Mechanical properties of clay‐reinforced polyamide

Intercalated and exfoliated nanocomposites were prepared by extrusion and injection of polyamide‐6 and highly swollen or slightly swollen montmorillonite, respectively. The microstructure of the nanocomposites has been studied previously. In this article, we investigated the influence of the preferential orientation of the montmorillonite sheets on the mechanical properties of the nanocomposites. Dynamic mechanical analysis and tensile tests showed that the elastic modulus depends mainly on the filler loading. A parallel coupling could well account for the behavior of the nanocomposites. The calculated elastic and storage moduli of montmorillonite were set to 140 and 40 GPa, respectively. Compression tests were performed to study the anisotropy of the mechanical properties. The elastic modulus and flow strain were sensitive to the filler orientation. A Tandon–Weng approach was applied to consider the geometry of the filler. In all low‐deformation tests, no significant difference between intercalated and exfoliated systems was observed. Finally, the influence of the dispersion and exfoliation state of the filler on the ultimate properties of the nanocomposites (tensile tests) is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 272–283, 2002     

Amorphous phase evolution during crystallization of poly(ethylene-terephthalate)

Crystallization of poly(ethylene terephthalate) from the amorphous state has been studied in the temperature range 90°–120°C to characterize the amorphous phase when crystalline microstructure is developing. Small-angle x-ray scattering, scanning electron microscopy, and density measurements were used to investigate the morphology of semi-crystalline materials. Differential scanning calorimetry and dynamical mechanical spectroscopy experiments were carried out on amorphous, partially crystallized and crystallized specimens and, when structural relaxation is allowed (thermal treatments close to but below glass transition temperature), strong evidence is obtained for the existence of two different amorphous phases with different mobilities.     

Dirac's aether in relativistic quantum mechanics

The introduction by Dirac of a new aether model based on a stochastic covariant distribution of subquantum motions (corresponding to a vacuum state alive with fluctuations and randomness) is discussed with respect to the present experimental and theoretical discussion of nonlocality in EPR situations. It is shown (1) that one can deduce the de Broglie waves as real collective Markov processes on the top of Dirac's aether; (2) that the quantum potential associated with this aether's modification, by the presence of EPR photon pairs, yields a relativistic causal action at a distance which interprets the superluminal correlations recently established by Aspect et al.; (3) that the existence of the Einstein-de Broglie photon model (deduced from Dirac's aether) implies experimental predictions which conflict with the Copenhagen interpretation in certain specific testable interference experiments.     

Time-dependent neutron interferometry: Evidence against wave packet collapse?

If the energy-absorbing radio-frequency spin-flipping device used in perfect crystal neutron interferometry is an intermediate measuring device, then the experimental results contradict the associated wave packet collapse and support the real existence of the de Broglie pilot waves in both arms while the neutron travels in only one.On leave from the University of Crete, Physics Department, Heraklion, Crete, Greece, at Institut Henri Poincaré, Laboratoire de Physique Théorique, 11, Rue P. et M. Curie, 75231 Paris Cedex 05, France.     

Small strain behavior of polyethylene: In situ SAXS measurements

Stack lamella deformation depends on their orientation with respect to the loading axis, the intrinsic properties of the lamellae, and the mechanical coupling between crystalline and amorphous phases. The aim of this work is to investigate the influence of the stress transmitter (ST) density and the crystallinity X_c on the local deformation. A wide experimental campaign has been undertaken on several polyethylenes with controlled molecular parameters and subjected to different thermal treatments. The ST density has been evaluated by the natural draw ratio and calculated by the Brown's model. The local deformation was measured by SAXS along a tensile test by using the long period stretching of the equatorial lamella stacks. The ratio ε_local/ε_macro was found to be a constant close to 0.5. This surprising low value has highlighted that the equatorial regions could be either the stiffest zone of the spherulite or submitted to a lower stress. It is proposed that the stability of the ratio ε_local/ε_macro is the result of two opposite phenomena: On one hand, the increase of X_c leads to unload the equatorial regions due to partial percolation of the crystalline phase and so decreases the stresses. On the other hand, when increasing X_c, the ST density decreases which causes the decrease in the local equatorial modulus. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1535–1542, 2010     

Causal phase-space approach to fermion theories understood through Cliford algebras

A Wigner-Moyal phase-space approach is developed for the Dirac and Feynman-Gell-Mann equations. The role of spinors as primitive elements of the spacetime and phase-space Clifford algebras is emphasized. A conserved phase-space current is constructed.     

Possible test of the reality of superluminal phase waves and particle phase space motions in the Einstein-de Broglie-Bohm causal stochastic interpretation of quantum mechanics

Recent double-slit type neutron experiments ⁽¹⁾ and their theoretical implications ⁽²⁾ suggest that, since one can tell through which slit the individual neutrons travel, coherent wave packets remain nonlocally coupled (with particles one by one), even in the case of wide spatial separation. Following de Broglie's initial proposal, ⁽³⁾ this property can be derived from the existence of the persisting action of real superluminal physical phase waves considered as building blocks of the real subluminal wave field packets which surround individual particle paths in the Einstein-de Broglie-Bohm interpretation of quantum mechanics.     

Influence of the β‐crystalline phase on the mechanical properties of unfilled and calcium carbonate‐filled polypropylene: Ductile cracking and impact behavior

The β‐crystalline form of isotactic poly(propylene) (PP) has been long recognized to have a greater mechanical absorption capacity than the α‐crystalline form. This is of major importance for improving impact properties and crack resistance of injection‐molding parts. Unfilled PP samples together with calcium carbonate‐filled PP samples having various β/α‐phase ratios, with nearly constant morphological parameters, have been investigated from the standpoint of ductile crack propagation and impact behavior. The presence of the β‐crystalline phase turned out to improve both properties. The β spherulites are notably more prone to craze initiation than α spherulites that display a propensity for cracking. Subsequent crack propagation appears to be faster in the latter ones. The plastic zone ahead from the crack tip broadens, and the specific plastic energy increases with increasing β‐phase content. The lower elastic limit of the β phase is likely to promote the early crazing. However, the suspected higher density of tie molecules in β spherulites provides more numerous and stiffer microfibrils. The impact strength of PP is also improved by the presence of β crystals as a result of greater energy‐absorption capabilities. However, filled samples turned out insensitive to the β phase. A discussion is made about the origins of the β‐phase‐induced improvement of the mechanical properties. The possible role of the β → α transition is also explained. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 31–42, 2002