EPR studies on film formation of colloidal dispersions, 1 - Site selectivity and techniques

For the first time, electron paramagnetic resonance (EpR) spectroscopy of spin probes is applied to the characterisation of colloidal polymer dispersions and of films obtained from diem. The different domains of the dispersions and films can be selectively addressed by simply adding various, readily available spin probes to the initial dispersions. Evidence for the localisation of these probes is obtained from the comparison of their rotational correlation times or rotational diffusion tensors. from the observation of local order in the case of surfactant probes, and from the variation of fluorine matrix hyperfine couplings in the case of probes in poly(fluoroalkyl acrylates). The introduced methodology forms the basis for a new approach to studies of film formation, film annealing, and film rewetting by spin probe EPR. Structure of the spin probes used in this work. a) Nearly spherical spin probes with a radius of approximately 350 pm. For TEMPO the p(z) orbital on the nitrogen atom is shown in which about 40% of the spin density is located. The z axis of the molecular frame is along the symmetry axis of this orbital, and the x axis along the N-O bond. b) Surfactant spin probes