Anomalous tracer diffusion in film forming colloidal dispersions

EPR Studies on Film Formation of Colloidal Dispersions, 2. Drying, Film Annealing, and Film Rewetting

“…These films were prepared by drying the dispersions at temperatures below the MFT and the particles are thus not expected to be deformed. Note that such an anomalous diffusion mechanism in drying dispersions of the same polymers was suggested for non-polar dye molecules on the basis of forced Rayleigh scattering experiments by Bartsch et al [11] These authors also showed that the anomalous diffusion is re-established after rewetting of PBMA films. After annealing, the inner surface is lost and TEMPO can penetrate into the film only by normal, slower diffusion.…”

“…This result is in agreement with the observation of Bartsch et al by forced Rayleigh scattering that the diffusion coefficient of a dye molecule in serum/surfactant channels decreases significantly with decreasing water content under similar conditions. [11] The probe TEMPOL apparently interacts somewhat stronger with the surfactant layer, as can be concluded from the larger g in the fresh dispersions. Furthermore, the increase in g with decreasing water content is more continuous.…”

Tracer diffusion properties of core–shell latex films studied by photoinduced grating relaxation

“…The major incentive for the reported work, the correlation between the diffusion path M s and the dimension of the domain in a latex film which the tracer dye traverses that was observed in previous work,7, 38 does still hold for more complex geometries like core–shell particles. For homogeneous latex particles, the identification of the slow state as representing the particle interior in comparison to the hydroplasticized particle interfaces was achieved by demonstrating a clear correlation between the particle diameter and the root mean squared displacement M s 7, 38. For the core–shell particles the presented results hint partly into this direction as in System 1 with a (thick) shell of 37 nm the analysis of the apparent diffusion coefficient yielded an M s value of 32 nm that is close to the shell thickness.…”

“…Recently, we could show that the peculiar enhancement of the tracer diffusion coefficient with increasing grating distance, which was observed in wet latex films could be quantitatively understood and analyzed by assuming that a hydrophobic tracer is distributed between the polymer phase and the interfacial area between the particles 7, 38. On its diffusion path the dye enters and leaves a given phase with a certain exchange rate.…”

“…The root mean squared displacements can be considered as a measure of the distance travelled by the tracer in a given phase within a residence time. In the analysis7, 38 the M s,f and D s,f are the fit parameters, which are varied in order to equate the calculated D app (Λ) to the experimentally determined values. The D s,f enter eq 6b directly.…”