Small-angle neutron scattering studies of polymer interdiffusion during latex film formation

An equation relating the growth of the radii of gyration of labeled latex particles, commonly observed in small-angle neutron scattering (SANS) experiments on interdiffusing latex films, to the interdiffusion coefficient of the polymers was derived from Fick's law of diffusion. SANS experiments were conducted on interdiffusing latex films consisting of isotopic latex particles with large mismatch in molecular weight. The interdiffusion coefficient, the interpenetration depth, and the extent of intermixing were extracted from the scattering data. The interdiffusion process can be described by Fick's law of diffusion with a time dependent interdiffusion coefficient. The measured interdiffusion coefficients decreased with increasing annealing time, suggesting that faster moving species control the interdiffusion process at short times. An analysis of the scattering data from completely interdiffused latex films based on de Gennes' scattering function for polymer blends reveals that molecular-level intermixing has been achieved in these latex films.