Determination of the thickness of the surface layer on polymer blocks

A dependence of the thickness of the surface layer on the mechanical and wave characteristics of polymers has been obtained from joint solution of the equations of surface-wave motion and surface-layer equilibrium. From the dependence derived, the thicknesses of the surface layers have been calculated for four polymers. The dependence of surface-layer thickness on mechanical properties of the polymers and loading characteristics has been established.Institute of the Chemistry of High-Molecular-Weight Compounds, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 2, pp. 195–201, March–April, 1972.     

Investigation of polytetrafluorethylene surface texture

Results are given of an X-ray investigation of the formation of a textured surface layer on polytetrafluorethylene (PTFE) film and its dependence on external mechanical factors — unit load and sliding speed. It is established that the thickness of the surface texture of PTFE is determined by the relation between the processes of texture formation under the influence of frictional forces and its destruction by wear. These processes, in turn, are determined by the working parameters of the moving joint. Data on the kinetics of polymer surface texture formation in the presence of friction are extremely useful in relation to the design of efficient antifriction materials.Mekhanika Polimerov, Vol. 1, No. 2, pp. 129–132, 1965     

Stress on the interatomic bonds near the surface of a polymer

The stresses on the interatomic bonds in the interior and at the surface of polyethylene terephthalate film in uniaxial tension have been determined by means of infrared transmission and reflection spectroscopy. The stresses are found using the shift in the frequency of the atomic vibrations produced by the application of a mechanical load. It is shown that the stresses on some bonds in the specimen reach 700 kgf/mm², i.e., approach their theoretical strength. The concentration of these bonds in a surface layer 1 µ thick is approximately an order greater than the concentration in the interior of the specimen.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 512–514, May–June, 1976.     

Investigation of the mechanical properties of polymer surface layers using surface waves

It is possible to excite ultrasonic surface waves at the surface of polymer materials and to determine the dependence of the wave parameters on the mechanical properties of the surface. The nature of the variation of the surface wave characteristics with material, temperature, and the frequency of the exciting vibrations has been established.Mekhanika Polimerov, Vol. 3, No. 5, pp. 933–939, 1967     

Relation between the strength of polyethylene-steel adhesion bonds and the thickness of the ultrathin layer of polymer remaining on the surface of the metal

On the basis of the principle of ellipsometry and, moreover, the method of pyrolitic decomposition of the polymer with subsequent chromatographic analysis of the products of pyrolysis, a procedure has been developed for experimentally determining the thickness of the ultrathin layer of polymer that remains on the metal after failure of a polyethylene-steel adhesion bond. The nature of the relationship between the thickness of the residual polymer layer (200–800 Å) and the strength of the adhesion bond is established. It is concluded that the cohesion strength and the deformation at failure of the layer of adhesive next to the more rigid and stronger boundary layer have a decisive influence on the strength of the adhesion bond.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 3, pp. 420–424, May–June, 1976.     

Effect of fillers on the viscosity and viscoelasticity of low-density polyethylene melts. Communication 1

An investigation of low-density polyethylenes filled with up to 30% by volume dispersed particles, has shown that for both the matrix and the composites the apparent viscous flow activation energy does not depend on the shear stresses and increases starting from a certain filler concentration at which the conformation range in the matrix is depleted. The dependence of the relative viscosity of the compositions on the volume filler content is satisfactorily described by an equation that contains the reduced filler concentration, defined as the ratio of the nominal filler concentration to the limiting concentration at which the adsorption layers on the particles extend throughout the matrix. The thickness of the polymer layer adsorbed on the particles must be determined from the specific exterior particle surface, with allowance for the volume of the polymer in the sorption space of the porous filler.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 478–486, May–June, 1976.     

A new method of measuring the viscoelastic properties of polymer systems in fluid and highly elastic states using forced vibrations in the ultralow-frequency region

A method is considered for measuring the dynamic mechanical characteristics of polyer systems using forced vibrations in the ultralow-frequency region down to 10^–6 Hz. The essence of this method lies in the fact that during the measurement process the motion of the polymer sample is controlled with a set amplitude and frequency, and the dynamic characteristics of the polymer are determined from the controlling mechanical stress. The method is illustrated using the results of measurements of the components of the complex modulus for polybutadiene over a wide range of temperatures and frequencies without making use of superimposition.The Central Constructional Bureau for Prototype Instrument Construction, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 344–347, March–April, 1976.     

Investigation of the self-healing of cracks in polymers

The effect of the medium and the thickness of the polymer film on the self-healing of cracks in polyvinyl acetate has been investigated. The medium in which the specimen "recovers" may either facilitate or impede the self-diffusion of macromolecules and other structural units in the contact zone formed by the closing of the edges of the crack. The "recovery" coefficient decreases when healing takes place in the presence of the vapor of a surface-active agent and increases under conditions such that water molecules are desorbed from the surfaces of the crack; transition from a thick to a thin layer of polymer slows the self-healing process as a result of the reduced mobility of the kinetic units.For communication 2 see [2].Deceased.Karpov Scientific-Research Physicochemical Institute, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1110–1113, November–December, 1970.     

Investigation of the transfer process in polymer friction

It is shown that infrared spectroscopy can be used to investigate material transfer in external polymer friction. The kinetics of the process of transfer of Teflon to a polyethylene surface are examined and it is shown that the thickness of the transferred layer depends on the conditions under which the rubbing pair operates.Institute of Mechanics of Metal-Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mekhanika Polimerov, No. 4, pp. 750–752, July–August, 1971.     

Certain properties of the surface layer of AG-4V glass-reinforced plastic

It is shown that after a glass-reinforced plastic (GRP) has been molded the properties of the surface layer differ sharply from those of the interior layers of material. The surface layer is stronger and less moisture-absorbent. The properties of the surface layer and its thickness are determined by the parameters of the molding process. The surface layer of the GRP AG-4V is thickest, hardest and least moisture-absorbent after molding at 130° C and 200 kg/cm². In this case the microstructure is characterized by a highly uniform fiber distribution without signs of splitting or other damage.Mekhanika Polimerov, Vol. 1, No. 5, pp. 118–122, 1965     

Some mechanical properties of film-reinforced plastics

Model cylindrical shells have been wound from glass and Dacron (Mylar) film strip in accordance with a technique developed by the authors. A layer of glass-reinforced plastic, oriented in the direction of the circumferential tensile stresses, was applied to the outer cylindrical surface of the shells. Certain mechanical properties of the film plastics and their ability to cooperate with the glass-reinforced plastic outer layer were investigated by subjecting the shells to internal liquid pressure. The possibility of obtaining impermeable shells, equally strong in the axial and circumferential directions, was confirmed.Bauman Moscow Higher Technical College. Translated from Mekhanika Polimerov, No. 1, pp. 135–139, January–February, 1971.     

On the extrusion of polymers

Solutions are given for two problems relating to the theory of polymer deformation: extrusion of a viscous liquid from a slot, and the creep of a viscoelastic layer between two plates with a slot. It is shown that if the ratio of the thickness of the working layer to the width of the slot is less than 0.66, the polymer lags behind the plunger and a funnel begins to form.All-Union Correspondence Polytechnic Institute, Moscow. Translated from Mekhanika Poilmerov, Vol. 4, No. 6, pp. 1112–1118, November–December, 1968.     

Analysis of the Adhesion and Adhesion Strength of Two-Layer Polymer Films and Coatings

The formation of adhesion bonds during the creation of two-layer polymer films and coatings capable of acid–base interaction is considered. The coatings are obtained from polymer solutions, and the second layer is formed from the polymer solutions and their mixtures on a hard polymer coating. As a result of absorption by the coating of a considerable amount of solvents (to 14%), polymer macrochains are able to approach one another at a distance necessary for the formation of acid–base (hydrogen) bonds and a transition layer. The polar component of the work of adhesion is equal to about 50% of the whole work W _a. There is no interrelation of the thermodynamic work W _a between the films and the work of their separation into layers. The main part of the external work upon the separation is spent (if strong donor–acceptor bonds are formed) for extracting the segments and macrochains of polymers out of the films.     

Effect of liquid media on the deformation of the surface layers of a polymer-metal pair in sliding friction

The relation between the high-elastic component of polyurethane deformation and the deformation of the surface layers of metals has been investigated for sliding friction in various media. The surface layers of polymer and metal are plastically deformed. There is a certain correlation between the coefficient of friction and the amount of deformation.Kiev Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 147–149, January–February, 1970.     

High-frequency periodic deformation of polymers in the viscous-flow state

The propagation of high-frequency periodic vibrations in melts and solutions is considered in the case where the acoustic characteristics of the material are determined by the deformation amplitude. It is shown that in sufficiently large specimens the consequences of periodic deformation are concentrated near the vibration source, as a result of which a layer of material with strongly modified mechanical characteristics develops. It is suggested that when periodic high-frequency deformation is superimposed on steady-state flow, owing to the presence of a boundary layer there is effective slippages of the material at the vibration-emitting surfaces.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 722–728, July–August, 1973.     

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.     

Heating of polymer surfaces during the vacuum deposition of metals

Conclusions 1. The heating of polymer surfaces associated with vacuum metal deposition is determined by the deposition rate and the deposition time and also by the thermo-physical characteristics of the substrate—growing film system, and at high deposition rates may reach the phase-transition temperatures of the polymers.2. At deposition rates up to 5 Å/sec the rise in surface temperature can be calculated by solving the usual heat-conduction equation, and at higher rates by solving the nonstationary heat-conduction equation, which makes it possible to take into account the heat transfer characteristics of the substrate— growing film system.3. The temperature of the polymer condensation surface can be regulated by varying the initial substrate temperature and, moreover, by using the pulsed metal vaporization process.Institute of Mechanics of Metal—Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mekhanika Polimerov, No. 1, pp. 50–55, January–February, 1977.     

Parametric Vibrations of a Three-Layer Conical Piezoshell

Based on the Kirchhoff-Love hypotheses and adequate supplementary hypotheses for the distribution of electric field quantities, a model for parametric vibrations of composite shells of revolution made of a passive (without a piezoeffect) middle layer and two active (with a piezoeffect) surface layers under the action of harmonic mechanical and electric loads is developed. The dissipative material properties are taken into account by linear viscoelastic models. Since the vibrations on the boundary of the main domain of dynamic instability (MDDI) are harmonic, the investigation of this domain, in a first approximation, is reduced to generalized eigenvalue problems, which are solved by the finite-element method. The problem on parametric vibrations of a three-layer conical shell under harmonic mechanical loading is considered. The influence of the shell thickness, dissipation, and electric boundary conditions on the MDDI is investigated. Two limiting cases of electric boundary conditions are considered, where the electrodes are short-circuited or not. The curves presented show a considerable influence of the electric boundary conditions on the characteristics of the MDDI, namely on its width and position on the frequency axis and on the critical parameter of excitation.     

Nature and mechanism of friction of rubberlike polymers in different physical states

We have investigated the frictional properties of crosslinked butadiene-nitrile and butadiene-styrene copolymers and natural rubber in friction against polished steel under vacuum conditions in the temperature interval from –200 to +150° C, which embraces the glassy and high-elastic states, as well as the transition region between them. The temperature dependence of polymer friction is characterized by two maxima, a principal and a low-temperature maximum. The principal maximum, observed in the glass transition region, is not associated with the mechanical loss maximum observed in the polymers themselves. The temperature dependence of the force of friction is composed of three parts. In the high-elastic region there is an increase in the force of friction with fall in temperature, in accordance with the molecular-kinetic theory of friction of rubberlike polymers. In this region the nature of friction is associated with mechanical losses in the surface layer of polymer. The mechanical losses inside the polymer itself are unimportant. The deviation from the theoretical curve and the fall in the force of friction below a certain temperature in the transition region are chiefly associated with a decrease in the actual area of contact as the polymer passes into the glassy state. In the glassy region the friction is significantly determined by the mechanical losses in the polymer itself associated with the repeated elastic and forced-elastic deformation of the asperities in the layer of polymer in contact with the rigid surface. Therefore the low-temperature maximum is closely related to the mechanical loss maximum observed in the same temperature region in dynamic tests. Apart from this, the friction maximum is also associated with the increase in the forces of adhesion and the reduction of the actual area of contact at temperatures at which a forced-elastic mechanism of compression of the polymer asperities is not realized.Mekhanika Polimerov, Vol. 3, No. 1, pp. 123–135, 1967     

Equations for the vibrations of a plate with general anisotropy

The exact form of the displacement field for an elastic layer with general anisotropy and nonuniform thickness is constructed. The low-frequency part of the solution, which satisfies the equations for the vibrations of a plate, is found.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 165, pp. 122–135, 1987.