Film thickness influencing apparent surface

Torres and co-workers (304) studied the dependence of Tg on film thickness, and found both increases and decreases in the apparent Tg of thin films, depending on whether the film is free or deposited on an attractive substrate. Rranbuehl and co-workers (305) found that Tg decreases with confinement by noninteracting surfaces consisting of planes (one dimensional, 1-D), tubes (2-D), and spheres (3-D). Perhaps the surface-to volume ratio, and the influence of free volume at the constraint surface, creates additional freedom of motion for the chains in these types of confinement. Consistent with this view is the observation that when chains are attracted to a surface, and thereby immobilized, the Tg increases (304). Similar conclusions were reached by Aoyagi and co-workers (306) in a spring-bead model simulation of confined chains. 

In experiments where a thin film of polymer is applied to an elastic substrate, the thickness of the film strongly influences the apparent surface energy, as expressed in equation (26) and shown in Figure 11. In applying this result, it must also be... 

The yellowing tendency of autooxidatively dried paints has been shown to be significantly dependent on film thickness, film exposure time and metal cation type, whereas the influence of drier concentration and anion type are less apparent. The yellowing effect of two driers has been found to be additive. In the case of paints, the drier efficiency has often been shown to decrease as a result of paint storage. This has been assigned to the adsorption of driers on the pigment surface. ... 

The nature of thin films may also be influenced by rapid, thermally driven fluctuations in the local density of liquids. Heuberger, Zach and Spencer performed force and refractive index measurements of hexane confined to nanometer thickness using fast spectral correlation spectroscopy, and observed the fluctuations in density. This finding may help explain observations of high surface mobility, anomalously fast selfdiffusion, and apparent solidification in liquid films. 

Employing atomic composition data, obtained by XPS, one is, however, led to believe that the atmosphere may affect the type of oxide that forms. Co/O ratios for dry and moist air cured films are 1.7 and 0.9, respectively whereas, Sn/0 ratios are 1.6 and 1.7. Thus, the electrical properties are apparently influenced by both the type of oxide formed during the thermal cure and by the spatial distribution and amount of metal oxide within the surface of host polymer. The thickness of both the oxide layer and polymer overlayer also appear to be very important here in achieving improved surface electrical resistivity. 

In this study, a polymer thin film/substrate configuration was used to study the influence of substrate confinement on the polymer property. PS films supported on a graphite surface were chosen as a model system to resemble the structural element of PS-CNF nanocomposites. Specifically, an apparent property, Tg a, was measured and interpreted as an indicator of the polymer chain mobility. Using films with different thicknesses, the competition between the free surface-induced Tga depression and the substrate-induced Tga increase was observed. For films with sufficient thinness, a higher Tg,a compared with its bulk counterpart was observed. ile for weak polymer-substrate interactions (PS/SiOa systems) the T a of thin PS films was further reduced compared with the surface T a-... 

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