High-field EPR studies on polymer film formation from colloidal dispersions

High-field EPR on nitroxide spin probes is applied to characterize the dynamics of small additive molecules and surfactants in polymer films obtained from colloidal dispersions. Due to the increased width of the spectra and the smaller influence of hyperfine-dependent relaxation on the spectral lineshape at W band (94 GHz) compared to X band (9.6 GHz), it is possible to measure subnanosecond rotational correlation times for the isotropic motion of the unpolar spin probe TEMPO in the free volume of poly(acrylate) films. Likewise, the anisotropies of the rotational diffusion tensors of a surfactant and a small ionic additive molecule in poly(fluoroacrylate) films can be determined with better confidence at W band. From these anisotropies it is concluded that the surfactant aggregates exhibit low molecular order, whereas the ionic additives are strongly attached to immobilized ionic clusters. High-field EPR lineshapes at W band are also found to be more sensitive to slow motions on a microsecond time scale than X-band EPR lineshapes. The design of a Fabry-Pérot resonator for measurements on polymer films is discussed and its sensitivity is demonstrated on a wet polymer film with a thickness of 160 μm.