Kateryna Fatyeyeva

Deep impact of the template on molecular weight, structure, and oxidation state of the formed polyaniline.

In this work we find that polyaniline (PANI), synthesized by aniline chemical polymerization at a surface of template polycarbonate (PC) particles, is significantly different in molecular weight, structural order, oxidation state, and conductivity from a neat PANI. Molecular weight of the PANI phase in the composite (Mw = 158,000) is 1.6 times higher than that of the neat PANI synthesized in the absence of the template particles. Moreover, XRD analysis shows that crystallinity of the PANI phase in the composite is three times higher than that of the neat PANI. Raman spectroscopy indicates that the oxidation level of PANI in the PC/PANI composite is lower than that of the neat PANI. These noticeable changes of the PANI phase properties suggest specific interactions of reagents in the polymerization medium and formed PANI with the template phase as well as an orientation effect of the latter surface. FTIR spectroscopy reveals that hydrogen bonding in the neat doped PANI is weaker than one between -NH- of PANI and C═O of PC at their interface. The discovered differences are supported by the fact that conductivity of the PANI phase in the composite is more than three times higher than that of the neat PANI.

Effect of cold plasma treatment on surface properties and gas permeability of polyimide films

The surface functionalization of polyimide (Matrimid® 5218) films was carried out by cold plasma treatment with CF4, N2 and O2 gases using a radio frequency discharge and the optimum plasma conditions were evaluated by water contact angle measurements. The surface hydrophobicity of polyimide films was obtained after CF4 plasma treatment, while O2 and N2 plasma treatments contributed to the hydrophilic surface functionalization. X-ray photoelectron spectroscopy (XPS) results revealed the presence of CFx, amino or oxygen-containing groups attached to the polyimide film surface depending on the treatment gas. A strong influence of the used plasma gas on the film roughness was determined by atomic force microscopy (AFM) measurements. The influence of the surface modification on CO2, N2 and O2 gas permeation through the plasma treated films was evaluated. The permeation behaviour was characterized in terms of transport parameters, namely, coefficients of permeability, diffusion and solubility. The permeability coefficient of all plasma treated polyimide films for the studied gases (CO2, N2 and O2) was found to decrease following the order of increasing the kinetic molecular diameter of the penetrant gas. Besides, the selectivity coefficient was found to be significantly increased after the plasma treatments – αCO2/N2 was increased up to 36% and 98% for O2 and N2 plasma treated Matrimid® 5218 films, respectively. The relationship between the gas permeation behaviour and the surface modification of polymer film by cold plasma was discussed.

Application of the Maxwell–Wagner–Hanai effective medium theory to the analysis of the interfacial polarization relaxations in conducting composite films

A new approach to explain the interfacial polarization phenomenon in conducting composite films is proposed. HCl-doped poly(ethylene terephthalate) (PET) and polyamide-6 (PA-6) matrices with embedded polyaniline (PANI) particles as filler were investigated and analysed, combining dielectric spectroscopy and AFM electrical images with the effective medium theory analysis. Up to three relaxation peaks attributed to the interfacial polarization phenomena were detected in the studied frequency range (0.1 Hz–1 MHz). The AFM electrical images revealed that the doped PA-6/PANI composite can be modelled as a single-type particle medium and the PET/PANI one as a two-type particle medium. A simple dielectric loss expression was derived from the Maxwell–Wagner–Hanai mixture equation and was applied to the experimental data to identify the interfaces involved in each of the relaxation peaks. The parameter values (permittivity, conductivity, volume fraction of the PANI particles) were found to agree well with the measured one, hence validating the models.

Application of polymer-based membranes containing ionic liquids in membrane separation processes: a critical review

Abstract The interest in ionic liquids, particularly in polymerizable ionic liquids, is motivated by their unique properties, such as good thermal stability, negligible vapor pressure, and wide electrochemical window. Due to these features ionic liquids were proposed to be used in the membrane separation technology. The utilization of conventional ionic liquids is, however, limited by their release from the membrane during the given separation process. Therefore, the incorporation of polymerizable ionic liquids may overcome this drawback for the industrial application. This work is a comprehensive overview of the advances of ionic liquid membranes for the separation of various compounds, i.e. gases, organic compounds, and metal ions.

Impact of hydrophobic plasma treatments on the barrier properties of poly(lactic acid) films

Different hydrophobic plasma treatments (CF4, CF4/H2, CF4/C2H2, tetramethyl silane (TMS)) were applied to the poly(lactic acid) (PLA) film in order to improve its water and oxygen barrier properties. The plasma parameters, such as power, gas flow and treatment time, were optimized according to the water contact angle measurements. X-ray photoelectron spectroscopy measurements revealed the presence of either fluorine (CF, CF2, CF3) or silicon (SiOxCy) functional groups on the film surface after the fluorinated or TMS plasma treatments, respectively. The thermal properties of the treated PLA films were studied by means of the differential scanning calorimetry (DSC) measurements and were found not to be influenced by the plasma treatment. The water permeability measurements showed an improvement of the PLA barrier properties as a result of all plasma treatments used and, particularly, after CF4/C2H2 plasma. The water vapour sorption measurements confirmed well the improvement of the water barrier properties by the reduction of the water solubility. No impact of the plasma treatment on the oxygen barrier properties of the PLA film was observed, even at high relative humidity (up to 90%).

Ab initio study of cationic polymeric membranes in water and methanol

The work is devoted to a computational study of three types of cationic polymeric membranes in Li+-ionic form, in water and methanol environments, at various solvation levels. The studied membranes Nafion, IonClad, and M3 possess the perfluorinated backbone; however, various side chains were terminated with the functional groups of distinctly different ionic strength. The paper discusses the structural features of the membrane-solvent clusters as well as an influence of the side chain nature on the dissociation of the functional groups and the binding energy of the solvent molecules. Additionally, the paper compares the obtained results for Li+-Nafion membrane in water with the results published earlier for H+ and Na+ forms.

Water sorption properties of room-temperature ionic liquids over the whole range of water activity and molecular states of water in these media

The water sorption behavior for various RTILs ([C4C1im][BF4], [C4C1im][PF6], [C6C1im][PF6], [C4im][DBP], [C4im][BEHP] and [Et3HN][CF3SO3]) was studied over the whole range of water activity using a continuous gravimetric method. Analysis of the water sorption isotherms using the non-random two-liquid model (NRTL) and the combination of a dual-mode sorption (Henry-clustering) allowed a better understanding of the RTIL-water interactions. It is noticed that the sorption of water by RTILs is mainly controlled by the anions nature. Anions interact with water molecules by hydrogen bonds that promotes the formation of a hydrogen bond network between the water molecules. The water uptake by RTILs increases in the following order (up to 0.8 in the water activity a): [C6C1im][PF6] ≤ [C4C1im][PF6] 0.8), water molecules are aggregated only in water-miscible RTILs (case of [C4im][DBP] and [Et3HN][CF3SO3]) because of their stronger anion basicity. To complete the sorption study, the molecular state of water dissolved in RTILs was studied by the infrared spectroscopy. The water molecules dissolved in water-immiscible RTIL such as [C4C1im][PF6] are not self-associated independently of the water content and, thus, can be defined as “free” water molecules interacting via H-bonding with the anions in the symmetric complex: anion⋯HOH⋯anion. On the contrary, the water molecules sorbed in water-miscible RTILs such as [C4im][DBP] or [Et3HN][CF3SO3] are strongly associated by H-bonds and also with the anions even at low water activity, and are easily aggregated when the water content reaches the critical concentration at high activity.

Hydrophobic surface treatments of sunflower pith using eco-friendly processes

The aim of the present paper is to report the reduction of the water uptake of sunflower pith, sustainable raw by-product without current added-value in oilseed crops production. The water-sensitivity is ascribed to its structure, because mainly constituted of carbohydrates, due to the formation of additional hydrogen bondings with water molecules. Two environmentally-friendly approaches were applied to provide a modified layer presenting water resistance in surface of sunflower pith in order to keep its low-density property. The first approach based on vegetable oil corresponds to thermal and photochemical treatments. A thin layer of virgin or acrylated epoxidized soybean oil was sprayed on the pith surface, and thereafter was thermally cured or photocured, respectively. The second approach consisted in a solventless chemical modification of the pith surface by a cold plasma treatment. Both approaches were successfully performed: water resistance of sunflower pith was clearly enhanced, especially with oil-based treatments; while maintaining its integrity. Developing new and promising ecological water-resistant products of low density from sunflower pith is thought of increasing interest with potential practical applications.

New Polyimide Based Composite Films for Fuel Cells: Study of the Porous Structure

New porous polyimide films were elaborated by vapor induced phase separation process. The influence of different parameters such as the nature of the solvent, the molecular weight of the porous agent, and relative humidity on the structure of the film was investigated. It was shown that the porous film prepared from NMP presents the most original morphology with micro-and nanopores. Moreover, such structure is only obtained when the porous agent used has a high molecular weight. The synthesized porous film was swelled in protic ionic liquid for fuel cell application. The performed conductivity measurements as a function of temperature have shown that the conductivity of the impregnated polyimide film increases when the temperature rises up to 150 °C following Arrhenius behavior.

The Effect of Reactive Ionic Liquid or Plasticizer Incorporation on the Physicochemical and Transport Properties of Cellulose Acetate Propionate-Based Membranes

Pervaporation is a membrane-separation technique which uses polymeric and/or ceramic membranes. In the case of pervaporation processes applied to dehydration, the membrane should transport water molecules preferentially. Reactive ionic liquid (RIL) (3-(1,3-diethoxy-1,3-dioxopropan-2-yl)-1-methyl-1H-imidazol-3-ium) was used to prepare novel dense cellulose acetate propionate (CAP) based membranes, applying the phase-inversion method. The designed polymer-ionic liquid system contained ionic liquid partially linked to the polymeric structure via the transesterification reaction. The various physicochemical, mechanical, equilibrium and transport properties of CAP-RIL membranes were determined and compared with the properties of CAP membranes modified with plasticizers, i.e., tributyl citrate (TBC) and acetyl tributyl citrate (ATBC). Thermogravimetric analysis (TGA) testified that CAP-RIL membranes as well as CAP membranes modified with TBC and ATBC are thermally stable up to at least 120 °C. Tensile tests of the membranes revealed improved mechanical properties reflected by reduced brittleness and increased elongation at break achieved for CAP-RIL membranes in contrast to pristine CAP membranes. RIL plasticizes the CAP matrix, and CAP-RIL membranes possess preferable mechanical properties in comparison to membranes with other plasticizers investigated. The incorporation of RIL into CAP membranes tuned the surface properties of the membranes, enhancing their hydrophilic character. Moreover, the addition of RIL into CAP resulted in an excellent improvement of the separation factor, in comparison to pristine CAP membranes, in pervaporation dehydration of propan-2-ol. The separation factor β increased from ca. 10 for pristine CAP membrane to ca. 380 for CAP-16.7-RIL membranes contacting an azeotropic composition of water-propan-2-ol mixture (i.e., 12 wt % water).