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  • 1995-1999  (5)
  • 1940-1944
  • polymer blends  (3)
  • Life and Medical Sciences  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Drop deformation during elongational flow in blends of viscoelastic fluids. Small deformation theory and comparison with experimental results (1995)
    Springer
    Rheologica acta 34 (1995), S. 525-533 
    Details
    ISSN: 1435-1528
    Keywords: Emulsion model ; polymer blends ; drop deformation ; elongational flow ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The deformation of dispersed droplets in immiscible polymer blends was studied in elongational flow, with an original method based on quenching specimens elongated in the melt. Results for high capillary numbers and different viscosity ratios were compared to the linear theory of viscoelastic emulsions of Palierne. Simple expressions for the drop deformation could be obtained for Maxwell fluids, and the influence of viscoelasticity of matrix and inclusions on the drop deformation process was discussed. With respect to the Newtonian approximation, the description of some experimental data could be improved. However, the predictions of the viscoelastic model appeared to be very sensitive to the choice of relaxation times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712313
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Rheology/morphology/flow conditions relationships for polymethylmethacrylate/rubber blend (1996)
    Springer
    Rheologica acta 35 (1996), S. 369-381 
    Details
    ISSN: 1435-1528
    Keywords: Melt rheology ; linear and non-linear viscoelasticity ; polymer blends ; reinforced polymers ; morphology ; Cox-Merz rule ; aggregation ; percolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Viscoelastic behavior, phase morphology and flow conditions relationships in polymer/rubber blends have been investigated. The importance of such correlations is illustrated on polymethylmethacrylate (PMMA)/rubber blends subjected to different flow conditions both under small and large deformations. In small-amplitude oscillatory shear (the morphology does not change during the flow) the elastic modulus G′ of the concentrated blends shows a secondary plateau, G′ p , in the low frequency region. This solid-like behavior appears for rubber particle contents beyond the percolation threshold concentration (15%). Morphological observations revealed that for concentrations higher than 15%, the particles are dispersed in a three-dimensional network-type structure. In capillary flow it was found that the network-type structure was destroyed and replaced by an alignment of particles in the flow direction. This morphological modification resulted in a decrease in both viscosity and post-extrusion swell of the blends. Morphological observations revealed that the ordered structure in the flow direction was concentrated only in the skin region of the extrudate, where the shear stress is higher than the secondary plateau, G′ p . A simple kinetic mechanism is proposed to explain the observed morphology. Similarly, steady shear measurements performed in the cone-and-plate geometry revealed alignment of particles in the flow direction for shear stress values higher than G′p.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403538
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Relationship between structure and rheological properties in the melt of polymers containing spherical inclusions (1995)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 6 (1995), S. 301-308 
    Details
    ISSN: 1042-7147
    Keywords: polymer blends ; melt rheology ; crosslinked rubber ; structured latex ; 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: The linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pat.1995.220060508
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    P-glycoprotein stability is affected by serum deprivation and high cell density in multidrug-resistant cells (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 163 (1995), S. 538-544 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The control of P-glycoprotein (Pgp) expression in multidrug-resistant cells (MDR) is complex and may be regulated at different levels. We have investigated Pgp stability in four different human and hamster MDR cell lines. Using a pulse-chase procedure we show that Pgp half-life is between 14 and 17 h in all these cell lines when they are growing exponentially. However, in the presence of a low level of serum, Pgp half-life is increased four to sixfold. A similar effect is observed when the cell cultures are maintained in high cell density. The increased Pgp stability appears to be differently regulated as serum deprivation results in a general enhanced degradation of total cytoplasmic and membrane proteins. Moreover, the observed serum effect suggests the involvement of growth factors in the control of Pgp stability. These findings suggest that protein stability may be an important factor in the regulation of Pgp expression. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041630314
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Ubiquitin in homeostasis, development and disease (1995)
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 677-684 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Ubiquitin is the most phylogenetically conserved protein known. This 8,500 Da polypeptide can be covalently attached to cellular proteins as a posttranslational modification. In most cases, the addition of multiple ubiquitin adducts to a protein targets it for rapid degradation by a multisubunit protease known as the 26S proteasome. While the ubiquitin/26S proteasome pathway is responsible for the degradation of the bulk of cellular proteins during homeostasis, it may also be responsible for the rapid loss of protein during the programmed death of certain cells, such as skeletal muscle during insect metamorphosis. In addition, alterations in the expression and regulation of ubiquitin may play significant roles in pathological disorders. For example, dramatic increases in ubiquitin and ubiquitin-protein conjugates are observed in a wide variety of neurodegenerative disorders, including Alzheimer's disease. Patients suffering from the autoimmune disease systemic lupus erythematosus generate antibodies reacting with ubiquitin and ubiquitinated histones. At present, it is not known whether these changes in ubiquitin expression and regulation initiate pathological changes in these diseases or if they are altered as a consequence of these disorders.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950170804
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    Paper (German National Licenses)
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