M. S. Arzhakov

A new approach to the description of mechanical behavior of polymer glasses

Abstract Temperature-induced relaxation of plastic deformation of polymer glasses based on PMMA was studied. Plastic deformation of polymers and their mechanical properties were described in terms of contributions from low-temperature and high-temperature components to the recovery of residual deformation. The above components of relaxation were treated as physical parameters of deformation and relaxation in polymer glasses. The ratio between low-temperature and high-temperature components was shown to be controlled by physicochemical modification of polymer materials.

Structural and mechanical aspects of interaction of polymers with low-molecular-mass substances

Abstract Specific features of complexation between low-moiecular-mass compounds (LMs) and polymers were discussed in terms of structural inhomogeneity of amorphous glassy polymers. Introduction of LMs into the polymers was shown to be associated with distribution of the LMs between two different forms, which are characterized by different energetics of bonding with polymer matrix. This factor was responsible for a complicated character of molecular dynamics of the polymer/LM system and mechanical behavior of such complex materials in whole. The cases, when macroscopic mechanical behavior of the polymer containing LM was primarily controlled by the form, in which this compound existed in polymer matrix, were considered. The future development of this direction of polymer modification was discussed and possibilities of its practical application for controlled improvement in mechanical response of polymer materials were outlined.

Physical and Mechanical Behavior of Polymer Glasses in Terms of Temperature-Induced Relaxation of Plastic Deformation

Abstract Temperature-induced relaxation of residual plastic deformation of polymer glasses was discussed in terms of structural inhomogeneity of glassy polymers. Mechanical properties of glassy polymers were shown to be controlled by the ratio between low-temperature and high-temperature components of temperature-induced relaxation of residual deformation. This ratio was treated as a new physical parameter describing physical and mechanical behavior of polymer glasses. The applied aspects of studying temperature-induced relaxation of residual deformation concerning the prepartion of modern polymer materials were discussed.

Physical and Mechanical Behavior of Polymer Glasses. VI. the Role of Free Volume

Abstract For various polymer glasses, the temperature-induced recovery of residual deformation was studied. The ratio between the low-temperature and high-temperature recovery components is controlled by the difference between deformation temperature and glass transition temperature T g of polymer samples independently of their chemical structure. This ratio correlates with polymer macroscopic mechanical characteristics such as elastic modulus and yield stress. Experimental results were treated in terms of the dynamics of segmental mobility within different structural sublevels with different packing densities. To correlate this mechanical response with the structural state of glassy polymers, positron annihilation lifetime spectroscopy (PALS) was used. For different polymer glasses, the microscopic segmental mobility and resultant macroscopic mechanical properties were shown to be controlled only by the development of the adequate free volume content which depends on the difference between testing temperature and T g . These results allowed us to propose the general correlation between microstructure, microscopic molecular mobility, and Macroscopic mechanical behavior of polymer glasses.

Physical and Mechanical Behavior of Polymer Glasses: Polymeric Powders

Abstract Deformation behavior of glassy thermoplastic powders under the parallel action of pressure and temperature was studied. Three “pressure-temperature” regions of preparation of monolithic polymer samples with quite different physical and mechanical properties were found. The existence of these regions was shown to be controlled by the relaxation in powderlike polymer during compression. Speculations concerning segmental mobility within polymer glassy state were proposed to describe specific relaxation behavior in the bulk polymer samples.

Physical and Mechanical Behavior of Polymer Glasses. III. Copolymers of Methyl Methacrylate

Abstract Physical and mechanical behavior of copolymers of methyl methacrylate and PMMA was studied. The contribution from low-temperature component to total temperature-induced relaxation of plastic deformation was shown to correlate well with the mechanical characteristics of polymer samples. This correlation was discussed in terms of the structural inhomogeneity of polymer glasses: coexistence of structural sublevels with characteristic values of relaxation time and energy of activation of segmental mobility. From this standpoint, plastic deformation and, in general, physical and mechanical behavior of polymer glasses is likely to be controlled by a gradual involvement of segmental mobility within above structural sublevels in deformation and relaxation processes.

Studies of Deformed Poly(Methyl Methacrylate) Using Positron Annihilation Lifetime Spectroscopy

Abstract Structural rearrangements in glassy PMMA on polymer plastic deformation and recovery of residual plastic deformation in glassy state were studied by positron annihilation lifetime spectroscopy. Uniaxial compression was shown to be accompanied by a decrease in concentration of free volume microregions in disordered polymer regions, which were characterized by low packing density. Recovery of residual deformation at elevated temperatures but below glass transition point Tg proceeds without any noticeable changes in fractional content of free volume both in disordered and ordered polymer regions. The advantages of positron annihilation lifetime spectroscopy for studying microstructure and structural rearrangements in polymers were discussed.

Physical and mechanical behavior of polymer glasses. IV. cross-linked poly(methyl methacrylate)

Abstract Temperature-induced relaxation of plastic deformation in cross-linked PMMA samples was studied. For cross-linked PMMA with low concentration of cross-linking agent (less, than 5.2 mol.%), relaxation curves: involve low-temperature component at temperatures well below glass transition temperature and high-temperature component at temperatures close to glass transition. Increasing concentration of cross-linked agents in polymer samples to 11.2 mol.% is accompanied with degeneration of high-temperature component of relaxation, and complete relaxation of plastic deformation proceeds via low-temperature component. The effect of cross-linking on temperature-induced relaxation of plastic deformation was discussed in terms of restriction of segmental mobility within certain structural regions in polymer sample.

An Approach to Improvement in the Mechanical Properties of Nylon-6 in a Humid Atmosphere

Abstract Mechanical properties of Ny-6 isotropic films modified with oxyaromatic compounds were studied. The introduction of oxyaromatic compounds into Ny-6 is accompanied by an increase in the elastic modulus and strength of the polymer. The resistance of mechanical parameters to the action of moisture is controlled by an intermolecular interaction in the Ny-6/oxyaromatic compound systems and can be enhanced by going from low-molecular-mass oxyaromatic compounds to high-molecular-mass ones. The results observed were discussed in terms of a complexation between the components of the Ny-6/oxyaromatic system taking place in amorphous regions of the polymer.

Physical and Mechanical Behavior of Polymer Glasses. V. Structural Plasticization

Abstract For poly(methyl methacrylate) (PMMA) containing incompatible diethyl siloxane oligomer (DES), the effect of DES on the mechanical behavior of polymer was discussed in terms of the structural plasticization. Using positron annihilation lifetime spectroscopy (PALS), the introduction of DES to polymer was shown to change the free volume content primarily within structural sublevels with lowered packing densities. Examination of polymer samples using the studies in the temperature-induced recovery of residual deformation, dynamic mechanical analysis, differential scanning calorimetry, and thermostimulated luminescence evidenced that the changes in the polymer microstructure control the variations in the molecular and segmental mobility in PMMA. Enhancement of the molecular and segmental mobility decreases the mechanical parameters such as elastic modulus and yield stress whereas the restriction of molecular and segmental mobility increases the above mechanical characteristics. Mechanism of structural plasticization of glassy polymers involves the effect of a plasticizing agent on the local free volume in the certain structural sublevels, the resultant changes in the microscopic molecular and segmental mobility, and the corresponding modification of the macroscopic mechanical behavior of polymer materials.