Shyamal Sengupta

Unified study of the different physical properties of amorphous polymers

Uptil now it has not been possible to explain the different physical properties of amorphous polymers using a model based on a single conceptual scheme. In this paper, a phenomenological model is proposed which tries to explain the mechanical, optical and thermal properties (both thermal conductivity and expansivity) of amorphous polymers. The model has similarities with the composite model, proposed by the present authors, which has proved to be successful in interpreting the different physical properties of semicrystalline polymers. The present model considers the bulk form of the polymer as an aggregate of microscopic units possessing intrinsic physical properties. On drawing, the development of anisotropy in different physical properties is supposed to be due to the development of preferred orientation of these units. The development of the preferred orientation has been estimated directly from birefringence data. The agreement between the calculated and experimental values of the elastic modulus, thermal conductivity and thermal expansivity of PVC, PMMA and PS is found to be reasonable good.

Unified study of lead: Energy-dependent pseudopotential calculation

A Unified study of lattice-mechanical properties of lead using energy-dependent pseudopotential is carried out. Energy dependence in pseudopotential is considered through the effective mass approximation; the pseudopotential model chosen is the local Heine-Abarenkov model potential. Properties studied include cohesive energy, equilibrium lattice parameter, second-order elastic constants, pressure derivative of second-order elastic constants, equation of state (atT=0 K), phonon-dispersion and effective two-body interaction. The results show fairly good agreement with experiment especially with a modified Heine-Abarenkov potential.

Mechanical properties of oriented fibres of semicrystalline polymers based upon orientation function from optical properties

The computation of the orientational averages is a great problem in the case of semicrystalline polymers. In a previous communication [1] it has been shown that sinθ=f(λ) sinθ′ describes the orientational changes satisfactorily for a certain class of polymers. In this paper some alternative deformation schemes are also discussed. It has been concluded that birefringence provides a useful guideline in the choice of a deformation scheme.

Pseudopotential theory of effective interaction in simple metal

The second order pseudopotential theory suggests the possibility of a break-up of the total energy of simple metals into a purely volume-dependent part and an effective central pairwise interaction between ions. In the present paper finite contributions for these two parts of the energy have been extracted in a form convenient for calculation. Using the local Heine-Abarenkov model potential, a reliable effective ion-ion interaction is generated and the volume-dependent energy is calculated for Al. The relative contributions of the effective interaction and the volume-dependent energy term to various metallic properties are also calculated. The importance of volume dependence on the effective interaction is also discussed.The interactomic force constants upto eighth neighbour are derived from the effective interaction and it is found that the force constants beyond the third neighbour are negligibly small. This result is also confirmed by the calculation of dispersion curves with force constants obtained from the effective interaction upto the third neighbour which is found to reproduce the results of the full pseudopotential calculations. The force constants obtained are also used to study some finite temperature properties of Al in the quasi-harmonic approximation and the limitations of the theory are pointed out.

Mechanical properties of semicrystalline polymer-polypropylene

The elastic properties of polypropylene have been investigated in terms of a phenomenological model, which is a modified form of the Takayanagi’s two-phase model. In the present model both the change of crystallinity and orientation of the crystalline chains have been taken into account. The orientation effect at the drawn state has been considered in a simplified manner. It has been shown that a partially aligned crystalline phase may be considered as a superposition of a perfectly aligned crystalline region in an elastically isotropic randomly oriented crystalline phase. The predicted values of elastic modulus agree with experimental values.