It has been found that by the addition of low concentrations of an amphiphilic block copolymer to an epoxy resin, novel disordered morphologies can be formed and preserved through curing. This article will focus on characterizing the influence of the block copolymer and casting solvent on the templated morphology achieved in the thermoset sample. The ultimate goal of this work is to determine the parameters that would control the microphase morphology produced. Epoxy resins blended with a series of amphiphilic block copolymers based on hydrogenated polyisoprene (polyethylene-alt-propylene or PEP) and polyethylene oxide (PEO), specifically, were investigated. In this article, the cure-induced order-order phase transition from the spherical to wormlike micelle morphology will also be discussed. It is proposed that the formation of the wormlike micelle structure from the spherical micelle structure is similar to the phase transition behavior that occurs in dilute block copolymer solutions as a function of the influence of the solvent on micelle morphology.
A tensile mechanical test suitable to measure the adhesion between brittle coatings and ductile substrates was applied to measure the adhesion of painted layers on polypropylene blends. The test involves the tensile deformation of the painted assembly, resulting in the periodic cracking of the brittle coating on the ductile substrate. The interfacial shear strength was determined by measuring the strength of the coating, the thickness of the coating, and the average width of paint fragment after the crack density reaches saturation. Apparent interfacial shear strength was obtained for different paints on the same kind of blend, which gave consistent results over the experimental strain rate range from 10-4 to 10-3 sec-'. Interfacial delamination was studied by optical microscopy (OM) and transmission electron microscopy (TEM). The delamination was observed to mainly occur near the adhesion promoter and substrate interface.
A microstructural characterization approach has been developed to study the mechanisms of near-surface deformation under surface scratches in injection-molded polypropylene blends with over 20% rubber modifier (thermoplastic polyolefin or TPO). The near-surface microstructure of the material before and after scratching was characterized with different techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy and X-ray diffraction. It was observed that the TPO material plastically deformed by forming shear band structure under surface scratches. Materials inside shear band dilated and the extent of dilation could be measured from the characteristic angles between the shearband boundary and rubber particles. At a higher applied normal load (>200 g for the test in this study), evidence for surface fracture was observed. At even higher loads (>400 g), significant amounts of sub-surface voiding were observed, due to the delamination between the rubber phases and the polypropylene matrix. The observation of both the dilation of materials inside shearbands and the subsurface voiding at high normal loads advanced the understanding of scratching whitening mechanism in this kind of important materials. It was observed that the talc additives had no obvious influence on shear band nucleation and propagation. Results obtained in this study suggest that a strong interfacial adhesion between rubber phase and PP matrix is crucial to improving the scratching resistance of rubber modified polypropylene blends.
Battery active materials are routinely evaluated via the electrochemical performance of their composite electrodes which are prepared with standard formulations and routine processing conditions. The relationship between electrochemical responses and these experimental variables are not commonly explored. Mechanical properties and their relationship to durability are almost never considered. We therefore offer some quite basic studies of the effects of formulation on these properties. Electrochemical and mechanical properties of composites across a broad formulation range are provided for the most common Li-Ion chemistry -LiCoO 2 electroactive particles with PVDF binders. Mechanical characterizations include evaluations of both the constituent materials and the porous electrode structures. We will show that composite electrode designs which optimize mechanical durability and ruggedness will degrade electrochemical performance for these LiCoO 2 /PVDF binder-based systems.
Ultrathin multilayers are important for electrical and optical devices, as well as for immunoassays, artificial organs, and for controlling surface properties. The construction of ultrathin multilayer films by electrostatic layer-by-layer deposition proved to be a popular and successful method to create films with a range of electrical, optical, and biological properties. Dendrimer nanocomposites (DNCs) form highly uniform hybrid (inorganic-organic) nanoparticles with controlled composition and architecture. In this work, the fabrication, characterization, and optical properties of ultrathin dendrimer/poly(styrene sulfonate) (PSS) and silver-DNC/PSS nanocomposite multilayers using layer-by-layer (LbL) electrostatic assembly techniques are described. UV-vis spectra of the multilayers were found to be a combination of electronic transitions of the surface plasmon peaks, and the regular frequency modulations attributable to the multilayered film structure. The modulations appeared as the consequence of the highly regular and non-intermixed multilayer growth as a function of the resulting structure. A simple model to explain the experimental data is presented. Use of DNCs in multilayers results in abrupt, flat, and uniform interfaces.
Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009
Based on the exploiture of turbine blade super cooling technology, porous medium is installed in a new kind of cooling configuration with cooling tunnels. Experiments and numerical simulations are carried out to investigate the thermally driven heat transfer rules in the new kind of cooling configuration with different porosity in a centrifugal force field. The results of experiments and numerical simulations are consistent basically. The results of study show that the heat transfer rules of the new cooling configuration are identical under different porosity. The thermally driven heat transfer of the cooling configuration filled with porous medium can be enhanced with increase of the rotate speed, heat flux and cooling air speed. At the same time, the heat transfer effect can be weakened with increase of the porosity under high porosity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.