Abstract: Dynamic lattice Monte Carlo simulation was used to study the adsorption of symmetric and unsymmetric
nonionic-surfactants at the water-oil interface.The time needed to reach equilibrium,the numbers of the surfactant on the interface, the thickness of the interface between water and oil phases, the density distribution of segments A and B in the system and the interfacial tension,both static and dynamic were obtained and the effect of the structure and concentration of the nonionic-surfactants on these properties was studied too.The time needed for the system to reach equilibrium was related to the structure and concentration of the nonionic-surfactant.For the nonionic-surfactant with the same structure,the time increased when concentration of the surfactant increased under the situation that the concentration was below CMC.The time was determined by the length and structure of the chain when the number concentration was same.The symmetry of the density distribution curve of segments A and B was related to the composition of the nonionic-surfactant.The surface activity of nonionic-surfactant was decided by its structure mainly.For symmetric nonionic-surfactant, it was more active as its length increases.For unsymmetrical one, it was determined by the structure; The interfacial tension decreased as the concentration of the nonionic-surfactant increased and would not change when it reached a stable value when the length of the nonionic-surfactant is same.