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  • 1
    Electronic Resource
    Electronic Resource
    Retinal repair by transplantation of photoreceptor precursors (2006)
    [s.l.] : Nature Publishing Group
    Nature 444 (2006), S. 203-207 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Photoreceptor loss causes irreversible blindness in many retinal diseases. Repair of such damage by cell transplantation is one of the most feasible types of central nervous system repair; photoreceptor degeneration initially leaves the inner retinal circuitry intact and new photoreceptors ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05161
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  • 2
    Electronic Resource
    Electronic Resource
    Role of blend morphology in rubber-toughened polymers (1996)
    Springer
    Journal of materials science 31 (1996), S. 3945-3954 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of blend morphology on mechanical behaviour of rubber-toughened polymers was investigated. Diglycidyl ether of bisphenol A epoxies toughnened by core-shell rubber particles were employed as the model systems. The blend morphology was varied by changing the composition of the shell of particles, the curing agent, and the extent of agitation prior to casting. It is shown that the most uniform dispersion of particles is obtained when the shell of the modifiers contains reactive groups. In the absence of the reactive groups and when a slow curing agent is employed, however, a highly connected microstructure is obtained. It was found that a blend with a connected microstructure provides significantly higher fracture toughness compared to a similar blend containing uniformly dispersed particles. The reason for this observation is that the connected morphology enables the shear bands to grow further from the crack tip and thus consume more energy before fracture occurs. Also, the yield strength in uniaxial tensile testing is significantly lower in the blend with the connected morphology. Therefore, it should contribute to a larger plastic zone size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352655
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  • 3
    Electronic Resource
    Electronic Resource
    Fatigue of rubber-modified epoxies: effect of particle size and volume fraction (1996)
    Springer
    Journal of materials science 31 (1996), S. 3777-3789 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A change in crack-tip plastic zone/rubber particle interactions induces a transition in the fatigue crack propagation (FCP) behaviour of rubber-modified epoxy polymers. The transition occurs at a specific K level, K T, which corresponds to the condition where the size of the plastic zone is of the order of the size of the rubber particles. At ΔK〉ΔK T, rubber-modified epoxies exhibit improved FCP resistance compared to the unmodified epoxy. This is because the size of the plastic zone becomes large compared to the size of the rubber particles and, consequently, rubber cavitation/shear banding and plastic void growth mechanisms become active. At ΔK〉ΔK T, both neat and rubber-modified epoxies exhibit similar FCP resistance because the plastic zone size is smaller than the size of the rubber particles and hence, the rubber cavitation/shear banding and plastic void growth mechanisms are not operating. As a result of these interactions, the use of smaller 0.2 μm rubber particles in place of 1.5 μm rubber particles results in about one order of magnitude improvement in FCP resistance of the rubber-modified system, particularly near the threshold regime. Such mechanistic understanding of FCP behaviour was employed to model the FCP behaviour of rubber-modified epoxies. It is shown that the near threshold FCP behaviour is affected by the rubber particle size and blend morphology but not by the volume fraction of the modifiers. On the other hand, the slope of the Paris-Erdogan power law depends on the volume fraction of the modifiers and not on the particle size or blend morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352793
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  • 4
    Electronic Resource
    Electronic Resource
    Toughening mechanisms in elastomer-modified epoxies (1986)
    Springer
    Journal of materials science 21 (1986), S. 2475-2488 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The toughening mechanisms of elastomer-modified epoxies are examined by scanning electron microscopy, transmission electron microscopy, and optical microscopy, DGEBA epoxies toughened by various levels of several types of carboxyl terminated copolymers of butadiene-acrylonitrile (CTBN) liquid rubber are studied. The materials are deformed in uniaxial tension and in three-point bending with an edge notch. Scanning electron microscopy of fracture surfaces indicate cavitation of the rubber particles to be a major deformation mechanism. Particle-particle interaction is also found. Optical microscopy of thin sections perpendicular to the fracture surface shows that the cavitated particles generate shear bands. The toughening effect is hypothesized to be due to cavitation, which relieves the triaxial tension at the crack tip, and shear band formation, which creates a large plastic zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114294
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  • 5
    Electronic Resource
    Electronic Resource
    Toughening mechanisms in elastomer-modified epoxies (1989)
    Springer
    Journal of materials science 24 (1989), S. 2571-2580 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The role Of matrix ductility on the toughenability and toughening mechanism of elastomer-modified, diglycidyl ether of bisphenol A (DGEBA)-based epoxies is investigated. Matrix ductility is varied by using epoxide resins of varying epoxide monomer molecular weights. These epoxide resins are cured using 4,4′ diaminodiphenyl sulphone (DDS) and, in some cases, modified with 10 vol% carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN). Fracture toughness values for the neat epoxies are found to be almost independent of the monomer molecular weight of the epoxide resin used. However, the fracture toughness of the elastomer-modified epoxies is found to be very dependent upon the epoxide monomer molecular weight. Tensile dilatometry indicates that the toughening mechanism, when present, is similar to the mechanism found for piperidine cured, elastomer-modified epoxies studied previously. Scanning electron microscopy and optical microscopy techniques corroborate this finding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01174528
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies (1991)
    Springer
    Journal of materials science 26 (1991), S. 3828-3844 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01184979
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  • 7
    Electronic Resource
    Electronic Resource
    Toughening mechanisms in elastomer-modified epoxies (1986)
    Springer
    Journal of materials science 21 (1986), S. 2462-2474 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Some brittle epoxies can be toughened significantly by the addition of an elastomeric phase. A great deal of controversy still exists on the nature of the toughening mechanisms. In this work tensile dilatometry at constant displacement rates was used to determine whether voiding, crazing or shear banding are the deformation mechanisms. Diglycidyl ether-bisphenol A epoxies toughened by various levels of several types of carboxyl-terminated butadiene nitrile liquid rubber were studied. The results indicate that at low strain rates the rubber particles simply enhance shear deformation. At sufficiently high strain rates the rubber particles cavitate and subsequently promote further shear deformation. No indication of crazing as an important toughening mechanism is found. No significant effect of rubber particle size or type can be ascertained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114293
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of rubber particle-plastic zone interactions on fatigue crack propagation behaviour of rubber-modified epoxy polymers (1994)
    Springer
    Journal of materials science 13 (1994), S. 1460-1464 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00419135
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  • 9
    Electronic Resource
    Electronic Resource
    Multicomponent latex IPN materials. I. Morphology control (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2193-2206 
    Details
    ISSN: 0887-624X
    Keywords: multicomponent ; latex ; interpenetrating polymer networks ; IPN ; core/shell ; morphology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of novel structured latex particles with interpenetrating polymer network (IPN) cores and glassy SAN shells were developed in an attempt to investigate the feasibility of these polymers as both toughening and damping agents in thermoplastics. The IPN cores were composed of one impact part (polybutadiene based) and one damping part (acrylic based, with Tg around +10°C). The particle morphologies of these polymers were determined by TEM. The glass transitions and mechanical behavior of the polymers were characterized from DMS. The effect of different components on the final core/shell particle morphologies and mechanical properties was studied. The mechanical behavior of core/shell particles with IPN cores was also compared with that of separate core/shell and multilayered core/shell particles. In addition, normal core/shell synthesis (rubbery part first then the glassy part) and inverted core/shell synthesis (glassy part first then the rubbery part) were performed to provide another access for morphology control. It was found that the core/shell latex particles with poly(butyl acrylate) based copolymers are more miscible than poly(ethylhexyl methacrylate)-based copolymers. The high grafting efficiency of poly(butyl acrylate) plays an important role in governing phase miscibility. The latex particles synthesized by the inverted core/shell mode showed higher miscibility than the normal synthesized ones. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2193-2206, 1997
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Interfacial studies in CTBN-modified epoxies (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 427-437 
    Details
    ISSN: 0021-8995
    Keywords: 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 , Physics
    Notes: Rubber particle cavitation and concomitant shear deformation of the matrix is known to be a major source of toughening in rubber-modified epoxies. The role of the rubber-matrix interface in this toughening mechanism, however, is not well studied. It has been claimed by Chen and Jan [Polym. Eng. Sci., 31,577 (1991)] that introduction of a ductile interphase around the rubbery phase enhances plastic dilation of particles and thus contributes to fracture energy of modified blend. In spite of this promising development in rubber toughening, very few studies on the use of ductile interfaces to improve the fracture resistance of rubber-modified polymers have been initiated. The objective of this investigation is to examine the role of ductility of interface on the fracture toughness of rubber-modified epoxies. Both ductile and rigid interphases are incorporated around CTBN particles in a DGEBA epoxy matrix via end-capping of rubber with epoxy monomers different from that of the matrix. The results of this investigation suggest that introduction of a ductile interphase may indeed further improve the crack growth resistance of material under certain test conditions. In contrast, introduction of the rigid interphase, in the system studied, promoted interfacial debonding and plastic dilation but did not alter the mechanical performance of the rubber-modified blend. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070580221
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