Dynamical scaling of single chains on adsorbing substrates: diffusion processes

We study the dynamics of tethered chains of length N on adsorbing surfaces, considering the dilute case; for this we use the bond fluctuation model and scaling concepts. In particular, we focus on the mean-square displacement of single monomers and of the center of mass of the chains. The characteristic time tau of the fluctuations of a free chain in a good solvent grows as tau approximately N(a), where the coefficient a obeys a=2nu+1. We show that the same coefficient also holds at the critical point of adsorption. At intermediate time scales single monomers show subdiffusive behavior; this concurs with the behavior calculated from scaling arguments based on the dynamical exponent a. In the adsorbed state tau(perpendicular), the time scale for the relaxation in the direction perpendicular to the surface, becomes independent of N; tau(perpendicular) is then the relaxation time of an adsorption blob. In the direction parallel to the surface the motion is similar to that of a two-dimensional chain and is controlled by a time scale given by tau(parallel) approximately N(2nu(2)+1)L(-2Delta(nu/nu)), where nu(2) is the Flory exponent in two dimensions, nu is the Flory exponent in three dimensions, and Deltanu=nu(2)-nu. For the motion parallel to the surface we find dynamical scaling over a range of about four decades in time.     

Influence of surface structure on surface analytical statements

The influence of surface structure of technical materials on results and statements of surface analytical methods has been investigated. Especially surface roughness as a typical property of rolled products has been observed. For this purpose samples of steel (technical surface, roughness up to 5 m) and silicon wafers (polished surface) have been analyzed by SNMS and GDOS in order to get information about changes of the surface roughness as function of the sputtering time and their influence on the statements about the depth profiles obtained.     

A concept for bifocal contact‐ or intraocular lenses: liquid single crystal hydrogels (“LSCH”)

The synthesis of liquid single crystal hydrogels (“LSCH”) in suitable molds offers an innovative concept to realize bifocal contact‐ or intraocular‐lenses. LSCH combine the properties required for applications as bifocal ophthalmic lenses: the soft and water‐containing hydrogel enables oxygen permeation and exhibits high birefringence due to the liquid crystalline phase structure built up by rigid rod‐like amphiphiles. Via a photo‐initiated crosslinking reaction of aqueous solutions of monomeric lyotropic liquid crystalline amphiphiles in the macroscopically ordered liquid crystalline state, we obtain optically uniaxially ordered and transparent LSCH. The orientation process and the phase structure of the anisotropic hydrogel is analyzed by deuterium NMR‐spectroscopy. Copyright © 2002 John Wiley & Sons, Ltd.     

Orientation of a chiral smectic C elastomer by mechanical fields

It is well known that, with respect to the director, nematic elastomers can be macroscopically aligned by uniaxial mechanical fields. Extending this method to a chiral smectic C elastomer, depending on the experimental set-up either smectic layer orientation or director orientation parallel to the stress axis occurs. In order to align the director and the smectic layers a biaxial mechanical field (e.g. shear field) consistent with the phase symmetry has to be used to achieve a macroscopically uniform orientation of the untwisted smectic C^* structure.     

Spektrophotometrische Titanbestimmung mit Chromotrops?ure

Zusammenfassung Die Chromotropsäure ist ein analytisch wertvolles Reagens auf Eisen (III)₂₃, Chrom (VI)⁹, Kupfer, Niob²⁴ und besonders auf Titan (IV). Die Reaktion mit Chromotropsäure ist die empfindlichste (pD 5,9) und in Gegenwart von Ascorbinsäure weitgehend selektive Titanreaktion.In den Titan(IV)-lösungen bilden sich mit Chromotropsäure abhängig von der Zusammensetzung und dem p_H-Wert der Lösung sowie von der Konzentration der Reaktionspartner stufenweise mehrere Chelate. In den Lösungen mit Reagensüberschuß liegen folgende Chelatgleichgewichte vor: TiO²⁺ + 2 H₂R² TiO(RH)₂ ^4– + 2 H⁺ (Absorptionsmaximum470 m), P_H 0–2; TiO²⁺ + 2 H₂R^2– TiOR₂ ^6– + 4 H⁺ (470 m), p_H1–3,5; TiOR₂ ^6– + H₂R² TiOR₃ ^10– + 2 H⁺ (420 m), p_H 3,2–7,0; TiOR₂ ⁶ + 2H₂R^2– TiR₄ ^12– + 2 H + H₂O (470 m), p_H 1,7–2,4.Die beiden stabilen Chelate TiOR₂ ^6– und TiOR₃ ^10– können bei begrenzten Reaktionsbedingungen zur spektrophotoinetrischen Titanbestimmung ausgenutzt werden. Die Bestimmung bei p_H 2,9–3,2 und 467m in Gegenwart von Ascorbinsäure ermöglicht die Titanbestimmung neben einer Zahl von fremden Ionen. Sie ist die für die Praxis geeignetste Methode.Herrn Prof. Dr. A. Oká zum 55. Geburtstag gewidmet.Den Firmen E. Merck, Darmstadt und Reagencia, Kralupy, bin ich für das freundliche Überlassen der Präparate der Chromotropsäure mit herzlichem Dank verpflichtet.     

Continuous selections and convergence of best Lp –approximations in subspaces of spline functions

The chief purpose of this paper is to study the problem of existence of continuous selections for the metric projection and of convergence of best L_p–approximations in subspaces of polynomial spline functions defined on a real compact interval I. Nürnberger-Sommer [8] have shown that there exists a continuous selection s if and only if the numberof knots k is less than or equal to the order m of the splines. Using their construction of s the author [12] has proved that the sequence of best L_p–approximations of f converges to s(f) as ρ→∞ for every continuous function f. The main results of this paper say that also in the case when k>m there exists always a continuous selection s (it is even pointwise-Lipschitz-continuous and quasi-linear) provided that the approximation problem is restricted to certain subsets I_epsilon; of I. In addition it is shown that anologously as for k≤m the sequence of best L_papproximations of f converges to s(f) for every continuous function f on Iε     

Early/Late Heteronuclear Complexes Bridged by Bifunctional Phosphorus-Based Ligands

Substituted bifunctional phosphorus-based ligands HX(CRR') n PR"H (or -PR" 2 ) [where X = O, S, NR', (substituted) cyclopentadienyl; n = 1, 2, 3; R, R', R" = alkyl, aryl, H] were employed as bridging ligands in the synthesis of early/late bridged transition metal complexes. Synthetic routes to the bifunctional ligands were also developed. First, mononuclear complexes, such as [TpZr(OCH 2 PPh 2 ) 3 ] (Tp = trispyrazolylborato), [Cp 2 Zr(1-O-2-PHR-C 6 H 10 )(Me)] (R = 2,4,6-Pr i 3 C 6 H 2 (Tipp)), [Cp 2 Zr(SCH 2 CH 2 PHR) 2 ] (R = Ph, Mes, Tipp), and phosphinoferrocene derivatives, were prepared. These complexes are suitable precursors for the introduction of a second metal (as in, for example, [TpZr( w -OCH 2 PPh 2 ) 3 Mo(CO) 3 ]).     

Site-specific C content by quantitative isotopic C Nuclear Magnetic Resonance spectrometry: A pilot inter-laboratory study

Isotopic ¹³C NMR spectrometry, which is able to measure intra-molecular ¹³C composition, is of emerging demand because of the new information provided by the ¹³C site-specific content of a given molecule. A systematic evaluation of instrumental behaviour is of importance to envisage isotopic ¹³C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular ¹³C composition by NMR. The main goals of the ring test were to establish intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise on the basis of a qualification test. Reproducibility at the natural abundance of isotopic ¹³C NMR was then assessed on vanillin from three different origins associated with specific δ¹³C_i profiles. The standard deviation was, on average, between 0.9 and 1.2‰ for intra-variability. The highest standard deviation for inter-variability was 2.1‰. This is significantly higher than the internal precision but could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ¹³C_i in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument was satisfactory, correction factors for each carbon in vanillin could be calculated to harmonize the results.