A. L. Volynskii

Mechanical buckling instability of thin coatings deposited on soft polymer substrates

Deformation of rubber and poly(ethylene terephthalate) coated with a platinum or a gold film was studied. The thickness of the coating film was approximately ten nanometers. The polymer substrates were 104 to 105-fold softer than the coating. Folding of the coating leading to the appearance of a wave-like pattern on an originally smooth surface was observed both in tension and after shrinkage. In tension the wave crests are oriented along the elongation direction. After shrinkage the wave crests are perpendicular to the shrinkage direction. For rubber substrates, the appearance of the wave is explained by a mechanical buckling instability of the coating under compressive force. The length of the surface wave depends on the thickness of the coating layer and the rigidity of the polymer substrate. In addition to folding, regular fragmentation of the coating film on long and comparatively narrow bands is observed. The cracks are perpendicular to the wave crests both in tension and after shrinkage.

Multiple cracking of rigid platinum film covering polymer substrate

Multiple cracking of a thin platinum film deposited on polyethylene terephtalate, isoprene rubber, and natural rubber substrates under tensile deformation was studied by light and scanning electron microscopy. The cover fractures on several fragments elongated in the direction perpendicular to the loading direction. The width of the fractured platinum fragments depends on the thickness of the deposited layer and applied tensile stress. A semiempirical equation describing the average width of the cover fragments was obtained. Appearance of a wavy pattern on an originally smooth surface of composites with rubberlike polymer substrate was observed. The mechanism of the appearance of the surface wave is a mechanical buckling instability of the cover under compressive force.

Mechanical behavior of glassy polyethylene terephthalate deformed in liquid adsorption active media

Abstract A study was made of the relation between mechanical, thermo-mechanical properties of amorphous glassy PETP and the degree of elongation in liquid adsorption active media. It was shown that with an increase in the degree of elongation starting from ∼200%, the mechanical and thermo-mechanical properties of PETP change markedly. Using results a mechanism was proposed for the effects observed, according to which deformation of PETP in an adsorption active medium is regarded as a transition process to the oriented, highly dispersed state inside micro-cracks. As deformation develops the amount of highly dispersed material continously increases, which results in the accumulation by the system of a considereable excess of a highly developed surface and the possibility of coagulation of the material of micro-cracks directly in the adsorption active medium.

STRUCTURE OF POLYMER BLENDS BASED ON SOLVENT-CRAZED POLYMERS

Abstract Blends based on polymers (PET, HDPE) prepared by deformation via the mechanism of classical and delocalized solvent crazing are described. The second component of polymer blends may be represented by various polymers such as PMMA, PS, PBMA, PEG, polyaniline, etc. The above polymers are characterized by a high level of mutual dispersion of components. Structure and mechanical properties of the blends are studied.

Structural Aspects of Physical Aging of Polymer Glasses

Published data concerning the problem of the physical aging of glassy polymers are surveyed. Basic attention is given to an analysis of structural rearrangements that accompany the physical aging of glassy polymers. The processes of aging (spontaneous change in the properties of polymer glasses during the storage at a temperature below the glass transition temperature) can be classified into the two following categories: first, the aging of undeformed polymer glasses and, second, the mechanical stress-induced aging of a polymer. It is shown that in the former case, the processes occur throughout the entire body of the polymer and, in the latter case, the aging processes is concentrated in microscopic zones (shear bands) that emerge during polymer deformation. The current concepts of the aging of polymer glasses are discussed.

A new approach to the preparation of nanocomposites based on a polymer matrix

A new approach to the preparation of nanocomposites is advanced. This approach includes preliminary formation of a nanoporous matrix and subsequent loading of the formed pores by the second component. These advantageous opportunities are provided by one of the most fundamental phenomena of the physical chemistry of polymers: solvent crazing of polymers in the presence of the liquid media. Several examples illustrate that solvent crazing not only provides a universal means of self-induced dispersion of a polymer material into nanoscale aggregates but also offers a universal route for the delivery of diverse low-molecular-mass compounds to the nanoporous structure of the solvent-crazed polymer. The results on the preparation of new types of nanomaterials, such as porous polymeric sorbents, polymeric separation membranes, new types of polymer-polymer nanoblends, fireproof and conducting polymer nanocomposites, and metal-containing polymers, are reviewed. Some aspects of the practical application and technological design of solvent crazing of polymers as a means for the preparation of diverse nanocomposites are discussed.

Atomic force microscopic study of the structure of high-density polyethylene deformed in liquid medium by crazing mechanism

A procedure has been developed for the direct atomic force microscopic (AFM) examination of the native structure of high‐density polyethylene (HDPE) deformed in an adsorption‐active liquid medium (AALM) by the crazing mechanism. The AFM investigation has been carried out in the presence of a liquid medium under conditions preventing deformed films from shrinkage. Deformation of HDPE in AALM has been shown to proceed through the delocalized crazing mechanism and result in the development of a fibrillar‐porous structure. The structural parameters of the crazed polymer have been determined. The obtained AFM images demonstrate a nanosized nonuniformity of the deformation and enable one to observe the structural rearrangements that take place in the deformed polymer after removal of the liquid medium and stress relaxation. A structural similarity has been revealed between HDPE deformed in the AALM and hard elastic polymers.

Healing of interfacial surfaces in polymer systems

Literature data on the problems related to the healing of interfacial surfaces in polymers are revisited. Specific features and behavior of the contacting surfaces of polymer films in the rubbery and glassy states, as well as in heterophase polymer systems, are analyzed. Particular details associated with the healing of interfacial surfaces in polymers, which are capable of chemical interactions with each other, are considered. Special attention is focused on the analysis of the phenomena taking place on the newborn interfaces formed owing to the deformation of polymers in different physical states. Processes providing healing of shear bands and crazes during annealing of deformed polymer glasses are discussed. The above phenomena are shown to present evident practical interest from the viewpoint of the development of advanced nanocomposites based on polymer matrices.

Spontaneous elongation of crystallizing polymers

Abstract Spontaneous elongation was observed with samples of amorphous PETP and polycarbonate, which had previously been deformed in n-propanol. A structural and mechanical study was made of the effect and it is shown that it may be regarded as primarily a surface effect.

Nanocomposites on the Basis of Crazed Polymers

Analysis of published data on the mechanism of structural rearrangements in solid polymers on their crazing in liquid media is presented. The experimental evidence characterize crazing not only as a kind of spontaneous polymer dispersion under joint action of a mechanical stress and an active liquid medium, but also as the method of colloidal dispersion of low-molecular substances in a polymer. In the process of crazing, active liquid fills the porous structure of crazes, thereby transporting various low-molecular substances to the polymer volume. Crazing is believed to open the ways for preparing various nanocomposites on the basis of a wide variety of glassy and crystalline polymers, on the one hand, and target additives on the basis of practically any low-molecular substances, on the other.