The interfacial tension of bitumen in contact with sand and water is measured to be 90 and 20 mN/m, respectively. The interfacial tension of sand and water is 75 mN/m. The surface tension of sand, water and bitumen is determined to be 36, 72.8 and 30 mN/m, respectively. You are asked to: 1) Calculate the contact angle of a pure water droplet on sand in air; calculate the work of adhesion of water to sand and cohesion of water in air; and defense or oppose the water spreads on sand surface in air spontaneously. 2) Calculate the water contact angle of a bitumen droplet on sand in water; calculate the work of adhesion of bitumen to sand and cohesion of bitumen in water; and defense or oppose the bitumen spreads on sand surface in water spontaneously. 3) What is the critical contact angle that bitumen droplet spreads on the air bubble surface (i.e., full engulfment)?