Measurement of the density distributions in quenched polycarbonate specimens by a quantitative schlieren optical technique

A new technique for the determination of spatial density distributions is described. The density is derived from the refractive index gradient as determined with a quantitative Schlieren optical technique. The advantages of this technique are a high spatial resolution and sensitivity. Gapwise profiles can be measured without slicing the sample so that more reliable data are obtained quickly. This is demonstrated for the gapwise density distributions in quenched polycarbonate specimens. It is shown that the density distribution is determined by a competition between the local cooling rate variation and the cooling stress distribution. The residual density is predominantly determined by the coolant temperature. The density in the core is higher than at the surface for high coolant temperatures, whereas for low coolant temperatures the density in the core is lower than at the surface. The observed effects are explained semiquantitatively by a simple model using calculated cooling stresses and cooling rates.     

The use of load separation criterion and normalization method in ductile fracture characterization of thermoplastic polymers

Load separation is the theoretical basis for the single-specimen J-integral experiment and the incremental calculation of J-integral crack growth resistance (J-R) curves. This criterion has been experimentally studied in nongrowing crack records in several materials, and more recently a new method to extend the applicability to growing crack experiments has been proposed in testing steel. This article examines the applicability of the load separation criterion for evaluating ductile fracture mechanics parameters in rubber-modified polystyrenes and thermally treated polypropylene in the bending configuration. This criterion allows the load to be represented as the multiplication of two independent functions: a material deformation function and a crack geometry function. Its validity is evaluated with both stationary and growing crack experiments. η-factor calculation for smooth and side-grooved specimens was also tried using the simple method of Sharobeam and Landes, in order to identify material dependency. This article also investigates the applicability of the normalization method, based on the load separation criterion for evaluating J-R curves on PP and PS. A simple approach which combines a blunt notched and a precracked specimen experiment is proposed to determine the J-R curve of the materials studied. The resulting J-R curves are compared with multiple specimen results available in the literature for these materials. A good agreement between the J-R curves obtained from this simple method and from the multiple specimen technique was found. © 1996 John Wiley & Sons, Inc.     

Staining of proteins for 2D SDS‐PAGE using Coomassie Blue—speed versus sensitivity?

Several new fast staining protocols for the visualization of proteins separated by SDS‐PAGE utilizing Coomassie Blue staining (CBS) have been described in literature. The sensitivity of a newly designed staining protocol is usually estimated using 1D SDS‐PAGE of serially diluted protein samples. However, this approach is not predictive and satisfactory for 2D SDS‐PAGE capable of resolving hundreds or thousands of different proteins in a single analysis. In this work, a new fast staining protocol recently introduced by Dong et al. (PLoS One 2011, 6, e22394) was compared to colloidal CBS. The number of detectable spots in 2D SDS‐PAGE of identical blood plasma samples in repeated runs was chosen as a sensitivity criterion. Further, the influence of gel boiling on the subsequent protein identification by MS was investigated. In spite of its advantages, the staining protocol according to Dong et al. (PLoS One 2011, 6, e22394) seems to be less sensitive than colloidal Coomassie staining when the number of detected spots is the evaluating criterion. No obvious influence of gel boiling on the protein identification was observed.     

Study of solid-state polymerization by positron lifetime measurements

The positron lifetime measurement technique was applied to analyze the structural changes occurring in solid-state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ₂ and I₂, which show a marked change as a function of the γ-ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ₂, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior of I₂ may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization process.     

An optimal method of DNA silver staining in polyacrylamide gels

A silver staining technique has widely been used to detect DNA fragments with high sensitivity on polyacrylamide gels. The conventional procedure of the silver staining is tedious, which takes about 40-60 min and needs five or six kinds of chemicals and four kinds of solutions. Although our previous improved method reduced several steps, it still needed six kinds of chemicals. The objective of this study was to improve further the existing procedures and develop an optimal method for DNA silver staining on polyacrylamide gels. The novel procedure could be completed with only four chemicals and two solutions within 20 min. The steps of ethanol, acetic acid, and nitric acid precession before silver impregnation have been eliminated and the minimal AgNO3 dose has been used in this up-to-date method. The polyacrylamide gel of the DNA silver staining displayed a golden yellow and transparent background with high sensitivity. The minimum 0.44 and 3.5 ng of DNA amount could be detected in denaturing and nondenaturing polyacrylamide gel, respectively. This result indicated that our optimal method can save time and cost, and still keep a high sensitivity for DNA staining in polyacrylamide gels.     

Reactive rubbers as toughening agents for thermoset polyester resins. Molecular analysis by FTIR and fracture behavior of the resulting blends

A reactive rubber obtained by isocyanation of hydroxyl-terminated polybutadiene was used as toughening agent for an unsaturated polyester resin. Both the isocyanation and the successive reaction between the modified rubber and the polyester were investigated by Fourier-transform infrared spectroscopy (FTIR). Fracture measurements at high and low strain rate were carried out on the cured materials to test their toughness. The failure mechanisms were established by morphological analysis of fractured surfaces, performed by scanning electron microscopy. © 1993 John Wiley & Sons, Inc.     

Generalized composite degradation kinetics for polymeric systems under isothermal and nonisothermal conditions

A composite degradation methodology is extended to the conversion-dependence function in order to explain the importance of multiple reaction mechanisms which might be considered to be involved in degradation processes. Based on two elementary reaction mechanisms, a specific form of the model equation is derived, which is capable of describing various types of degradation behavior showing sigmoidal rate as well as deceleratory rate. The conversion-dependence function is derived to be independent of the Arrhenius-type reaction constant or temperature, and thus the kinetic parameters are determined by analytic methods that have been developed for isothermal and dynamic-heating experiments without any modification or additional assumptions. The developed model equation is tested by predicting the isothermal master curve of polyether-ether-ketone (PEEK), which is used as a model system in this study. The activation energies of the model system are analyzed using comparable methods for isothermal and dynamic experiments, which compare favorably in terms of the activation energy as a function of conversion. The resulting model equation, based on the kinetic parameters determined by isothermal experiments, can accurately predict both isothermal and dynamic-heating thermogravimetry utilizing the same constants and identical reaction mechanisms without additional assumption.     

用于观察橡胶改性聚氯乙烯结构的制样方法——氯磺酸-重金属染色法

<正> 使用丁腈橡胶(NBR),氯化聚乙烯(CPE)、乙烯-醋酸乙烯酯共聚物(EVA)、甲基丙烯酸甲酯-丁二烯-苯乙烯三元共聚物(MBS),丙烯酸酯弹性体(ACR)等材料,可以改善聚氯乙烯(PVC)的抗冲击性能。由于PVC树脂由数种结构层次不同的微粒组成,橡胶改性PVC的性能依赖于加工条件及体系的相结构。观察改性PVC的相结构是研     

An optimal method of DNA silver staining in polyacrylamide gels

DNA silver staining has widely been used to detect DNA fragments in polyacrylamide gels with high sensitivity. We developed an optimal method for DNA silver staining on polyacrylamide gels. The novel procedure can be completed within 10 min instead of over 20 min with the conventional methods. The sensitivity is significantly improved by the silver-ion sensitizer (Eriochrome black T (EBT)) and the minimum of 0.11 and 1.75 ng of DNA amount can be detected in denaturing and nondenaturing polyacrylamide gel, respectively. Compared with the conventional silver staining methods, the improved optimal method can save time and display high sensitivity, color uniformity, and long storage time of the staining gels.     

Rapid and easy protein staining for SDS-PAGE using an intramolecular charge transfer-based fluorescent reagent

High-performance staining for 1-D and 2-D SDS-PAGE was carried out using a novel protein-binding fluorophore (Dye 1), which noncovalently interacts with proteins and provides a fluorescence emission response to proteins by intramolecular charge transfer. In order to achieve the high-throughput analysis of proteins for SDS-PAGE, the general protocols for in-gel protein staining (SDS-PAGE, fixation, staining, washing, and detection) were simplified to produce an easy and rapid protocol (SDS-PAGE together with staining, washing, and detection). This method was performed by preparation of an electrophoresis buffer containing Dye 1 under optimum conditions, and by the binding of Dye 1 to proteins in the gel during the SDS-PAGE. As a result, this study required only 15 min for protein staining as a minimum time. On the other hand, it takes several hours for the general protein staining method, such as SYPRO Ruby staining (18 h) and CBB staining (105 min). Moreover, the protein-to-protein variation was low, and the detection limit was 7.0 ng/band of BSA (S/N = 3.0) in this method, which was as sensitive as the short-protocol silver staining methods. On the basis of these results, this rapid and easy protocol for SDS-PAGE using Dye 1 may be widely applicable and convenient for users in the various scientific and medical fields.     

CBB staining protocol with higher sensitivity and mass spectrometric compatibility

Various CBB‐based methods for staining proteins separated by 2‐D gel electrophoresis were compared with regard to sensitivity and resolution. A modified Kang's CBB staining protocol, which we have modified, includes phosphoric acid in a concentration of 8% instead of the original 2%. This proved to be the best approach. Protein amounts as low as 2 ng and ∼2300 spots in the gel can be detected by employing this protocol. The modified procedure takes less time to carry out. Moreover, this practice is more sensitive and resolves more protein spots than most protocols reported to date and is compatible with subsequent mass spectrometric analysis.     

橡胶活性官能团对增韧环氧树脂动态力学性能的影响

用动态扭摆法测试聚丙烯酸丁酯橡胶增韧环氧树脂的动态力学行为,研究在环氧树脂低固化度和高固化度时,橡胶活性官能团种类(环氧基官能团与羧基官能团)和数量(官能度)对其影响。研究体系中橡胶玻璃化转变温度(Tg)的移动大小,与橡胶和基体树脂健合程度之间的关系。     

The effect of lattice compressibility on the thermodynamics of gas sorption in polymers

A compressible lattice model with holes, the glassy polymer lattice sorption model (GPLSM), was used to model the sorption of carbon dioxide, methane, and ethylene in glassy polycarbonate and carbon dioxide in glassy tetramethyl polycarbonate. For glassy polymers, an incompressible lattice model, such as the Flory–Huggins theory, requires concentration-dependent and physically unrealistic values for the lattice site volumes in order to satisfy lattice incompressibility. Rather than forcing lattice incompressibility, GPLSM was used and reasonable parameter values were obtained. The effect of conditioning on gas sorption in glassy polymers was analyzed quantitatively with GPLSM. The Henry's law constant decreases significantly upon gas conditioning, reflecting changes in the polymer matrix at infinite dilution. Treating the Henry's law constant as a hypothetical vapor pressure at infinite dilution, gas molecules in the conditioned polymer are less “volatile” than those in the unconditioned polymer. Flory–Huggins theory was used to model the sorption of carbon dioxide, methane, and ethylene in silicone rubber. Above the glass transition temperature, the criterion of lattice incompressibility for Flory-Huggins theory was satisfied with physically realistic and constant values for the lattice site volumes. © 1992 John Wiley & Sons, Inc.     

Modular approach for novel nanostructered polycondensates enabled by the unique selectivity of carbonyl biscaprolactam

New enabling chemistries have been developed to produce novel well‐defined polymeric materials through the additions of small amounts of reactive functional compounds to standard polymers during regular processing steps. We found that carbonyl biscaprolactam and its derivatives couple polymer chains in a strictly linear fashion. The requirements for fast and well‐controlled coupling reactions, a prerequisite to apply this modular concept, were met. The breakthrough to produce a wide variety of novel polymers came when we found that many building blocks, provided with functional groups and blocked isocyanate groups, could be made on the basis of this chemistry. Blocked isocyanate groups are very suitable coupling units to fix desired functions onto polymer backbones. In one example, antifouling coatings were prepared by introducing fluorine groups. In another case, blocked isocyanate functional acrylates were built into a polyacrylate to make self‐crosslinkable coatings. In another illustration, the concept was demonstrated by a novel route to prepare polyrotaxanes from rotaxane monomers provided with blocked isocyanates as polymerizable stopper groups. These reactive functional compounds gave, in a controlled manner, polymeric materials with substantially improved properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3198–3205, 2003     

Detection of Escherichia coli O157:H7 bacteria by a combination of immunofluorescent staining and capillary electrophoresis

As the number of incidents of bacterial infections continues to rise around the globe, simpler, faster, and more sensitive diagnostic techniques are required to improve the safety of the food supply and to screen for potential bacterial infections in humans. We present here direct and indirect approaches for the detection of bacteria, which are based upon a combination of immunofluorescent staining and capillary electrophoresis. In the direct approach, Escherichia coli O157:H7 bacteria stained with fluorescein-tagged specific antibodies are detected by CE, while in the indirect approach fluorescein-tagged specific antibodies to E. coli are first captured by E. coli O157:H7 bacteria and then released and detected by CE. We have identified suitable bacteria staining and CE protocols, which involved a 10 mM Tris-borate-EDTA (TBE) buffer, 0.25 micro g antibody/1 million bacteria, and capillaries dynamically coated with poly-N-hydroxyethylacrylamide (polyDuramide). We have also successfully detected the presence of E. coli O157:H7 in contaminated meat. The total time required for analysis was 6-8 h, which is less than that realized in most commercial assays presently available.     

Preparation of CO2/N2‐Triggered Reversibly Coagulatable and Redispersible Polyacrylate Latexes by Emulsion Polymerization Using a Polymeric Surfactant

We report here a novel approach for making reversibly coagulatable and redispersible polyacrylate latexes by emulsion (co)polymerization of methyl methacrylate (MMA) using a polymeric surfactant, poly(2‐(dimethylamino)ethyl methacrylate)₁₀‐block‐poly(methyl methacrylate)₁₄. The surfactant was protonated with HCl prior to use. The resulted PMMA latexes were readily coagulated with trace amount of caustic soda. The coagulated latex particles, after washing with deionized water, could be redispersed into fresh water to form stable latexes again by CO₂ bubbling with ultrasonication. The recovered latexes could then be coagulated by N₂ bubbling with gentle heating. These coagulation and redispersion processes were repeatable by the CO₂/N₂ bubbling.     

Synthesis and Characterization of PEG‐Based Drug‐Responsive Biohybrid Hydrogels

Interactive materials being responsive to a biocompatible stimulus represent a promising approach for future therapeutic applications. In this study, we present a novel biohybrid material synthesized from biocompatible components being stimulus‐responsive to the pharmaceutically approved small‐molecule novobiocin. The hydrogel design is based on the gyrase B (GyrB) protein, which is covalently grafted to multi‐arm polyethylene glycol (PEG) using a Michael‐type addition reaction. Upon addition of the GyrB‐dimerizing substance coumermycin, stable hydrogels form which can be dissolved in a dose‐adjustable manner by the antibiotic novobiocin. The switchable properties of this PEG‐based hydrogel are favorable for future applications in tissue engineering and as externally controlled drug depot.     

Diffusion in glassy polymers: A model using a homogenization method and the effective medium theory

Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows Henry's law and others where it follows Langmuir's law. It is assumed that the linear dimensions of these regions are small compared with the macroscopic length of interest but large compared with the mean free path of the penetrant gas molecules. Applying an homogenization method it is shown that the average flux is directly proportional to the concentration gradient in the polymer. This relationship can be expressed in terms of an effective diffusion coefficient D_eff, which depends on the details of the microstructure. D_eff is evaluated in the framework of the effective medium theory and compared with experimental data for diffusion of five vapors in ethylcellulose.     

Comparative study between core-shell and interpenetrating network structure polyurethane/polyacrylate composite emulsions

Anionic aqueous polyurethane dispersion was prepared by using carboxyl acid group to make the polyurethane dispersible, and then nanograde core-shell and crosslinked IPN structure polyurethane/polyacrylate composite latex (PUA) were synthesized by soap-free emulsion polymerization method with polyurethane dispersion as seed. FTIR, DSC, dynamic light scattering, TEM, ESCA, TGA, electronic tensile machine were employed to investigate the structures and properties of the composite latex and their polymers. Meanwhile the core-shell composite PUA emulsion and the crosslinked IPN composite PUA emulsion were compared. The results showed that the particle morphology of PUA composite emulsion is inverted core-shell structure with polyacrylate as the core and with polyurethane as the shell. The morphology of the crosslinked PUA emulsion was multi-core structure. The surface in core-shell PUA contains rich PU phase. The phase structure of the crosslinked PUA is more uniform. Three transition temperatures are observed for the core-shell composite PUA, two transitions are observed for the film from the crosslinked PUA. The TGA curves of core-shell PUA and crosslinked PUA exhibit two stages, the first stage corresponds to the thermal decomposition of hard segments in seed polyurethane; the second stage corresponds to the decomposition of soft segments in PUA and decomposition of polyacrylate. With the increase of glycidyl methacrylate (GMA) amounts in PUA composite emulsions, the tensile strength of the PUA films as well as the average diameter of the PUA composite emulsion particles increase, the elongation at break of the PUA films decreases.     

Evaluation of free-volume theories for solvent self-diffusion in polymer–solvent systems

An evaluation of free-volume theories for solvent self-diffusion is carried out using recent comprehensive data sets for penetrant self-diffusion in polymer solutions. Different theories are compared, and free-volume theories in the prediction of penetrant self-diffusion coefficients in glassy polymer systems is also evaluated. © 1993 John Wiley & Sons, Inc.