Dynamic alterations of fibronectin layers on copolymer substrates with graded physicochemical characteristics

Desorption and exchange of preadsorbed fibronectin layers in pure buffer solution and solutions of human serum albumin or fibronectin, respectively, were studied in dependence on the physicochemical characteristics of maleic acid copolymer films used as substrates. Although the preadsorbed amount of fibronectin differed only slightly, the protein was found to exhibit a significantly enhanced anchorage at the more hydrophobic polymer surface as compared to the more hydrophilic and more negatively charged polymer surface. The preadsorbed fibronectin layer was most efficiently exchanged by fibronectin (i.e., in the homodisplacement process) while pure buffer solution and human serum albumin solutions induced desorption or exchange of fibronectin to lower and similar degrees. An increase of the total adsorbed amount of protein due to additional adsorption of fibronectin or human serum albumin accompanied the partial exchange of the preadsorbed fibronectin in the displacement experiments. Evaluation of the kinetics of desorption and exchange of fibronectin at any of the substrates revealed two kinds of surface-attached protein populations--a fast desorbing species and a species with a slow desorption and exchange rate. By a multivariate regression analysis the surface characteristics of the polymer substrate were confirmed to determine the degree of protein desorption and exchange while the dynamics of the layer alteration was found to solely depend on the diffusion behavior of the proteins.     

Structure and Properties of Ethene Copolymers Synthesized by Metallocene Catalysts

Abstract

The microstructure of ethylene copolymers based on 1-hexene, 1-octene, and norbornene as comonomers was studied and related to its melting, crystallization, and glass transition behavior as well as to tensile strength.     

pH Tuning of Water-Soluble Arylazopyrazole Photoswitches

Arylazopyrazoles are an emerging class of photoswitches with redshifted switching wavelength, high photostationary states, long thermal half-lives and facile synthetic access. Understanding pathways for a simple modulation of the thermal half-lives, while keeping other parameters of interest constant, is an important aspect for out-of-equilibrium systems design and applications. Here, it is demonstrated that the thermal half-life of a water-soluble PEG-tethered arylazo-bis(o-methylated)pyrazole (AAP) can be tuned by more than five orders of magnitude using simple pH adjustment, which is beyond the tunability of azobenzenes. The mechanism of thermal relaxation is investigated by thorough spectroscopic analyses and density functional theory (DFT) calculations. Finally, the concepts of a tunable half-life are transferred from the molecular scale to the material scale. Based on the photochromic characteristics of E- and Z-AAP, transient information storage is showcased in form of light-written patterns inside films cast from different pH, which in turn leads to different times of storage. With respect to prospective precisely tunable materials and time-programmed out-of-equilibrium systems, an externally tunable half-life is likely advantageous over changing the entire system by the replacement of the photoswitch.     

Gas-dynamic consideration of the laser evaporation synthesis of single-wall carbon nanotubes

The abundance of carbon single-wall nanotubes (SWNTs) in soot synthesized by pulsed laser evaporation of graphite is studied over a wide range of synthesis conditions. The derived SWNT growth time-scale appears to be much longer than any characteristic time-scale in a simplified model of the relaxation of a high-pressure hot condensing gas bubble in a background atmosphere. It is concluded that SWNT nucleation and growth take place in relaxed, condensed, thermalized evaporation products at an optimal temperature between 850-1250 °C at a rate of few 7m length per second, which is consistent with a condensed state "precipitation" mechanism for the SWNT formation.     

Preparation and TG—DTA analysis of manganese silicon nitride

Manganese silicon nitride was prepared quantitatively as a precipitated phase by treating a Mn; Si-alloy (Mn: 1.84 w/o, Si: 1.12 w/o) in a mixture of 2% NH₃ and H₂ at 700°C. Nitriding was carried out in situ in a thermobalance and the nitrogen uptake was recorded as a function of time. The nitride phase was isolated and investigated by means of the combined TG-DTG-DTA technique both in an atmosphere of nitrogen at 25–1600°C and in a mixture of Ar+O₂ (p_O2 = 0.20 atm) at 25–1000°C. In the nitrogen atmosphere MnSiN₂ appears to be stable up to 1000°C. Oxidising the nitride in the Ar/O₂ mixture caused three distinct exothermic processes to occur at characteristic temperatures. The final oxidation products as identified by diffractometry and IR-spectroscopy are manganese oxide silicate (braunite) and silicon dioxide.     

Thermoanalytical study of water-based aluminium rolling fluids combined with direct observation

During cold-rolling of aluminium sheets the auxiliary lubricant fluids used decompose giving rise to discolouring of the sheet surface. In the present study a combined TGA-DTG-DTA analysis has been used in combination with direct observation of the colour change of carboxylate-based fluids in oxidizing and inert atmosphere to determine the temperature region of decomposition and/or polymerization. Significant effects have been observed depending not only on the type of atmosphere but also on the type of the cationic part of the organic component in these fluids.     

Zur Grenzschichtdämpfung von Verbundwerkstoffen mit kurzfasrigen Einlagerungen

Composite materials with discontinuous fibres are theoretically examined under alternating tension. By the aid of simple models for a composite with elastic matrix, elastic fibres, and plastificable interface the behaviour of the composite material can be described. The mechanical damping, caused by slipping of the interface, is computed for the cases of a perfect-plastic, a viscous and a visco-plastic boundary layer. Damping peaks occur in dependence of the stress amplitude and the frequency, respectively. From the position of these peaks we can conclude to the parameters of the interface, in particular, to its shear strength. Thus damping measurements render it possible to determine the properties of the interface within the composite.     

Evidence of distributed interstitialcy-like relaxation of the shear modulus due to structural relaxation of metallic glasses

The interstitialcy theory is used to calculate the kinetics of shear modulus relaxation induced by structural relaxation of metallic glasses. A continuous distribution of activation energies is shown to be a salient feature of the relaxation. High precision in situ contactless electromagnetic acoustic-transformation shear modulus (600- kHz) measurements performed on a Zr-based bulk metallic glass are found to strongly support the approach under consideration. It is revealed that the activation energy spectra derived from isothermal and isochronal shear modulus measurements are in good agreement with each other. It is concluded that the increase of the shear modulus during structural relaxation can be understood as a decrease of the concentration of structural defects similar to dumbbell interstitials in simple crystalline metals.