is intuitively assumed that the surface tension of a solid, 7s, can be assigned as if it is a material constant. In a practical sense, Eq. (25.3) is valid if the surface tension of the solid does not change after the contact with the liquid (sessile droplet) is made. While Young s equation describes the force balance at the three-phase line, it does not give information relevant to the true interfacial tension at the interface that is beneath the droplet, which is the major concern of surface dynamics. In general cases, 7s and 7sl are 

An empirical method to estimate the surface tension of a solid is Zisman s plot (cos 9 as a function of yl), which obtains the critical surface tension of wetting. In the absence of specific interaction between the surface and the liquids used for the measurement of contact angles, the critical contact angle of wetting can be accurately estimated and its value used as the surface tension of the surface. However, if a surface interacts with liquids used as the sessile droplet for the contact angle measurement, to the extent that the surface tension is altered, Zisman s plots deviate from the ideal linear relationship. In a strict sense, the plot is applicable only to imperturbable surfaces with which liquid contact does not alter surface configuration, i.e., no surface dynamics applies. 

Surface dynamics is concerned with the kinetic aspect of this specific question of whether or not the surface tension of polymer changes by contacting with liquid water. If ys changes by the interaction of water with polymer molecules, Ysl also changes accordingly. 

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