When a fiber covered with a layer oil or wax, is immersed in a warm aqueous solution of soap and it will be seen that the film bunches up and ultimately collects itself into spherical globules which are very easily detached.
In a drop of oil, lenticular in foam, adheres to a fiber, its actual shape will be determined by the inter action of the following three forces….
1. T1= The surface tension between the drop and the surround in aqueous phase
2. Tls= The surface tension between the fiber and the oil
3. Ts= The surface tension between the fiber and the water plant any solute which it may contain.
In the figure, any increase in (Tls+Tl) in relation to Ts will decrease the area of contact between the oil and fiber. The result of this is that the shape of the oil drop will approach more and more to that of a sphere. θ is the contact angle which is drawn at the contact point of solid surface and oil drop. When the forces are equilibrium their relationship is
Ts= Tls+ TlCosθ
Cosθ = (Ts-Tls)/ Tl
Tl= Ts-Tls When θ = 0°
To fulfill this condition, the solid surface must be covered with that phase of the lowest surface tension. If Ts is greater, than TlsCosθ will be positive and θ will be less than 90º. If θ is greater than 90º the value of COSθ will be negative and then Tls will be greater than Ts. It indicates that the aqueous phase will displace the oil.
Wetting of Surface:
When a fiber converged with a layer of oil or wax, is immersed in a warm aqueous solution of soap and it will be seen that the film bounces up and ultimately collects itself into spherical globules which are very easily detached.
Surface tension Or Interfacial tension:
In a liquid each molecules are attracted by the neighboring molecules from all directions and remain stationary. But the molecules on the top line of the surface only attracted by its liberating molecules. As a result a pull down effect acts on the surface then the surface become convex. This phenomenon of the liquid is called surface tension or interfacial tension.
Surface active agents or surfactants or detergents:
The compound which get oriented at the interface ( Between water and air ) dissolved in water and reduce the interfacial tension or surface tension are called surface active agent or surfactant.