I. S. Kuryndin

Surface texture and percolation effects in microporous oriented films of polyolefins

The surface structure of polypropylene and polyethylene microporous films prepared by the extrusion of the polymer melt with the subsequent stages of annealing, uniaxial extension, and thermal fixation of the samples has been analyzed using scanning electron microscopy. It has been shown that percolation through pores corresponds to the axial texture of the surface with the channel structure described by the fractal cluster model. The transition from open pores (through-flow channels) to closed pores leads to the formation of surface regions with a biaxial texture. An increase in the density of the solid phase cluster is accompanied by the formation of a homogeneous biaxial texture with a period of alternation of the density in two mutually perpendicular directions, one of which coincides with the direction of orientation of the films.

Topological structure of microporous oriented polypropylene films

According to the data of scanning electron microscopy, gravimetry, and permeability measurements, the porous structure of membrane samples obtained in a multistage process including extension of annealed polypropylene films formed at the stage of polymer melt extrusion has been studied. It has been shown that, as the cooperativity of lamella ordering (self-assembly) increases at the stage of film extension (pore formation), the topological model of the porous phase of membranes changes from model (1), i.e., a random network of channels, to model (2), i.e., oriented through flow channels. The transition between two models is controlled by the melt spin draw ratio.

Superlattices of lamellae in microporous oriented polyolefine films

The structure and mechanism of the formation of superlattices lamellae in microporous polyolefine (polyethylene and polypropylene) films obtained by polymer melt extrusion followed by annealing, uniaxial extension, and thermal fixation stages have been studied by scanning electron and atomic-force microscopy. It has been shown that oriented anisometric particles, i.e., lamellae aggregates, are formed in films as the spin draw ratio λf increases. At the stage of uniaxial extension (pore formation) of annealed films, a particle ensemble transforms to spatial superlattices of lamellae. Numerical processing of electron microscopy images of the film surface show that the nonmonotonic dependences of the correlation length of density fluctuations and the ratios of the alternation period of particles along extension to their thickness on the parameter λf correspond to a unified mechanism of lamellae ordering.

Percolation transitions in porous polyethylene and polypropylene films with lamellar structures

Conditions of the formation of a well-developed system of through-flow channels in porous polyethylene and polypropylene films prepared via a method based on extrusion of the polymer melt are investigated. It is found that attainment of the percolation threshold is determined by the relationship of such factors as the degree of melt orientation during its extrusion, the annealing temperature, and the degree of uniaxial extension of films initiating the formation of pores. The effect of structural factors on percolation transitions is analyzed.

Self-organization of lamellae and permeability of microporous oriented polypropylene films

The effect of the annealing temperature Tann of extruded polypropylene films on the structure of membranes prepared by the uniaxial extension of annealed films with the subsequent thermal fixation has been investigated using small-angle X-ray scattering and scanning electron microscopy. It has been shown that an increase in the permeability of membranes with increasing temperature Tann is due to the self-organization of elements of the lamellar structure of the polymer as a result of the ordering and aggregation of particles.

Regularities of lamellae ordering in the formation of polypropylene membrane porous structure

The lamellar structure of porous polypropylene membranes prepared by the extrusion of the polymer melt, annealing of extruded films, and their uniaxial extension has been investigated using data of computer analysis of scanning electron microscopy images. It has been shown that the formation of pores at the stage of uniaxial extension is accompanied by an ordering of lamellae or their self-organization controlled by the annealing temperature Tann. It has been found that the self-organization of lamellae can occur through two mechanisms depending on the spin draw ratio at the stage of extrusion of the polymer melt: in the first case, an increase in the temperature Tann leads to a gradual transition of the disorder-order type; in the second case, a bifurcation transition occurs with a nonmonotonic change in the order parameter. The conditions of the preparation of regular spatial lattices of lamellae have been discussed.

Hybrid hydrogels based on cross-linked polyacrylic acid and polyvinyl alcohol as electrically controlled artificial muscles

A procedure was developed for preparing hybrid hydrogel specimens of preset configuration from cross-linked polyacrylic acid and polyvinyl alcohol. The specimens exhibit higher mechanical characteristics compared to hydrogels of cross-linked polyacrylic acid. Hydrogel specimens fabricated in the form of elastic rings demonstrate an electromechanical response, contraction on passing electric current through their cross section. This effect is more pronounced for the specimens swollen in a sodium sulfate solution than for those swollen in distilled water. The results obtained show that the hydrogels can be used as a linearly operating mechanical force generator (artificial muscle).

Electromechanical Response and Structure of Chitosan–Polyaniline Composite Systems

Swelling chitosan–polyaniline composite systems demonstrating a pronounced electromechanical response are obtained. The formation of a crosslinked structure in chitosan allows one to enhance elasticstrain properties of composites, but this is accompanied by a decrease in the bending angle under an electric field. Polyaniline as an electroactive component improves the composite system capability of deformation induced by an electric field. The factors contributing to the deformation value are investigated.

Light scattering by porous oriented polypropylene films

Oriented porous polypropylene films with lamellar crystal structure are studied by the laser radiation scattering method. The dependence of the scattering pattern on the degree of film orientation is determined. It is shown that the sizes of the central maximum of the scattering pattern depend linearly on the degree of film extension. The results obtained can be used in developing methods of optical nondestructive testing of polymeric materials.

Structure and piezoelectric properties of microporous polyvinylidene fluoride films

A method to produce microporous polyvinylidene fluoride films characterized by a high content of a piezoactive crystalline phase and a developed relief surface is elaborated. The porous films are obtained in the process based on melt extrusion with subsequent isometric annealing and uniaxial extension. It is found that the samples have an oriented lamellar structure containing both α- and β-modifications of the crystallites. The effect of temperature and degree of uniaxial extention of the annealed films on the characteristics of the porous samples, that is, the content of the piezoactive crystalline β-phase, overall porosity, breakdown voltage and the piezoelectric modulus is studied.