Far-infrared studies on Nafion and perfluoroimide acid (PFIA) and their alkali salts

The terahertz/far-infrared spectra (<300 cm⁻¹) of perfluorinated sulfonic acid (Nafion NR211 polymer) and perfluoroimide acid (PFIA polymer) and their alkali (M⁺) salts have been analyzed and the results are presented. Pronounced features in the spectra of these ionomers that correlate systematically with the corresponding cation mass are reported and from their spectral position the force constants are derived. The average vibrational force constants for Nafion/M⁺ and PFIA/M⁺ are found to be 54 ± 7 and 39 ± 4 N/m, respectively. Such terahertz/far-infrared signatures probe the detailed structure of the Nafion/M⁺ and PFIA/M⁺ ionic clusters and, in turn, provide benchmarks for elucidating the ionomer “water channels” or water molecules located in the ionomer–water interface upon hydration. Qualitative trends in the vibrational energies of Nafion and PFIA can be explained by consideration of electronic and/or structural (ionic domain-size) effects.     

提高原子力显微镜(AFM)成像质量的方法

针对原子力显微镜AFM不要求样品具有导电性的优点,分析了影响原子力显微镜AFM扫描图像质量的原因及提高AFM成像质量的方法。     

Effective refractive index and intermolecular forces associated with a phase of functional groups

Cases in which a functional groups form distinct phases are known in material science in general and specifically in polymer and surfactant sciences. To calculate the van der Waals forces associated with such phases there is a need to evaluate the refractive index of those phases. We expand and generalize a method to estimate the refractive index of such ‘functional group phase’ and discuss how to use the refractive indices to calculate the interaction energies associated with such functional group phases and thereby modify the total theoretically calculated van der Waals forces.     

Stereochemistry and tautomerism of stentorin,isostentorin, and fringelit D: Force field investigations

Summary Stereochemistry and tautomerism of stentorin, isostentorin, and fringelit D were investigated using an MM2 derived force field method. For these pigments, the 7,14-dioxo tautomers were derived to be the most stable ones, with a gap of about 50 kJ/mol separating them from the less stable species. The three quinones display propeller and double butterfly conformers. The double butterfly conformers were found to be slightly more stable than the propeller conformers. Compared to hypericin the interconversion barriers between these conformers and between enantiomeric conformers of the same type are lower. They were estimated to be in the order of 40 kJ/mol; thus an isolation of enantiomers is improbable.

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Stereochemie und Tautomerie von Stentorin, Isostentorin und Fringelit D: Untersuchungen mit Hilfe der Kraftfeld-Methodik

Zusammenfassung Die Stereochemie und Tautomerie von Stentorin, Isostentorin und Fringelit D wurden mit Hilfe einer von MM2 abgeleiteten Kraftfeldmethodik untersucht. Für diese Pigmente wurde abgeleitet, daß die 7,14-Dioxotautomeren am stabilsten sind und daß sie durch eine Energielücke von etwa 50 kJ/Mol von den weniger stabilen Tautomeren getrennt sind. Diese drei Chinone liegen jeweils als Propeller- und Doppelschmetterlings-Konfomere vor, wobei letztere geringfügig stabiler als erstere sind. Verglichen mit Hypericin sind die Interkonversionsbarrieren zwischen diesen Konformeren, wie auch zwischen enantiomeren Konformeren desselben Typs, niederer. Sie wurden zu etwa 40 kJ/Mol abgeschätzt und lassen damit eine Isolierung von Enantiomeren unwahrscheinlich werden.

     

Analysis of effects of differential gain on dynamic stability of digital force control

The paper presents an analytical investigation of the dynamics of digital force control. A one degree-of-freedom (DoF) mechanical system with low viscous damping is subjected to proportional-derivative (PD) force control. Analytical results are presented in the form of stability charts in the parameter space of sampling time, control gains and mechanical parameters. Simple closed form results include the largest stable proportional gain and the least steady state force error that provide synthesis of mechanical and control system parameter influences for the design of digital force control. Also, a novel analytical explanation is given why even the properly filtered force derivative signal is rarely used in practice, and why the occurring vibrations have frequencies one range smaller than that of the sampling frequency of the digital control.     

Observed transition from linear to non-linear friction-load behavior using a lateral force microscope

The most commonly observed friction behavior for sliding systems is that described by Amontons laws of friction. In this case, sliding friction is independent of the gross or apparent area of contact between the materials and a linear function of the applied normal load, where the constant of proportionality is called the friction coefficient. However, for dry sliding solids in contact via a single-asperity junction, Amontons (linear) friction-load behavior is not strictly relevant. In experiments measuring sliding friction between a silicon tip and a quartz surface using an atomic force microscope (AFM), a transition from linear to non-linear friction-load behavior has been observed. This is proposed to result from a nanoscale ‘conditioning’ of a multiple-contact tip-surface interface to form a single-asperity contact.     

Force constants from intensity analysis of molecules CH3Cl and CD3Cl

The secular equation (GF - Eλ)L = 0 contains more force constants than can be calculated from the equations formulated using the frequencies. For a 3 × 3 matrix, there are 6 force constants but only 3 frequencies. Attempts were made by others to estimate all the 6 constants to satisfy the frequencies and Coriolis constants and rotation distortion constants. However, many attempts are not made in these estimations to satisfy the intensities. A full complement of equations is derived to evaluate all the force constants combining the intensity equationsI =L’A withLL’ =G and evaluated the force constants ofA ₁ species of CH₃Cl and CD₃Cl. A simple analysis of a 2 × 2 matrix shows thatF ₁₂/F ₂₂=G ₁₂ ⁻¹ /G ₂₂ ⁻¹ as reported earlier.     

Simulation of centrifugal inertia forces on a test bed of blow-molding machines

This paper deals with the simulation of the centrifugal inertia forces on a fixed test bed that reproduces only the opening and closing motions of the half-molds of blow-molding machines. The suggested solution is realized by the addition of springs, which allows the reproduction of the moment of the inertia forces about the vertical axis of the mold. By using the approximation method based on the mean-square-value minimization, satisfactory results are obtained. The efficiency of such a solution is illustrated by numerical example.     

Berechnungen des Metathese-Gleichgewichtes zwischen Cyclopentenylverbindungen, 4-Octen und 4,9-Tridecadien-Derivaten

Empirical force field calculations are used to interpret the occurrence of cyclopentenyl compounds in the course of metathesis degradation of partially isomerized modified poly(1-butenylenes).

     

On the calculation of force constants using isotopic frequencies by parametric method: Application to systems of (3×3) order

A method is proposed for the determination of angle parameters for ONF, ONCl and ONBr, utilising the isotopic frequencies of two isotopically substituted molecules. The force constants, Coriolis coupling constants, inertia defect, mean amplitudes of vibration and rotational distortion constants were also calculated and compared with literature values.