A. A. Shcherbina

Adhesive properties of ethylene and vinyl acetate copolymers

Surface properties of ethylene and vinyl acetate copolymers (EVAs) are considered depending on their composition and history of surface formation. The kinetics of structural transformations in the near-surface layers of copolymers is investigated. Relaxation times and the equilibrium state of the EVA surface are determined. The orrelation dependence between the surface energy of copolymers and their adhesive properties for substrates of different natures is constructed.

Plasma chemical modification of polymer surface. Polyethylene terephthalate

Methods of electron microscopy, atomic force microscopy, contact angles, multiple attenuated total internal reflection IR spectroscopy, and X-ray photoelectron spectroscopy were used to study the molecular-chemical, structural and morphological, and energy characteristics of polyethyleneterephthalate (PET) surfaces before and after treatment in plasma of high-frequency air discharge. It is shown that modification of PET surface results in a change in the structural-morphological surface properties and the formation of oxidized near-surface layers. The peel test was used to determine the adhesion characteristics of the substrate with respect to a standard adhesive. It is shown that the decisive role in providing high strength of adhesive joints in the course of plasma chemical modification is played by a significant increase in the surface energy of the substrate, namely its polar component. The kinetics of relaxation of surface characteristics of the substrate are studied in the case of long-term storage under laboratory conditions.

Sorption and Diffusion of Water in Poly(vinylpyrrolidone)

The effect of molecular mass, thermal prehistory, physical state, and three-dimensional chemical crosslinked structure of a polymer on dissolution and diffusion in the PVP-water system has been studied. The kinetic dependences of sorption that correspond to the Fickian or pseudonormal type have been measured. In a certain concentration range, sorption is accompanied by transition of the system to the rubbery state. In the glassy state, the negative concentration dependence of the diffusion coefficient related to the nonequilibrium state of the polymer sorbent is observed. Sorption isotherms are described by S-shaped curves. It has been shown that the thermal prehistory of the polymer sorbent has the most pronounced effect on its sorption behavior. The effect of molecular mass is insignificant, while three-dimensional chemical crosslinks in PVP manifest themselves only in the region of the rubbery state. In accordance with the double sorption model, the experimental isotherms are represented as the superposition of two isotherms described by the Langmuir and Flory-Huggins equations. For the glassy state of the polymer sorbent, the degree of the nonequilibrium state has been estimated. With due regard for the excess free volume, the detailed thermodynamic analysis of isotherms has been performed; namely, the pair interaction parameters and the free energy of mixing have been calculated. The state of water in the polymer has been examined within the framework of hydrate contributions and clusterization theory.

Phase equilibria in a polystyrene-poly(butyl acrylate) system

Phase equilibria in polystyrene-poly(n-butyl acrylate) systems containing polystyrene of various molecular masses were studied for the first time via optical interferometry at temperatures between 280 and 500 K. The phase diagrams of the systems were obtained, the pair interaction parameters were determined, and the dependences of the parameters on the molecular mass of polystyrene and temperature were found. The possibility of thermodynamic analysis of phase diagrams in terms of the classical Flory-Huggins-Scott theory and the possibility to predict generalized phase diagrams of polystyrene-poly(n-butyl acrylate) systems on the basis of the experimental values of the pair interaction parameters were shown.

Mutual diffusion and self-diffusion in systems of poly(vinyl chloride) and copolymers of vinyl chloride and vinyl acetate

Electron-probe microanalysis was used to study diffusion in systems composed of poly(vinyl chloride) and statistical copolymers of vinyl chloride and vinyl acetate. The coefficients of mutual diffusion and the activation energies of diffusion were determined. The ability to calculate the self-diffusion coefficients of the homopolymer and the copolymers was shown.

The effect of self-organizing vinyl siloxane nanolayers on the corrosion behavior of aluminum in neutral chloride-containing solutions

The methods of quartz crystal microbalance, atomic force microscopy (AFM), scanning electron microscopy (SEM), Fourier-transform IR spectroscopy, and X-ray structural microanalysis were is used to show that adsorption of vinyl silane on an aluminum surface from an aqueous solution results in formation of a uniform, self-organizing protective vinyl siloxane nanolayer covalently bound with surface metal groups. Its thickness can be controlled by variation of application conditions. The effect of a vinyl siloxane nanolayer on dissolution of aluminum is studied in chloride-containing solutions. It is found that an ordered vinyl siloxane nanolayer with a thickness of up to 5 molecular layers causes efficient inhibition of uniform and local corrosion of aluminum. It is shown that the vinyl siloxane nanolayer is preserved on the surface of aluminum after 10 days of corrosion tests, which indicates its stability at exposure to water and corrosive components.

Adhesive properties of ethylene and vinyl acetate copolymer. Deformation strength characteristics: Contribution of plastic deformation work

The deformation-stress curves of ethylene and vinyl acetate copolymer (EVA) are determined by traditional methods with respect to composition at various rates of deformation. The residual deformations after relief are estimated. The deformation work is calculated and the effect of copolymer composition on the value of plastic deformation is evaluated. According to the previously suggested model, the contribution of deformation characteristics of EVA adhesive to the adhesive joint fracture energy is estimated.

Topology of concentration-gradient transition zones in polymer adhesive compounds

This work provides an overview of data on the topology of concentration-gradient transition zones forming in polymer adhesive compounds with different thermodynamic compatibilities of components and phase states of the system. It is shown that the structural organization of a transition zone involving an existence and extension of areas of diffusional mixing, nature, and dimensions of phase aggregates depends heavily on the thermal prehistory and formation conditions and usages of compounds and can be determined by the phase equilibrium diagrams for an adhesive–substrate system.

Surface-energy characteristics of films of molecular brushes based on polyimide and poly(methyl methacrylate)

Surface characteristics of film samples of molecular brushes with a polyimide backbone and PMMA side chains, as well as of films of polyimide constituting the backbone and linear PMMA homopolymers obtained via the selective destruction of the polyimide backbone of these brushes, are investigated for the first time. The surface-energy characteristics of the films of molecular brushes are determined by the structure and conformational state of the PMMA side chains. The conformations of molecular brushes possessing a polyimide backbone well screened by side chains are preserved after the transition from solutions to “dry” copolymer films and are characterized by high stability. The observed surface activity of molecular brushes is due to adhesion interactions with functional groups of the substrate. The difference in surface activities is caused by small-scale conformational changes in the side chains of molecular brushes. A globular core of molecular brushes formed by the polyimide backbone remains practically spherical and probably does not change in volume.

Kinetics and mechanism of formation of adhesive joints based on ethylene-vinyl acetate copolymers

The structure of transient zones in PVC-poly(ethylene-co-vinyl acetate), PET-poly(ethylene-co-vinyl acetate), and steel-poly(ethylene-co-vinyl acetate) adhesion systems is studied. It is shown that PET-poly(ethylene-co-vinyl acetate) and PVC-poly(ethylene-co-vinyl acetate) are related in incompatible and partially compatible systems, respectively. In the temperature range 100–180°C, diffusion coefficients and the activation energy of diffusion are determined. The depth of penetration of copolymer macromolecules into the PVC phase is calculated. The kinetics of adhesive-joint formation is studied. For all systems, the increase in joint strength has a common character; for each temperature, the steady state is attained. The results are analyzed in terms of wetting and diffusion theories. Both models satisfactorily describe the kinetics of joint formation in compatible and incompatible systems (including steel-poly(ethylene-co-vinyl acetate). The effective activation energy of the kinetics of adhesive-joint formation is determined and compared with the activation energies of diffusion, the viscous flow of copolymers, the β transition, and the rate of conformation rearrangements in the surface layers of ethylene-vinyl acetate copolymers. It is suggested that the data obtained can be generalized in terms of the Bikerman theory of a “weak boundary layer.”