Dimensions of branched polymers formed in simultaneous long‐chain branching and random scission

In free‐radical olefin polymerizations, the polymer‐transfer reactions could lead to chain scission as well as the formation of long‐chain branches. The Monte Carlo simulation for free‐radical polymerization that involves simultaneous long‐chain branching and random scission is used to investigate detailed branched structure. The relationship between the mean‐square radius of gyration 〈s²〉 and degree of polymerization P as well as that between the branching density and P is the same for both with and without random scission reactions—at least for smaller frequencies of scission reactions. The 〈s²〉 values were larger than those calculated from the Zimm–Stockmayer (Z‐S) equation in which random distribution of branch points is assumed, and therefore, the Z‐S equation may not be applied for low‐density polyethylenes. The elution curves of size exclusion chromatography were also simulated. The molecular weight distribution (MWD) calibrated relative to standard linear polymers is much narrower than the true MWD, and high molecular weight tails are clearly underestimated. A simplified method to estimate the true MWD from the calibrated MWD data is proposed. The MWD obtained with a light scattering photometer in which the absolute weight‐average molecular weight of polymers at each retention volume is determined directly is considered a reasonable estimate of the true MWD. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2960–2968, 2001     

Modular Breath Analyzer (MBA): Introduction of a Breath Analyzer Platform Based on an Innovative and Unique,Modular eNose Concept for Breath Diagnostics and Utilization of Calibration Transfer Methods in Breath Analysis Studies

Exhaled breath analysis for early disease detection may provide a convenient method for painless and non-invasive diagnosis. In this work, a novel, compact and easy-to-use breath analyzer platform with a modular sensing chamber and direct breath sampling unit is presented. The developed analyzer system comprises a compact, low volume, temperature-controlled sensing chamber in three modules that can host any type of resistive gas sensor arrays. Furthermore, in this study three modular breath analyzers are explicitly tested for reproducibility in a real-life breath analysis experiment with several calibration transfer (CT) techniques using transfer samples from the experiment. The experiment consists of classifying breath samples from 15 subjects before and after eating a specific meal using three instruments. We investigate the possibility to transfer calibration models across instruments using transfer samples from the experiment under study, since representative samples of human breath at some conditions are difficult to simulate in a laboratory. For example, exhaled breath from subjects suffering from a disease for which the biomarkers are mostly unknown. Results show that many transfer samples of all the classes under study (in our case meal/no meal) are needed, although some CT methods present reasonably good results with only one class.     

Continuous and discrete adjoint approaches for aerodynamic shape optimization with low Mach number preconditioning

Discrete and continuous adjoint approaches for use in aerodynamic shape optimization problems at all flow speeds are developed and assessed. They are based on the Navier–Stokes equations with low Mach number preconditioning. By alleviating the large disparity between acoustic waves and fluid speeds, the preconditioned flow and adjoint equations are numerically solved with affordable CPU cost, even at the so‐called incompressible flow conditions. Either by employing the adjoint to the preconditioned flow equations or by preconditioning the adjoint to the ‘standard’ flow equations (under certain conditions the two formulations become equivalent, as proved in this paper), efficient optimization methods with reasonable cost per optimization cycle, even at very low Mach numbers, are derived. During the mathematical development, a couple of assumptions are made which are proved to be harmless to the accuracy in the computed gradients and the effectiveness of the optimization method. The proposed approaches are validated in inviscid and viscous flows in external aerodynamics and turbomachinery flows at various Mach numbers. Copyright © 2007 John Wiley & Sons, Ltd.     

Some inverse problems in rheology leading to integral equations

Two inverse problems of the integral type, which are of the general importance to rheology, are discussed. The first of them is the possibility of calculating the molecular weight distribution (MWD) from the flow curve and the second one is the interrelation between creep and relaxation functions. It was shown that the first problem is incorrect and any solution is unstable in respect to minor experimental errors. It means that the general solution of this problem is impossible in principle and only estimations of the width of unimodal MWD can be received from the curvature of the flow curve. The possibility of the correct calculation of the creep function exists in case the relaxation curve being approximated by the sum of exponential members. But the approximation of the relaxation curve within the experimental accuracy is the necessary, but not sufficient condition for the correct solution of this integral inverse problem, because not every mode of approximation leads to the satisfactory prediction of creep function.Delivered as the Courtaulds Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.     

电感耦合等离子体质谱法测定中低合金钢中痕量铝

应用电感耦合等离子体质谱法测定了中、低合金钢中痕量铝,并对质谱仪的工作条件作了优化.用微波加热消解技术对样品进行前处理,用混合比例为3比1比1的浓硝酸、浓盐酸及浓氢氟酸的混合酸作为溶解酸.对微波炉的操作程序及参数作出详细叙述.此方法的检出限为ω(Al)1.9×10-6%,对浓度水平为ω(Al)1.4×10-4%的试样进行精密度试验,其结果的标准偏差值均小于6.0%.     

Investigation on LCST behavior of a new amorphous/crystalline polymer blend: Poly(n‐methyl methacrylimide)/poly(vinylidene fluoride)

The liquid–liquid phase‐separation (LLPS) behavior of poly(n‐methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small‐angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (T_c) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min^?1 and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, T_c of PMMI/PVDF is higher than its melting temperature (T_m) and a large temperature gap between T_c and T_m exists. At the early phase‐separation stage, the apparent diffusion coefficient (D_app) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn‐Hilliard‐Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1923–1931, 2008     

Classification Performance of a Low Pressure Differential Mobility Analyzer for Nanometer-sized Particles

Size distribution measurements and classification tests by a low pressure differential mobility analyzer (LPDMA) for nanometer-sized silver particles and cesium iodide particles under low pressure conditions (123–300 Torr) were performed using a transmission electron microscope (TEM) and the tandem DMA technique. When the ratio of the sheath gas flow rate and the aerosol gas flow rate was set at 5 : 1, the targeted sizes calculated from the classification voltage applied to the LPDMA at 160 Torr are found to be in good correlation with the count mean Feret diameter obtained from the TEM observation of the particles collected after a classification ranging from 6 to 25 nm, although the targeted sizes set by the LPDMA were approximately 15% greater than the count mean Feret diameter measured by the TEM after classification. The geometric standard deviations of DMA-classified particles measured by TEM and those obtained from the tandem DMA method ranged from 1.08 to 1.17 and from 1.05 to 1.13, respectively. They were slightly greater than the ideal geometric standard deviations (1.05) of the particles classified with the LPDMA, which was calculated by neglecting the broadening effects due to Brownian diffusion. We experimentally demonstrated the validity of our LPDMA system for size measurements and classification of the nanometer-sized particles under low pressure conditions.     

Direct patterning of poly(amic acid) and low‐temperature imidization using a crosslinker,a photoacid generator,and a thermobase generator

A positive‐type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA), a crosslinker 1,1,1‐tris{4‐[2‐(vinyloxy)ethoxy]phenyl}ethane (TVPE), a photoacid generator (PAG) (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA), and a thermobase generator (TBG) t‐butyl 2,6‐dimethylpiperidine‐1‐carboxylate (BDPC) has been developed as a promising material in microelectronics. The PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianiline (ODA) in dimethyl sulfoxide (DMSO). The PSPI, consisting of PAA (69 wt %), TPVE (21 wt %), PTMA (3 wt %), and BDPC (7 wt %), showed high sensitivity of 21 mJ/cm² and a high contrast of 6.8 when it was exposed to a 436‐nm line (g‐line), postbaked at 90 °C for 5 min, and developed with 1.69 wt % TMAHaq. A clear positive image of 8 μm line and space pattern was printed on film, which was exposed to 50 mJ/cm² of g‐line by a contact printing mode and fully converted to the corresponding polyimide (PI) pattern on heating at 200 °C, confirmed by FTIR spectroscopy. Thus, this system will be a good candidate for next generation PSPIs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3362–3369, 2009     

Electrochemical synthesis of ammonia using a cell with a Nafion membrane and SmFe_(0.7)Cu_(0.3-x)Ni_xO_3(x=0―0.3) cathode at atmospheric pressure and lower temperature

Samaria-doped ceria Ce0.8Sm0.2O2-δ(SDC) and SmFe0.7Cu0.3-xNixO3 have been synthesized by the sol-gel method and characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM) and scanning electron microscopy(SEM).The electrochemical synthesis of ammonia was investigated at atmospheric pressure and low temperature,using the SFCN materials as the cathode,a Nafion membrane as the electrolyte,nickel-doped SDC(Ni-SDC) as the anode and silver-platinum paste as the current collector.Ammonia was synt...