Molecular properties of hybrid macromolecular antioxidants: Dextran hydrophobically modified by sterically hindered phenols

The conformation properties of clinically relevant hybrid macromolecular antioxidants (dextran hydrophobically modified by sterically hindered phenols) in aqueous solution were characterized by a combination of dynamic light scattering (DLS), size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). We were able to split and analyze separately two different types of polydispersity -polydispersity over molecular weights and the one over substitution degree. The properties of the hybrid macromolecules are determined by the number of hydrophobic antioxidants in a single molecule. An insertion of hydrophobic groups into a hydrophilic chain changes the conformation of a single conjugate macromolecule. We have established that with the increasing of a number of hydrophobic antioxidant groups, a conformational transition occurs where a single conjugate undergoes a transition from a Gaussian coil conformation to a more compact structure.     

Dynamic Scaling in Miscible Viscous Fingering

We consider dynamic scaling in gravity driven miscible viscous fingering. We prove rigorous one-sided bounds on bulk transport and coarsening in regimes of physical interest. The analysis relies on comparison with solutions to one-dimensional conservation laws, and new scale-invariant estimates. Our bounds on the size of the mixing layer are of two kinds: a naive bound that is sharp in the absence of diffusion, and a more careful bound that accounts for diffusion as a selection criterion in the limit of vanishingly small diffusion. The naive bound is simple and robust, but does not yield the experimental speed of transport. In a reduced model derived by Wooding [20], we prove a sharp upper bound on the size of the mixing layer in accordance with his experiments. Woodings model also provides an example of a scalar conservation law where the entropy condition is not the physically appropriate selection criterion.     

多孔介质内混溶流体间粘性指进现象的格子Boltzmann模型

提出一个模拟多孔介质内混溶流体间粘性指进现象的格子Boltzmann模型.采用双分布函数分别求解压力场和浓度场.在浓度场平衡态分布函数中引入与浓度扩散相关的参数.通过调节参数,使粒子碰撞过程中的松弛时间保持恒定.模拟了粘度相同的流体间的混相驱替问题.不同网格下的模拟结果均与解析解吻合良好,验证了模型的可行性.进一步研究粘度比和贝克莱数(Pe)对粘性指进现象的影响.结果显示,增大粘度比会促进"手指"的增长.当粘度比不变时,存在Pe的临界值.当Pe超过临界值时,"手指"前缘会出现分裂现象.对横向平均浓度场的研究显示,混合区域的长度随时间的变化分为两个阶段,它首先随着t^1/2成线性增长,然后随着t成线性增长.     

Electrolytic conduction in amorphous salt complexed polyethers

Phosphate ester extended and crosslinked poly(ethylene glycol)s were prepared from reaction of the glycols with chlorophosphates. Fully amorphous electrolytes formed with lithium trifluoromethanesulphonate showed enhanced conductivity over comparable poly(ethylene oxide) electrolytes in the temperature range 293–373 K. With O/Li=27.6, α=5.2×10⁻⁶S cm⁻¹ at 293 K. A conductivity maximum was detected at ca. 1 mol dm⁻³ concentration consistent with the increase in charge carrier density opposed by medium viscosity. For all complexes the temperature dependence of conductivity obeyed the Vogel-Tamman-Fulcher and Williams-Landel-Ferry equations, with T_g(onset) for the parent polymer as the ideal glass transition temperature. Activation energy parameters from use of the VTF equation and Adam-Gibbs configurational entropy model showed a linear dependence on salt concentration.     

A new crystal mounting method for macromolecular cryocrystallography

The fundamental advantage of soft-X-ray ARPES (SX-ARPES) with photon energies around 1 keV compared to the conventional vacuum-ultraviolet ARPES (VUV-ARPES) is an increase of the photoelectron escape depth. This enhances the bulk sensitivity of the ARPES experiment as well as enables access to buried systems such as interfaces, heterostructures, and impurities. This advantage combines with resolution in three-dimensional (3D) momentum k, which, on the other hand, degrades upon further increase of energy into the hard-X-ray range. The main challenge of SX-ARPES is the valence band (VB) photoemission cross-section decreasing by a few orders of magnitude compared to the VUV-ARPES energy range. This problem can only be overpowered with advanced synchrotron radiation instrumentation delivering high photon flux. In this article, after a recap of the main virtues and current challenges of SX-ARPES, we report on the recent instrumental progress at the Swiss Light Source (SLS), where a new SX-ARPES facility was installed at the Advanced Resonant Spectroscopies (ADRESS) beamline. The high photon flux above 10¹³ photons/s/0.01%BW delivered by this beamline, combined with the optimized endstation geometry, has allowed us to break through the cross-section problem and, furthermore, push the applications of SX-ARPES from bulk materials to extremely photon-hungry cases of buried systems. Complementing the recent review of the whole field of soft- and hard-X-ray ARPES published in this magazine [1 C.S. Fadley, Synchr. Rad. News 25, 26 (2012).[Taylor &; Francis Online] , [Google Scholar]], we here focus on the recent SX-ARPES applications emerging with the advanced instrumentation of the SLS.     

Automatic analysis for biochip based on macromolecular compound material

This paper illustrates a way of quantifying fluorescent chromogenic information through the image processing and identification, and analyzes the correlations between fluorescent chromogenic reaction and a probe. This analytical method is an important reference for probe development, and also used for analyzing the biochip interaction. The relationship between the same type but differing concentrations of probe and fluorescent images was derived. With light field analysis of probe attachment, we performed numerical analysis of the fluorescent signal in accordance with the method of biological area analysis. Through this method, biochips can simultaneously provide many types of quantitative and qualitative figures for research reference.     

Miscible displacement of non-Newtonian fluids in a vertical tube

The influence of rheology on the miscible displacement of a viscous fluid by a less viscous, Newtonian one in a vertical tube is studied experimentally as a function of the flow velocity. For Newtonian displaced fluids the transient residual film thickness is nearly of the tube radius at large viscosity ratios between the two fluids in agreement with experimental and numerical results from the literature. For shear-thinning fluids with a zero yield stress (mostly xanthan-water solutions), decreases down to of the radius for the most concentrated solutions. For fluids with a non-zero yield stess, further decreases down to 24-25% of the radius. The orders of magnitude of these values can be obtained through numerical simulations (commercial code) for the various types of fluids. Instabilities of the film at its boundary develop downstream and lead to a reduction of the final thickness of the film at longer times: this reduction is larger for lower viscosity ratios and larger velocities.Received: 15 February 2003, Published online: 8 July 2003PACS: 47.20.Gv Hydrodynamic stability: Viscous instability - 83.60.Wc Rheology: Flow instabilities     

Equation of state of polymer crystals: Application to polyethers

This paper discusses experimental isotherms and isobars of polyoxymethylene, polyethyleneoxide, and poly(tetrahydrofuran) that have been analyzed in terms of our theory of anharmonic polymer crystals. The trends shown by various characteristic parameters for these polyethers are interpreted in terms of their chemical structure.     

Supercontinuum generation in macromolecular media

The interaction of intense, ultrashort (femtosecond) pulses of infrared light with water leads to the generation of a white light supercontinuum due to nonlinear optical effects. This supercontinuum extends over the wavelength range 400–900 nm. The blue-sided components of this supercontinuum are due to laser-induced plasma effects and are found to sensitively depend on the presence in water of minute quantities of protein dopants (dilutions of 0.025%–0.1%). Salivary proteins like mucin and immunoglobulin-A lead to pronounced suppression of the blue-sided components, while proteins found in blood serum, such as transferrin, immunoglobulin G (IgG) and human serum albumin (HSA), do not show any such suppression. It is postulated that major salivary proteins have a propensity to efficiently scavenge plasma electrons and thereby extinguish the plasma that is formed upon laser irradiation.     

Absorbed dose calculations for macromolecular crystals: improvements to RADDOSE

Radiation damage is an unwelcome and unavoidable aspect of macromolecular crystallography. In order to quantify the extent of X‐ray‐induced changes, knowledge of the dose (absorbed energy per unit mass) is necessary since it is the obvious metric against which to plot variables such as diffraction intensity loss and B factors. Significant improvements to the program RADDOSE for accurately calculating the dose absorbed by macromolecular crystals are presented here. Specifically, the probability of energy loss through the escape of fluorescent photons from de‐excitation of an atom following photoelectric absorption is now included. For lighter elements, both the probability of fluorescence and of its subsequent escape from the crystal are negligible, but for heavier atoms the chance of fluorescence becomes significant (e.g. 30% as opposed to Auger electron decay from a K‐shell excited iron atom), and this has the effect of reducing the absorbed dose. The effects of this phenomenon on dose calculations are presented for examples of crystals of an iron‐containing protein, 2‐selenomethionine proteins, a uranium derivatised protein, and for a nucleic acid sample. For instance, the inclusion of fluorescent escape results in up to a 27% decrease in the calculated absorbed dose for a typical selenomethionine protein crystal irradiated at the selenium K‐edge.     

Glass Transition Behavior and Dynamic Fragility of PMMA-SAN Miscible Blend-Clay Nanocomposites

An investigation of the segmental dynamics and glass transition behavior of a miscible polymer blend composed of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) and its melt intercalated nanocomposite by dynamic mechanical analysis is presented. The principle goal was to address the effect of intercalation on local molecular structure and dynamics. The results showed that the intercalation of polymer chains in the galleries of organoclay (Cloisite 30B) led to a lower temperature dependence of the relaxation time (fragility) and activation energy of α-relaxation. Moreover, calculation of the distribution of the segmental dispersion showed a narrower dispersion in the glass transition region so that the Kohlrausch-Williams-Watts (KWW) distribution parameter (β_KWW) increased from 0.21 for neat PMMA to 0.34 for the 50/50 PMMA/SAN blend nanocomposite containing 3 wt% organoclay. Furthermore, the relaxation behavior of the blends showed a negative deviation from mixture law predictions based on the responses of the neat PMMA and SAN. These behaviors were attributed to the lack of specific interactions between the blend components (PMMA, SAN, and nanoclay layers) and the less cooperative behavior, i.e., less constraint for segmental relaxation, of the intercalated chains.     

A mixed method for measuring low-frequency acoustic properties of macromolecular materials

A mixed method for measuring low-frequency acoustic properties of macromolecular materials is presented. The dynamic mechanical parameters of materials are first measured by using Dynamic Mechanical Thermal Apparatus(DMTA) at low frequencies, usually less than 100 Hz; then based on the Principles of Time-Temperature Superposition (TTS), these parameters are extended to the frequency range that acousticians are concerned about, usually from hundreds to thousands of hertz; finally the extended dynamic mechanical parameters are transformed into acoustic parameters with the help of acoustic measurement and inverse analysis. To test the feasibility and accuracy, we measure a kind of rubber sample in DMTA and acquire the basic acoustic parameters of the sample by using this method. While applying the basic parameters to calculating characteristics of the sample in acoustic pipe, a reasonable agreement of sound absorption coefficients is obtained between the calculations and measurements in the acoustic pipe.     

Investigation of Phase Separation in a Partially Miscible Polymer Blend by Rheology

The phase boundary and phase‐separation dynamics of a binary poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase‐separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase‐separation mechanisms.