Interface growth morphologies in pulsed laser deposited, room temperature grown multilayer hard coatings

The mechanical behaviour - hardness, elasticity, and adhesion - of multilayer coatings is strongly influenced by the type of the formed interfaces between the different layers. In industrially applied tribological coatings the interface region is predominantly not a perfect sudden change of the chemical composition of the adjacent crystal planes, but a transition zone of a thickness, which is strongly dependent on the energetic conditions during deposition. Multilayer coatings grown by high-energetic deposition techniques always struggle with high atomic mixing of both adjacent coating materials due to high energetic ion implantation.One of these high-energetic deposition techniques is the Pulsed Laser Deposition (PLD), characterized by pulsed and within one pulse alternating high- and low-energetic particle fractions, hitting successively the substrate surface. Such deposition conditions were shown to be highly advantageous for low temperature deposition by the densification of the growth structures due to activated diffusion and re-sputtering, but increases the difficulty in depositing multilayer structures.The current paper addresses these specific growth conditions based on Ti/TiN and Cr/CrN multilayer coatings. High resolution transmission electron microscopy results show that the atomic mixing at the interface is not highly critical for the deposition of multilayer coatings and that extremely dense growth structures are forming even in the interface regions.     

Depletion of Grain-Boundary Phase and Elastic Creep Deformation Upon Ultra-Long Flexural Stress Rupture Experiments of NC-132 Silicon Nitride

A unique grain-boundary structure evolution was observed in two MgO-doped silicon nitride specimens (Norton, NC-132) that were tested in ultra-long flexure stress rupture experiments with an applied stress of 266 MPa and fractured at 14 941 and 17 376 h. Transmission electron microscopy showed that, although the starting material had a secondary glass phase both at multi-grain junctions and along grain boundaries, the tested specimens contained no residual glass phase. Concurrent with the elimination of the secondary glass phase, a continuous network of cracked grain boundaries was observed after long-term flexure testing consistent with the concept of elastic creep. It is, therefore, concluded that at ultra-long annealing times, this material is affected by creep deformation via microcrack nucleation and growth due to the depletion of the amorphous siliceous grain-boundary phase, which is seen as a truly transient, fugitive secondary phase.     

Stereochemical and steric control of the UDP-glucuronosyltransferase-catalyzed conjugation reaction: a rational approach for the design of inhibitors for the human UGT2B7

A set of 76 derivatives of the epimeric tricyclic sesquiterpenols longifolol and isolongifolol was subjected to inhibition and glucuronidation assays employing the human UDP-glucuronosyltransferase (UGT) 2B7. Detailed structure-activity relationships (SARs) with respect to functionality, stereochemical properties, and steric features were derived. To gain further insight into the SARs of UGT2B7 ligands herein, we have developed a 3D-quantitative structure-activity relationship (3D-QSAR) using Comparative Molecular Similarity Analysis (CoMSIA). The formation of the enzyme-inhibitor complex was predominantly controlled by spatially directed hydrophobic interactions. The glucuronidation rate was significantly influenced by the steric demand of substituents in proximity of the nucleophilic hydroxy group. The glucuronidation of the compounds was prevented by the introduction of bulky substituents such as isopropyl, tert-butyl, and phenyl groups. The epimeric longifolol derivatives of series D were the best inhibitors displaying IC(50) values as low as 4.6 nM. This study shows that high-potency substrates can be turned into potent inhibitors by addressing functional, stereochemical, and steric properties.     

Evolution of the fractal dimension for simultaneous coagulation and sintering

Simulation results on the evolution of aggregate structure in aerosol processes with coagulation and sintering as the dominant mechanisms are presented. A model for simulation of the three-dimensional morphology of nano-structured aggregates formed by concurrent coagulation and sintering is applied. The model is based on a stochastic diffusion controlled cluster-cluster aggregation algorithm and sintering is modeled as a successive overlapping of spherical primary particles, which are allowed to grow in order to maintain mass conservation. This leads to computer simulated structured aggregates which are then subject to evaluation. Two different methods to determine the fractal dimension are presented which give comparable results. It is shown that even very small particles show the same fractal behavior. Furthermore, equilibrium structures assuming a constant ratio of the characteristic collision time to the characteristic fusion time are considered as well as the kinetics of structural changes due to a change in the ambient conditions.     

Elastic properties of adhesive polymers. II. Polymer films and bond lines by means of nanoindentation

Seven different polymers used frequently as adhesives and/or matrix polymers in wood, wood composites, and natural fiber‐reinforced composites were studied by uniaxial tensile tests and nanoindentation. It was shown that the elastic modulus, the hardness, the creep factor, and the elastic‐, plastic‐, and viscoelastic work of indentation of the seven different polymers is essentially the same regardless whether the polymers were tested in the form of pure films or in situ, i.e., in an adhesive bond line with spruce wood. An excellent correlation was found between the elastic modulus measured by tensile tests and the elastic modulus measured by nanoindentation. In spite of the good correlation, the elastic modulus measured by nanoindentation is significantly higher than the elastic modulus measured by tensile tests. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1234–1239, 2006     

Rapid production of micropatterned surfaces using a fluid dynamical instability

The continuous, high speed patterning of polyethylene films with a micron‐structured silicone coating was investigated in a roll coating process that did not depend on the use of prestructured tools. Thermally curable polydimethylsiloxane (PDMS) resin was rheologically modified by the addition of highly agglomerated, aerosol‐derived silica and resulted in a Herschel–Bulkley fluid. Application of the modified siloxane in a roll coating process resulted in a fluid dynamical instability at high capillary numbers promoting the spontaneous formation of randomly branched surface structures. The shear‐thinning properties of the nanoparticle‐doped PDMS resin were adjusted as to preserve the wet, structured coating during the following thermal curing step. The highly regular pattern was characterized in terms of averaged branch width and could be controlled from micro‐ to millimeter size by adjusting coating roll velocity and roll gap distance. The adhesive properties of the structured coating were compared to unstructured conventional silicone coatings by measuring the release force of pressure‐sensitive adhesives. For rubber‐based tape, the release force of patterned PDMS was reduced by a factor of up to eight if compared to smooth reference silicone. These ultra‐low adhesive coatings may find applications in packaging, food processing, and for covering sanitary surfaces, offering a cost‐effective alternative to conventional surface structuring methods. POLYM. ENG. SCI., 46:1541–1547, 2006. © 2006 Society of Plastics Engineers     

Synthesis and Functionalization of Fullerenes Encapsulating Atomic Phosphorus

Synthesis, purification, and electron spin properties of the endohedral fullerene P@C₆₀ are reported. Highly enriched material could be obtained for the first time, making this molecule accessible for further experiments. We report the first successful chemical modification of P@C₆₀ via cyclo-propanation to the C_2v symmetric monoadducts P@C₆₁(COOCH₃) and P@C₆₁(COOC₂H₅). X-band electron spin resonance data are presented and discussed. The phosphorus atom shows anisotropic hyperfine coupling in the modified fullerenes, in contrast to the unmodified case, and in contrast to similarly modified N@C₆₀.     

Synthese und Reaktionen chiraler,von (R)-(−)-bzw. (S)-(+)-2-Methoxymethylpyrrolidin abgeleiteter Dithiocarbamate

Synthesis and Reactions of Chiral Dithiocarbamates Derived from (R)-(−)- or (S)-(+)-2- The synthesis, diastereoselective alkylation reactions, dithiocarboxylation, and aldol condensation of several substituted methyl (R¹ CH₂) (S)-2-(methoxymethyl)-pyrrolidine-1-dithiocarboxylates (S)- 2 and of the corresponding (R)-derivatives (R)- 2 are described. The new enantiomeric dithiocarbamates (S) -2a – e , and (R) -2a – d are obtained by reaction of (S)-(+)-[(S) -1 ] or (R)-(−)-2-(methoxymethyl)-pyrrolidine [(R) -1 ], respectively, with carbon disulfide in dry methanol/anhydrous sodium acetate and the appropriate alkylating agent. The cyclic ketene dithioacetals (S) -3 and (R) -3 are formed by dithiocarboxylation procedure of (S) -2a and (R) -2a whereas (S) -6 and (R) -6 are obtained by aldol reaction with isobutyraldehyde. (S)- 2c , d and (R) -2c , d react in a diastereoselective manner after deprotonation with n-BuLi or LiTMP/LiBr at −78°C in THF with alkyl halides to the enantiomeric compounds 4a /ent -4a, 4b /ent -4b and 5 /ent -5 , respectively.     

How Different Characterization Techniques Elucidate the Nature of the Gold Species in a Polycrystalline Au/TiO2 Catalyst

TiO₂‐supported gold species were prepared via the deposition‐precipitation route, with conservation of the initial speciation by freeze‐drying. The structural and electronic properties of the Au species were investigated by X‐ray absorption spectroscopy, electron microscopy, and IR spectroscopy of adsorbed CO in four states. Exclusively Au^III was deposited on the TiO₂ surface in patches ranging from isolated Au ions to three‐dimensional clusters. This paper illustrates in detail the unique contributions of all characterization techniques to this structural model.