Polyvinyl Alcohol Films Research Articles

Fabrication of CNTs-reinforced poly(vinyl alcohol) nanocomposite film with tailored structural, surface chemical and optical properties

Purpose This study aims to fabricate multiwalled carbon nanotubes (MWCNTs)-mediated polyvinyl alcohol (PVA) composite films using the solution casting approach. Design/methodology/approach The prepared films were evaluated for diverse structural, surface, optical and electrical attributes using advanced analytical techniques, i.e. electron microscopy for surface morphology, Fourier transform infrared spectroscopy for tracing chemical functionalities, x-ray diffraction (XRD) for crystal patterns, water contact angle (WCA) analysis for surface wettability and UV visible spectroscopy for optical absorption parameters. The specimens were also investigated for certain rheological, mechanical and electrical properties, where applicable. Findings The surface morphology results expressed a better dispersion of MWCNTs in the resultant PVA-based nanocomposite film. The XRD analysis exhibited that the nanocomposite film was crystalline. The surface wettability analysis indicated that with the inclusion of MWCNTs, the WCA of the resultant nanocomposite film improved to 89.4° from 44° with the pristine PVA film. The MWCNTs (1.00%, w/w) incorporated PVA-based film exhibited a tensile strength of 54.0 MPa as compared to that of native PVA as 25.3 MPa film. There observed a decreased bandgap (from 5.25 to 5.14 eV) on incorporating the MWCNTs in the PVA-based nanocomposite film. Practical implications The MWCNTs’ inclusion in the PVA matrix could enhance the AC conductivity of the resultant nanocomposite film. The prepared nanocomposite film might be useful in designing certain optoelectronic devices. Originality/value The results demonstrated the successful MWCNTs mediation in the PVA-based composite films expressed good intercalation of the precursors; this resulted in decreased bandgap, usually, desirable for optoelectronic applications.

Improvement of Hydrophobicity and Gas Permeability of the Polyvinyl Alcohol Film Utilizing Monoglyceride Coating and Diatomaceous Earth Filling and Its Application to Fresh-Cut Mango

Improvement of Hydrophobicity and Gas Permeability of the Polyvinyl Alcohol Film Utilizing Monoglyceride Coating and Diatomaceous Earth Filling and Its Application to Fresh-Cut Mango

Preparation of Nanocellulose from Coffee Pulp and Its Potential as a Polymer Reinforcement.

Coffee is one of the most valued agricultural products regarding its high commercialization rate. During the production of coffee beans, coffee pulp is obtained as one of the main byproducts with a cellulose content of more than 30% of dry weight. This research focused on the value-added potential of coffee pulp fiber as the reinforcement in composite materials. The nanocellulose coffee pulp (NCP) from the coffee pulp (CP) was prepared and subsequently used as a filler to reinforce the polyvinyl alcohol (PVA) matrix for the improvement of PVA composite properties. The CP was treated via alkali and bleaching treatment before the production of NCP using the acid hydrolysis treatment. The TEM result of NCP showed the successful preparation of NCP with an average diameter of 16.03 ± 4.70 nm with increasing crystallinity size and crystallinity index. The effect of glycerol (G) in the PVA matrix was observed. The result showed that glycerol had a play-role as a plasticizer for increased flexibility and decreased hardness and brittleness of PVA nanocomposite film. The nanocomposite film of PVA/G/NCP was fabricated with various ratios of NCP through the casting method. It was shown that the physical properties were improved with the presence of NCP in the PVA matrix compared to the neat PVA film.

Polyvinyl alcohol flame retardant film based on halloysite nanotubes, chitosan and phytic acid with strong mechanical and anti-ultraviolet properties

The research of additive biomass flame retardants is becoming more and more popular. In this work, amino modified halloysite nanotubes (A-HNTs), chitosan (CS) and phytic acid (PA) were introduced into polyvinyl alcohol (PVA) matrix to construct PA/A-HNT/CS/PVA organic-inorganic composite film with hydrogen bond and covalent bond cross-linking network structure. Adding PA/A-HNT/CS can remarkably improve the mechanical strength, UV resistance and thermal stability of PVA film. Compared with control PVA film, the transmittance of composite film in ultraviolet region decreases from 90 % to <15 %, and the tensile strength raises from 19.8 MPa to 31.0 MPa. The thermal decomposition temperature of the composite film increases, the weight loss rate decreases obviously, and the carbon residue can reach 26 wt% at 700 °C. The limiting oxygen index increases from 18.5 % to 32.2 %. Furthermore, the addition of this flame-retardant system can obviously reduce the combustion intensity of PVA, and its flame-retardant grade can reach V-0. It is of great significance to expand the application of PVA and the development of biomass flame retardant.

Preparation, characterization, and performance evaluation of composite films of polyvinyl alcohol/ cellulose nanofiber extracted from Imperata cylindrica

In recent years, production of cellulose nanofiber (CNF) from waste materials has achieved great interest owing to their renewable nature, biodegradability, high mechanical properties, economic value, and low density. Because Polyvinyl alcohol (PVA) is a synthetic biopolymer with good water solubility and biocompatibility, the composite material formed of CNF and PVA, is a sustainable way of monetizing to address environmental and economic issues. In this work pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, and PVA/CNF2.0 nanocomposite films were produced using the solvent casting approach with the addition of 0, 0.5, 1.0, 1.5, and 2.0 wt% of CNF concentrations respectively. The strongest water absorption behaviour was found as 25.82% for pure PVA membrane, followed by PVA/CNF0.5 (20.71%), PVA/CNF1.0 (10.26%), PVA/CNF1.5 (9.63%), and PVA/CNF2.0 (4.35%). The water contact angle of 53.1°, 47.8°, 43.4°, 37.7°, and 32.3° was formed between water droplet and the solid-liquid interface of pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, PVA/CNF2.0 composite films respectively. The SEM image clearly shows that a network structure like a tree form at the PVA/CNF0.5 composite film, where the sizes and number of pores are apparent. XRD analysis suggested that unique peaks found at 2θ = 17.5°, 28.1°, 33.4°, and 38° for nanocomposites indicating new crystal plane generated upon cross-linking in presence of malic acid. The maximum loss rate temperature (Td,max) for PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5 was determined by TG analysis to be around 273.4 °C. FTIR studies suggested that PVA/CNF0.5 composite film showed the highest peak at 1428 cm−1 as compared to other PVA/CNF composite films representing the presence of higher crystalline band in the composite film matrix. PVA/CNF0.5 composite film was found to have a surface porosity and mean pore size of 27.35% and 0.19 μm respectively, classifying it in the MF membrane category. The maximum tensile strength (TS) of 5.27 MPa was found for PVA/CNF0.5, followed by PVA/CNF1.0, PVA/CNF1.5, pure PVA, and PVA/CNF2.0. The maximum young's modulus (111 MPa) was found for PVA/CNF1.0, followed by PVA/CNF0.5, PVA/CNF2.0, PVA/CNF1.5, and pure PVA, which could be attributed to the cyclization of the molecular structures by cross-linking. PVA/CNF0.5 exhibits greater elongation at break (21.7) than the other polymers, indicating a material's ability to undergo significant deformation before failure. Performance evaluation of the PVA/CNF0.5 composite film showed that 46.3% and 92.8% yield were found in the retentate for 200 mg/L of BSA, and 5 × 107 CFU/mL respectively. However, more than 90% E. coli was retained by PVA/CNF0.5 composite film, therefore absolute rating of this membrane is 0.22 μm. The size of this composite film may be therefore considered in the range of MF.

Effect of the Chemical Nature of Polyvinyl Alcohol on the Microstructure of Cement Hydration Products

The influence of chemical nature of polyvinyl alcohol (PVA) on the microstructure of cement hydration products was investigated. Thermal analysis, X-ray diffraction, Si29 nuclear magnetic resonance (NMR), and scanning electron microscope were used to explore the microstructure and content of cement hydration products. The pore structure of the matrix was measured by a mercury intrusion porosimeter. Ca(OH)2 in PVA-modified cement composites showed multidirectional growth, and its platelike structure was distorted due to the intersection of different growth orientations. The decomposition temperature of Ca(OH)2 in PVA-modified cement composites was lower than in unmodified cement composites, which was greatly affected by degrees of polymerization of PVA. Besides, the mean chain length of calcium silicate hydrate (C-S-H) gels showed an increasing trend with the increase of degrees of hydrolysis and polymerization of PVA, but it was less than that of unmodified cement composites. The incorporation of PVA increased the porosity, but refined the pore-size distribution of the matrix. PVA film between layered Ca(OH)2 and on the surface of cement hydration products acted as an additional bond and increased the internal cohesion of the matrix.

Comparative studies of starch blends on the properties of PVA films

This research studied the effects of pregelatinized starch (PST) and hydrolyzed starch (HST) at various contents with 20 phr glycerol on the properties of polyvinyl alcohol (PVA) film. FTIR analysis showed that the increase of HST preferably interacted with the hydroxyl (OH) groups and CH molecules, while the interaction of hydrogen bonding with PST interacted with OH groups of PVA, but did not affect CH stretching molecules. The blend with HST possessed lower overall thermal degradation than the blend with PST. Tensile strength by blending with PST increased from 14 MPa to 30 MPa, while the elongation at break decreased by a factor of two. On the other hand, elongation at break of the blends with HST improved from 300 (when no HST) to 350%, and its tensile strength improved slightly only with 10 and 20% blending. Regarding the water-soluble properties, hydrogen bonding interaction of starch, PVA and glycerol showed hardly any effect on the rate of dissolving the blends. However, the chemical structure of starch and the size of molecules, especially in HST dramatically increased the rate of dissolving in water.

Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition is commonly assessed using infrared spectroscopy, which provides an average fingerprint of the various materials contained in the volume probed. However, this approach does not offer any details on the arrangement of the phases in the material. Interfacial regions between two polymeric phases, often in the nanoscale range, are also challenging to access. Photothermal nanoscale infrared spectroscopy monitors the local response of materials excited by infrared light with the sensitive probe of an atomic force microscope (AFM). While the technique is suitable for interrogating small features, such as individual proteins on pristine gold surfaces, the characterization of three-dimensional multicomponent materials is more elusive. This is due to a relatively large volume of material undergoing photothermal expansion, defined by the laser focalization onto the sample and by the thermal properties of the polymeric constituents, compared to the nanoscale region probed by the AFM tip. Using a polystyrene (PS) bead and a polyvinyl alcohol (PVA) film, we evaluate the spatial footprint of photothermal nanoscale infrared spectroscopy for surface analysis as a function of the position of PS in the PVA film. The effect of the feature position on the nanoscale infrared images is investigated, and spectra are acquired. Some perspectives on the future advances in the field of photothermal nanoscale infrared spectroscopy are provided, considering the characterization of complex systems with embedded polymeric structures.

Optical properties of Ag2S quantum dots

Colloidal solutions of silver sulfide quantum dots of various sizes were synthesized from low-concentration water solutions of silver nitrate, sodium sulfide and sodium citrate as stabilizer. The size of Ag2S quantum dots in colloidal solutions was determined by dynamic light scattering. The produced Ag2S quantum dots were dispersed in a polyvinyl alcohol (PVA) film matrix. The transmission and absorption spectra of PVA films containing Ag2S were measured in the wavelength interval 190–900 nm. A comparative study of the optical properties of PVA films with Ag2S quantum dots showed that a decrease of quantum dots to ∼ 6 nm leads to an increase in the band gap Eg of silver sulfide to ∼ 1.6 eV, which is almost twice larger than the band gap of bulk Ag2S. The optical properties of PVA films with Ag2S quantum dots smaller than 5 nm exhibit specific features associated with exciton transitions.

Enhanced photocatalytic efficiencies in a bifunctional ZnO/PVA nanocomposites derived from Capparis zeylanica L.

The modern food sector demands versatile nanocomposites of polymers for food to wrappers to inactivate germs linked to foods in order to ensure quality throughout the packaging process. Recently, it has become quite appealing to use zinc oxide nanocomposite with polyvinyl alcohol (PVA) assistance for food storage containers. Variable combinations of zinc acetate and Capparis zeylanica leaf extract (3:1, 1:7, 1:3, and 1:1) were used to create nanostructured ZnO at the desired pH (10.5). ZnO/PVA nanocomposites films were created with different weight % of (16, 13, 9 and 5%) ZnO nanoparticles by using solution casting method. The generated ZnO and ZnO/PVA nanocomposites (NCs) were characterized using analytical techniques like X-ray diffraction spectroscopy (XRD), ultraviolet spectroscopic analysis (UV–Vis), Fourier-transform infrared analysis (FT-IR), and field emission scanning electron microscopic study (FE-SEM). The generated ZnO and ZnO/PVA NCs were tested for their efficacy as antibacterial agents against Gram + ve (Streptococcus pyogenes, Staphylococcus aureus) and Gram -ve (Pseudomonas aeruginosa, and E. coli) bacteria. Under UV–visible irradiation, the methylene blue (MB) breakdown caused by the fabricated undoped ZnO and ZnO/PVA nanomixture was investigated. The FE-SEM investigation for synthesized ZnO from a 1:1 ratio exhibited spherical shaped appearance. However, the nanocomposite made with 5% ZnO showed equally scattered nanoflake particles in the matrix of PVA film as well as on the surface. The XRD results showed that ZnO synthesized with a higher proportion of plant extract produced smaller crystallites, whereas ZnO synthesized with a lower percentage of plant extract produced bigger crystallite sizes. The optimum concentration for the breakdown of methylene blue (MB) among the various concentrations examined was 5% ZnO/PVA. Furthermore, a study of the biomedical efficiency of undoped ZnO and ZnO/PVA revealed that 5% ZnO/PVA had the potential antibacterial efficacies.

Polymer-Based Long-Lived Phosphorescence Materials over a Broad Temperature Based on Coumarin Derivatives as Information Anti-Counterfeiting.

The development of new polymer-based room-temperature phosphorescence materials is of great significance. By a special molecule design and a set of feasible property-enhancing strategies, coumarin derivatives (CMDs, Ma-Mf) were doped into polyvinyl alcohol (PVA), polyacrylamide (PAM), corn starch, and polyacrylonitrile (PAN) as information anti-counterfeiting. CMDs-doped PVA and CMDs-doped corn starch films showed long-lived phosphorescence emissions up to 1246 ms (Ma-PVA) and 697 ms (Ma-corn starch), reaching over 10 s afterglow under naked eye observation under ambient conditions. Significantly, CMDs-doped PAM films can display long-lived phosphorescence emissions in a wide temperature range (100-430 K). For example, the Me-PAM film has a phosphorescence lifetime of 16 ms at 430 K. The use of PAM with the strong polarity and rigidity has expanded the temperature range of long-life polymer-based phosphorescent materials. The present long-lived phosphorescent systems provide the possibility for developing new polymer-based organic afterglow materials with robust phosphorescence.

Transparent, High-Strength, and Antimicrobial Polyvinyl Alcohol/Boric Acid/Poly Hexamethylene Guanidine Hydrochloride Films

It is still crucial to improve the mechanical characteristics of polyvinyl alcohol (PVA) films without resorting to chemical cross-linking. In this study, boric acid (BA) was used to enhance the mechanical characteristics of PVA films while maintaining their excellent transparency and biodegradability. The hydrogen bond interaction between PVA and BA resulted in a 70% increase in tensile strength (from 48.5 to 82.1 MPa) and a 46% increase in elongation at break (from 150 to 220%). To introduce antibacterial properties, polyhexamethylene guanidine hydrochloride (PHMG) was incorporated into PVA/BA composite films resulting in PVA/BA/PHMG composite films. The PVA/BA/PHMG films exhibited 99.99% bacterial inhibition against Escherichia coli and Staphylococcus aureus with negligible leaching of PHMG. The PVA/BA/PHMG films maintained a tensile strength of 75.3 MPa and an elongation at a break of 208%. These improved mechanical and antimicrobial properties make PVA/BA and PVA/BA/PHMG films promising for applications in food and medicinal packaging.

Embeddable Soil Moisture Content Sensor Based on Open-End Microwave Coaxial Cable Resonator

In this paper, we propose and demonstrate a novel corrosion-resistant, embeddable open-end coaxial cable soil moisture sensor. This microwave resonator is constructed using two reflectors along the coaxial line. The first reflector is a metal post at the signal input end, short-circuiting the inner conductor to the outer conductor. The second reflector comprises a welded metal plate parallel to the open-end of the coaxial line, maintaining a fixed gap. A moisture-sensitive Polyvinyl Alcohol (PVA) film is inserted into this gap. The resonance frequency of the open-end coaxial cable resonator is highly dependent on the fringe capacitance, which varies with soil moisture levels. As such, tracking resonance frequency changes allows for correlation with soil moisture fluctuations. We provide a detailed discussion of the embeddable open-end microwave coaxial cable resonator (EOE-MCCR) mathematical model and a proof of concept for soil moisture measurement. The demonstration experiments investigate soil moisture content ranging from 4% to 24%. The prototype device exhibits a soil moisture measurement sensitivity of 0.76MHz/% for soil moisture between 4% and 10%, and 1.44MHz/% for soil moisture between 10% and 24%. The soil moisture sensor presented here is robust, easy to manufacture, chemically resistant, low-cost, and suitable for long-term applications and potential industrial uses. This innovative sensor is ideal for sensing applications in harsh environments, advancing the field of chemical trace sensing.

Determination of Mucoadhesion of Polyvinyl Alcohol Films to Human Intestinal Tissue.

The absorption of drugs with narrow absorption windows in the upper small intestine can be improved with a mucoadhesive drug delivery system such as enteric films. To predict the mucoadhesive behaviour in vivo, suitable in vitro or ex vivo methods can be performed. In this study, the influence of tissue storage and sampling site on the mucoadhesion of polyvinyl alcohol film to human small intestinal mucosa was investigated. Tissue from twelve human subjects was used to determine adhesion using a tensile strength method. Thawing of tissue frozen at -20 °C resulted in a significantly higher work of adhesion (p = 0.0005) when a low contact force was applied for one minute, whereas the maximum detachment force was not affected. When the contact force and time were increased, no differences were found for thawed tissue compared to fresh tissue. No change in adhesion was observed depending on the sampling location. Initial results from a comparison of adhesion to porcine and human mucosa suggest that the tissues are equivalent.

Investigation of the properties of composites goethite/polyvinyl alcohol

Goethite and composite films of polyvinyl alcohol (PVA)-goethite have been synthesized. The characteristics of the initial substances and the composite were carried out using the methods of scanning electron microscopy, optical microscopy, and X-ray phase analysis. It has been established that the mechanical characteristics of goetite/PVA composite obtained by processing in a bead mill are improved. Synthesized PVA-goethite composites containing 3 wt% goethite showed a 20% improvement in maximum tensile strength compared to PVA. X-ray phase analysis showed that the chemical structure of goethite, which contains hydroxyl groups, makes it possible to obtain a very strong bond with the polymer matrix. This effectively contributes to the mechanical strengthening of the polymer due to the chemical interaction of nanoparticles and the matrix with hydrophilic fragments on the polymer chains due to strong hydrogen bonding.

Effect of Salt Content and Operating Temperature on the Nitrogen Dioxide Gas Sensing Performance of Sodium-Ion Conducting Solid Polymer Electrolyte

Sodium-ion conducting solid polymer electrolyte (Na-SPE) films based on polyvinyl alcohol (PVA) with various weight percentages of sodium iodide (NaI) were prepared using the casting technique. The films’ structural, morphology and electrical conductivity were examined to understand the sensing mechanism of the as-prepared Na-SPE films. The X-ray diffraction (XRD) and atomic force microscopy (AFM) data, respectively, showed the amorphous and homogeneous granular structure of Na-SPE films due to the high dissociation of NaI in the PVA matrix for all concentrations. The changes in the FTIR vibrational modes of Na-SPEs provide evidence of interactions between cations and functional groups of the host matrix. The effect of salt content, operating temperature and gas concentration on the performance of the Na-SPE sensor towards NO2 were investigated. In contrast to the pure PVA film, which did not respond to NO2 gas at low concentrations, Na-SPE films exhibit higher sensitivity to NO2 gas with faster response and recovery times. At low NO2 gas concentration (50 ppm), a sample containing 20 wt.% of NaI exhibits the highest sensitivity at the operating temperature of 200 °C. In comparison, at a high NO2 gas concentration (550 ppm), a sample containing 40 wt.% of NaI exhibits a maximum sensitivity at 150 °C. These findings suggest that Na-SPE films would be suitable for gas sensor applications. HIGHLIGHTS Na-SPEs films based on PVA with various salt contents have been prepared using the casting method The Hall effect data confirm the n-type conductivity of the Na-SPEs Na-SPE structure exhibits high sensitivity towards NO2 with rapid response/recovery times SPE film has a maximum sensitivity of 127.3 % at low NO2 gas concentration and a maximum sensitivity of 126 % at high gas concentration These results imply that this compound would be suitable for environmental and industrial uses GRAPHICAL ABSTRACT

Structural and Magnetic Properties of Ni Nanoparticles Embedded in Vinyl Polymer Nanocomposite Films

Ni nanoparticles layer of nominal thickness in the range of 5–40[Formula: see text]nm were deposited on polyvinyl alcohol (PVA) film by using the ion beam sputtering (IBS) technique. PVA films were made on a quartz substrate by the solution casting technique. Grazing incidence X-ray diffraction (GIXRD) results reveal Ni is present in a metallic form in the FCC phase. AFM shows that roughness increases with increase in thickness of Ni layer and corresponding MFM images of magnetic domains were recorded. Soft X-ray absorption spectroscopy (SXAS) studies on the PVA/Ni nanocomposites films were recorded using synchrotron radiation. This study is used to study the electronic structure of the as-prepared nanocomposite films and reveals that Ni nanoparticles are present in their metallic form. Magnetic properties were measured using the magneto-optical Kerr effect (MOKE) magnetometer and the films were found to be magnetically soft with higher value of coercivity at lower thickness of Ni nanoparticles layer. The results of magnetic studies are discussed in light of the microstructure and morphological features of PVA/Ni nanocomposite films. The PVA/Ni nanocomposites showed interesting anisotropic magnetic behavior; thus the investigative results may be useful for the development of futuristic flexible functional magnetic material system.

Flame‐resistant and tough polyvinyl alcohol film with ultraviolet‐absorbing capacity

AbstractFireproofing the polyvinyl alcohol (PVA) membrane is an essential and urgent reinforcement to ease the restriction in flame‐resistant requirements. The traditional method by the physical and heterogenous introduction of a large number of metal hydroxides, halogenated and organic compounds efficiently enhance the flame‐retardancy but severely weakens the biocompatibility, mechanical strength, and transparency of PVA membranes. In this work, two bio‐extracted compounds, phytic acid (PA) and creatine (CR) are employed to construct a fireproof, tough and transparent PVA membrane. The LOI of the PVA/PACR membrane increases from 18% to 30% and reaches a V–0 grade in UL‐94 testing. Meanwhile, the mechanical strength receives 20% reinforcement due to a chemical crosslinking between PVA, PA, and CR. Intriguingly, unsaturated chemical bonds from PA and CR endow a favorable UV‐absorbing capacity to the PVA membrane, which will benefit the anti‐aging and food freshness retaining demands in advanced packaging applications.

Improvement of Optical Properties of Functionalized Polyvinyl Alcohol-Zinc Oxide Hybrid Nanocomposites for Wide UV Optoelectronic Applications

The functionalized polyvinyl alcohol (PVA) based nanocomposites thick films of 80 μm containing 1–3 wt% zinc oxide (ZnO) nanoparticles (NPs) were studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy were utilized for studying the structural parameters and formed chemical bonds of the synthesized PVA-ZnO films. In addition, extensive characterization has been done on their linear and nonlinear optical properties. The structural analysis of the PVA-ZnO nanocomposites revealed the formation of a wurtzite hexagonal ZnO phase embedded inside the monoclinic PVA phase. The interaction between Zn–O, and functional groups of the PVA as well as the molecular vibration exhibited in the PVA-ZnO nanocomposites were confirmed by the Raman and FTIR spectroscopy and revealed that the PVA-ZnO is a hybrid nanocomposite. The incorporated ZnO NPs ratios slightly affect the PVA films' structure, meanwhile, exhibited a detectable change in the linear/nonlinear optical properties of PVA. For example, as ZnO concentration increased from 1 wt% to 3 wt%, the direct/indirect optical band gap of PVA slightly decreased from 5.1/4.93 eV to 4.45/4.89 eV, respectively. Other optical characteristics, such as optical conductivity, dielectric constants, absorption coefficient, refractive index, etc., were evaluated. All observed optical properties versus energy/wavelength display a distinct pulse at 1.4 eV/850 nm which corresponds to the difference between the direct and indirect optical band gaps. It is expected that PVA-ZnO hybrid nanocomposites have become appropriate for implementation in numerous electronic applications due to their improved optical characteristics.

High intrinsic thermal conductive polymer films by engineered interchain hydrogen bond interactions

AbstractA series of polyvinyl alcohol (PVA) composite films containing different hydrogen bond acceptors 4,4′‐dihydroxydiphenyl (BP), 1,1′‐biphenyl‐4,4′‐diyl dihexanoate (DHB) and benzene‐1,3,5‐triyl tribenzoate (TBB) were prepared by casting method. Due to the existence of strong intermolecular interaction, the highest in‐plane thermal conductivity of the above films is 1.298 Wm−1 K−1, which is about 65% higher than pure PVA films. Fourier Transform infrared spectroscopy (FT‐IR) and wide‐angle X‐ray diffraction (WXAD) demonstrated that the TBB acts as a thermal bridge to enhance the internal interaction force and make the internal structure more regular. Strong molecular contact forces were demonstrated by mechanical tensile testing. The thermal expansion rate of the system was explored through molecular dynamics. Thermal expansion experiments proved that hydrogen bond can effectively reduce the free volume. Molecular dynamics simulations were also performed in this work. The number and density of hydrogen bonds inside different polymers were calculated, and the phonon thermal transport was quantitatively analyzed. The thermal bridge and intermolecular contact force were discovered to effectively restrict the molecular chain's activity and reduce its free volume. The results of the experiments and molecular dynamics reveal that strong intermolecular interactions and thermal bridges can significantly improve polymer intrinsic thermal conductivity.