Interface contact angle measurements

G() is related to the reversible work of adhesion obtained using contact angle measurements, but in general is greater than W. This is because once an interface is formed and the adhesive solidifies, strain energy is required to mechanically disrupt the interface. This strain energy arises because of the physical connection between the attachment sites between the adhesive and the substrate and the connectivity between this interface and the adhesive bulk. 

Young s equation is a plausible, widely used result, but experimental verification is often rendered difficult e.g., the two terms which involve the interface between the solid and the two other phases cannot be measured independently. Furthermore, many complications can arise with contact angle measurements ys values of ionic solids based on contact angle measurements are different from those estimated from solubility (Table 6.1) (cf. Table A.4.1). 

J.A. De Feijter and A. Vrij Contact Angles in Thin Films, n. Contact Angle Measurements in Newton Black Soap Films. J. Colloid Interface Sci. 64, 269... 

As we see in Chapter 6, surface tension and contact angle measurements provide information on liquid-liquid and solid-liquid adhesion energies (Fig. 1.26c). Contact angles measured under different atmospheric environments or as a function of time provide valuable insights into the states of surfaces and adsorbed films and of molecular reorientation times at interfaces. 

Water drops were formed at the mercury-benzene interface by means of a syringe, and the contact angle (measured in the water) was recorded as a function of time. For the interface between Hg and benzene saturated with water, y was measured independently as a function of time. The following table summarizes these data (all measured at 25°C) ... 

Contact angle measurements provide information on the wettability of the sample, the surface energetics of the solid, and the interfacial properties of the solid-liquid interface. The samples were immersed in water and captive air and octane bubbles were determined by measuring the bubble dimensions. By measurement of both air and octane contact angles the surface free energy (.y) of the solid-vapor ( > ) interface may be calculated by use of Young s equation and the narmonic mean hypothesis for separation of the dispersive and polar components of the work of adhesion. This method for determination of surface and interfacial proper-... 

Adao MHVC, Saramago BJV and Fernandes AC (1999) Estimation of the surface properties of styrene-acrylonitrile random copolymers from contact angle measurements. J Colloid Interface Sci 217 94—106. 

Platinum plates with 1 cm area per side were metallographically polished to a mirror finish, rinsed with distilled water, and flamed just before exposure to sea water for either ellipsometric or contact angle measurements. The platinum plates were wetted with photo-oxidized sea water before immersing into experimental sea water, so that passage of the surface through the air—sea water interface would not cause any film present there to be transferred to the plate. For the same reason plates removed from the experimental sea water were immediately immersed while still visibly wet in photo-oxidized sea water and then rinsed. 

D. Li, P. Cheng and A.W. Neumann, Contact Angle Measurement by Axisymmetric Drop Shape Analysis (ADSA), Adv. Colloid Interface Set 39 (1992) 347, and references to the Neumann group in sec. 5.12 D.Y. Kwok, A.W. Neumann, Contact Angle Measurement and Contact Angle Interpretation, Adv. Colloid Interface Set 81 (1999) 167-249. 

Besides plates, contact angle measurements are adso possible with spheres. We refer to work by Zhang et al. ). Huethorst and Leenars J obtained the angles from the centrifugal force needed to pull a sphere through the interface. 

Allain, C. Ausserre, D. Rondelez, F. A new method for contact angle measurements of sessile drops. J. Colloid Interface Sci. 1985,107 (1), 5-13. 

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