Contact Angle Surface Energy Conversion

Surface tension of solid of the substrate.

Contact angle surface energy conversion.

In practice this analysis is done automatically by a contact angle meter. This is commonly referred to as a contact angle measurement using the sessile drop method. The angle between the droplet outline and the solid surface is the contact angle. For complete data the advancing receding and static contact angles must be measured.

This value corresponds to the surface energy level in the equilibrium. When a droplet of a liquid is formed on a flat solid surface the balance on the three phase interface is expressed by young s equation γs γsl γl cosθ 1 where γl is surface tension of liquid θ contact angle between the liquid air interface and the surface γsl is interfacial tension and γs is surface free energy of a solid. Static contact angles are also used to define the surface free energy i e. The most common way to measure surface energy is through contact angle experiments.

Static contact angle offers a quick easy and quantitative measurement of wettability. This may raise the question of how we equate surface energy density units j m 2 with surface tension units n m. It is most suitable for relatively smooth and homogenous surfaces. By measuring the contact angle formed by probe liquids with known surface tensions values the surface free energy components are calculated using analysis models.

2 arc tan h r where. Contact angle ca measurements provide quantitative data on the interfacial energy between a liquid drop and a solid surface. Tantec s half angle method is based on the formula for determining contact angles from the droplet dimensions. I would like to calculate the surface free energy of solid by using contact angle measurement of liquid by the relation of young s equation.

In this method the contact angle of the surface is measured with several liquids usually water and diiodomethane. Based on the contact angle results and knowing the surface tension of the liquids the surface energy can be calculated. The contact angle is measured as the inward angle between the base and the tangent at the point of contact between the liquid and the surface. Where the subscripts s and l stand for the solid s and the liquid l whilst the subscript v stands for vapor.

ϒ s ϒ sl ϒ l cos θ where the inter facial. Is contact angle h is the height of a droplet and r is the radius of droplet s base see fig. Once the contact angle is measured the interfacial energies can be calculated from the young laplace equation as described in eq. A more general approach to understanding a surface s wettability is through surface free energy analysis.

This can occur with a low surface energy solid or a high surface tension liquid such as water.