  We study the dynamics of contact angle of a droplet of binary solution
evaporating on a super wetting surface. Recent experiments show that although
equilibrium contact angle of such droplet is zero, the contract angle can show
complex time dependence before reaching the equilibrium value. We analyse such
phenomena by extending our previous theory for the dynamics of an evaporating
single component droplet to double component droplet. We show that the time
dependence of the contact angle can be quite complex. Typically, it first
decreases slightly, and then increases and finally decreases again. Under
certain conditions, we find that the contact angle remains constant over a
certain period of time during evaporation. We study how the plateau or peak
contact angle depends on the initial composition and the humidity. The theory
explains experimental results reported previously.
