Casting aqueous solutions of certain water-soluble polymers with heteropolyacids (cluster compounds of early-transition metal oxides) gives photochromic nanocomposites that are currently attracting considerable attention as functional materials for inkless and erasable printing, sensors, smart windows. Here, with the goal of improving the performance of such nanocomposites in these applications, effects of low-volatile polyol co-solvent (ethylene glycol, EG) addition to aqueous poly(vinyl alcohol)-heteropolyacid (PVA-HPA) solutions on the photochromic response of PVA-HPA nanocomposite films cast from these solutions are investigated. The main and unexpected finding of this study is that although the films from EG-containing solutions are EG free (due to its complete evaporation from the films during drying) and thus compositionally identical to those from solutions without EG, their photochromic efficiency increases (up to 50

The effects of glycerol (GL) addition on the coloration and bleaching of photochromic poly(vinyl alcohol)tungstophosphoric acid nanocomposite films were studied at GL concentrations (CGL) 2.1-33 wt%. A 50 % enhancement of the coloration efficiency was observed at CGL >= 8.3 wt%. The bleaching rate rapidly increased with increasing CGL above 8.3 wt% so that the 33 wt%-GL films were almost completely bleached in several hours while the GL-free films retained their initial color for at least 10 days. This paper represents a simple and effective way of achieving dramatic improvement in the bleaching performance of photochromic polymer-heteropolyacid nanocomposites and simultaneously enhancing their coloration efficiency.

Fluorescent noble metal nanoclusters (NCs) are emerging optical nanomaterials with properties similar to those of quantum dots. Their applications can be expanded by combining them with polymer matrices to obtain flexible and transparent light-emitting nanocomposites. However, achieving highly fluorescent nanocomposites of this type remains challenging due to phase separation and aggregation of NCs in polymer hosts leading to a strong reduction in fluorescence efficiency. We address this key issue by covalently grafting a layer of a specifically selected matrix polymer onto a transparent plastic film and photochemically synthesizing the fluorescent metal NCs directly in the grafted layer. The surface-grafted matrix polymer effectively captures the noble metal (Ag) ions, photo-reduces them to atoms, acts as a capping ligand for the growing Ag NCs, and immobilizes them on the substrate surface. The Ag NCs were produced by both wet and dry synthesis, and effects of synthesis method, reaction time, and matrix polymer layer thickness on the fluorescence properties of the resulting nanocomposites were investigated and discussed. Importantly, the fluorescence intensity of these nanocomposite films is sensitive to submicromolar concentrations of aqueous Hg2+ that makes them useful as fluorescent sensing materials for selective and ultrasensitive detection of Hg2+ ions in water. Besides, the nanocomposite films obtained by the dry synthesis of NCs exhibit an intensive emission covering the whole green to red range of the visible spectrum and, hence, produce bright white light under illumination with a blue LED that makes them attractive as down-conversion materials in one-phosphor-converted white LEDs.

Poly(vinyl alcohol) (PVA)-phosphotungstic acid (PTA) nanocomposite films were prepared from aqueous solutions with added ethylene glycol (EG), which is a plasticizer for PVA and contains OH groups, capable of being electron donors in the photoreduction of PTA. Spectroscopic studies have shown that the addition of EG significantly enhances the photochromic properties of the resultant nanocomposites due to photoinduced electron transfer from the organic matrix of the nanocomposite to PTA molecules.

A detailed analysis of the previously discovered effect of the concentration of phosphotungstic acid (PTA) on its reduction within nanocomposite films with poly(vinyl alcohol) (PVA) induced by gamma radiation indicated that the molar absorption coefficient of the maximum of the PTA band due to intervalence charge transfer in reduced PTA heteropolyanions at low PTA concentrations is eight times higher than at high concentrations. Only 20

Ultracompact (~300 g) fluorescence LIDAR is developed to be installed on a small drone for remote sensing of agricultural fields. The LIDAR is based on a diode laser (405 nm, 150 mW) and a mini spectrometer allows reducing the device sizes and power consumptions for its placing on small aircraft drones. For field testing, the LIDAR was placed on a quadcopter for remote sensing of plants in maize field. Field testes proved the feasibility and perspectives of autonomous LIDAR sensing from drones for early detection and field locations with plants under stress.

Coloration of polyvinyl alcohol–phospho-tungstic acid (PVAPTA) films by gamma radiation was studied at different concentrations of PTA. It was found that at a minimum concentration (1%), the coloration of the films occurs as a result of radiation-induced two-electron reduction of the heteropolyanion, while one-electron reduction takes place at high concentration (≥20%). In the intermediate concentration range, the fraction of PTA heteropolyanions reduced by two electrons decreases with a concurrent increase in the fraction of one-electron-reduced anions.

Radiochromic films composed of polymer matrices and organic dyes are widely used for routine dosimetry purposes in operation of various radiation facilities-gamma and X-ray-irradiation, electron accelerators, and so on. However, the sensitivity of these films rapidly decreases at doses exceeding 30-50 kGy due to a saturation of their optical response, making them unsuitable for accurate dosimetry in radiation processing of polymers and composites where doses up to 200 kGy are typically employed. To overcome this limitation, the use of inorganic substances as the coloring agents of polymer-based radiochromic films was proposed in this paper, specifically, heteropolyacidacid H3PW12O40 (tungstophosphoric acid) in the matrix of poly(vinyl alcohol) (PVA). Nanocomposite PVA/H3PW12O40 films were prepared by solution casting and their optical responses toward Co-60 gamma radiation and beams of 6 MeV electrons for a dose range of 10-200 kGy were investigated. It was established that upon exposure to gamma rays and electron beams, the films turn blue and a broad absorption band at 750 nm appears in their spectra. Importantly, the radiation-induced optical absorption increases in a linear fashion up to the dose of 150 kGy and only slightly deviates from linearity at 200 kGy. Moreover, it was found that the PVA/H3PW12O40 films have a long shelf life, are dose-rate independent within a wide range, and color-stable after irradiation. All these features make the nanocomposite PVA/H3PW12O40 films promising for use as routine dosimeters and dose labels in a much wider range of high doses as compared to radiochromic films based on organic dyes.

Flexible SERS substrates were obtained by the photo-activated synthesis of silver nanoparticles in a thin (10–170 nm) layer of poly(acrylic acid) chemically grafted to the surface of a polypropylene fi lm. The plasmonic absorption and the SERS activity of the substrates were studied as a function of the thickness of the grafted layer for a fixed time of nanoparticle synthesis. The results indicate dense three-dimensional packing of plasmonic nanoparticles in the grafted polymer layer. The substrates have a storage-stable and surface-uniform SERS activity.

We report on a new type of poly(vinyl alcohol)(PVA)-based dichroic polarizing films whose visible dichroism is due to long-chain linear polyenes, –(CH=CH) n –, formed in the course of acid-catalyzed thermal dehydration of the polymer. The distinguishing feature of these films is that the solid acid catalyst (12-tungstophosphoric acid, TPA) is used instead of the liquid ones. Thin PVA films with embedded TPA nanoparticles were fabricated by solution casting technique. Subsequent stretching and annealing of these PVA/TPA nanocomposites produced PVA–polyene/TPA dichroic polarizing films with the thickness below 10 µm. Transmission electron microscopy, Fourier-transform infrared spectroscopy, and UV–Vis spectroscopy techniques were used to characterize the films at various stages of preparation. The fabricated polarizing films showed polarization efficiency exceeding 94% and transmittance higher than 40% in the visible range. The polarizing properties of the films did not deteriorate upon prolonged exposures to hot humid air (60 °C, 90% RH) and high temperature (90 °C). The nanocomposite polarizing film proposed in this study may have application potential in thin and flexible optoelectronic devices that must operate under harsh environmental conditions.

Films obtained from the aqueous solutions of poly(vinyl alcohol) and MX salts, where M = Li, Na, K, and Cs and X = Cl, Br, and I (salt concentration is 10 mol % in relation to the polymer) are studied by Fourier transform infrared spectroscopy. It is shown that the degree of crystallinity of PVA films containing non-lithium salts is higher by a factor of 1.5 than that of the film without salt (51–57 and 37%, respectively), while films with lithium salts contain an almost completely amorphous polymer (0–7%). It is shown that lithium salts completely dissolve in the polymer, while the non-lithium ones exhibit only a partial dissolution. Salt addition leads to the shift of maximum of the band corresponding to the stretching vibrations of PVA hydroxyl groups. Direction and value of the shift depend on the size of anion and cation of the added salt. This fact is explained by the breakage of ОН···ОН hydrogen bonds and formation of OH···Х– bonds and donor-acceptor M+···OH bonds between ions of salts and ОН groups of the polymer. These bond strengths decrease in the sequence Cl– > Br– > I– and Li+ > Na+ > K+ > Cs+. A high solubility of lithium salts in PVA and the suppression of its crystallization by these salts are provided by a high affinity of the oxygen atom of ОН group of the polymer for the lithium ion.

Fluorescent silver nanoclusters immobilized on a plastic substrate are obtained by photoinduced template synthesis using polyacrylic acid chemically grafted to the substrate surface as a template. The electronic absorption and fluorescence spectra of nanoclusters are studied depending on the polyacrylic acid grafting density. It is found that the optical absorption and fluorescence intensities of nanoclusters monotonically increase with increasing grafting density. The position and shape of the absorption and emission spectra almost do not change. The higher the polymer template grafting density, the higher the fluorescence stability of samples during storage at room temperature.

AbstractFluorescent silver nanoclusters immobilized on a plastic substrate are obtained by photoinduced template synthesis using polyacrylic acid chemically grafted to the substrate surface as a template. The electronic absorption and fluorescence spectra of nanoclusters are studied depending on the polyacrylic acid grafting density. It is found that the optical absorption and fluorescence intensities of nanoclusters monotonically increase with increasing grafting density. The position and shape of the absorption and emission spectra almost do not change. The higher the polymer template grafting density, the higher the fluorescence stability of samples during storage at room temperature.

A microfiber carboxylic cationite is prepared via the photoinduced polymerization of acrylic acid on the surface of nonwoven polypropylene material. Changes in the amount of the graft polymer (grafting density) and in the strength of hydrogen bonds between its carboxyl groups, depending on the polymerization time, are investigated by attenuated total internal reflectance FTIR spectroscopy. The sorption properties of the obtained ionite in the acidic (COOH) and salt (COONa) forms with respect to Zn2+ ions at various grafting densities are studied. The sorption capacity of the investigated cationite in its salt form is higher than that in the acidic form, and this difference increases quickly with the grafting density. The data of IR spectroscopy showed that this behavior is caused by the formation of stronger hydrogen bonds between COOH groups of the grafted polyacrylic acid, complicating their ionization and, thus, preventing the ion exchange.

Получен микроволокнистый карбоксильный катионит путем фотоиндуцированной прививочной полимеризации акриловой кислоты на поверхности нетканого материала из полипропилена. Методом ИК-фурье-спектроскопии нарушенного полного внутреннего отражения исследовано изменение количества привитого полимера (плотности прививки) и водородных связей между его карбоксильными группами в зависимости от времени полимеризации. Изучены сорбционные свойства полученного ионита в кислой (СООН) и солевой (СООNa) формах по отношению к ионам Zn2+ при различной плотности прививки. Сорбционная емкость исследуемого катионита в солевой форме выше, чем в кислой, причем это различие быстро усиливается с ростом плотности прививки. При помощи данных ИК-спектроскопии выявлено, что такое поведение обусловлено образованием более сильных водородных связей между группами СООН привитой полиакриловой кислоты при увеличении плотности прививки, что затрудняет ионизацию этих групп и, соответственно, препятствует ионному обмену.

The degree of crystallinity of poly(vinyl alcohol) in cryogels obtained by single freezing at–20°С followed by thawing of 13% aqueous solutions of the polymer bearing dissolved NaCl, KCl, CsCl, KBr, and KI in the concentration of 0.7 mol/kg is determined by attenuated total reflectance Fourier transform IR spectroscopy. It is established that the addition of NaCl, KCl, and CsCl to the poly(vinyl alcohol) solution leads to a substantial increase (by 1.5–1.7 times) in the degree of crystallinity in the cryogel prepared from this solution. The effect of KCl, KBr, and KI on the degree of crystallinity strongly depends on the salt anion. The replacement of the Cl– anion by the larger Br– anion reduces dramatically the crystallizing effect of the salt, while the even larger I– anion, in contrast, reduces rather than increases the degree of crystallinity relative to that of the cryogel without a salt. The effect of the salts on the crystallinity of poly(vinyl alcohol) cryogels is explained by the simultaneous action of two processes. One of them facilitates crystallization and consists in the strengthening of dehydration of poly(vinyl alcohol) owing to competition between the polymer molecules and the salt ions for the liquid water molecules during its freezing. The other process hampers crystallization and is connected with a reduction in the water freezing point under action of the salt ions.

Physics, Chemistry and Application of Nanostructures, pp. 327-330 (2017) No AccessFLUORESCENT SILVER NANOCLUSTERS IRREVERSIBLY BOUND TO PLASTIC SUBSTRATESA. A. Gorbachev, T. M. Sheypak, P. P. Pershukevich, and O. N. TretinnikovA. A. GorbachevB. I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, Minsk 220072, Belarus, T. M. SheypakB. I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, Minsk 220072, Belarus, P. P. PershukevichB. I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, Minsk 220072, Belarus, and O. N. TretinnikovB. I. Stepanov Institute of Physics NASB, Nezavisimosti Ave. 68, Minsk 220072, Belarushttps://doi.org/10.1142/9789813224537_0076Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: A method for the preparation of fluorescent Ag nanoclusters (NCs) irreversibly bound to the surface of a plastic substrate is described. It consists in surface functionalization of the plastic substrate with chemically end-grafted poly(acrylic acid) (PAA) followed by photo-activated template synthesis of Ag NCs in the grafted polymer. The surfaceimmobilized Ag NCs show bright visible fluorescence with intensity and wavelength dependent on the surface density of PAA template and on the time of NCs synthesis. FiguresReferencesRelatedDetails Physics, Chemistry and Application of NanostructuresMetrics History PDF download

The Raman spectra of polyvinyl alcohol-potassium thiocyanate polymer films are studied. The parameters of the vibrational and orientational relaxation of thiocyanate ion in the polymer matrix are determined. At salt concentrations c > 0.3, the character and velocity of the vibrational dephasing and orientational relaxation become identical to the vibrations of SCN ion in the aqueous solution.