Deformation of thin films

Glad [37] studied the micro deformations of thin films prepared from DGE-BA/MDA by electron microscopy. His results are also shown in Fig. 7.5. The deformation of the sample with high strand density was small and consequently its image in the EM rather blurred. Therefore, the result on Mc = 0.5 kg/mol should perhaps have been omitted. 

Force/pressure transducers The simplest force measures use load cells based on an LVDT, which displaces by a small amount as a force is applied. Strain gauges can measure the (small) deformation of thin film attached to a surface by measuring the resistance of an attached conducting element. 

Deformation of thin films or semithin or ultrathin sections in a tensile device and investigation after deformation or in situ by TEM, HEM, ESEM, or AFM. Changing from Method 1 to Methods 2 and 3 allows larger magnifications and yields more details on the micromechanicai processes and their dependence on the actual morphology. 

Progress toward resolving such questions is summarized in this chapter. The discussion begins with the issue of fundamental dislocation interaction phenomena and nonequilibrium behavior of interacting dislocations. Attention is then shifted from consideration of films with low dislocation density to the modeling of inelastic deformation of thin films with a relatively high densities of dislocations. For this purpose, constitutive models for time-independent and time-dependent deformation of thin films are examined by appeal to continuum plasticity theory. Overall features of material behavior captured by such theories are then compared with available... 

Deformation of thin films or semi-/ultrathin sections in a tensile device and investigation after deformation or in situ by TEM, HEM, ESEM, or AEM. 

Other researchers have also observed an increase in HIPE viscosity with increasing phase volume ratio [77] however, the effects of droplet size, polydis-persity or continuous phase viscosity were not investigated. Further studies [78] revealed that the viscosity increased for smaller mean droplet radii this effect was found to be greater at higher internal phase ratios. The total interfacial area increases as droplet size decreases, so viscosity also increases as more energy is required to deform the larger network of thin films [79]. 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

A number of peculiar properties are displayed, including rheology characterised by viscoelasticity. Viscosities are far higher than that of either bulk phase this is a result of the large amount of energy required to deform the network of thin films of the continuous phase. A yield stress is observed, below which HIPEs behave as elastic solids and will not flow. Resistance to flow occurs from the inability of compressed droplets to easily slip past each other. Above the... 

Fig. 29 Typical example of shear deformation zone. Thin film of PMMA at 53 °C and a strain rate of 2 x 10-3 s 1...

Fig. 80 Diagram of thin film deformation behaviour as a function of temperature for unaged and aged BPA-PC (Mw = 31000) strain rate of 4 x 1CT4 s 1 (From [58])...

The ATR-FTIR spectra of ENR and transmission spectra [158] of thin film of the coupling agent are shown in Figure 3.9b, in which the band at 1085 cm"1, is characteristic of Si—OCH3 stretching vibration, the band at 1602,1627 cm"1 are characteristic of NH2+ deformation modes and C=C (vinyl benzene) stretching, respectively. 

The development of the thermodynamics of thin films is related to the problem of stability of disperse systems. An important contribution to its solving are the works of the Russian scientists Derjaguin and Landau [1] and the Dutch scientists Verwey and Overbeek [2], known today as the DVLO theory. According to their concept the particular state of the thin liquid films is due to the change in the potential energy of molecular interaction in the film and the deformation of the diffuse electric layers. The thermodynamic characteristic of a state of the liquid in the thin film, as shown in Section 3.1, appears to be the dependence of disjoining pressure on film thickness, the n(/t) isotherm. The thermodynamic properties of... 

AFM can also be used to probe local mechanical properties of thin films of food biopolymers, which are difficult to measure using traditional rheological methods. Several mechanical models have been developed to analyze the Young s modulus of food systems. One of the simplest models, the Hertz model, assumes that only the elastic deformation exists in a surface with spherical contacts, and the adhesion force can be neglected (Hugel and Seitz 2001). Equation (8.2) describes the relationship between the loading force, F and the penetration depth, d, where a is the radius of contact area, R the curvature of the tip radius, Vi and the Poisson s ratios of the two contact materials that have Young s modulus, Ei and E2. ... 

The ESCR performance of a resin is not easily modeled. A laboratory technique for the preparation of thin films of HIPS materials for the study of deformation processes by microscopy allows the deformation process to be better understood. The transmission electron microscope (TEM) allows direct visualization of the crazes themselves in thin films. For good contrast between the crazes and the bulk polystyrene, thin, cast films from 0.5 to 2 p,m are required, and also staining of the rubber phase with a heavy atomic species to provide contrast between the rubber and the polystyrene. Another intricacy of this method requires a solution of the HIPS material in a 65 35 methyl ethyl ketone-toluene solution to prevent significant swelling of the rubber particles during the preparation process. 

In isolation, the BHT ion is tetrahedral, and consequently only two fundamentals, the asymmetric BH stretch (V3) and asymmetric BH4 deformation (V4) are IR active for the isolated ion, whereas all four fundamentals are Raman active. The Raman active fundamentals were characterized in liquid ammonia solutions, whereas IR spectra of thin films of NaBH4 on alkali halide crystals or diluted in an alkali halide host crystal have been reported ". Raman and IR studies focused specifically on NaBH4 and LiBH4 have also been reported. The vibrational modes in borohydrides are of three distinct types librational (below 1000 cm ), B-H bending (1127 cm ) and B-H stretching (2200-2400 cm ). The overtone of the deformation mode (2V4) occurs around 2228 cm ... 

A transmission electron micrograph of a craze in a thin film of poly(styrene-acrylo-nitrile), shown in Fig. 1 a, will serve to introduce the principal microstructural features of crazes. The direction of the tensile stress is marked and it can be seen that the craze grows with the primary direction of its fibrils parallel to this tensUe stress and with the interfaces between the craze and the nearly undeformed polymer matrix normal to the stress. Since the overwhelming portion of the experiments to be reviewed here rely on the use of thin film deformation and transmission electron microscopy techniques, a brief review of the general methods of these experiments is in order. 

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