Graphitic nanofillers in PMMA nanocomposites—An investigation of particle size and dispersion and their influence on nanocomposite properties

Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ～10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007     

N-Allyl-1,3-oxazines via a facile keto-ene/cyclization tandem reaction

The intramolecular keto-ene/cyclization tandem reaction of γ-N-allylamino ketones is an effective means of producing 1,3-oxazines. The reaction usually requires high temperatures and/or pressures. We discovered that N,N-diallyl amines undergo the reaction at lower temperatures than their monoallyl analogs. An extreme example, 1-N,N-diallylamino-9,10-anthraquinone, undergoes the keto-ene reaction near ambient temperature. In the case of 1-N,N′-dialkylaminoanthraquinones, electron deficient ene components can even be used, allowing the preparation of a broad spectrum of oxazines. Furthermore, the N-allyl-1,3-oxazine can be easily deallylated to produce a 1,3-oxazine that contains a secondary amine.     

Effect of particle agglomeration and interphase on the glass transition temperature of polymer nanocomposites

In this article, we utilize finite element modeling to investigate the effect of nanoparticle agglomeration on the glass transition temperature of polymer nanocomposites. The case of an attractive interaction between polymer and nanofiller is considered for which an interphase domain of gradient properties is developed. This model utilizes representative volume elements that are created and analyzed with varying degrees of nanoparticle clustering and length scale of interphase domain. The viscoelastic properties of the composites are studied using a statistical approach to account for variations due to the random nature of the microstructure. Results show that a monotonic increase in nanofiller clustering not only results in the loss of interphase volume but also obstructs the formation of a percolating interphase network in the nanocomposite. The combined impacts lead to a remarkable decrease of T_g enhancement of clustering nanofillers in comparison with a well‐dispersed configuration. Our simulation results provide qualitative support for experimental observations that clustering observed at high nanofiller concentrations negatively impacts the effects of the nanofiller on overall properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Strain Measurement Within a Single-lap Joint Using Embedded Strain Gages

Experimental Techniques -     

The ductile fracture of polycarbonate

The fracture of a known ductile polymer (polycarbonate) is investigated. It is shown that polycarbonate obeys the Dugdale model of ductile yielding by comparing measured plastic-zone sizes and displacements to the theoretical predictions. Strain-energy release rates are calculated and the critical value is shown to be one or two orders of magnitude higher than critical values for brittle polymers. Photoelastic photographs of the fracture process are presented and it is shown that the photoelastic effect definitely enhances the definition of the yield zone. Microscopic photoelastic photographs are also presented which are used to give a new interpretation to the photoplastic effect. Finally, suggestions for future work are presented.     

An interpretation of inelastic birefringence

The relationship between plastic thickness change and plastic isochromatics occurring beyond the plostic tensile instability point of a uniaxial tensile specimen is investigated. Mechanical thickness-change measurements and a hologram of thickness change are shown to be in close qualitative agreement with isochromatics in a region of gross plastic yielding. Analytical observations are discussed to aid the interpretation of the experimental results obtained. Finally, possible extensions and applications are discussed.     

Structural Characteristics and Properties of a New Graphitic‐Based Material

The hydrogenation of commercial graphite using lithium/ammonia as the reducing agent and tert‐butyl alcohol as a proton source was investigated. Characterization of the products after successive reductions of the same material by high‐resolution transmission electron microscopy revealed a new material that was replete with edge and circular dislocations. Analysis by solid‐state ¹³C NMR spectroscopy indicates that after three reductions, the remaining aromatic rings appear to be interior benzene rings. NMR spectroscopy also offers strong evidence for the presence of small amounts of tert‐butyl alcohol and ethanol (workup solvent) that could not be removed in vacuo from the samples. These compounds could be observed to move freely between the layers of the hydrographene.     

Cumulative creep damage for polycarbonate and polysulfone

The literature for creep-to-failure cumulative-damage laws are reviewed. Creep-to-failure tests performed on polycarbonate and polysulfone under single- and two-step loadings are discussed. A semiempirical cumulative-damage rule or modified time-fraction rule is developed, using as the starting point a power law for transient creep response. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested. performed this work Visiting Scientist, Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University. Paper was presented at the 1985 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 9–13.