摘要:

Pore-size distributions have been measured for cationic acrylamide-based hydrogels of different compositions maintained at the same swelling capacity (27.8 ± 0.7 g swollen gel/g dry gel) by varying the ionic strength of the surrounding solution. Swelling equilibria were measured at about 6°C in pure water and aqueous sodium azide solutions ranging in concentration from to 10−3to 10−1M. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve, which represents the amount of imbibed liquid inside the gel inaccessible to a solute of radiusr.The pore-size distribution was obtained by using Casassa's Brownian-motion model and numerically solving the Fredholm integral equation. The modes of the pore radii range from 20.4 to 47.1 Å for acrylamide-based hydrogels containing varying amounts of cationic comonomer (1.5 and 4.0 %M), crosslinker (0.3 and 1.0 %C), and initial concentration of total monomer (15 and 35 %T).

ISSN:0022-2348    

DOI:10.1080/00222349408248092

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper reports a study of compatibilization and the mechanism of compatibilization of polypropylene (PP)/thermoplastic polyurethane (TPU) blends with maleated polypropylene (PP-MA) and its graft copolymer with polyethylene oxide (PEO), (PP-MA)-g-PEO. The results of scanning electron microscope (SEM) and dynamic mechanical analysis showed that (PP-MA)-g-PEO was a very good compatibilizer for PP/TPU blends, while PP-MA also produced some compatibilization. The cocrystallization between bulk PP and PP segments of the compatibilizers was evidenced by differential scanning calorimetry studies. The specific interaction between TPU and polar parts of the compatibilizers was studied with Fourier transform infrared spectroscopy.

ISSN:0022-2348    

DOI:10.1080/00222349408248093

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The dynamic mechanical spectrum of PEEK at low temperature shows a relaxation band which is affected by the presence of water. A mechanism based on the interaction between water and oxygen atoms present in the polymer chain was previously suggested. In the present paper, direct evidence of the role of the water at the molecular level is reported. The analysis was carried out using two different experimental techniques, dynamic mechanical relaxation spectroscopy in monodirectional stretching, and low-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Both techniques give information on molecular mobility phenomena. The comparison between data obtained using the two techniques, and the analysis of samples with a controlled water content, supports a model in which the motions of the water molecules play a relevant role in the relaxation mechanism involving the polymer chains.

ISSN:0022-2348    

DOI:10.1080/00222349408248094

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Melt blends of styrene-co-acrylonitrile (SAN) with phenoxy were prepared over a full range of compositions and were evaluated in terms of morphological, rheological, thermal, and mechanical properties. Viscosity-composition plots showed a crossover with the additivity line at 50/50 (SAN/phenoxy by weight), and deviations from semicircles in Cole‐Cole plots were seen for 70/30, 50/50, and 30/70 blends. Scanning electron micrographs (SEM) of the blends showed a two-phase morphology with a finer dispersion and well-elongated fibrils seen when SAN formed the dispersed phase. The glass transition temperature (Tg) of SAN was almost unchanged in the blends, whereasTgof phenoxy was increased over 5°C. Tensile modulus and strength generally showed synergistic effects in phenoxy-rich blends. In the 10/90 blend, the ultimate elongation was greater than for pure phenoxy, and a dramatic drop of Izod impact strength was observed.

ISSN:0022-2348    

DOI:10.1080/00222349408248095

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The degradation of samples of amorphous and semicrystalline PET with different molecular weights by means of hydrolysis at 180°C has been investigated by measuring the weight loss and the x-ray crystallinity as a function of etching time. It is shown that during the first hours of etching, a concurrent crystallization of the amorphous samples takes place. It is found that weight loss values of amorphous samples after long etching times are higher than the weight loss of the crystallized materials. Results also indicate that weight loss depends to some extent on the initial degree of crystallinity of the material. It is emphasized that the lateral size of the crystallites is a major parameter in determining the total amount of etched material. Analysis of results further confirms that mainly the amorphous regions lying outside of the lamellar stacks are removed by hydrolysis. However, the crystals formed during annealing of the amorphous samples at 180°C are less perfect and the lamellar stacks in these samples are more affected by the hydrolysis attack than in the previously crystallized PET samples.

ISSN:0022-2348    

DOI:10.1080/00222349408248096

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Sorption and diffusion of dichloromethane vapor in the helical forms—that is, δ and γ—of syndiotactic polystyrene were investigated. The thermal transition from the δ to the γ form occurs through an intermediate mesomorphic form, also characterized by chains in helical conformation but lacking true crystalline order. The mesomorphic phase was found impermeable to the vapor at low activity, becoming permeable at higher activities. The presence of a mesomorphic phase, along with the crystalline and the amorphous forms, was suggested in the crystallized samples, too, and its fraction increases greatly going from the δ to the γ form.

ISSN:0022-2348    

DOI:10.1080/00222349408248097

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Time-resolved small-angle x-ray scattering has been used to study the phase transformation kinetics of a thermally quenched, asymmetric, diblock copolymer. The roles played by homogeneous and heterogeneous nucleation in the microdomain ordering process are considered through comparison of results from pure samples and samples doped with impurities. This crystallization process is unique in that it involves constituent particles (microdomains) that are hundreds of angstroms in size ordering onto a lattice with spacings on a similar length scale. Models derived from classical nucleation and growth theories are used to analyze results from pure and doped samples. Clear experimental evidence of a heterogeneous nucleation process occurring in the doped samples suggests that impurity effects cannot be ignored in these materials. In addition, it is proposed that the late-time coexistence of crystalline and amorphous microdomain structures is due to strain energy effects induced by the volume constraints of the sample cell.

ISSN:0022-2348    

DOI:10.1080/00222349408248098

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A method is proposed for the determination of birefringence in thin transparent anisotropic films. The modifications produced by the thin anisotropic films in the channeled spectra of an anisotropic crystal are used. The channeled spectra were recorded on a spectrophotometer provided with a device developed by us.

ISSN:0022-2348    

DOI:10.1080/00222349408248099

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Polyvinyl alcohol (PVA)-Cu(II) and PVA-Cr(III) complexes were prepared with different concentrations of CuC12and Cr(NO3)3salts. The structures of the obtained complexes were investigated using UV spectroscopy and x-ray analysis. The thermal properties (volumetric heat capacity, thermal diffusivity, and thermal conductivity) of aqueous solutions of PVA-metal complexes have been measured using the hot-wire (and strip) technique as a function of temperature (20°-80°C). The results show that the values of the thermal properties depend on the type and the concentration of metal ions bound to the polymeric chains of PVA and the temperatures. However, a considerable increase in the values of the thermal properties was observed for PVA-Cu(II) complex. The type of metal salt under investigation affects the structure of PVA. The complex of PVA-Cr(III) is more thermally stable than the complex of PVA with Cum. However, both polymer-metal complexes showed good properties which may make them acceptable for some practical uses.

ISSN:0022-2348    

DOI:10.1080/00222349408248100

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor