Abstract
In conclusion, we can say that the properties of thin polymer films and their relaxation behavior are strongly dependent on their thickness. This is related to the restriction of molecular mobility at the phase boundary (independent of its nature) as a result of the reduced number of possible chain conformations. The less the polymer thickness, the more pronounced is the contribution of surface layers with diminished molecular mobility to the mechanical properties. This statement may be illustrated by Figure 12, which shows the dependence of the elastic modulus and surface-to-volume ratio on film thickness. Diminishing film thickness leads to increase in film rigidity, beginning at the point where the surface-to-volume ratio increases sharply. This suggests that the effect is associated with change in mechanical properties of thin surface layers, which contributes significantly to total mechanical properties. We have other data which show also that the relaxation spectrum of a film is changed when its thickness changes. The findings discussed above indicate that the solid surface has a noticeable and complex effect on the properties and relaxation behavior and relaxation time spectra of polymer coatings on solid surface, both inorganic and organic. The principal reasons for these changes are the adsorption interaction with the solid surface, decrease of molecular mobility, and strong intermolecular interaction transferring the influence of the solid surface to more remote layers of polymer.
Positron depth profiling in solid surface layers
