Intermolecular interactions in fiber-forming linear polymers and certain of their mechanical properties

Values of the specific volumetric intermolecular interaction energies of a series of linear polymers have been calculated on the basis of data on the interatomic and intermolecular interactions of the functional groups in the polymer molecules. It is shown that the specific volumetric intermolecular interaction energy is closely correlated with the elastic and relaxation properties of the polymers, which makes it possible to predict a series of mechanical properties of chemical fibers.Leningrad Branch, All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 5, pp. 790–795, September–October, 1971.     

Relationship between the molecular structure and certain mechanical properties of oriented polymers

The correlations between the molecular structure and intermolecular energy and the fatigue and elastic properties of fibers are considered. It is shown that the maximum of these properties corresponds to an optimal value of the intermolecular energy.Leningrad Branch of the All-Union Scientific-Research Institute of Synthetic Fibers. Translated from Mekhanika Polimerov, No. 4, pp. 734–735, July–August, 1969.     

Creep of polymers during tension under conditions of hydrostatic pressure

Hydrostatic pressure results in decrease in the creep rate of a polymer loaded by tensile stress. The decrease in the creep rate is associated with the increase in intermolecular interaction. The correlation found between the creep rate of material loaded by a constant tensile force and with change in the melting temperature of a polymer under pressure appears to be commensurate with change in intermolecular interaction.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 359–362, March–April, 1976.     

Elastic modulus of a nonpolar polymer

A theoretical calculation of the elastic modulus of a nonpolar polymer (polyethylene) is carried out after deriving the appropriate relationships. Intramolecular forces (retarded rotation) play a far more important part than intermolecular forces. A simple method is proposed for finding the entropy and energy forces from the corresponding elastic moduli. The intra- and intermolecular energy effects are separated for one particular case.K. D. Ushinskii Yaroslav State Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 450–454, May–June, 1973.     

Theoretical strength of polymers in a completely oriented state

A solution is presented of the problem on the theoretical strength of a completely oriented polymer by accounting for the intermolecular interaction and finiteness in the length of polymer chains.V. I. Lenin Moscow State Pedagogical Institute, Research Laboratory of the Physics of Polymers. Translated from Mekhanika Polimerov, No. 3, pp. 458–464, May–June, 1970.     

Temperature-time dependence of the adhesion strength for polymer — Polymer systems

The temperature — time dependence of the adhesion strength has been studied for polymer systems differing in the thermodynamic compatibility of the substrate and adhesive and in the rate of polymerization of the latter. The fracture-activation energies of these systems have been calculated. It is shown that the temperature — time dependence of the adhesion strength varies depending on whether chemical intermolecular forces are responsible for the strength of the joint.Perm Scientific-Research Institute of Polymer Materials. A. M. Gor'kii Ural State University. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 665–671, July–August, 1968.     

Improvement of the deformative characteristics of poly-β-hydroxybutyrate by plasticization

Plasticized systems of poly--hydroxybutyrate (PHB) are studied, where low-molecular compounds traditionally used for this purpose for various systems, i.e., dioctyl sebacate, dibutyl sebacate, polyethylene glycol, Laprol 503, and Laprol 5003, are used as plasticizers. All of them are nontoxic and biodegradable compounds with a similar molecular weight and comparable polarity of molecules. The main purpose of this study is to improve the deformability of PHB taking into account the structural changes in plasticized PHBs. The plasticizers chosen are completely compatible with the polymer and form a monophase system up to a plasticizer content of 15–20%. An increase in the plasticizer content allows us to increase efficiently the deformability of the polymer (the relative breaking elongation of PHB at room temperature grows up to 250–300%). At the same time, the system becomes considerably weaker and therefore there is no point in increasing the concentration of plasticizers by more than 20 wt.%. According to the data obtained from DSC measurements, the ratio between the amorphous and crystalline regions of PHB in the presence of plasticizers mentioned remains practically constant. The changes in the elastic properties of PHB/low-molecular plasticizer systems are mainly due to efficient weakening of intermolecular interactions in the amorphous regions of the polymer. A slight decrease in the crystalline order of PHB is of secondary importance.Institute of Polymer Materials, Riga Technical University, Riga, LV-1048, Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 527–538, July–August, 1999.     

Instability of the crystallites in oriented polymers under load

Large-angle x-ray diffraction and infrared spectroscopy have been used to investigate the behavior of the crystalline zones in oriented polymers under load. It is shown that under the influence of a load applied along the axis of orientation the crystallites are partially destroyed, the more so the greater the applied stress. For different polymers the destruction of the crystallites is the greater the weaker the intermolecular bonds. The stability of the crystallites is improved by orientation.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 516–520, May–June, 1976.     

Comparative analysis of the relaxation spectra of different classes of polymers

The relaxation spectra of different classes of polymers, calculated from successive approximation formulas based on the dynamic and static characteristics at different temperatures, are compared. The effect of the structure of the polymer and the intra- and intermolecular forces on the shape of the relaxation curves is determined.Mekhanika Polimerov, Vol. 4, No. 3, pp. 445–449, 1968     

The potential strain energy of a polymer molecule in nonlinear approximation

The intermolecular interaction mechanism is analyzed, and the results are used to derive a general semiempirical formula for the strain energy of a helical polymer molecule in nonlinear approximation. Formulas are given for the homogeneous straining of specific polymers. The relationship between the elastic constants of the molecule and the final strain is computed.Mekhanika Polimerov, Vol. 3, No. 4, pp. 608–614, 1967     

Deformation and fracture of polymers

On the basis of experimental research it is suggested that in polymers under load two physically different kinetic processes — deformation and fracture — develop simultaneously. Their rates depend on different components of the stress tensor; accordingly, the relation between these rates can be experimentally controlled. It is suggested that these processes involve the overcoming of physically different potential barriers and that their elementary events embrace essentially different activation volumes. Deformation involves the overcoming of the forces of intermolecular interaction, and fracture, with the rupture of the main chains.Review of work carried out in the Materials Laboratory of the A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR.A. F. Ioffe Physico-Technical Institute, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 95–106, January–February, 1975.     

Structural susceptibility of strength characteristics of polystyrene under uniaxial stretching

The structural susceptibility of the strength characteristics of polystyrene under uniaxial stretching and under test conditions with = const and v_elong = const was studied at 20–100°C. The low structural susceptibility of the durability and durability-equation parameters is due to a change in the elementary fracture volume at different test conditions. It was proposed to characterize the degree of participation of chemical and intermolecular forces by the value U₀/.Moscow Technological Institute of Meat and Milk Industry. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1974.     

Effect of certain factors on the vibrations of polymers

The authors' work on the effect of various factors on the vibrations of the polymer chain is reviewed. A method of calculating chain vibrations is briefly described, an expression is given for the strain energy of a polymer molecule in the nonlinear approximation, the frequency shift of the vibrations of a molecule under load is calculated and discussed, the effect of intermolecular interaction in the polymer crystal and the disorder of the chain on the vibration spectrum is taken into account, and the change in the intensity of the normal vibrations when the chain is loaded and the effect of anharmonicity on the band width are investigated. In conclusion, the stress distribution over the interatomic bonds is estimated.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 33–46, January–February, 1975.     

Thermodynamics of high-elastic deformation of polyurethanes

The thermoelastic behavior of polyurethanes based on diethylene glycol adipate and tolylene diisocyanate with different network densities has been investigated in connection with their tensile deformation. The change in entropy and internal energy is calculated at strains up to 100%. It is shown that during extension both the entropy and the internal energy decrease. The reduction in internal energy depends on the relative importance of the physical and chemical bonds in the network and is attributable to the redistribution of intermolecular bonds.Mekhanika Polimerov, Vol. 4, No. 3, pp. 450–453, 1968     

Effect of plasticization on the activation energy of failure of nitrocellulose

The authors investigate the temperature-force dependence of the service life of plasticized nitrocellulose under uniaxial tension. They show that when the plasticizer content of the polymer is sufficiently high, the activation energy U₀ of mechanical breakage is higher than the value for the same polymer without plasticizer. The authors propose the hypothesis that when the plasticizer content of the polymer is increased, an increasingly important part in the development of breakage is played by rupture of the intermolecular bonds and by mutual slippage of the segments of the macromolecules, while the part played by chemical bond rupture decreases.Presented at the Sixth Symposium on the Rheology of Polymers, Moscow, May 1971.D. I. Mendeleev Moscow Chemical Technology Institute. A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 355–358, March–April, 1974.     

Small deformations of oriented polymers

On the basis of a phenomenological analysis of the temperature dependence of the modulus of instantaneous elasticity and the stress relaxation process, it is suggested that in the region of small deformations there are no breakages of the macromolecules that might affect the elasto-relaxational behavior of highly oriented polymers (fibers) as in the region of large deformations. To judge from the values obtained for the energy constants, these properties are determined by the number of intermolecular bonds in the amorphous regions (modulus of instantaneous elasticity) and the physical events associated with the reorganization of these bonds and hindered rotation of the chain units (relaxation process).S. M. Kirov Leningrad Institute of Textiles and Light Industry. Translated from Mekhanika Polimerov, No. 6, pp. 976–980, November–December, 1971.     

Theory of nonlinear vibrations of free and loaded polymer molecules

The contributions of three- and four-phonon processes to the halfwidth of the valence vibration band of the linear chain are numerically estimated. It is concluded that the experimentally observed halfwidths of the skeletal vibration bands of polymers are attributable to anharmonic phonon interactions. The effect of chain loading on the halfwidth is also investigated.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 579–585, July–August, 1971.     

Effect of annealing temperature on the mechanical properties of polyethylene terephthalate fiber

The mechanical properties of polyethylene terephthalate fibers stretched at 45 and 110° C have been investigated in relation to annealing temperature. It is shown that for fibers with the maximum degree of stretch the annealing temperature has no effect on mechanical strength. Reduction in the stretch of the fibers leads to an increase in strength upon annealing, and this may be associated with densification of the amorphous zones due to the formation of a large number of intermolecular bonds between the links of the polymer chains.Mekhanika Polimerov, Vol. 3, No. 3, pp. 503–506, 1967     

“Fundamental” and “practical” adhesion in polymer-fiber systems

The relationship between adhesion and bond strength in thin fiber-polymer matrix systems was studied. Adhesive interaction in composite materials was analyzed within the scope of thermodynamic and molecular-kinetic theories of adhesion. Methods based on wetting are shown to give poor estimation of the work of adhesion in fiber-polymer systems, which is due to their low sensibility to donor-acceptor interactions taking place at the interface. Important information about the acidity and basicity of contacting surfaces can be obtained by using inverse gas chromatography to investigate the thermodynamics of adsorption. The calculation of the work of adhesion including acid-base interactions shows the best agreement with the bond strength in the same systems. The local (ultimate) interfacial shear strength is proposed to characterize the quality of fiber-matrix bonding. Analysis of the relationship between the work of adhesion and adhesive pressure for various systems allowed us to differentiate the dispersive and acid-base components of the local bond strength as well as to estimate distances characteristic of these twoTypes of interaction. For dispersive forces, our estimation gives 7–8Å, i.e., of an order of magnitude of the center-to-center distance for van der Waals interactions. At the same time, the acid-baseInteractions have a characteristic range of 4–5Å and can be attributed to hydrogen bonding. The agreement between the calculated distances and literature data is evidence for the applicability of the proposed method to the analysis of the adhesive interaction in fibrous polymer composites.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 431–446, July–August, 1998.     

Thermodynamic Potential of a System of Electrons and Phonons in a Disordered Alloy

We obtain a cluster expansion for the two-time retarded Green's functions and the thermodynamic potential of a disordered crystal taking the electron–phonon and electron–electron interactions into account. The electron states of the system are described in the framework of a multiband tight-binding model. The calculations are based on the diagram techniques for the temperature Green's functions. The coherent potential approximation is chosen as a zeroth-order one-site approximation in this cluster expansion method. We show that the contributions from the processes of scattering of elementary excitations on clusters decrease as the number of sites in the cluster increases in accordance with certain small parameters. Analytic estimates of the influence of the electron–phonon interaction on the energy spectrum of electrons of an alloy being ordered are obtained in a one-band model. The applicability of these results to describing the influence of strong electron correlations on the electron structure and properties of alloys of transition metals with narrow energy bands is illustrated with the example of the Fe–Ti alloy.