Thin film technique microtoming

Another technique we used to observe these distributions is scanning electron microscopy with energy dispersive x-ray analysis (EDAX). Concentrations of Cyasorb UV 1084, [2-2 -thiobis(4-ter -octylphenolato)-n-butylamine nickel], a nickel-containing UV absorber, were point counted to obtain nickel concentrations along a spherulite diameter. Figure 3 shows results for 1 and 4 wt % additive. This shows a uniform melt concentration, a boundary peak, a lower concentration within the spherulite, and a central dip. The resolution and sensitivity with this technique are poorer than with the optical microscopy. With every method, thin film crystallized samples and microtomed sections of bulk samples gave similar results. 

There are a number of methods available for examining polymer samples [7, 8]. If the polymer is a thermoplastic, it can be softened by warming and formed in a hydraulic press into a thin film. Alternatively, the polymer may be dissolved in a volatile solvent and the solution allowed to evaporate to give a thin film on an alkali halide plate. Some polymers, such as cross-linked synthetic rubbers, can be microtomed (cut into thin slices with a blade). A solution in a suitable solvent is also a possibility. If the polymer is a surface coating, reflectance techniques may be used. 

In a second TEM technique, a thin layer of gold was evaporated under high vacuum onto a microtomed thin film of the blend containing the maleated elastomer. TEM in Figure 3, shows small islands of gold (of order 5 nm) on the surface of the specimen which are more densely packed on the crystalline polyamide than on the amorphous rubber. The presence of subinclusions within the rubber domain is clearly revealed by the gold decoration. 

While often simply exposing a microtomed surface is sufficient for the purpose, sometimes specimens require support, especially thin films which cannot stand by themselves and where the top and bottom layers would be removed by the etchant. Sandwiching techniques have been developed, whereby the top and bottom surfaces are supported and protected by a material which can be etched along with the polymer specimen. An example is a work oti woven polypropylene tapes, both before and after consolidation (Jordan et al. 2003). 

The Fourier Transform Infra-Red spectroscopy (FTIR) technique is a valuable method for investigating the kinetics of sorption of organic molecules in polymers, hi further works (Safa and Abbes, 2002 Safa et al., 2007 Zaki et al. 2009), we have used such method to study the sorption rate of different esters by polypropylene. The ester function is characterized by absorption band in regions where the polypropylene does not absorb. The sorption can be evaluated by the ratio of the carbonyl ester (CO) band area at 1747 cm to the area of a characteristic peak of the PP at 841 cm used as a reference band. The polymer samples are cut-out in thin films of 50 pm thickness by using a microtome. These films are then put on a support adapted for the spectroscopic analysis. Figure 5 shows FTIR spectra of a polypropylene sample after contact with 5000 ppm of amyl acetate solution at 23°C after 5 hours, 4 days and 15 days of immersion. The absorption characteristic band of esters at 1747 cm and its growth is clearly observed. 

The distribution of components in BHJ thin-films normal to the surface of the film is also critical in defining the performance of the material. In the simplest extreme, if there is a preferential segregation of one component to an electrode interface, device performance can be poor even with an idealized morphology in the remaining part of the BHJ active layer. Given that charge transfer and collection occur at the electrode, transport to these interfaces requires transport normal to the surface of the film. Normally, the BHJ layer is 100-200 nm in thickness. Consequently, methods are needed to assess composition profiles normal to the film surface or techniques must be used to examine cross-sections normal to the film surface. In the latter case, cryo-microtoming or focused ion beam (FIB) are required. 

Profilometry makes use of a stylus that is dragged over a film surface. Thickness measurements are most accurate when there is a clean transition between the bare substrate and thin film coating. In most cases the thin film must be more than 100 nm thick to get an accurate profile, which is a limitation for LbL assembly. Transmission electron microscopy (TEM) can be used to directly observe the film, but requires the sample to be microtomed. The process of sectioning the film can lead to compaction or other defects that distort the thickness observed in TEM. The best study of layer-by-layer assembly thickness will use at least three of these techniques to ensure accuracy. 

Morphology of select star blocks was investigated by transmission electron microscopy (TEM). Films were cast from toluene and annealed for 2 days at 120 °C. Ultra thin sections (-50 nm) of unstained samples were cut by cryogenic microtome techniques. Samples were viewed by a JOEL (JEM-1200EXII) TEM. 

Electron microscopy samples were prepared by techniques similar to that of Kato (8). Film samples were fixed with OSO4, potted in polymethyl methacrylate and then microtomed into thin sections ( 100 nm) for transmission examination using a Philips 100B electron microscope. 

As discussed in Section 2.23.1.2, one of the advantages of AFM over electron miaoscopy is that it enables 3D imaging of untreated samples in a physically relevant environment. Given the surface nature of the technique, initial AFM studies of phase separation processes in polymer mixtures have been primarily focused on thin or ultrathin films. " " The confinement in a film and component segregation to the interfaces have been shown to have a profound effect in both spinodal decomposition, and nucleation and growth processes of the phase separation. The spectrum of AFM applications has been extended to bulk phase separation of polymer mixtures using conventional and oblique microtoming of polymer blend films. 

---