The sensitivities of infrared spectra of thin adsorbate layers measured in either transmission, internal reflection or external reflection can be greatly increased if a light incidence medium with a high refractive index such as an IR-transparent solid material is used. This increase in sensitivity is due to the strong enhancement of the perpendicular electric field in a thin layer of low refractive index sandwiched between two high refractive index materials. Based on model calculations of a hypothetical sample layer, the influence and optimization of experimental parameters such as incidence angle, sample layer thickness and optical contact between layers are investigated. Under optimized conditions, this enhancement can exceed a factor of 100 when compared to conventional surface IR techniques. In addition, the spectra of sandwiched sample layers are governed by a uniform surface selection rule, such that only the perpendicular vibrational components are enhanced, and they permit a straightforward, substrate-independent analysis of surface orientations. Experimental examples of monolayer spectra of long-chain hydrocarbon compounds adsorbed onto gold and silicon substrates and contacted with a germanium crystal used as the incidence medium demonstrate the simple experimental realization and unprecedented sensitivity of this sandwich technique, and they offer novel insights into the chemistry and structure of monolayers confined and compressed between two solid surfaces.

PP was modified with elastomer and wood to prepare materials with large stiffness and impact resistance. Three wood fibers with different particle characteristics were used, and elastomer as well as wood content changed in a wide range. and to increase the plastic deformation of the matrix polymer.

Monolayer films adsorbed on substrates with high refractive indices such as metals or semiconductors yield strongly enhanced infrared reflection spectra when they are contacted with a transparent, high refractive index ambient medium and are probed with p-polarized light at high incidence angles. The sensitivity increase arises from the enhancement of the perpendicular electric field within a thin, low refractive index layer sandwiched between two high refractive index materials and gives rise to signal intensity gains up to 2 orders of magnitude in combination with an essentially exclusive detection of only perpendicular surface vibrations. Experimental spectra of ordered monolayer films of octadecanethiol on gold and of octadecylsiloxane on silicon in this sandwich configuration yield enhancement factors between 15 (on Si) and 30 (on gold) compared to conventional grazing incidence external reflection spectra and are governed by a common, simple surface selection rule, which allows immediate quantitative evaluation and comparison of the film structures on different substrates.

The impact resistance of polypropylene (PP)/wood composites was improved either by the traditional approach of adding an elastomer or by the use of poly(ethylene terephthalate) (PET) fibers. Composites were prepared with various elastomer and PET fiber contents at a constant wood content of 20 wt% for all hybrid composites. Interfacial adhesion was improved by the addition of a maleic anhydride modified PP (MAPP). The components were homogenized in a twin-screw compounder and injection molded into standard tensile bars. Properties were characterized by tensile and impact testing, while scanning electron microscopy (SEM) was applied for studying the structure. A combination of acoustic emission measurements (AE) and SEM was used to understand local deformation processes, the results showing that the traditional route of impact modification with elastomers does not work in wood reinforced PP, since the simultaneous fracture of large wood particles and the cavitation of the elastomer result in limited fracture toughness. On the other hand, polymeric fibers (PET) increase the impact resistance of rigid PP homopolymer matrices reinforced with wood fibers, because they initiate new local deformation processes. The concept of using polymeric fibers for the impact modification of rigid PP/wood composites is an efficient way to extend the field of application of such reinforced materials.

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