Variation of the Microwave Brightness Temperature of Sea Surfaces Covered with Mineral And Monomolecular Oil Films

Airborne microwave radiometer measurements over mineral and monomolecular oil films and adjacent clean sea surfaces are reported. An artificial crude-oil spill experiment in the New York Bight area showed a brightness temperature increase of the sea surface at 1.43 GHz as expected from a multilayered system with different dielectric constants. However, a monomolecular surface-film experiment with oleyl alcohol conducted in the North Sea during MARSEN in 1979 showed a strong brightness temperature depression at 1.43 GHz and no change in brightness temperature at 2.65 GHz. It is postulated that the monomolecular layer, because of its physical and chemical properties, polarized the underlying water molecules so strongly that the emissivity decreased from 0.31 to 0.016. It is estimated that the effective dielectric constant changed from 90 to 5.2 × 104. Because these phenomena occurred at 1.43 GHz it may be concluded that this frequency is very close to the center of a new anomalous dispersion region resulting from a restructuring of the water layer below the surface film.     

Temperature-sensitive behaviour of poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers

Temperature-sensitive poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers (PGl₅₅PNIPAAm_y) were synthesised and their aqueous solutions investigated by different methods including differential scanning calorimetry (DSC), UV-VIS spectroscopy as well as dynamic and static light scattering. The cloud point temperature (T _c) depended on the composition of the investigated block copolymers and increased with decreasing length of the PNIPAAm block in PGl₅₅PNIPAAm_y copolymers. In contrast, the enthalpy of phase separation of PNIPAAm segments measured by DSC decreased with decreasing length of the PNIPAAm block in the polymer. These findings can be correlated with the behaviour of homo-PNIPAAm with similar molecular weights indicating that the influence of PGl on the local environment and phase separation of PNIPAAm chains is similar to the influence observed for PNIPAAm chains bearing different low molecular weight end group. Using DLS measurement, it was shown that the aggregation process depended on the PGl/PNIPAAm block ratio. If the PGl/PNIPAAm ratio was low, stable core-shell aggregates were formed. In contrast, the tendency to formation of large unstable, loose aggregates was observed for copolymers with high PGl/PNIPAAm ratio.     

Synthesis and Characterization of New Adhesion Promoter for Grafting Conducting Polymer on Oxide Substrate

For grafting polypyrrole layers on oxidic substrates, the synthesis and characterization of a new adhesion promoter 11‐(pyrrol‐3‐yl) undecyl trimethoxysilane (PyTMS) were described in this article. The oxidation potential of PyTMS was determined by cyclic voltammetry. The grafting behavior of such an adhesion promoter on oxidized surface and chemical deposition of polypyrrole over the modified oxidized surface were studied. The adsorbed layer on the oxidized substrates thus formed was determined by both contact angle measurements and X‐ray photoelectron spectroscopy. Chemical polymerization of terminal pyrrole moieties on such substrates yielded adhesive polypyrrole films, and SEM image showed that the morphology of the polypyrrole films was influenced by the experimental conditions.     

Emission Reduction and Capacity Increase in GSM Networks by Single Antenna Interference Cancellation

There is an increasing demand to utilize the frequency spectrum of mobile communication systems most efficiently. This means in particular to GSM networks that the frequency reuse shall be planned as low as possible. In this case the system may become limited by interference rather than coverage. One promising technology for GSM mobiles in interference-limited systems is single antenna interference cancellation (SAIC). This receiver technology allows both for increasing the network capacity and for reducing the base station transmit power. The aim of this paper is to assess the emission reduction as well as the system capacity capabilities when SAIC technology is applied in downlink receivers.     

Pyrrole-substituted alkyl silanes as new adhesion promoters on oxidic substrates

ω-(Pyrrol-1-yl alkyl) dimethylchlorosilanes with different chain length were synthesized and characterized with IR, NMR and elemental analysis. The growth of self-assembled monolayers of ω-(pyrrol-1-yl alkyl) dimethylchlorosilanes on oxide surfaces has been investigated. The order gradually improved with adsorption time and highly ordered SAMs were obtained for nearly 2 days adsorption time. Characterization of the films has been performed with contact angle measurements, ellipsometry, SPR and grazing incident FTIR. The chemical deposition of polypyrrole on the modified surface was investigated. The thickness of polypyrrole layer was influenced by the concentration of monomer, the deposition time, and the ratio of monomer to oxidant.     

Novel branched blockcopolymers from poly(vinylpyridine) by chromium allyl compounds

Novel branched blockcopolymers from polyvinylpyridine are formed by chromium allyl compounds. Our present work shows results for the homopolymerization of vinylpiridine (VP), dimethylacrylamide (DMAA), tert - butylacrylate (t - BA) as well as the graftcopolymerization of poly(vinylpyridine) (PVP), using tris (π - allyl) chromium (TPC) as initiator. PVP activated by TPC was used for grafting with DMAA - “grafting from”. On the other hand living PDMAA polymerized by TPC, was able to react with PVP chain - “grafting onto”.     

Ultra-thin layers of phosphorylated cellulose derivatives on metal surfaces

Cellulose as natural and non-toxic material is very interesting for biological applications. Its poor solubility in organic solvents can be improved by introduction of long alkyl chains. Phosphate-substituted cellulose derivatives form ultra-thin layers on several metal surfaces [1, 2]. The layers were applied on the surfaces via dip coating from dilute solutions and characterised by contact angle measurements. Initial corrosion tests were performed. These polymers were applied as adhesion promoters for steel-, titanium- and hydroxy apatite surfaces. Medical implants were pre-treated by UV irradiation, coated with the cellulose derivatives and activated by hot water treatment. The adhesion of the implants surpassed that of conventionally used PMMA systems.     

Growth of hydroxyapatite nanocrystals on polymer particle surface

In the present paper, we describe the preparation of hybrid particles consisting of polymeric core with deposited hydroxyapatite (HAp) nanocrystals. Polystyrene submicron particles modified by β-diketone groups have been used as templates for the growth of HAp. Hybrid particles with HAp nanocrystal content between 7 and 50 wt% have been prepared. Microscopy studies indicate that hybrid particles exhibit “raspberry” morphology, and HAp nanoparticles are not homogeneously distributed on the polymer particle surface. The increase in the HAp content on the polymer particle surface reduces the colloidal stability of the hybrid particles because of the vanishing of the surface charge.     

Strukturdynamische organometall-komplexe: III. Synthese,struktur und bindungsverhältnisse der komplexe (η5-C5H5)Pd(η1-C5H5)PR3

The complexes (η₅-C₅H₅)Pd(η¹-C₅H₅)PR₃ which are prepared from [Cl(PR₃)-Pd]₂(μ-OCOCH₃)₂ and TlC₅H₅ are fluxional in solution. According to the ¹H and ¹³C NMR spectra at various temperatures, two dynamic processes occur. The process with the higher activation energy is a π/σ (η⁵/η¹) exchange of the two different cyclopentadienyl ligands, whereas the second one with the lower activation energy presumably is a metallotropic rearrangement (1,2-shift). The coalescence temperature for the η⁵/η¹ exchange depends on the size of the phosphine. The X-ray structural analysis of (C₅H₅)₂PdPPrⁱ₃ proves that it exists as a “frozen” η⁵ + η¹ structure in the crystal with the palladium approximately in a square-planar coordination. The η⁵-bonded cyclopentadienyl ring shows some unusual bonding patterns which are obviously electronic in nature. EHT-MO calculations for (η⁵-C₅H₅)PdCH₃(PH₃) indicate that in this model system alternating CC distances in the ring and a stronger bond of the metal to one of the five carbon atoms of the C₅H₅ ligand are to be expected. The calculations suggest that in similar complexes possessing a six-electron donor ligand like C₅H₅^? and a metal fragment which is isolobal to PdCH₃(PH₃)⁺, analogous distortions should be observed. Some reactions of the compounds (η⁵-C₅H₅)Pd(η¹-C₅H₅)PR₃ are described.     

Synthesis and characterization of polypyrrole dispersions prepared with different dopants

Stable polypyrrole dispersions were prepared by chemical oxidative polymerization of pyrrole in an aqueous medium containing different anionic salts - sodium benzoate, potassium hydrogen phthalate and sodium hydrogen succinate. Results of the elemental analysis and FT-IR spectroscopy confirmed that the anionic salts are incorporated in the conducting polymers and functioned as the dopants. The retardation of pyrrole polymerization was observed when a certain amount of the salt was used as dopant. SEM images of polypyrrole dispersions indicate large spherical particles (150-180nm). The conductivity of polypyrrole composites has also been investigated.