Abstract
The surface tension of coal extract solution in N-methyl-2-pyrrolidinone were measured by Wilhelmy method. A discontinuity point corresponding to the critical micelle concentration was observed in the surface tension and logarithm concentration relationship. The non-linearly curved dependency of the surface tension on logarithm concentration could be explained by a simple association equilibrium qualitatively. The decrease in the dynamic suface tension was slow in coal extract solutions, taking over sevaral hours to an equilibrium value. The higher is the rate of decrease in surface tension, the higher is the concentration of the solution. The time profile could not be described in the theory of the diffusion-controlled process of adsorption to a surface. An kinetic mechanism of consecutive reaction was applied favourably to explain the time profile.
