A RECONSIDERATION OF THE MEASUREMENT OF POLYMER INTERDIFFUSION BY FLUORESCENCE NONRADIATIVE ENERGY-TRANSFER

A general formalism has been developed for quantitative determination of polymer self-diffusion coefficients, D(p), using fluorescence nonradiative energy transfer (NRET). The experimental geometry consists of a ''sandwich'' of two thin polymer films, one labeled with NRET donor chromophores and the other with NRET acceptor chromophores. D(p) can be characterized self-consistently by steady-state fluorescence intensity measurements of donors or acceptors or by transient donor fluorescence intensity decay measurements as a function of interdiffusion time, t. For t < x2/(16D(p)), where x is the thickness of the donor-labeled polymer layer, increases in the normalized acceptor intensity and normalized energy transfer efficiency with interdiffusion are the same and equal to k(n)(D(p)t)1/2x, where k(n) is a function of the initial acceptor concentration. Similarly, the decrease in the normalized donor intensity with interdiffusion is proportional to (D(p)t)1/2/x. The general formalism presented here has been compared to earlier approaches, revealing that a previous method of analyzing the steady-state acceptor intensity in terms of polymer diffusion is merely a limiting case of the present formalism while a previous method of analyzing the donor intensity decays results in underestimates of D(p).