Contact angle with vapor present

Recently, dimethylamino and zwitterion end-fimctionahzed block copolymers were used in the construction of smart polymer surfaces [39]. These surfaces were fovmd to respond almost reversibly to external stimuli, being able to alter the wetting characteristics of a polymer surface when it is exposed to a humid environment, hi this process the abihty of a diblock copolymer, having the hydrophilic group attached to the mostly surface active block, to accumulate at the polymer/air interface was utilized. The end group is hidden below the polymer surface when in contact with dry air while it is present on the surface when the material is exposed to water vapor. Due to the increase of the concentration of the polar groups on the polymer surface, the water contact angle is reduced. This process could be reversed and... 

The values of Kelvin radius, calculated for water vapors in accordance with Eq. (18.1), are presented in Table 18.1. For these calculations, the following data and assumptions were used the contact angle between the liquor and the wall of concave (0) is constant the and y are 1.8x10" L/mol and 72.8 mN/m (20 °C), respectively the temperature (7) is about 293 K and x=cos 0. It is seen that the Kevin radius increases with the relative humidity, and the rate of change (the slope) also increases with relative humidity. This means that the pores with smaller diameter are filled first, while bigger pores are filled later. 

Slavutsky et al. (2014) prepared starch/cellulose nanocrystals (CNCs) films and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/CNC films have a lower affinity to water molecules than starch films. Permeability, dififusivity, and solubility coefficients indicated that the permeation process was controlled by the water diffusion and was dependent on the tortuous pathway formed by CNC incorporation. The decrease in surface hydrophilicity and the improvement in water vapor barrier properties with the addition of CNC showed that these nanocomposites present excellent potential as a new biomaterial for application in food packaging and conservation. 

Let us consider a picture presented in Figure 1.4. Let us say that the three-phase contact line is the line where three phases liquid, solid, and vapor meet. Consideration of forces in the tangential direction at the three-phase contact line results in the well-known Young s equation, which connects three interfacial tensions, Ys/. Ysv. and y with the value of the equilibrium contact angle, (Figure 1.4), where y, and y are solid-liquid, solid-vapor, and liquid-vapor interfacial tensions, respectively ... 

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