Pavel Geydt

Structure and Transport Properties of Mixed-Matrix Membranes Based on Polyimides with ZrO2 Nanostars

Mixed-matrix membranes based on amorphous and semi-crystalline polyimides with zirconium dioxide (ZrO2) nanostars were synthesized. Amorphous poly(4,4′-oxydiphenylenepyromellitimide) and semi-crystalline polyimide prepared from 1,4-bis(4-aminophenoxy)benzene and 4,4’-oxydiphthalic anhydride were used. The effect of ZrO2 nanostars on the structure and morphology of nanocomposite membranes was studied by wide-angle X-ray scattering, scanning electron microscopy, atomic force microscopy, and contact angle measurements. Thermal properties and stability were investigated by thermogravimetric analysis and differential scanning calorimetry. Transport properties of hybrid membranes containing 5 wt % ZrO2 were tested for pervaporation of a mixture of butanol–water with 10 wt % H2O content. It was found that a significant amount of the ZrO2 added to the semi-crystalline polyimide is encapsulated inside spherulites. Therefore, the beneficial influence of inorganic filler on the selectivity of mixed-matrix membrane with respect to water was hampered. Mixed-matrix membranes based on amorphous polymer demonstrated the best performance, because water molecules had higher access to inorganic particles.

Surface selective removal of xylan from refined never-dried birch kraft pulp

In this study, the effect of enzyme treatment on refined, never-dried bleached birch kraft pulp was investigated, using an endo-1,4-β-xylanase, that is substantially free from cellulase activity. The xylanase treatment of refined never-dried pulp revealed a rapid initial hydrolysis rate with a time-dependent saturation level in the amount of hydrolyzed pulp carbohydrates. Surprisingly short xylanase treatment times were found to have an impact on the fiber surface structure and on the physicochemical properties of kraft pulp fibers. Xylanase treatment led to mild microscopic differences in the ultrastructure of a never-dried fiber, whereas local topographical differences were distinguishable with atomic force microscopy. Results from the analysis of dissolved carbohydrates and the interfacial properties of the xylanase-treated never-dried fibers thus confirm a selective removal of xylan from the fiber surfaces. The zeta-potential charge and dewatering properties of the pulp slurry, fiber morphology, and strength properties of the paper were affected, which is a concomitant of xylanase treatment. However, the papermaking properties of the fibers were mainly preserved with simultaneous improvement in the dewatering rate of the pulp. Thus, optimized xylanase treatment of refined bleached kraft pulp provides a fiber for papermaking or fiber modification purposes with a selectively modified chemical composition of the fiber surface layer.

Influence of Annealing on the Surface Topography and Magnetic Properties of Thin Films of the FINEMET-Type Alloy

Surface structure and magnetic properties of thin films of the FINEMET-type alloy modificated by Mo (FeCuNbSiBMo) were studied in the aim of establishing of their dependence on heat treatment conditions. The thicknesses of the films were varied from 10 to 800 nm. Dependence of the microstructure of the films surface on the annealing temperature was analyzed using scanning probe microscopy. Parameters of the topography features were estimated as a function of the films thickness and annealing temperature. Magnetic hysteresis loops were measured using vibrating sample magnetometer and discussed in the focus of surface and thickness influences.

Direct measurement of elastic modulus of InP nanowires with Scanning Probe Microscopy in PeakForce QNM mode

In this manuscript, we present the study of elastic properties of InP nanowires with help of scanning probe microscope in advanced PeakForce Tapping® regime. The measuring method was developed in order to investigate the Youngs modulus of these cone-shaped structures with significant accuracy. The difference in InP elasticity for wurtzite phase and zinc- blende phase was revealed. It was shown that elastic modulus of InP nanowires significantly increases from 60 GPa to more than 100 GPa when diameter of a nanowire is reduced below 50 nm. The core-shell model for InP nanowire was used for the explanation of this effect.

Inkjet ink spreading on polyelectrolyte multilayers deposited on pigment coated paper

Mechanisms of inkjet ink spreading and absorption on a coated paper have been studied using a polyelectrolyte multilayering technique. By applying alternating sequences of cationic and anionic polyelectrolyte layers on a mineral coated paper, the role of the interfacial chemistry was evaluated. The polyelectrolyte multilayer was created to imitate a thin resin-like liquid-absorptive layer and to clarify the role of the charge of the protruding polyelectrolyte layer on ink spreading and colorant fixation. The formation of a thin polyelectrolyte layer and coating coverage was confirmed by X-ray photoelectron spectroscopy (XPS). A submolecular mechanical imaging of the polyelectrolyte complexes with an atomic force microscope (AFM) revealed differences in modulus and different nanosize agglomerates were identified which were ascribed to polyion complexes. The polyelectrolyte coatings significantly affect the solid-liquid interaction and particularly the ink spreading revealed as intercolor bleeding and wicking. The interfacial interaction between the ink and the applied polyelectrolyte layers showed differences between dye- and pigment-based colorants, which could be emphasized by the polyelectrolyte chemistry.

Corona Treatment of Filled Dual-polymer Dispersion Coatings: Surface Properties and Grease Resistance

Dispersion coating layers consisting of hydroxypropylated starch, 0–30 pph of barrier-grade talc and 0–10 pph of styrene-butadiene latex were subjected to both positive and negative direct-current corona treatments utilizing a specially developed dynamic treatment unit. The effects of the surface composition (barrier coating) on the response to the direct current corona treatment were evaluated by measuring contact angles and determining the surface energy. The effects of corona treatment on the properties of the barrier coating were further determined by measuring the contact angle of rapeseed oil and the grease resistance. It was found that the grease resistance of the corona-treated barrier coatings was substantially lower than that of untreated samples, which was ascribed to holes caused by corona discharge strike-through and to chemical changes on the treated surfaces. The corona treatment lowered the surface energy of the coatings, as indicated by an increase in the contact angles of water and rapeseed oil. Changes in the dispersion part of the surface energy were recorded, particularly after positive treatment voltage, whereas a negative discharge led to greater changes in the polar part of the surface energy. X-ray photoelectron spectroscopy (XPS) tests revealed an increase in the proportion of talc at the surface after corona treatment, which indicates a migration caused by the applied electric field. The peak force tapping mode of an atomic force microscope revealed moderate topographical changes in the coatings and a decrease in surface elasticity, supporting the migration of talc particles. In addition, significant changes in the physicochemical properties of the untreated reverse side were observed.

Structure of Composite Based on Polyheteroarylene Matrix and ZrO2 Nanostars Investigated by Quantitative Nanomechanical Mapping

It is known that structure of the interface between inorganic nanoparticles and polymers significantly influences properties of a polymer–inorganic composite. At the same time, amount of experimental researches on the structure and properties of material near the inorganic-polymer interface is low. In this work, we report for the first time the investigation of nanomechanical properties and maps of adhesion of material near the inorganic-polymer interface for the polyheteroarylene nanocomposites based on semi-crystalline poly[4,4′-bis (4″-aminophenoxy)diphenyl]imide 1,3-bis (3′,4-dicarboxyphenoxy) benzene, modified by ZrO2 nanostars. Experiments were conducted using quantitative nanomechanical mapping (QNM) mode of atomic force microscopy (AFM) at the surface areas where holes were formed after falling out of inorganic particles. It was found that adhesion of AFM cantilever to the polymer surface is higher inside the hole than outside. This can be attributed to the presence of polar groups near ZrO2 nanoparticle. QNM measurements revealed that polymer matrix has increased rigidity in the vicinity of the nanoparticles. Influence of ZrO2 nanoparticles on the structure and thermal properties of semi-crystalline polyheteroarylene matrix was studied with wide-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry.

GaAs Wurtzite Nanowires for Hybrid Piezoelectric Solar Cells

The properties of the hybrid energy sources “piezoelectric nanogenerator-solar cell” based on GaAs nanowires with the wurtzite crystal structure were investigated. Measurements were performed by the bending of the nanowire by the probe of the atomic force microscope with simultaneous recording of short circuit current in dark and illuminated conditions. We show that a piezoelectric current pulse of ~10 pA arises in the “nanowire-probe” circuit during the deformation of nanowire by the AFM probe. Under laser illumination, the value of the pulse increases by two orders of magnitude as a result of the piezophototronic effect. Deformation of the nanowire boosts the photocurrent by 40% up to 0.5 nA.

Plasticizing of chitosan films with deep eutectic mixture of malonic acid and choline chloride

Chitosan (CS) films containing deep eutectic solvent (DES) based on malonic acid (MA) and choline chloride (ChCl) were successfully prepared by solution casting method by using DES content ranging from 0 to 82 wt%. A strong interaction of CS with the components of DES was demonstrated by analyses of water sorption isotherms, atomic force microscopy and FTIR results. The plasticizing effect of the MA and ChCl mixture on the CS matrix was shown by static bulk mechanical measurements, thermal analysis and quantitative nanomechanical mapping (QNM). Elongation at break increased from 3 to 62% at increase of DES content from 0 to 67 wt%, while further increase of DES content led to the decreasing of maximal elongation. Introduction of DES into CS films led to the appearance of glass transition temperature in the region +2 - -2.3 °C. QNM results indicated homogeneity of the films containing up to 75 wt% of DES.

I-V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

The control of nanowire-based device performance requires knowledge about the transport of charge carriers and its limiting factors. We present the experimental and modeled results of a study of electrical properties of GaAs nanowires (NWs), considering their native oxide cover. Measurements of individual vertical NWs were performed by conductive atomic force microscopy (C-AFM). Experimental C-AFM observations with numerical simulations revealed the complex resistive behavior of NWs. A hysteresis of current-voltage characteristics of the p-doped NWs as-grown on substrates with different types of doping was registered. The emergence of hysteresis was explained by the trapping of majority carriers in the surface oxide layer near the reverse-biased barriers under the source-drain current. It was found that the accumulation of charge increases the current for highly doped p+-NWs on n+-substrates, while for moderately doped p-NWs on p+-substrates, charge accumulation decreases the current due to blocking of th...