Polymer Science, Series A最新文献

Amorphous polyethylene terephthalate was oriented by rolling at room temperature on laboratory rollers. During rolling, a system of shear bands appeared, which was observed using crossed polarizers. The effect of rolling speed and degree on the shear band system was studied. At low rolling speeds (6.5 mm/min), plastic flow occurs through numerous fine shear bands. At higher speeds (above 1300 mm/min), a single serrated deformation zone is observed. This is explained by thermal softening of the polymer and a decrease in yield strength, which suppresses the formation of competing shear bands. At intermediate rolling speeds, two, three, four, or five serrated zones appear, spaced approximately equally. Increasing the degree of rolling leads to an increase in the number of serrated shear zones and homogenization of the flow process. The temperature in the shear bands was estimated, and it was shown that very slight heating of the bands is sufficient to prevent the formation of multiple fine shear bands. A significant difference was noted between the adiabatic deformation of the sample and the adiabatic shear bands.

The feasibility is considered of targeted production of interpolyelectrolyte complexes (IPECs) with an ordered supramolecular structure by polymerization in the composition of various polyelectrolyte–colloid complexes, direct mixing of polyelectrolytes in solution, and an interfacial reaction of polyelectrolytes. Using scanning electron microscopy and small-angle X-ray scattering, differences in the structure of interpolyelectrolyte complexes due to synthesis have been demonstrated. Methods for synthesizing IPEC dispersions with a controlled particle radius and the stability of such dispersions to dissociation into individual components are discussed, as well as some practical aspects of their use including laboratory testing of application potential.

The properties of nonionic and cationic molecular brushes, the copolymers of methoxy- or higher n-alkoxyoligo(ethylene glycol) methacrylates with dodecyl methacrylate and terpolymers additionally containing cationic units of N-methacryloylaminopropyl-N,N-dimethyl-N-propylammonium bromide, in water, organic solvents, and two-phase systems water–hydrocarbon and aqueous saline solution–hydrocarbon have been studied. Effect of the composition of molecular brushes, calculated values of their hydrophilic–hydrophobic balance, solvent polarity, and temperature on the solubility of the polymers, micellization (critical micelle concentration and sizes of macromolecular associates), phase transition conditions, and interfacial activity is estimated. A set of properties of the presented molecular brushes allows their inclusion in a number of potential polymeric micellar nanocontainers for controlled drug delivery into the body.

The drift of multiply protonated poly(ethylene oxide) chains in helium in electrostatic fields of various strengths is simulated using the molecular dynamics method. The simulation results are compared with the predictions of the kinetic theory of ion mobility, which relates the effect of increasing field strength to increasing ion temperature. As would be expected, the internal temperature of the ion T_ion increases with increasing random kinetic energy received by the ion from the field. However, it grows more slowly than expected in the two-temperature theory. Ion mobility is calculated as a function of the field strength E at constant gas temperature T (300 K) and as a function of T at low E. The results of these two series of calculations are compared at the same internal ion temperatures. The results coincide at T_ion close to T. At high ion temperatures, they diverge somewhat (by about 8% at T_ion = 600 K), which does not agree with the theory. Conformations and sizes of drifting ions, as well as their collision cross sections, calculated from the mobility, indicate that an increase in the number of attached protons leads to unfolding of the polymer chain. This effect is in satisfactory agreement with the Rayleigh criterion for the stability of a charged drop. An increase in field strength affects the collision cross section for several reasons. They include an increase in ion temperature leading to larger ion sizes, a decrease in the influence of long-range attractive interactions, and dipole alignment that is more pronounced with fewer protons attached.

In recent years, more and more researchers devote attention on the development and application ofbiodegradable, renewable, abundant, environmental-friendly and low-cost active packaging films, with appropriate antioxydante and antimicrobial properties. This paper focuses on developing composite poly (ε-caprolactone) (PCL) membranes reinforced with silver-zeolite nanoparticles (AgZ) prepared by solvent casting method. The resulting structural, thermal and surface properties of the nanocomposite materials were studied by using experimental characterization techniques such as Fourier-transform infrared (FTIR) analysis, UV-visible spectrophotometry, X-Ray diffraction (XRD), contact angle (CA), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The water vapor permeability (WVP) and the mechanical properties have been investigated. Experimental results showed that AgZ nanoparticles were well dispersed into PCL matrix leading to thermally stable nanocomposites with semi-crystalline structure and hydrophilic surfaces. More importantly, the nanocomposite films showed good antibacterial activity against Staphylococcus aureus and Salmonella enteric strains, demonstrating a potential application as an effective and safe packaging material to prolong the shelf life of food products.

Magnetorheological elastomers (MREs) are known to be smart composite materials able to storing and dissipating part of the energy when subjected to external excitation (magnetic field, temperature, frequency). In this paper, anisotropic magnetorheological elastomers containing 20, 30, and 40% of the micrometric iron particles MRE prepared. The magnetorheological characteristics such as, storage modulus, loss modulus and loss factor MRE measured by dynamic mechanical analysis (DMA) over a range of frequencies (0.01 to 100 Hz), strain amplitudes (0.01 to 20%) and temperatures (0 to 100°C). The magnetorheological elastomer during dynamic mechanical characterization is subjected to a constant magnetic field intensity value of 0.2 T. Increasing the excitation frequency also increases the magnetomechanical properties of the MRE. The temperature has a reversible effect with the frequency, we see that when we increase the temperature, the magnetomechanical properties of the MRE decrease. The experimental results precisely showed the variation of the dynamic moduli (storage modulus, loss modulus and shear loss factor) of the anisotropic MRE loaded with 20, 30, and 40% ferromagnetic particles as a function of the parameters of influence such as: frequency and temperature.

Comprehensive thermodynamic analysis of mixing of poly(diallyldimethylammonium chloride) (PDADMAC) with water at 25°C has been performed. Isotherms of water sorption with linear and network poly(diallyldimethylammonium chloride) have been measured by means of interval sorption. Enthalpy of dilution of solutions of linear poly(diallyldimethylammonium chloride) and enthalpy of swelling of network poly(diallyldimethylammonium chloride) have been measured over the entire composition range by means of isothermal calorimetry. Concentration dependences of the Gibbs energy of mixing and enthalpy of mixing of poly(diallyldimethylammonium chloride) with water have been computed. It has been shown that these thermodynamic functions are negative over the entire range of composition of the solution and swollen hydrogel. The experimental data have been used in thermodynamic modeling of the interaction process, accounting for different contribution to the thermodynamic functions of mixing of poly(diallyldimethylammonium chloride) with water. It has been shown that the thermodynamic of mixing is predominantly affected, on one hand, by the molecular interaction described in the scope of the Flory–Huggins theory and, on the other hand, by the nonequilibrium disruption of glass structure of the polymer during formation of the solution and swelling of the gel. The modeling has given the values of the Flory–Huggins parameter: –0.05 ± 0.02 for aqueous solution of linear poly(diallyldimethylammonium chloride) and 0.20 ± 0.01 for hydrogel of network poly(diallyldimethylammonium chloride). Basing on the model parameters, individual contributions into the enthalpy, Gibbs energy, and entropy of mixing of poly(diallyldimethylammonium chloride) with water have been calculated.

The interaction of pectin and arabinogalactan macromolecules in aqueous solutions has been studied. It is shown that polymer complexes are formed due to hydrogen bonding between macromolecules. Crosslinking of the polymer complex by Са²⁺ ions leads to the formation of hydrogels whose properties are considerably determined by the content of arabinogalactan. At low concentrations of Са²⁺ ions (from 0.05 to 0.15 wt %), the introduction of arabinogalactan contributes to an increase in shear modulus and crosslink concentration and results in a reduction in polymer network sizes compared with hydrogels based on native pectin. With increasing arabinogalactan content the contribution of Fick’s diffusion to swelling of the synthesized hydrogels grows.

An alginic acid derivative containing amide and amino groups was synthesized by adding ethylenediamine to the carboxyl groups of the polysaccharide activated by carbodiimide. Our analysis of its structure using NMR spectroscopy confirms that the addition of ethylenediamine occurs with the formation of an amide bond and the appearance of free primary amino groups in an equimolar ratio. Using the methods of rotational and capillary viscometry in combination with dynamic light scattering and potentiometric titration, it was shown that the critical concentration for the transition to the solution mode with Ce entanglements correlates with the degree of substitution and the change in the zeta potential of the modified polysaccharides. The latter are characterized by a lower Ce concentration and, on average, a lower activation energy for the viscous flow of solutions than sodium alginate. In the pH range 6.5–6.0 for semi-diluted solutions of modified polysaccharide and sodium alginate, an oppositely directed change in the size of macromolecular aggregates is observed. The hemocompatibility of the modified polysaccharide was studied in vitro in tests of blood recalcification time, activated partial thromboplastin time, and platelet aggregation. It was shown that the modified polysaccharide does not affect blood coagulation (at concentrations of 0.033 and 2.22 mg/mL), plasma coagulation (at concentrations up to 0.0465 mg/mL), and platelet aggregation (at concentrations up to 0.182 mg/mL).

The possibility of using water-soluble heteronuclear metallamacrocyclic complexes of Sr(II)–Cu(II), Ca(II)–Cu(II), and La(III)–Cu(II) as crosslinking agents for alginate hydrogels has been investigated for the first time. The possibility of ion-induced crosslinking of alginate with metallacrown cations has been experimentally demonstrated. Alginate hydrogel microspheres have been prepared via extrusion, using the metallacrowns as crosslinking agents. The degree of cross-linking of the hydrogels depends on the nature of the central element of the metallacrown. In terms of their crosslinking ability, the considered metallacrowns (MC(M)) are arranged in the following series: MC(La) > MC(Sr) > MC(Ca).