Search results for "Elastic"

Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer

2003

The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (<15 meV), was determined from inelastic neutron scattering at low-temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.

Effects of inhomogeneities of cross-links on a microphase separation of polymer mixtures

1994

We generalize de Gennes' theory of the microphase separation of cross-linked polymer mixtures to take into account the spatial fluctuations of the elasticity constant c, preventing the mixture from complete segregation. Within a mean-field analysis we found that the spatial fluctuations of c(r), which are assumed to obey the Poisson distribution, enlarge the size of the domains. The latter is obtained to be temperature dependent.


Accurately evaluating Young’s modulus of polymers through nanoindentations: a phenomenological correction factor to the Oliver and Pharr procedure

2006

The Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] procedure is a widely used tool to analyze nanoindentation force curves obtained on metals or ceramics. Its application to polymers is, however, difficult, as Young’s moduli are commonly overestimated mainly because of viscoelastic effects and pileup. However, polymers spanning a large range of morphologies have been used in this work to introduce a phenomenological correction factor. It depends on indenter geometry: sets of calibration indentations have to be performed on some polymers with known elastic moduli to characterize each indenter.

Limits of the linear viscoelastic behaviour of polyamide 66 filled with TiO2 nanoparticles: Effect of strain rate, temperature, and moisture

2008

Abstract Limits of linear viscoelastic behaviour of TiO 2 nanoparticle-filled polyamides are estimated quantitatively by the results of uniaxial tension tests. The stress limit of the filled polymer is higher than that of the un-filled one. Their values are the lower, the higher the temperature and moisture content of test specimens, and the lower, the lower the strain rate. The concept of an energy threshold for the linear viscoelastic behaviour is used to comprehensively characterize the limits over a wide range of test conditions. The energy limit is not affected by the strain rate, temperature, or moisture, and its value for the filled polymer is higher than that for the un-filled one. …

Processing and properties of blends with liquid crystal polymers

1990

Experimental data on the processing behavior and on the rheological and mechanical properties of blends with a liquid crystal polymer as one component are presented. The blends with low amounts of LCP show easier processability and lower viscosity than the thermoplastic matrix. The elastic modulus is also improved. The reduction of viscosity has been attributed to the lower pressure entry, due to the formation of fibrils and to the immiscibility of the two phases.

Strain rate effect in the single-fiber-fragmentation test

2001

The single fiber fragmentation test (SFFT) has been widely used to characterize the interface in fiber-reinforced polymers. The purpose of the work reported here was to determine the effect of strain rate on the fiber fragment lengths obtained in the SFFT. Three materials systems were used to make single-fiber-composite specimens: E-glass fiber/polycarbonate matrix, AS4-carbon fiber/polycarbonate matrix, and AU4-carbon fiber/polycarbonate matrix. The fiber-matrix adhesion in all three systems is based on physisorption rather than chemisorption. Each system was tested at strain rates ranging over four orders of magnitude. Results are reported in terms of fragment length, the dependent variab…

Effect of cooling rate on the viscoelastic properties in the plastic zone of solid polymers

1979

PMMA and PC samples were subjected to several cooling rates from the glass transition temperature.

A simplified description of viscoelastic behavior of polymers as illustrated with biaxially-oriented poly(ethylene terephthalate)

1978

A rheological model of solid polymers is proposed. Its mechanical analog is a parallel of a linear spring and a Maxwell element with variable viscosity. The viscosity of the dashpot is allowed to change with stress both directly, by an Eyring-type mechanism, and through free volume changes according to the Doolittle equation. Predictions of the model reproduce many of the features shown, especially after yielding, by constant velocity stress-strain, stress-relaxation and creep data taken at room temperature on biaxially-oriented poly(ethylene terephthalate) over a wide range of loading rates.

2018

Star-shaped polymers show a continuous change of properties from flexible linear chains to soft colloids, as the number of arms is increased. To investigate the effect of macromolecular architecture on the flow properties, we employ computer simulations of single chain and star polymers as well as of their mixtures under Poiseuille flow. Hydrodynamic interactions are incorporated through the multi-particle collision dynamics (MPCD) technique, while a bead-spring model is used to describe the polymers. For the ultradilute systems at rest, the polymers are distributed uniformly in the slit channel, with a weak dependence on their number of arms. Once flow is applied, however, we find that the…

The effect of macromolecular architecture of ethylene copolymers with multi-alkenylsilsesquioxane on morphological, rheological and dynamic mechanica…

2021

Abstract The influence of the degree and the way of incorporation of multi-alkenylsilsesquioxane into the polymer chain on morphological, rheological and dynamic mechanical parameters were determined. It was found that POSS incorporated into the polymer chain was located outside the crystalline structure of lamella in amorphous phase. The incorporation of POSS-6-2 as a pendant group resulted in significant increase of separation of macromolecules. The key factor in rheological and dynamic mechanical behavior of copolymers turned out to be the way of POSS incorporation into the polymer chain. The incorporation of POSS into the polymer chain as a pendant group resulted in decreased relaxation…