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The process of open-porous structure development in highdensity polyethylene (HDPE) films during uniaxial deformation in supercritical carbon dioxide (SC-CO 2 ) fluid at 35 °C and 10 MPa has been studied and visualized by means of atomic force microscopy. We suggest that the supercritical fluid act as adsorption-active medium, and the porous structure is developed via the crazing mechanism due to the increasing the distance between of lamellae and the formation of oriented separate fibrils in the intercrystallite space. Effective bulk porosity of the films has been up to 40%. Small-angle X-ray scattering studies and ethanol permeability measurements have revealed that the pores and fibrils are about 10 nm in diameter. The prepared nanoporous materials exhibit good vapor permeability. Structural and mechanical behavior of the prepared porous films has been investigated. Large reversible deformation (up to 80%) of HDPE in the SC-CO 2 has been observed. Repeated drawing of the shrunk films in air under ambient conditions has led to the open-porous structure recovery.

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Tensile drawing of the poly(ethylene terephthalate) (PET) samples in semidilute solutions of poly(ethylene oxide) (PEO) with the molecular mass ranging from 4 × 104 to 1 × 106 proceeds via the mechanism of solvent crazing. This process is accompanied by the penetration of PEO into the porous structure of crazes, and this conclusion is proved by the data on the composition of the resultant blends as well as by the direct electron microscopic observations. Effective diameter of pores in the nanoporous structure of the solvent-crazed PET samples is estimated by the method of pressure-driven liquid permeability. Structure of PEOs is studied by the methods of dynamic light scattering and capillary viscometry as a function of the molecular mass and polymer concentration in the solutions. Penetration of PEO into the solvent-crazed nanoporous structure proceeds under so-called “confined” conditions when the hydrodynamic radius of a polymer coil is comparable or higher than the effective dimensions of pores in the crazes. Penetration of the PEO macromolecules into the porous structure of the solvent-crazed PET-based sample via diffusion under the action of the concentration gradient is compared with the flow-assisted penetration in the course of the tensile drawing of the PET samples in the PEO solutions. Content of PEO in the pores of the solvent-crazed polymer samples is higher than that in the surrounding solution, and this fact can be explained by the adsorption of PEO on the highly developed surface of the fibrillated polymer in crazes. Penetration of PEO into the porous structure upon tensile drawing proceeds much quicker (minutes) as compared with the attainment of the equilibrium content of the polymer under the action of the concentration gradient (days).

SummaryA procedure has been developed for the direct atomic force microscopic (AFM) examination of the native structure of highdensity 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.

E G Rukhlya), efimov@genebee.msu.ru (A V Efimov), yaryshev@gmail.com (L M Yarysheva), tel. (7-495) 332 58 46 (N F Bakeev)

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