We propose a model to describe energy transfer between donors and accepters chemically attached to the two different components of a polymer blend. The model describes the case of one polymer dispersed as spheres of identical diameter in a continuous matrix of the second polymer. The model takes explicit account of the segment distribution of the two polymers in the interface region. We used this model to characterize the interface between poly(butyl methacrylate) (PBMA) and poly(2-ethylhexyl methacrylate) (PEHMA) domains in a binary blend. The blend was prepared by casting films onto a solid substrate from mixed aqueous latex dispersions of the two polymers. The dispersions were prepared by emulsion polymerization under conditions in which both components were formed as spherical particles with a very narrow size distribution. By using a 14:1 particle ratio of PEHMA to PBMA, we obtained films in which the 120 nm PBMA particles were surrounded by the PEHMA matrix. For the ion-exchanged latex blend, the interface thickness in the film freshly prepared at room temperature was delta = 21 +/- 2 nm and upon annealing broadened to delta = 25 +/- 2 nm. Because of the low degrees of polymerization for the samples, it is difficult to have confidence in the value of the Flory-Huggins parameter chi calculated from the experimental value of delta, because the correction for the finite length of the component is larger than the term that depends on the interface width. Keeping in mind the limitations of this calculation, we estimate that chi is approximately equal to 0.02-0.03.