Search results for "amorphous"
showing 10 items of 790 documents
Ion irradiation of carbon nanotubes encapsulating cobalt crystals
2008
Abstract The response of multi-walled carbon nanotubes encapsulating Co nanorods to ion irradiation was studied. The irradiation experiments with medium ion energies (40–500 keV) were carried out at high temperatures and combined with transmission electron microscopy and Raman characterization of the irradiated samples. Contrary to electron irradiation and high-energy (100 MeV) ion irradiation, we did not see accumulation of pressure inside irradiated nanotubes. We found that nanotubes with Co nanorods inside were transformed to amorphous carbon rods encapsulating Co clusters with typical diameters of 3–6 nm. As Co is magnetic, such one-dimensional composite systems could be used for variou…
ESTIMATION OF INJECTION PRESSURE DURING MOLD FILLING.
1982
Dimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified, The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.
Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechani…
2012
[EN] This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystalli…
Size effects in micro- and nanoscale indentation
2006
Abstract The indentation size effect (ISE) has been studied in single crystals, polycrystals and amorphous solids using the Vickers microhardness test. The ISE is clearly present in single crystals but is absent in fine-grained polycrystals. A size-dependent hardness for amorphous solids is observed only in the sub-micrometre surface layer. The behaviour of the ISE in single crystals for micro- and nanoindentation is compared. Estimates of the surface hardness are made by the extrapolation of the experimental hardness–indentation depth curves. The extrapolated hardness in the surface region reaches values corresponding to the theoretical shear strength. The results confirm the multifarious …
Ellipsoidal core-shell cylindrical microphases in PS-b -PB-b -PCL triblock copolymers with a crystallizable matrix
1997
Polystyrene-block-polybutadiene-block-poly(e-caprolactone) SBC triblock copolymers with a PCL matrix exhibit microphase separation into three different phases within the spherulitic superstructures. Mixing of the PS-block can occur upon melting of the PCL-block if the molecular weight is low enough. Even though the crystallization takes place well below the PS-glass transition, a deformation of the amorphous microphases into ellipsoidal core-shell cylindrical microdomains is observed by TEM. These copolymers have mechanical properties which are dominated by the PCL (Poly(e-caprolactone)) matrix with an influence of the amorphous blocks.
Monte Carlo modelling of the polymer glass transition
1993
We are proposing a lattice model with chemical input for the computer modelling of the polymer glass transition. The chemical input information is obtained by a coarse graining procedure applied to a microscopic model with full chemical detail. We use this information on Bisphenol-A-Polycarbonate to predict it's Vogel-Fulcher temperature out of a dynamic Monte Carlo Simulation. The microscopic structure of the lattice model is that of a genuine amorphous material, and the structural relaxation obeys the time temperature superposition.
Chain conformation and structure in amorphous polymers as revealed by X-ray, neutron, light and electron diffraction
1976
Abstract The physical structure of the melt, the supercooled melt, and the glassy state of amorphous polymers can be characterized by the chain conformation, the local order, and the morphology. The conformation was studied by small-angle neutron scattering. The local order was characterized by pair distribution functions which were derived from electron scattering curves. In addition, model calculations were used to gain information about short-range order. The morphology was studied by means of light scattering (density and anisotropy fluctuations), small-angle X-ray scattering (density fluctuations), and magnetic birefringence measurements (orientational order). Experiments were performe…
Role of thermal history on quiescent cold crystallization of PET
2002
8 pags., 9 figs.
SAXS/WAXS study of the annealing process in quenched samples of isotactic poly(propylene)
1999
The structural rearrangement in samples of quenched isotactic poly(propylene) (iPP) submitted to different annealing treatments has been studied using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) at the synchrotron radiation source of DESY, Hamburg. From a quantitative analysis of the WAXS profiles the values of the α-monoclinic, mesomorphic, and amorphous mass fractions coexisting in the material were determined. It is demonstrated that the SAXS patterns were characterized by two different long-period values that are attributed to α- and mesomorphic periodicity, respectively. The related α- and mesomorphic volume phase fractions, calculated from the analysis of the SAXS …
Dielectric Spectroscopy of Recycled Polylactide
2014
The effects of multiple mechanical recycling on amorphous polylactide (PLA) were simulated by means of five successive injection-grinding cycles. The influence of the induced thermo-mechanical degradation on the dielectric properties of PLA was analysed. The relaxation spectra were studied in terms of the complex dielectric permittivity (ε0 and ε00) and the dielectric loss tangent, tg(d) in the frequency range from 102 to 107 Hz over the temperature interval from 0 C to 140 C. It was possible to distinguish two relaxations zones, one at low temperatures and high frequencies (b relaxation) and another at higher temperatures and lower frequencies (a relaxation). The individual relaxations wer…