Sandwiched Film

A textbook example for the application of the uncorrelated GDM is the recent study by Gambino et al. on a light emitting dendrimer [49]. The system consists of a bis (fluorene) core, meta-linked biphenyl dendrons, and ethylhexyloxy surface units. ToF experiments shown in Fig. 5 were performed on 300 nm thick sandwich films... 

Fig. 66. Magnetostriction hysteresis loops of a TbFeCo single-layer film and a Fe/TbFeCo/Fe sandwich films.

The electrochemical polymerization of pyrrole or thiophene readily lends itself to formation of composites. Polypyrrole-acetylene laminates have been made by using polyacetylene as an electrode 295). The polypyrrole forms as a 5 pm skin on the polyacetylene. If the polyacetylene is first doped, the polypyrrole completely permeates the film. In both cases the conductivity of the composite reached 30-40 S cm-1 and was much less sensitive than that of pure polyacetylene to exposure to moist air or water, so that the polypyrrole protects the polyacetylene even in the case where it permeates the film. In this latter case, treatment with ammonia caused the conductivity to drop by 30 x whereas for the sandwich films the conductivity dropped by 4600 x through the film but only 17 x in the surface layers. 

Figure 8.27 shows an actual Nyquist plot (negative of the imaginary part of the complex impedance, Zj versus the real part of the complex impedance Zr) obtained by measuring the impedance of a NilNa-X INi02 battery, which is composed of a wafer (with a diameter of 12mm) in which were sandwiched films of Ni powder (0.5 g), Na-X zeolite powder (0.5 g), and Ni02 powder (0.5 g) [132],... 

Figure 69 Variation of the current with applied voltage, recorded in a range of thickness between 10 and 300 nm. (a) SL sandwich film system of Al/Alq3(d)/Ca adapted from Ref. 355. (b) DL LED, ITO/TPD(20nm)/Gaq3(10—80nm)/Mg Ag with varying emitter layer of 8-hydroxyquino-line gallium complex (Gaq i) after Ref. 356. Copyright 1996 American Institute of Physics.

As typical examples, formation of ultrathin sandwich-structured films can be demonstrated in the multicomponent systems Ag(M/)/Pb, and Aa(fik )/Ag, Tl. The first system offers the possibility to form ultrathin sandwich films consisting of two monolayers with different composition of Pb and Tl depending on the polarization routine, as shown in Fig. 6.18. The first monolayer may contain either only Pb adatoms (Fig. 6.18a) or both Pb and Tl adatoms (PbjrTly with 0.5 z < 1, x -i- y = 1,... 

Wang SX et al (2000) Sandwich films-properties of a new soft magnetic material. Nature 407 150-151... 

To interpret the impedance data, a model of the anodic aluminium oxide film must be established. The anodic aluminium oxide film is a sandwich film consisting of two layers, a barrier layer and a porous layer (Figure 23.4A [2]). 

Figure 14. The region of OD stretching fundamental in the spectrum of HDO in Nafion 125 (sodium form, 95% H, 5% D). The top spectrum was obtained by the sandwiched film technique, the others by the vapor equilibrium technique. The point-by-point spectrum was recorded with 3-min time lapses between points to minimize...

Figure 15. Plot of the frequency of the B component of OD stretching of HDO in Nafion 125 as a function of water content. Key [], sandwiched film technique o, vapor equilibrium technique.

It is quite well known that the formation of nanophases plays an important role in adhesive technology although this fact was ignored for many years due to the difficulties relating to the imaging of such small structures. Nanometer-scale interdiffusion layers account for polymer/polymer adhesion. This is illustrated in Fig. 13.6 for the sandwiched films of the thermoplastic elastomer SEES and isotactic polypropylene, annealed at 160°C for several hours. The interdiffusion layer is approximately 100 nm wide. This interfacial nanodesign is the key to improved adhesion of polypropylene materials. 

Thin film La-Sm samples are prepared from two distinct evaporation sources such as tungsten crucibles. This procedure yields two different sorts of sandwich films Sm-La and Sm-La-Sm (Gasgnier, 1981). These samples are deposited at room temperature. Upon heating with the electron beam of the electron microscope the thinner lanthanum films of the two sequences show the formation of C- and B-Sm203 and A-La203. The thicker lanthanum films of the Sm-La-Sm... 

Giant magnetostrictive thin fihn materials 17 5.3. Magnetostriction of R-T sandwich films 41... 

After removing the sample from the magnetic field the polymer is photo-crosslinked from both sides (a few minutes are sufficient) using a UV-lamp. If Tg is relatively low it can be helpful to photo-crosslink under cooling with an ice-bath so that the mesogens do not reorient due to the heat produced by the UV-lamp. The sandwiched film should now be transparent and can be removed from the glass slide after dissolving the sacrificial layer in water. 

If e. denotes the thickness of the sandwiched film. its draining velocity, a the size of the flat portion of the elastomer lens, and r/ the viscosity of the liquid, wo can write the two following equations ... 

After the sandwiched film has dewetted, a dry contact of rcidius a forms between the elastic ball and the hydrophobic glass. II. Hertz was the first to calculate the size of the contact of an clastic ball pressed against a planar surface with a force In the absence of any adhesion forces between the elastomer and glas.s, the radius a of the flat portion of the contact and the penetration depth 6 of the ball can be determined by minimizing the energy of the squeezed ball ... 

Figure 9.32 illn.stratcs the profile of the lubricated ball U > V .o). The sandwiched film, of average thickness c. forms a litpiid wedge with a very small angle 6 eja ( lO" to 10" rad). The tliickne.sse.s of the wedge art e. and C2 at the leading and trailing edg< . respectively. 

In this chapter, we have seen how a sandwiched film can promote adhesion on a surface. We have examined the cstahlishment of an adhesive contact between a deformable elastomer lens and a rigid planar solid - -whether it is in motion or at rest immersed in a non-wetting liquid. 

---