Dynamic light scattering (DLS) technique is an effective method to investigate association behaviors of particles and molecules in solutions. Carbon disulfide (CS_2)-N-methyl-2-pyrrolidinone (NMP) mixed solvent (1:1 by volume) gives high extraction yields for many bituminous coals at room temperature, and the yields increase by the addition of tetracyanoethylene (TCNE). This effect was explained by the breaking of the association between coal molecules. In this study, the diffusion coefficient of coal extract solution in N, N-dimethyl-formamide was estimated by the DLS measurement, and the effect of addition of TCNE was investigated.
