Epoxy resin thin films

J. Kanzow, F. Faupel, W. Egger, P. Sperr, G. Kogel, C. Wehlack, W. Possart, Depth-resolved analysis of the ageing behaviour of epoxy resin thin films by positron spectroscopy, Proc. oral pres., 7th European Adhesion Conference EURADH 2004, Ereiburg im Breisgau, September 5-9, 2004. 

Let us consider the elastic properties of epoxy polymer thin films on substrates with various surface energies. The elasticity of the boundary layers and its contribution to the elasticity of the film on the substrate were assessed by the dependence of the modulus of elasticity on the thickness of the polymeric coating formed on high-energy (aluminum) and low-energy (polyethylene terephthalate) surfaces. ED-20 epoxy resin (molecular weight 420, epoxy number 21.6) was selected... 

Tertiary bismuthines appear to have a number of uses in synthetic organic chemistry (32), eg, they promote the formation of 1,1,2-trisubstituted cyclopropanes by the iateraction of electron-deficient olefins and dialkyl dibromomalonates (100). They have also been employed for the preparation of thin films (qv) of superconducting bismuth strontium calcium copper oxide (101), as cocatalysts for the polymerization of alkynes (102), as inhibitors of the flammabihty of epoxy resins (103), and for a number of other industrial purposes. 

Thermosets A number of thermosets have been used as adhesives. Phenolic resins were used as adhesives by Leo Baekeland in the early 1900s. Phenolic resins are still used to bind together thin sheets of wood to make plywood. Urea resins have been used since 1930 as binders for wood chips in the manufacture of particle board. Unsaturated polyester resins are used for body repair and PUs are used to bond polyester cord to rubber in tires, and vinyl film to particle board, and to function as industrial sealants. Epoxy resins are used in the construction of automobiles and aircraft and as a component of plastic cement. 

Small samples, such as dry polymer powders, fibers, or thin films, need to be held for sectioning by embedding in a suitable carrier material. Waxes, epoxy, or acrylic resins are widely used for this purpose. 

Figure 25 (a) Emission spectra at 293 K of/ac-ClRe(CO)3(4.7-Ph2-phcn) in the mixed epoxy system of bisphenol-A/novalac and DGEBA resin (0.05-mm thin film) containing a triarylsulfonium hexafluoroantimonate photoinitiator as a function of UV-irradiation time (A) 0 s, (B) 15 s, (C) 30 s, and (D) 60 s. The emission spectra are uncorrected for photomultiplier response and vertically displaced for clarity. Excitation wavelength is 420 nm in each case, (b) Plot of emission intensity at the MLCT band maximum of /ac-ClRe(CO)3(4,7-Ph2-phen) as a function of UV-irradiation time. (From Ref. 100.)... 

Brett, C. L., The Detection of Thin Films of Epoxy Resin on Metal Surfaces," Journal of Applied Polymer Science, vol. 18, 1974, p. 315. 

Fig. 11. Schematic diagram of continuous flow apparatus and structure of an enzymatically coupled FET. (a) Schematic diagram of continuous flow apparams S, enzymatically coupled FET sensor SC, sensor cell WB, water bath D, drtdnage P, peristaltic pump TV, three-way joint EV, electrical valve VC, valve controller WS, washing solution AS, analyte solution, (b) Detailed structure of flow-through cell OR, rubber O-ring. (c) Structure of enzymatically coupled FET (electrical insulation with epoxy resin is not shown here for simplicity) ISFET, ion-sensitive FET EM, enzyme membrane G, thin gold film TC, card edge connector. (Reproduced from Shiono et al. (9), with permission.)...

Previous work (8) on partially cured thin-films of two other epoxy resins showed much less temperature separation between softening, further reaction, and ultimate glass transition than is the case with Resin 5208. In fact, overlap between the dispersion regions made it impossible to identify the chemical reaction process. 

The distribution of the photoproducts in the thickness of the film can be determined by IR micro-spectrometric analysis. Irradiated films were embedded in an epoxy resin and thin slices of thickness ca 100 were analyzed. The variations of the absorbance at 1725 cm-1 versus the film thickness are plotted Figure 30.3. The middle of the film is almost as photooxidized as the front and rear sides. The film has a relatively high permeability to oxygen and the photoproducts are fairly homogeneously dispersed in the thickness of the film. 

Fig. 22. Large ZSM-5 crystals synthesized by J. Kornatowski (137, 138) and aligned by means of an electric field of strength 2.3 kV cm". Crystals are fixed in the upright position by a thin film of an epoxy resin (113). 

To circumvent the limitations described above, Plummer et al. have used a different method, suitable for observation of plastic zones in bulk samples [30]. They embedded a DCB sample in a low viscosity epoxy resin with the razor blade in place. The crack tip was therefore maintained under stress while the resin was left to cure at room temperature. The sample was then trimmed for thin sectioning, stained by immersion in a Ru04 solution, and microtomed in thin sections in the region of the plastic zone for observation by TEM. While this method gave particularly good results on ductile semicrystalline systems where a deformed thin film would not have been representative of the plastic deformation mechanisms taking place in bulk samples, it should in principle be applicable fairly generally. 

Figure 3.20. Successive FT-IR emission spectra from a thin film of resin from a carbon-epoxy-resin prepreg during cure. Bands that change during cure are marked (George et al., 2006).

Figure 3.21. Detail from Figure 3.20 marked with showing the decrease and growth of emission bands during cure of thin film of epoxy-resin prepreg.

It was shown that these equations could be used to analyse the CL from thin films of epoxy resins during cure (Schweinsberg and George, 1986) and there was a change in the parameter as cure passed through gelation. This was also shown to be applicable... 

PBO and PBZT films can be made very thin (less than 0.002 in.) and can be impregnated with secondary resins, resulting in a substrate with a dielectric constant less than 2.8, an isotropic planar CTE of 7 ppm per °C or less, and temperature resistance over 250°C. Copper circuits and ground planes can be added by a variety of additive or substrative means, and multilayer circuit boards can be fabricated using plated through holes. Further development of these thin film dielectric substrates should result in interconnection density over 100 times greater than is currently possible with fiber reinforced epoxy multilayer boards. 

It is interesting that, upon rubber modification, the CET resin matrix can no longer form dilatation bands (18). Only rubber-particle cavitation and matrix shear yielding are detected. This observation implies that a dilatational stress component is required to trigger the formation of dilatation bands. In other words, upon rubber-particle cavitation, the dilatational stress component in the matrix is reduced. This suppresses the formation of dilatation bands. This conjecture finds support in the work of Glad (27), who investigated thin-film deformation of epoxy resins with various cross-link densities and could not find any signs of dilatation bands in his study. 

When BF3 is produced in this fashion in an epoxy resin, it catalyzes the cationic polymerization of the resin as discussed earlier. Typically, a small amount of the diazonium compound is dissolved in the epoxy coating formulation and irradiated with UV light to form thin films (0.5 to 1 mil) deposited on metal, wood, or paper substrates. The high reactivity of the BF3 type cure makes it possible to prepare hard solvent-resistant coatings in a few seconds exposure time under a standard 200-W/in. mercury vapor lamp. 

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