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排序方式: 共有80条查询结果,搜索用时 296 毫秒
1.
Otakar Kouba 《Czechoslovak Journal of Physics》1998,48(5):517-522
Spectral energy transformation is one of the general properties of nonlinear systems. We examined the Fröhlich vibration system as a model nonlinear system. Energy is transferred down towards low frequency vibration modes with considerable damping. 相似文献
2.
θ-Conditions, the temperature coefficient of unperturbed dimensions of the macromolecules and the thermodynamic interaction parameters ψ and κ were determined for solutions of poly(methyl methacrylate) in 2-alkoxyethanols (methoxy, ethoxy and butoxy). The results for this series of solvents fit the data reported for other solvents and dln . The dependence of parameters ψ and κ exhibited deviations from the theoretical dependence, mainly near the limiting value ψ = 0.5. 相似文献
3.
By using non-Newtonian viscometry and the static light-scattering method, changes in the structure of particles of latex dispersions of ethyl acrylate-methacrylic acid copolymer during alkalization with ammonium hydroxide were investigated. It was found that in dispersions with an acid content up to 20 wt% the particles only swell; at acid content between 20 and 40 wt% they decompose to smaller units represented by supermolecular aggregates of macromolecules, and only when approximately starting from 40 wt% of acid does the copolymer become molecularly dissolved. This means that even if dispersions with an acid content from c. 20 wt% are clarified by alkalization, no complete dissolution takes place. 相似文献
4.
Jaroslav Stejskal Otakar QuadratIrina Sapurina Josef ZemekAlicja Drelinkiewicz Magdalena HasikIvo K?ivka Jan Prokeš 《European Polymer Journal》2002,38(4):631-637
Silica gel microspheres 7 and 15 μm in diameter were coated with an overlayer of polyaniline camphorsulfonate or hydrochloride during the oxidative polymerization of aniline. Coated silica gel and polyaniline precipitate were separated using a difference in sedimentation rate. In an alternative approach, the microspheres were modified with polyaniline in the presence of 35 nm colloidal silica. This technique prevented the macroscopic precipitation of polyaniline. Coatings of neat, 3-aminopropyl- and octadecyl-modified silica gel with polyaniline hydrochloride were compared. The surface composition of coated microspheres was characterized by X-ray photoelectron spectroscopy. Potential applications of particles in electrorheology, organic catalysis, and in modeling of conductivity behavior in composites are demonstrated. 相似文献
5.
A titration unit for automatic analysis systems is described. The titrator performs different titrations specified by strings of digital parameters. It has 4 independent titration stations with individual electrode systems. A multiburette with 20 cylinders provides all stations with the necessary reagents. End-point titrations, and incremental and equilibrium titrations are controlled by a microcomputer. In combination with a sample transport and a desk calculator, the titrator can be used to process automatically samples of different natures which require different treatment. 相似文献
6.
J. Šňupárek L. Mrkvičková O. Quadrat Z. Walterová P. Bradna 《Colloid and polymer science》2000,278(12):1205-1210
Model ethyl acrylate–methacrylic acid copolymer latices and latices of particles cross-linked by copolymerizing small amounts
of water-soluble N,N′-methylenebisacrylamide were prepared by nonseeded semicontinuous emulsion copolymerization. Dynamic and static light scattering
measurements indicated a slightly higher degree of polydispersity in the case of cross-linked particles, especially in the
initial stages of polymerization. The hydrodynamic volume of the alkalinized particles controlling the viscosity properties
of the dispersions decreased with the time of polymerization and in the case of cross-linked copolymer almost reached a constant
value at about 1 h. The different character of the particle structure was confirmed by differences in particle disintegration
after alkali addition or in the presence of methanol.
Received: 2 February 1999/Accepted: 28 June 2000 相似文献
7.
Summary The time dependences of shear and normal stress measured with a Weissenberg rheogoniometer were used in an investigation of the negative thixotropy of poly(methyl methacrylate) solutions in a low-viscosity solvent (mixture of cyclohexanone and isopropanol). A set of criteria was suggested for a complex quantitative evaluation of this phenomenon. The reproducibility of these criteria and their sensitivity towards a change in the velocity gradient were determined.
Dedicated to Prof. Dr.G. Rehage on the occasion of his 60th birthday.
With 6 figures and 1 table 相似文献
Zusammenfassung Es wurde die negative Thixotropie der Lösungen von Polymethylmethacrylat in niedrigviskosem Lösungsmittel (Gemischen von Cyclohexanon und Isopropanol) studiert. Zeitänderungen der Schub- und Normalspannung wurden mit dem Weissenbergschen Rheogoniometer verfolgt und Kriterien zur komplexen quantitativen Beschreibung dieses Effektes wurden entworfen. Die Reproduzierbarkeit und Empfindlichkeit auf die Änderungen des Geschwindigkeitsgefälles wurden ermittelt.
Dedicated to Prof. Dr.G. Rehage on the occasion of his 60th birthday.
With 6 figures and 1 table 相似文献
8.
9.
O. Quadrat 《Colloid and polymer science》1986,264(5):399-402
An investigation of the degradation of poly(methyl methacrylate) in the case of negative thixotropy of its solutions in tricresyl phosphate showed that the number of polymer bonds broken by flow as expressed through the decrease of molecular weight in the course of the effect is determined by shear energy imposed on the system, irrespective of the velocity gradient and temperature used. 相似文献
10.