Stresses during film formation

The properties of silicon dioxide films also depend upon all plasma deposition parameters. Temperature is the critical parameter (240), although the compressive stress level varies with rf frequency (237, 240). Film topography can be varied during deposition by altering ion bombardment conditions (242, 243). In particular, the incorporation of Ar in the deposition atmosphere enhances sputtering and thus promotes conformal step coverage during film formation (243). 

Stress can build up in a coated plastic part and can affect coating mechanical properties. Stress can accumulate during film formation and from variation in relative humidity and/or temperature (33). Even differences between thermal expansion coefficients of the substrate and the coating can induce stress. The dissipation of accumulated stresses is key to avoiding premature system failure. 

As an aqueous dispersion can only dry above 0 °C, the MFFT and white-point temperature are only defined above this value. The control of the polymer layer thickness is crucial for the measurements. Mechanical stress may develop during film formation (particularly when crosslinking is involved) which leads to crack formation above a certain layer thickness. A further point which should be considered is that very short drying times are often used in dispersion processing, for example on coating machines. In this case, the MFFT may well he above the value determined according to ISO 2115. The discrepancy is caused by kinetic limitations in water evaporation and polymer interdiffusion [24]. 

Near-surface structure occurs up to approximately 50 pm and is affected by surface hardening or reaction film formation in this regime. Near-surface structure is particularly susceptible to severe deformation and is important because the residual stresses in these regions will affect crack propagation during lubrication failure. 

The details of thin-film formation by PVD or CVD on the atomic and molecular scale are unknown in most cases, but such knowledge would be very helpful to design new processes and to tailor film properties. Information is lacking due to the high reactivities, short lifetimes, and low concentrations of the relevant transient gas-phase species. Furthermore, many of the thin-film properties in statu nascendi are unknown due to the experimental difficulties of thin-film characterization during deposition, particularly with non-crystalline films and if established methods such as RHEED and FEED cannot be applied. Among the film properties, mechanical stress in thin films can lead to unwanted (uncontrolled) instabilities and peel-off phenomena. Therefore, in situ diagnostic methods have been developed to... 

In some cases the adhesive film cannot contract in thickness during ciming—for example, in the csise of tube-in tube adhesive-bonded joints. Then the tangential internal stresses are added to the normal ones. The total stresses in this case increase substantially. The occurrence of internal stresses during formation of the polymeric film on the... 

In order to overcome these drawbacks, various solutions can be considered. One would be to destroy the surfactants after polymerization and film formation. Some efforts have been made to make surfactants photosensitive [1] with a scissile covalent bond in between the hydrophilic and the hydrophobic parts of the surfactant Tlie second one, which is considered in this review, is to permanently anchor the surfactants onto the particle surfaces during the polymerization. In such a way, the adventitious desorption of the surfactants under stresses is no longer possible. Even if such anchored surfactants cause the coalescence process to be more difficult their migration is not possible and the process erf hydrophilic domain formation is hindered. Then it may be expected that the water solubilization inside the film is limited so that the water permeability decreases. A final advantage lies in the absence of surfactants in the serum after polymerization then, in such applications when the polymer material is separated from the water by flocculation, the absence of surfactant in the rejected water should make its purification and recycling easier. The use of such surfectants is also claimed to reduce the volume of foams [2] such things become increasingly imponant, when much more attention is paid to environmental problems. 

Rheological properties Rheology is the study of the deformation and flow of matter under the influence of an applied stress. The measurement of rheological properties is helpful to predict the physical properties of polymer nanocomposites during and after processing. Oberdisse [44] studied the rheological properties of a special nanocomposite material obtained by film formation of mixtures of colloidal silica and nanolatex solutions by means of uniaxial strain experiments. 

Table 1 summarizes the values of rheological parameters of some studied emulsion films stabilized by the gelatin/ lecithin complexes. These parameters were measured immediately after the film formation (at 1 min). It is worth noting that the yield stress, elastic modules and film shear viscosity increase in the increase of the lecithin concentration. Analysis of the experimental data demonstrates that the parameters of the films (when films have been formed during several minutes) have values in the same order as the analogous characteristics of the layer formed after 4 hours. 

Film Formation and Propoties.— Work on film preparation and subsequent processing of 2GT has been limited to studies on the transverse constriction and stresses observed during uniaxial orientation and the problems associated with the maintenance of planarity during heat relaxation. Orientation and shrinkage have been discussed in a number of papers with studies on orientational setf-ieinforcement and relaxation and its effects on orientation. The effect of the interaction of films with organic liquids has promoted studies on the structural arrangements in liquid-induced crystallization of cold-drawn 2GT films, and the effect of crystallization on adhesion and cohesion. ... 

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