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Interfacial bonding in a CdS/PVA nanocomposite: A Raman scattering study
... These vibration modes are activated depending on the excitation wavelength applied to the samples. In this work a green laser with Rocking deformation of the acetyl C-H J Mater Sci a wavelength of 532 nm was used to activate six of its vibrations, which will be discussed below [15]. Figures 3 shows the Raman spectra of the samples in the region between 50 and 3000 cm −1 . ...
... Similar features were also observed for the above band in the FTIR measurements. The other vibrations that do not exhibit a considerable change in their intensities are listed in Table 2 [15][16][17]. ...
In this work, the effect of lithium hydroxide (LiOH) amalgamation on the properties of polyvinyl alcohol thermoplastic membranes, obtained by the solvent casting method, is presented. FTIR and Raman spectroscopy show the effect of on vibrations of C=O, C–O and O–H functional groups. Moreover, DRX analysis confirmed the semi-crystalline nature of the samples. The density functional theory indicates an insulator–metal transition due to the lithium incorporation in the polymer. Moreover, the formation energy and structural properties have also been calculated to understand the PVA–Li interaction. The complex impedance study at room temperature indicates an improvement in the resistance values of the membranes, with the increase of the lithium content, up to 7% of (7 * 102 Ω). The results reveal the importance of this type of material as candidates in solid-state electrolytes.
... First, the broad peak around 3400-3200 cm −1 , associated with the OH stretching present greater intensity in the membranes of 6-0-0 and 6-5-0, but even more intensity in the EEHP-added membranes. This behavior can be related with the increment of the stretching vibrations due to the hydroxyl groups of water in the PVA chains [86] and the -NH 2 and -OH groups of the HC and/or the -OH groups from hypericin, hyperforin, or other metabolites from the ethanolic extract, which generates good compatibility in the blended membranes. ...
... Regarding the peak at 1657 cm −1 , in the region of amide I, the samples added with EEHP showed a greater peak, compared with the only-PVA (6-0-0), and even more so in those added with collagen peptides (6-5-8, 6-5-16, 6-5-32; Figure 3c), confirming the presence of these components, since said peak as mentioned is attributed to the stretching of CH into hypericin and hyperforin and to the characteristic peak region of Amide I. Other intensity changes in the peak at 831 cm −1 indicate greater stretching vibration due to the presence of benzene rings, which even suggests a good compatibility between the components used [77,86]. ...
Biological, physicochemical, structural, and thermal properties of PVA-based electrospun wound dressings added with hydrolyzed collagen (HC) and different concentrations of Hypericum perforatum ethanolic extract (EEHP) were studied. Membrane characterization was carried out by X-ray diffraction, Fourier infrared spectroscopy, differential scanning calorimetry, barrier properties, scanning electron microscopy, image analysis (diameter and pore size), as well as antimicrobial and anti-inflammatory activities. Results showed that the PVA/HC/EEHP materials, fabricated under controlled conditions of temperature and humidity, generated fiber membranes with diameters between 140–390 nm, adequate porosity and pore size for cell growth (67–90% and 4–16 µm, respectively), and good barrier properties (0.005–0.032 g·m⁻² s⁻¹) to be used in the treatment of conditions on the skin, and was even better than some commercial products. Finally, they showed to have anti-inflammatory (>80%), and antimicrobial activity against S. aureus and S. epiderm. Furthermore, higher crystalline structure was observed according to the EEHP concentration. In addition, this is the first report in which PVA/HC/EEHP membranes are successfully fabricated and characterized.
... A possible reason for that can be the relatively higher oxygen permeability of PVA films, with oxygen being an efficient scavenger of (photoexcited) electrons [4]. Additionally, recent detailed studies of similarly synthesized CdS/PVA NCs assumed an important role of the electronic trap states in the polymer in the PL properties of the NC [15,[52][53][54]. ...
... A more likely reason for the photoenhancement could be an improved crystallinity of the polymer and the NC/polymer interface, as suggested in the DPL photoenhancement study [32] of CdSe/PVA NCs similar to those in our work. In particular, it was suggested that in the NC/PVA composite, the individual functional groups of PVA as well as the fragments of the partially-broken polymer chains can passivate under-coordinated surface atoms of the NCs with the formation of chemical complexes between the -C=O group of the PVA matrix and the Cd 2+ ions on the NC surface [32,53]. However, if the specific bonding were dominant and common to all NC/polymer samples studied in this work, we would observe more similarity in the photoinduced behavior of different in situ and ex situ embedded NCs in the same polymers, on the one hand, and less similarity between similar NCs embedded in different polymers. ...
The environment strongly affects both the fundamental physical properties of semiconductor nanocrystals (NCs) and their functionality. Embedding NCs in polymer matrices is an efficient way to create a desirable NC environment needed for tailoring the NC properties and protecting NCs from adverse environmental factors. Luminescent NCs in optically transparent polymers have been investigated due to their perspective applications in photonics and bio-imaging. Here, we report on the manifestations of photo-induced enhancement of photoluminescence (PL) of aqueous colloidal NCs embedded in water-soluble polymers. Based on the comparison of results obtained on bare and core/shell NCs, NCs of different compounds (CdSe, CdTe, ZnO) as well as different embedding polymers, we conclude on the most probable mechanism of the photoenhancement for these sorts of systems. Contrary to photoenhancement observed earlier as a result of surface photocorrosion, we do not observe any change in peak position and width of the excitonic PL. Therefore, we suggest that the saturation of trap states by accumulated photo-excited charges plays a key role in the observed enhancement of the radiative recombination. This suggestion is supported by the unique temperature dependence of the trap PL band as well as by power-dependent PL measurement.
... It means, these are PVA characteristic peaks. At 2900 cm − 1 , a band corresponding to C-H vibration is observed, and a sharper peak for PVA-5 % LiClO 4 membrane at 1440 cm − 1 , and CH 2 rocking at 920 cm − 1 [17]. Table 2 specifies all the FT-IR and Raman assignments for PVA according to their wavenumbers. ...
This study aims to explore the structural and electrical properties of thermoplastic membranes made of polyvinyl alcohol (PVA) with Lithium Perchlorate (LiClO 4), which were prepared using the solvent evaporation method. The PVA crystalinity were calculated by using the Rietveld method on X-ray diffraction(XDR), thus, it was possible to notice modifications in the unit cell parameters that corresponded to P2 1 /m space group and monoclinic symmetry. Through the application of infrared and Raman spectroscopies, we demonstrate the influence of Li + on the vibrational modes of the polymer's polar group and carbon bonds. Additionally, our complex impedance analysis indicates a decrease in resistance as the salt content increases, reaching a minimum value of 1.4 * 10 3 Ω at a 10 % salt concentration. The applied structural and electrical characterization techniques indicated that PVA-5 % LiClO 4 exhibits the highest crystallinity and electrical conduction among all the membranes studied. Consequently, these findings highlight the promising potential of the synthesized material for further investigation and its possible applications in technological devices.
Water‐based electrolytes provide safe, reliable, and cost‐effective energy storage solutions; however, their application in aqueous lithium‐ion batteries is hindered by low energy density and short cycling life due to the limited electrochemical stability window. While high lithium salt concentrations can mitigate some of these issues, they often lead to increased solvent viscosity and higher costs, limiting commercialization. In this study, a boron‐stabilized anisotropic polyvinyl alcohol (PVA) hydrogel electrolyte, referred to as BaP, is proposed to address the challenges related to high lithium salt (LiTFSI) concentrations. Due to the Hofmeister effect, the BaP water‐in‐polymer electrolyte can retain a high concentration of lithium salt even when low concentrations of lithium salt are used. Briefly, the BaP promotes the salting‐in phenomenon of Li ions, while the TFSI ions induce salting‐out, allowing BaP to synergistically achieve high lithium salt concentrations. Due to these unique characteristics, the BaP hydrogel exhibits a wide electrochemical stability window similar to that of highly concentrated electrolytes, enabling stable operation in a LiMn2O4||Li4Ti5O12 full cell by suppressing hydrogen evolution. Moreover, the biodegradability of BaP contributes to the development of a more environmentally friendly battery system.
Tissue engineering has gained prominence during the past decade since it offers a key solution to defects associated with the tissue regeneration. The limited healing potential of the cartilage tissue damage has significant clinical implications. Herein, dysprosium (Dy3+) impregnated polyvinyl alcohol (PVA) hydrogels have been developed to enhance the therapeutic efficacy, enabling simultaneous diagnostic imaging and antibacterial drug delivery for potential applications in articular cartilage. Based on the favorable imaging features, Dy3+ impregnated PVA hydrogels with enhanced stability were formed through successive steps of repeated cycles of freezing at - 30 °C for 21 h, thawing at 25 °C for 4 h and lyophilization. The tensile and compression tests of the hydrogels respectively determined a maximum of 3.88 and 1.58 MPa, which reflected better compatibility towards cartilage. The hydrogels fetched a sustained drug release for a period of 12 h with an associated swelling ratio of 80%. The potential of the resultant hydrogels in image diagnosis has been deliberated through their blue and yellow emissions in the visible region. Further, the computed tomography (CT) and magnetic resonance imaging characteristics of the hydrogels respectively accomplished a maximum of 343 Hounsfiled units (HU) and relaxivity of 7.25 mM-1s-1. The cytocompatibility of the hydrogels is also determined through in vitro tests performed in Murine pro B cell line (BA/F3) and human Megakaryocyte cell line (Mo7e) cell lines.
Polymer gels can be effectively applied to plug fractured reservoirs and carbonate cave strata. Herein, polyvinyl alcohol (PVA), acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were used as raw materials to prepare interpenetrating three-dimensional network polymer gels using formation saltwater in the Tahe oilfield (Tarim Basin, NW China) as a solvent. The effect of AMPS concentration on the gelation properties of PVA in high-temperature formation saltwater was analyzed. Further, the effect of PVA concentration on the strength and viscoelastic properties of polymer gel was studied. The polymer gel could retain stable continuous entanglement at 130 °C and exhibited satisfactory thermal stability. Continuous step oscillation frequency tests showed that it exhibited an excellent self-healing performance. Scanning electron microscopy images of the simulated core by gel plugging showed that the polymer gel could firmly fill the porous media, indicating that the polymer gel exhibits excellent application prospects in oil and gas reservoirs under high-temperature and high-salinity conditions.
Hybrid piezo/triboelectric nanogenerators (H‐P/TENGs) are developed to compensate the drawbacks of a single nanogenerator by synergizing high triboelectric output voltage and piezoelectric output current in continuous contact‐separation cycles. In particular, piezoelectric zinc oxide (ZnO) has been widely used due to its excellent orientation along the c‐axis and tunable growth structures. Herein, various growth structures of ZnO, unoriented, oriented, and hierarchical structures, are incorporated in H‐P/TENGs, enhancing their power densities from 6 to 17 times. Particularly, oriented ZnO nanorod/PVA (ZnR) achieves a maximum power density of 15.9 W m⁻² (≈17‐fold increment compared to pristine PVA). The highly oriented ZnO growth along the c‐axis enables large deformation upon a vertical compression, subsequently generating a large piezoelectric polarization. Moreover, the enhancement mechanism via piezoelectric polarization is elucidated using a modified overlapped electron cloud model supported with Kelvin probe force microscopy measurements. The polarization of ZnO nanocomposites enlarges the difference in the highest electron energies (ΔE) between the two triboelectric layers, driving more electrons to transfer during contact electrification, thereby enriching their surface charge densities. This work highlights the significance of growth structure control in maximizing the piezoelectric responses of ZnO, consequently improving the output performances of H‐P/TENGs.
Long‐term wound healing and chronic wound care represent significant challenges for biomaterials science and engineering with many diverse requirements for the wound dressing properties, as well as antibacterial efficacy and antibacterial agent release to prevent and treat persistent infections. Silver nanoparticles, as a wide‐spectrum antibacterial agent that does not induce bacterial resistance, are very convenient for use as an active component in antibacterial hydrogel wound dressing materials with the controlled release ability. In this work, we aim to perform a comprehensive analysis of silver release from poly(vinyl alcohol)‐based hydrogels with electrochemically synthesized antibacterial silver nanoparticles (AgNPs), aimed for wound dressing applications. Different AgNPs concentrations were loaded in hydrogel matrices using the green electrochemical reduction method, and thus synthesized nanocomposite hydrogels were characterized by different techniques (scanning electron microscopy, Fourier‐transform infrared and Raman spectroscopy, and differential scanning calorimetry), in order to assess their physico‐chemical and thermal properties. Silver release was monitored for 28 days in physiologically‐relevant conditions (phosphate buffered medium, pH 7.4, 37°C). The obtained experimental data were evaluated against several theoretical release models (Korsmeyer‐Peppas, Higuchi, Makoid‐Banakar, Kopcha, and early‐time approximation), which confirmed the predominantly diffusion‐controlled mechanism of release. Finally, AgNP‐loaded hydrogels were assessed for antibacterial activity against Staphylococcus aureus TL and Escherichia coli ATCC25922 bacterial strains, to prove their strong potential for wound dressing applications.
In this work, flexible composite membranes of nanoparticles (CuO, ZnO, or both), poly(vinyl alcohol) (PVA), and glycerol (GL) plasticizer are fabricated of for X‐ray detector applications. The nanoparticles are synthesized by a modified solvothermal technique and introduced to PVA + GL solution to fabricate the membranes. The mean sizes of nanoparticles are 10∓4nm and 8∓3nm, for CuO and ZnO in order. The composition of nanoparticles and membranes are investigated by energy dispersive x‐ray spectroscopy and x‐ray spectroscopy. Increasing nanoparticle concentration within the membranes causes their glass transition temperature to shift to low temperatures and enhances their thermal resistance. Fourier‐transform infrared spectroscopy demonstrates the formation of hydrogen bonds between nanoparticles and PVA that are generated by the intermolecular and intramolecular hydrogen bonds. Impedance spectroscopy characterization reveals that the membranes hold negative temperature coefficient of the resistance. The activation energy decreases with increasing nanoparticle concentration. The composite membranes exhibit a decent response to x‐ray that is proportional to its energy. The best x‐ray response is for the membranes with both CuO and ZnO nanoparticles, because of their different bandgaps that cause a wide range of excitation energy to be involved. The fabricated membranes have numerous advantages such as their semiconductor features, flexibility, and feasibility of fabrication on a large scale with reasonable cost.
Physicochemical, structural, and thermal properties of electrospun membranes depend on process conditions and the type and concentration of the raw materials used to produce them. In this work, the electrospinning technique (ES) is used to synthesize membranes with hydrolyzed collagen (HC) and polyvinyl alcohol (PVA) at two different distances. The characterization of these membranes is then carried out by X‐Ray diffraction, Raman spectroscopy, differential scanning calorimetry, water vapor permeability (WVP), microscopy techniques, and porosity measurements. Results show that the morphology of the ES membranes depends mainly on the polymer/solvent system's physicochemical properties and the distance to the collector. Thicker samples (68–86 μm) are formed when using the furthest distance (10 cm), having fiber diameters smaller than 1 μm, porosity percentages up to 90%, and WVP values close to or in the recommended range for wound dressing commercial products. Moreover, the presence of HC results in samples with a less crystalline structure. To the best of our knowledge, this is the first report in which PVA and HC membranes are successfully synthesized by electrospinning and physicochemically characterized.
Nanocomposite of PVA and Cd0.9Mn0.1S was prepared by solution casting technique. The formed nanocomposite was irradiated by γ-ray with dosage ranging from 10 to 120 kGy. The dielectric properties of PVA/Cd0.9Mn0.1S nanocomposites were studied as a function of frequency (100 Hz–5 MHz) in a temperature range of (303–413 K). The data were analyzed in the dielectric loss (ε″), electric modulus (M″) and conductivity representation (σ′). Contributions from the polymer matrix and reinforcing phase are discerned in the relaxation response. The α-relaxation and a strong frequency dispersion are identified in the ε″ spectra at high temperatures, which are attributed to the segmental motion of the polymer main chain and to conductivity contribution and /or interfacial polarization, respectively. However, two peaks are detected in the M″ spectra: a main α-relaxation at high frequency and ρ-relaxation relating to the conduction process at low frequency. The temperature dependence of both the ρ-relaxation time obtained from the modulus and dc conductivity (σdc) obeys the Arrhenius law with almost similar activation energies, ≈ 0.67 eV. The change of the frequency exponent, s, with temperature reveals that the ac conductivity is governed by the correlated barrier hopping (CBH) mechanism. The dielectric constant (ε′) and dielectric loss (ε″) are dose dependent showing highest value for 30 kGy irradiated sample in the α-dipolar relaxation region. With increasing γ dose, the ac conductivity increases whereas the binding energy of the charge carriers Wm decreases supporting the dominance of the chain scission in polymer.
In the present study, a green synthesis approach has been employed to prepare cadmium sulphide nanoparticles (CdS NPs). The prepared CdS NPs were used as nanofiller (0‐3 wt%) to produce polyvinyl alcohol (PVA)/CdS nanocomposite films via solution casting technique. The Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and atomic force microscopy were employed to investigate various properties of PVA/CdS nanocomposite films. An enhancement in the structural, thermal, and morphological properties of the PVA/CdS nanocomposite films was noticed confirming the successful incorporation of CdS NPs in the PVA matrix and good interaction between the polymer and the nanofiller. Further, an impedance analyzer was employed to evaluate dielectric properties of the PVA/CdS nanocomposite films at various frequencies (50 Hz‐1 MHz) and temperatures (40°C‐140°C). The dielectric constant (ε) and dielectric loss (tanδ) values of PVA/CdS nanocomposite films loaded with 3 wt% of CdS NPs were found to be 423.71 and 4.18, respectively, at 50 Hz and at 140°C. An improvement in the dielectric properties evidenced the homogeneous distribution of CdS NPs within the PVA matrix making the nanocomposite films useful for electrical charge storage devices.
TiO2 sol–gel reaction induces nanowrinkling along the surface of electrospun poly(vinyl alcohol) (PVA) nanofibers. Nanowrinkling along nanofibers is influenced by electrospinning voltage, degree of nanofiber crosslinking, and the repetitive immersion of nanofibers in TiO2 precursors. Crosslinked nanofibers are dipped in alternating solutions of titanium tetraisopropoxide (TTIP) and water for up to five cycles. Interestingly, nanowrinkles only form along nanofibers that are spun at 45 kV and treated with three or more cycles of sol–gel precursor. Spectroscopy reveals that more PVA hydroxyl groups populate the nanofiber surface when electrospinning occurs at 45 kV than at 15 kV. In turn, surface PVA hydroxyl groups appear to nucleate TiO2 growth. Scanning probe phase micrographs confirm modulus differences between the attached TiO2 particles and PVA's surface. Those moduli differences result in wrinkling, as TTIP‐treated nanofibers undergo repetitive cycles of water swelling and isopropanol deswelling.
Silver/poly(vinyl alcohol), Ag/PVA, and silver/poly(vinyl alcohol)/graphene, Ag/PVA/Gr, composite hydrogel discs were produced by freezing/thawing, followed by electrochemical reduction of Ag⁺ ions inside respective matrices, at constant voltage in specially designed electrochemical cell. Raman, FT-IR and FE-SEM characterized interactions between PVA, graphene and silver nanoparticles. Ag/PVA and Ag/PVA/Gr discs classified as non-cytotoxic towards peripheral blood mononuclear cells (PBMC) according to MTT cytotoxicity test, while exhibiting antibacterial activity against Staphylococcus aureus and Escherichia coli. The slow silver release and high remaining silver content of ∼67–68 wt % after 28 day immersion in simulated body fluid confirmed that both composites can preserve their sterility over time.
We report on the observation of the long-lasting low-temperature photoluminescence decay in the hybrid system nano-CdS/polyvinyl alcohol with a characteristic time of about 1.7 s. The origin of the phosphorescence is ascribed to the accumulation of photo-excited excitons in the traps within the polymeric matrix with subsequent transfer of the excitation to the embedded CdS nanoparticles.
Nano-magnesium oxide (MgO) was prepared by wet chemical method using magnesium chloride and sodium hydroxide as precursors and soluble gelatin as stabilizing agent in this paper. The synthesized nano MgO was characterized by XRD, SEM, and FTIR. The results showed that the size of nano-MgO was about 20.62 nm. Polyvinyl alcohol (PVA) polymer based nanocomposites, with different concentrations of MgO (1, 2, 3, 4 wt%), have been prepared using solvent casting technique. The results of SEM revealed that the MgO nanoparticles are uniformly distributed in PVA polymer matrix. FTIR analysis evidently saw the interaction between MgO with hydroxyl group of PVA through hydrogen bonding. The influences of MgO nanoparticle on the optical characterisation of PVA have been considered using UV-Vis-NIR spectroscopy. Energy band gap and tail of localized state of PVA/MgO nanocomposites have been calculated by using Tauc and Urbach relations, respectively. The band gap of the nanocomposites samples decreases as MgO Wt% increases. Wemple-DiDomenico single-oscillator model has been applied to analyze the dispersion of the refractive index of the films, and the dispersion parameters are calculated to obtain the information about disorder degree.
In this work, CdS nanoparticle with different sizes dispersed in polyvinyl alcohol (PVA) matrixes in the form of (PVA/CdS) nanocomposite were prepared. Results of transmission electron microscopy (TEM) and XRay diffraction (XRD) indicates the well dispersed CdS uniform sphere nanoparticles with cubic phase have been formed in PVA. The infrared spectral data confirmed that the -OH group used as a coordinated site to aggregate the cadmium ions and different uniform sizes of CdS nanoparticles were formed at this site by releasing of S -2 ions. The blue shift and optical band gap as a function of the particle sizes were studied form the UV-Visible spectra. Dielectric properties were studied in the frequency range from (2.5 KHz-5 MHz) as a function of temperature and the effect of particle sizes on the relaxation time were discussed.
Silver nanoparticles filled polyvinyl alcohol (PVA) were prepared by casting method using water as a solvent. X-ray diffraction(XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis.) were used to characterize the prepared nanocomposites. X-ray results indicated the formation of Ag-nanoparticles with FCC phase within the PVA polymeric matrix. Scanning electron micrscopy shows that the prepared Ag-nanoparticles were dispersed and nearly uniform in diameter within the polymeric matrix. UV-Vis. absorption spectra were used to study the confined growth process of PVA-capped Ag-nanoparticles. The absorption showed a shift towards higher wavelength with increasing filler content.
CdS nanoparticles have been synthesized in aqueous solution using polyvinyl alcohol (PVA) as a capping reagent. The effects of exposure by ultraviolet (UV) light on optical properties of nanocomposites consisting of colloidal CdS nanoparticles and a polymer PVA matrix were studied by
employing photoluminescence (PL) spectroscopy. It is shown that UV-induced changes of the photoluminescence intensity in PVA are caused by creation and healing of non-radiative recombination centers. It is also concluded that in the nanocomposites, the UV-induced changes of the PL intensity
are predominantly governed by processes at the NP/PVA interface.
The process of doping of CdS nanoparticles with Mn during colloidal synthesis is analyzed by EPR and optical studies. Analysis of EPR results demonstrated that Mn(2+) ions are successfully incorporated into the nanoparticles and occupy the crystal sites both in the bulk of a NP and near the surface of a NP. Optical absorption measurements revealed the retardation of absorption edge shift during the growth for Mn-doped CdS NPs as compared to the undoped CdS NPs. It was concluded that the presence of Mn in the solution leads to the inhibition of NPs growth.
The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.
A new material, which can be used in solar energy utilization, is obtained here by adding different weights of poly(vinyl alcohol) (PVA) to the semiconducting material CdS. The effect of this addition was studied by using FT-Raman spectrometer (based on 1500 mW Nd : YAG laser at 1064 nm), UV–Vis-IR (190–800 nm) spectrophotometer, and X-ray diffractometer. Our experimental results indicated the appearance of several new Raman bands, which have not existed in both CdS and PVA. Some of the bands which are already existing in the Raman spectra of PVA showed an unexpected systematic increase in their intensities after the addition of CdS to the matrix. On the other hand, some of the new Raman bands appeared in special concentrations of PVA only, whereas some of the Raman bands of CdS were found to disappear after adding PVA. Finally, shifts in some bands associated with random increase in their intensities after adding PVA to CdS was detected in the FT-Raman analysis. The experimental evidence given here might be attributed to the occurrence of new bonds, indicating that the produced mixture is a new material. The assignment of the new bands as well as an interpretation of the obtained variations is given here. Our X-ray diffraction data confirmed the interpretation introduced here. Moreover, the UV–Vis spectra confirmed the existence of new absorption bands in the Visible region. The I-V characteristic curve was measured for a selected concentration of the new composite material, showing a remarkable increase in the values of the conduction current of about two orders of magnitude as compared with the pure PVA material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1984–1992, 2004
Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Inorganic nanoparticles possess outstanding optical, catalytic, electronic and magnetic properties, which are significantly different their bulk states. By combining the attractive functionalities of both components, nanocomposites derived from organic polymers and inorganic nanoparticles are expected to display synergistically improved properties. The potential applications of the resultant nanocomposites are various, e.g. automotive, aerospace, opto-electronics, etc. Here, we review recent progress in polymer-based inorganic nanoparticle composites.
Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades
from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization,
and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use
include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes
in live animals by near-infrared emission during surgery. The new generations of qdots have far-reaching potential for the
study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation
of cell trafficking, tumor targeting, and diagnostics.
By dropwise adding solutions of gellan (Gll) or gellan + poly(vinyl alcohol) (PVAL) mixture into different metal salt solutions-FeCl3 · 6 H2O, FeCl2 · 4 H2O, CoCl 2 · 6 H2O, CuCl2 · 2 H 2O-at 30 °C under constant stirring, preparation of spherical microparticles based on polymer-metal complexes has been performed. FT-IR spectroscopy, TGA analysis and swelling measurements of these microparticles in water showed the influence of the metal type ions on their structure, thermal stability and water swelling capacity. The FT-IR spectroscopy allows to explain the mechanism of polymer-metal complexes formation and the optical microscopy showed that the microparticles obtained had good sphericity with average diameter ranging from 719 μm to 830 μm. The thermal stability of the polymer-metal complexes was found to be higher than that of the gellan.
Polyvinyl alcohol (PVA) is a water-soluble polymer that is anticipated to be a good candidate for incorporation into multilayer coatings of organic solar cells due to its high transparency and ability to form a barrier to oxygen. Because a long lifetime is a prerequisite for successful applications, it was necessary to study the photochemical behavior of PVA under solar light. PVA films were exposed to UV-visible light irradiation (λ > 300 nm) in accelerated aging conditions representative of natural ageing. Modifications in the chemical structure of aged samples irradiated at ambient air were recorded. Due to the low oxygen permeability of PVA films, it was shown that the photooxidative degradation of PVA films is restricted to the surface (<5 μm) and results in a large amount of chain scissions, with a progressive erosion of the surface of the irradiated material. The oxidation products formed along the macromolecular chains, and low molecular weight species trapped in the matrix or emitted in the gas phase were also identified. An oxidation mechanism was then proposed to account for these modifications. However, irradiation in the absence of oxygen demonstrated the high photostability of PVA films, which permits the use of PVA as a sublayer in inorganic/organic multilayer encapsulation systems.
Nanocomposites of poly(vinyl alcohol) (PVA)/ZnS and PVA/CdS was prepared by in situ hydrothermal reaction. The intensity of the PVA crystalline diffraction peaks decreased after 8 h of treatment at 120 °C. The diffraction of PVA crystal resulted from the strong intermolecular interaction between PVA chains through the intermolecular hydrogen bonding. The intensity of the diffraction peaks and also the size of the crystals were determined by the number of PVA chains packing together. After being composited with sulfides, the intensity of PVA diffraction peaks was further decreased. This is because the interactions of PVA with ZnS and CdS led to a decreased in the intermolecular interaction between the PVA chains and thus the degree of crystallinity.
A series of poly(N,N-dimethylacrylamide)-g-poly(vinyl alcohol) (PDMAA-g-PVA) graft hydrogel networks were designed and prepared via a free radical polymerization route initiated by a PVA-(NH4)2Ce(NO3)6 redox reaction. Silver nanoparticles with high stability and good distribution behavior have been self-assembled by using these hydrogel networks as a nanoreactor and in situ reducing system. Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag+ would form complex via oxygen atom and nitrogen atom, and form weak coordination bonds, thus astricting Ag+. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope (FTIR). The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones were observed by a scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM micrographs revealed the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20nm, depending on their reduction routes. XRD results showed all relevant Bragg's reflection for crystal structure of Ag nanoparticles. UV–vis studies apparently showed the characteristic surface plasmon band at 410–440nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrated that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones. With increasing the DMAA proportion, the r0 and S∞ are enhanced for each system. The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA and reduction systems.
i) Densities, sorption of water vapor and infrared absorption spectra were measured on four kinds of PVA films, which were prepared from the same PVA powder specimen and subjected to different heattreatments.
ii) It was found by the present investigation that the 1146 cm−1 (8.74μ) band is the so-called crystallization-sensitive band.
iii) Since the degrees of crystallinity determined by these methods went in parallel, it was found that they may be used as relative measures for the crystallinity.
iv) Samples subjected to the heat-treatment at about 193°C, behave abnormally from the other three groups of samples. This deviation was found to be due to chemical changes occurring in the heat-treatment. This was confirmed by the measurement of ultraviolet absorption spectra.
The size dependence of the resonance Raman spectrum of CdS nanocrystals ranging in size from 10 to 70 Å radius has been studied. We find that while the lowest electronic excited state is coupled strongly to the lattice, this coupling decreases as the nanocrystal size is decreased. We demonstrate that the lifetime of the initially prepared excited state can influence the apparent strength of electron‐vibration coupling. Absolute resonance Raman cross section measurements can be used to determine the value of the excited state lifetime, thus removing this parameter. The coupling to the lattice, while less in nanocrystals than in the bulk, is still greater than what is predicted assuming an infinite confining potential. The width of the observed LO mode broadens with decreasing size, indicating that the resonance Raman process is intrinsically multimode in its nature. The frequency of the observed longitudinal optic (LO) mode has a very weak dependence on size, in contrast to results obtained from multiple quantum well systems. The temperature dependence of the frequency and linewidth of the observed LO mode is similar to the bulk and indicates that the LO mode decays into acoustic vibrations in 2.5 ps.
Samples of pure polyvinyl alcohol (PVA) and PVA doped with humic acids were exposed to gamma radiation. Gamma rays induced
the degradation of the pure polymer. Degradation changes were observed using ATR FT-IR equipment. Dehydration, double bond
creation, and their subsequent oxidation (surrounding atmosphere was air) were found out. Also, other degradation reactions
(e.g. chain scission, cyclization) occur simultaneously. Formation of C=C and C=O bonds is apparent from FT-IR spectra. In
contrast the presence of humic acids in the PVA sample showed stabilizing effect on PVA structure within the concentration
range 0.5–10%.
Low-dimensional semiconductor structures, often referred to as
nanocrystals or quantum dots, exhibit fascinating behavior and have a
multitude of potential applications, especially in the field of
communications. This book examines in detail the optical properties of
these structures, gives full coverage of theoretical and experimental
results, and discusses their technological applications. The author
begins by setting out the basic physics of electron states in crystals
(adopting a "cluster-to-crystal" approach), and goes on to discuss the
growth of nanocrystals, absorption and emission of light by
nanocrystals, optical nonlinearities, interface effects, and photonic
crystals. He illustrates the physical principles with references to
actual devices such as novel light-emitters and optical switches. The
book covers a rapidly developing, interdisciplinary field. It will be of
great interest to graduate students of photonics or microelectronics,
and to researchers in electrical engineering, physics, chemistry, and
materials science.
Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm−1, while a crystalline Raman band is found at 1147 cm−1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.
The adhesion of the biocompatible hydrophilic polymer, poly (vinyl alcohol) to a model substrate, silicon, was investigated. Contact angle measurements were used to reveal the effect of various substrate cleaning procedures including sonication and UV–ozone treatment prior to casting a 35 μm coating. Raman microspectrometry and X-ray reflectometry were used to characterise the composition and the thickness of PVA thin films. The use of mechanical abrasion of the substrate followed by a 131 nm primer layer of PVA in combination with vacuum treatment at temperatures higher than the glass transition temperature (Tg = 80 °C) provided the best resistance to delamination as demonstrated by visual observation during prolonged immersion of the coatings in water.
The limited swellability in polar media of the commonly used polystyrene/divinylbenzene (PS-DVB) support materials for solid-phase organic synthesis has led to the development of novel, highly swellable hydrophilic gels designed for use in aqueous or polar media. Poly(vinyl alcohol) beads crosslinked with epichlorohydrin (PVA-EP) were prepared by a two-step inverse-suspension polymerization method. While it is known that the morphology of the resulting beads can be controlled by the ratio of EP versus PVA as well as by the pre-crosslinking time, the actual degree of crosslinking of the beads and their mechanical properties remain unknown. It is therefore the purpose of this study to evaluate the actual degree of crosslinking of beads prepared with different quantities of crosslinker in the feed by spectroscopic (Raman, nuclear magnetic resonance) and chemical (functional group loading) methods. The mechanical properties of these swollen PVA-EP beads will be evaluated by single-bead unconfined compression in solvents such as water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) and compared to model PS-DVB beads commonly used for solid phase synthesis.
Poly(vinyl alcohol), PVA, microcomposites with montmorillonite, MMT, were prepared by their mixing in aqueous colloidal solution. Thin films of composites obtained by solvent evaporation were exposed to 254-nm radiation. The course of photochemical reactions leading to various products was monitored by FTIR and UV–vis spectroscopy. The chain scission reaction was confirmed by measurement of average molecular weights and polydispersity using gel permeation chromatography (GPC) method. The crosslinking was minor process whereas oxidation and degradation appeared more efficient in exposed PVA/MMT. It was found that the presence of clay filler (MMT) has slight influence on PVA photooxidative degradation.
A single-step synthesis of homogenous Ag/PVA nanocomposites is carried out and characterized by X-ray diffraction. A validation of the crystal information is established by transmission electron microscopy (TEM) and a homogenous mixing morphology is confirmed by SEM micrographs. Surface plasmon resonance (SPR) optical absorption shows a red shift compared to bare Ag NPs. The degradation mechanisms are explained for both pristine PVA and Ag/PVA nanocomposites, aided by the increase in thermal stability of the PVA support with an enthalpy change for each decomposition reaction.
Two-dimensional infrared spectroscopy was carried out on stereoselectively synthesized polyalcohols. Depending upon the stereochemical orientation of their hydroxyl groups, the polyols can either feature linear chains of hydrogen bonds that are stable for extended periods of time or they can display ultrafast dynamics of hydrogen-bond breakage and formation. In the former case, the OH-stretching vibrations and their transition dipoles are substantially coupled, hence prior to vibrational relaxation, the initial OH-stretching excitation is rapidly redistributed among the set of hydroxyl-groups constituting the hydrogen-bonded chain. This redistribution is responsible for an ultrafast loss of memory regarding the frequency of initial excitation and as a result, a pump-frequency independent vibrational lifetime is observed. In contrast, in the latter case, the coupling of the OH-groups and their transition dipoles is much weaker. Therefore, the OH-stretching excitation remains localized on the initially excited oscillator for the time scale of vibrational energy relaxation. As a result inhomogeneous relaxation dynamics with a pump-frequency-dependent lifetime are observed.
Colloidal heteronanocrystals (HNCs) can be regarded as solution-grown inorganic-organic hybrid nanomaterials, since they consist of inorganic nanoparticles that are coated with a layer of organic ligand molecules. The hybrid nature of these nanostructures provides great flexibility in engineering their physical and chemical properties. The inorganic particles are heterostructured, i.e. they comprise two (or more) different materials joined together, what gives them remarkable and unique properties that can be controlled by the composition, size and shape of each component of the HNC. The interaction between the inorganic component and the organic ligand molecules allows the size and shape of the HNCs to be controlled and gives rise to novel properties. Moreover, the organic surfactant layer opens up the possibility of surface chemistry manipulation, making it possible to tailor a number of properties. These features have turned colloidal HNCs into promising materials for a number of applications, spurring a growing interest on the investigation of their preparation and properties. This critical review provides an overview of recent developments in this rapidly expanding field, with emphasis on semiconductor HNCs (e.g., quantum dots and quantum rods). In addition to defining the state of the art and highlighting the key issues in the field, this review addresses the fundamental physical and chemical principles needed to understand the properties and preparation of colloidal HNCs (283 references).
Hybrid nanomaterials, composed of both inorganic and organic components, have recently been examined as promising platforms for imaging and therapeutic applications. This unique class of nanomaterials can not only retain beneficial features of both the inorganic and organic components, but also provides the ability to systematically tune the properties of the hybrid material through the combination of functional components. This feature article will summarize recent advances in the design and synthesis of hybrid nanomaterials and their applications in biological and biomedical areas. The hybrid nanomaterials to be discussed fall into two main categories, silica based materials and nanoscale metal-organic frameworks. Their applications as imaging contrast agents and nanotherapeutics will be highlighted.
The infrared spectrum of polyvinyl alcohol has been investigated between 3600 and 70 cm. −1 . Polarization measurements on stretched specimens were made down to about 330 cm. −1 . The spectrum of a deuterated specimen (about 90% of the OH having been replaced by OD) has also been obtained. These data confirm and extend the results of previous workers. The spectrum is discussed in detail in relation to three structures for polyvinyl alcohol proposed on the basis of x-ray diffraction studies. The data definitely rule out the structure proposed by Mooney, and are most consistent with the structure proposed by Bunn. A complete assignment of the bands in the spectrum is proposed. From this analysis it appears that the existence of interaction forces between molecules can be convincingly demonstrated. The proposed assignments suggest a new interpretation of the 1326–1446 cm. −1 doublet, viz. , that these bands arise from mixed CH and OH in-plane bending vibrations. This is shown to be in agreement with the results of studies on simple alcohols. An alternative assignment for the 1144 cm. −1 band is also considered. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/38619/1/1202210106_ftp.pdf
Electron paramagnetic resonance (EPR), luminescence and infrared spectral studies have been carried out on ions doped in polyvinylalcohol (PVA) films. The EPR spectra at room temperature exhibit sextet hyperfine structure (HFS), centered at characteristic of Mn2+ ions in octahedral symmetry. The zero-field splitting parameter (D) at room temperature has been evaluated from the intensities of allowed hyperfine lines. The EPR spectra exhibit a marked concentration dependence. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility (\chi ) is calculated from the EPR data at various temperatures. From the plot of versus T, the Curie constant and Curie temperature have been evaluated. The emission spectrum of Mn2+ ions doped PVA film exhibits three bands centered at 390, 448 and 465 nm. The band at 448 nm is attributed to transition of ions. The bands at 390 and 465 nm are attributed to the recombination of free charge carriers. The excitation spectrum exhibits two bands at 250 and 216 nm, which are attributed to host lattice absorption bands. The FT-IR spectrum exhibits few bands, which are attributed to , , C=C and groups of stretching and bending vibrations.
Poly(vinylalcohol) (PVA)/vanadium pentoxide xerogel (VXG) composites were prepared and exposed to different electron beam irradiation doses. Changes in the structural properties, crystallinity degree of composites with increasing irradiation doses and VXG content were subsequently investigated using the Fourier transformer infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) techniques. The crystallinity degree of the PVA matrix was found to decrease markedly due to VXG addition and/or irradiation process.
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