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  • 1
    ISSN: 1434-601X
    Keywords: 21.10.−Jx ; 21.10.Pc ; 25.45.−6h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Proton holes states have been studied up toE x=17 MeV andE x=3.5 MeV in the119In nucleus via the120Sn(d,3He)119In reaction respectively atE d=108.4 MeV andE d=51 MeV. DWBA analysis of angular distributions has allowedl attributions for a large number of new levels and the determination of valence and inner hole strength distributions. The first 1g 9/2, 2p 1/2 and 2p 3/2 levels only exhaust 40%, 60% and 32% of their respective sum rule limits. The missing strengths are shared among several low lying levels and significant higher lying contributions. The 1f strength, not identified in the previous experiments is spread fromE x=1 MeV to about 17 MeV. The low lying levels aroundE x=2.4 MeV could exhaust some 40% of the 1f 5/2 sum rule. The higher lying strength with a flat maximum aroundE x=7.5 MeV could account for the 1f 7/2inner hole strength and the missing 1f 5/2 valence strength. The experimental strength functions compare rather well with the predictions of the quasiparticle-phonon model.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-1536
    Keywords: Key words Characterization ; particle size distribution ; multi-sized ; latex ; centrifuge ; quasielastic light scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  A method for characterizing the particle size and size distribution of multi-sized polymer lattices was developed by combining quasielastic light scattering (QELS) with a centrifuge. Lattices were first fractionated by centrifugation and the different populations of particles were separated in successive steps. The size of these particles was measured by QELS, and the mass fraction of the particles was determined gravimetrically. The particle size and size distribution of several blends of monodisperse lattices and two industrial multi-sized lattices have been measured by this method. The results show that the particle sizes obtained using this method are in good agreement with the expected particle diameters, and that the relative amounts of the different groups of particles in the blends can be accurately determined. The efficiency of centrifuge-QELS was also confirmed by comparison with other techniques such as transmission electron microscopy (TEM), QELS, field-flow fractionation (FFF) and capillary hydrodynamic fractionation (CHDF). However, this method is not suited for the analysis of continuous, broad distributions or mixtures with a high number of different populations. It is better suited for distributions with a small number of families of particles, and then can be used for preparative propose on a laboratory scale.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 276 (1998), S. 305-312 
    ISSN: 1435-1536
    Keywords: Key words Rheology ; multi-sized ; high solid content ; latex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Four monodisperse latices with particle size of 75, 135, 340 and 477 nm were synthesized. The rheo-logical properties of mixture of the monodisperse latices were inves-tigated as a function of blending ratio, and compared with those of multi-modal latices, in a range of shear rate from 0.2 to 100 s-1. The maximum packing (highest solid contents) was observed at a weight fraction 80% of large particles with respect to total solids contents for both bimodal and trimodal latices, and the lowest viscosity was obtained when the ratio of large to medium to small particles was approximately 80/10/10 (by wt.). It was also demonstrated that this minimum in the viscosity is not strongly dependent on the actual size of each kind of particles present in the multimodal latices.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 1937-1959 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Batch emulsifier-free copolymerizations of styrene (S) and butyl acrylate (BuA) have been performed for a S/BuA weight ratio = 50/50 in the presence of two types of functional comonomers [methacrylic acid (MAA) at different pHs] or potassium sulfopropylmethacrylate (SPM) and two initiators [potassium persulfate or 4-4′azobiscyanopentanoic acid (AZO)]. The use of AZO/MAA system results in the formation of polymer particles with only surface carboxylic end groups. The particle size of the final latexes can be adjusted with the MAA concentration, provided the polymerization is carried out at pH 〉 6.5. However, the higher the MAA concentration, the sooner the polymerization levels off in conversion. With the K2S2O8/SPM system, particles bearing only sulfate and sulfonate groups are produced and the polymerization is complete. In that case, the particle size of the final latexes is smaller than with the previous system and 30% of the SPM is fixed on the particle surface, instead of 10% with MAA. Using SPM, a too high functional monomer concentration results in the latex destabilization caused by the formation of a large amount of polyelectrolytes. Kinetic studies indicate that most of the functional monomer is incorporated onto the particle surface during the last 30% conversion of the polymerization. A tentative explanation of such a behavior is discussed, based on the existence of two polymerization loci in the latex system.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Soapless emulsion copolymerization of styrene (S) and n-butyl acrylate (BuA) has been investigated using two types of initiator and different comonomer feed mixtures. When using K2S2O8 as initiator, the particle size and size distribution of the final latexes (500 nm and 1.003, respectively) is not significantly affected by the comonomer feed composition, whereas the molecular weight and surface characteristics were found to sharply change at high butyl acrylate content. Based on the most probable particle nucleation mechanism and type of chain termination in the monomer swollen particles, a tentative explanation of these results has been proposed. Replacing persulfate by a carboxylic initiator (4-4′-azobiscyanopentanoic acid) results in the formation of stable particles as α observed with the persulfate, provided the aqueous phase pH is fixed in between 6 and 7. Results on the initiator residue location as a function of the conversion point out that the particle flocculation mechanism is strongly significant in the preparation of such latexes.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1271-1281 
    ISSN: 0887-624X
    Keywords: potassium persulfate ; decomposition ; soap-emulsified systems ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two methods of analysis, potentiometry and capillary electrophoresis, were used to study the decomposition of potassium persulfate (KPS) in aqueous solutions. The experiments were carried out in a glass reactor equipped with continuous control of temperature and pH during the reaction. The effect of the pH on the decomposition of KPS was investigated. The rate of KPS decomposition in the presence of a variety of additives (surfactants, inhibitor, monomer-like molecules, and monomers), which are used in emulsion polymerization recipes, was also studied over the temperature range of interest. The rate of disappearance of the persulfate ion was greatly increased in the presence of hydroquinone, but changed very little in the presence of surfactants. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 137-152 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Emulsion terpolymerization of styrene (S), butylacrylate (BuA) and sodium acrylamido undecanoate (AUNa), a surface active functional monomer have been carried out using a batch process in the presence of sodium 4-4′-azobiscyanopentanoate as initiator. Varying the AUNa concentration, stable particles bearing only carboxylic charges have been produced with diameters ranging from 200 to 500 nm at solids content as high as 40%. However a low AUNa yield at the particle surface has been found (30-35%), which could be explained by very unfavorable reactivity ratios of AUNa with S and BuA. Most of the AUNa seems to be wasted in the water phase (unpolymerized and forming hydrosoluble chains). Furthermore, a concentration of AUNa higher than 10-2 mol L-1 results in the latex destabilization, presumably caused by the formation of a large amount of polyelectrolytes. Kinetic studies of the AUNa consumption show that the AUNa is mainly fixed at the particle surface between 90 and 100% conversion, which indicates that the AUNa is mainly polymerized in the water phase and not at the particle surface. An attempt has been made to increase the surface charge density by polymerizing a shell of AUNa/S/BuA on a seed latex. It turned out to be unsuccessful (low surface yield, formation of new particles).
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 157-168 
    ISSN: 0887-624X
    Keywords: emulsion polymerization ; reaction calorimetry ; chain transfer agents ; kinetics ; radical desorption ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of chain transfer agents (CTA) on the emulsion copolymerization of styrene and butyl acrylate was studied in a bench scale 7 L reactor. On-line estimates of conversion were obtained through the joint use of calorimetric measurements and fast gravimetric data. Off-line measurements of partial conversions, molecular weight distribution (MWD), glass transition temperature (Tg), and particle diameter were also performed in order to investigate the effect of two mercaptans (tert-butanethiol and n-dodecanethiol) on both the kinetics of the polymerization process and the microstructure-dependent properties of the copolymer. The obtained experimental results were interpreted in terms of radical desorption and diffusive limitations of the CTA between the oil droplets and the particles. A model has been derived to compute the kinetic constants, the number of radicals per particle, and both the GPC/SEC diagrams and DSC thermograms related to MWD and Tg measurements, respectively. Several batch and semibatch examples are proposed to show that these important variables are satisfactorily fit by the model. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 157-168, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 465-472 
    ISSN: 1042-7147
    Keywords: polystyrene, emulsion polymerization ; styrenic nonionic surfactant ; latex stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Among the variety of possible structures for polymerizable surfactants, it seems clear that the most interesting should be those with the reactive group located in the hydrophobic part of the molecule. We report here a study based on such a surfactant. Its general formula is \documentclass{article}\pagestyle{empty}\begin{document}$$ CH_2d\hbox{---}CH\hbox{---}C_6 H_4\hbox{---}CH_2\hbox{---}O(CH_2)_n\hbox{---}O(CH_2CH_2\hbox{---}O)_m\hbox{---}H $$\end{document}A set of surfactants has been produced with m varying from 23 to 48 and n = 6 or 12. The compounds have been characterised by 1H-NMR (nuclear magnetic resonance), size exclusion chromatography, surface tension measurements and turbidimetry.These surfactants have been copolymerized with styrene in emulsion polymerization. The coagulum is rather important, except if m is large enough. Although the incorporation of the surfactant in the latex is rather high. Most of the anchored surfactant remains at the surface and is not too buried inside. The particle size decreases with both the amount of surfactant and the length of its hydrophilic part. The use of these polymerizable surfactants leads to an excellent stability of the latex against the addition of electrolytes, and also against freeze-thawing constraints.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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