Novel approaches to flexible visible transparent hybrid films for ultraviolet protection

Herein, we present an overview of the most recent achievements and innovations regarding the development of flexible visible transparent films for selective ultraviolet (UV) shielding, with focus on those based on hybrid inorganic–organic materials. The main synthetic paths used nowadays to ensure a high degree of protection are reviewed. Polymers containing organic UV absorbing molecules, hybrid mixtures of polymers and nanoparticles, and the recently introduced series of structures displaying structural color, are identified as the three main types of materials used for this purpose. The use of biocompatible and flexible films to achieve spectrally selective UV protection can find applications in a wide diversity of fields such as photo‐treatment of skin diseases, food and beverage packing, and storage of cosmetics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Optical rotatory power of biodegradable polylactic acid films

Polylactic acid (PLA) is a polymer material on which biodegradability research has been the most advanced. PLA is a chiral polymer in which molecules containing asymmetric carbon atoms have a helical structure. Two optical isomers of PLA exist, PLLA (poly(L-lactic acid)) and PDLA (poly(D-lactic acid)). In this study, using various physical processes, we fabricated various samples such as oriented PLLA film, PLLA fiber, rolled PLLA film and forged PLLA plate. We observed a large optical rotatory power ρ in the cylindrical plate fabricated using a forging process. ρ of forged PLLA plates is 7200°/mm which is approximately 300 times larger than that of α-quartz.     

Characterization of linear and cyclic polylactic acids and their solvolysis products by electrospray ionization mass spectrometry

Linear and cyclic polylactic acids (PLAs) were characterized using electrospray ionization mass spectrometry (ESI-MS) as part of our ongoing investigation of the hydrolysis mechanism of biodegradable polymers. The condensation oligomers of linear polylactic acid (LPLA) were synthesized by thermal dehydration of L-lactic acid. The trimer and tetramer base polymers of cyclic polylactic acid (CPLA) were obtained by cyclization reactions of lactic acid trimers and tetramers, respectively. In the ESI-MS/MS measurement, LPLA yielded three types of product ion series, while CPLA yielded only one type, from which the repeated units of CPLA were removed. The MS/MS spectrum of the NH4+ adduct ion for both cyclic and linear PLA showed loss of one ammonia molecule. The postsource decay (PSD) spectrum of CPLA by matrix-assisted laser desorption ionization (MALDI) mass spectrometry was similar to the ESI-MS/MS spectrum, while that of LPLA was different. In addition, the degradation of cyclic and linear PLAs by solvolysis was investigated. Solvolysis with anhydrous MeOH was quite feasible, but did not readily occur in the presence of even a small amount of water in the MeOH solvent.     

Syntheses of biphenyl‐terminated polyhedral oligomeric octasilicate‐core dendrimers and their single‐component optical transparent free‐standing thermoplastic films

2‐Biphenylethyl and 2‐biphenylhexyl‐terminated polyhedral oligomeric octasilicate (OS)‐core polyester‐typed dendrimers, denoted as OS‐C2‐BP and OS‐C6‐BP, respectively, were prepared by ring‐opening reaction and subsequent condensation of octakis(propenyl succinicanhydrido)polyhedral octasilicate (OS‐SA) with 2‐(4‐phenylphenoxy)ethanol (BP‐C2‐OH) and 6‐(4‐phenylphenoxy)hexanol (BP‐C6‐OH), respectively. OS‐C2‐BP formed a transparent film, whereas OS‐C6‐BP formed an opaque whitish waxy film. The coating film of OS‐C2‐BP was easily peeled off from a substrate and formed a free‐standing film. The results of X‐ray diffraction and differential scanning calorimeter suggest that the film of OS‐C2‐BP was amorphous, whereas OS‐C6‐BP contained crystalline domains. Thermogravimetric analysis of OS‐C2‐BP and OS‐C6‐BP showed 5 wt % weight losses at 362 °C and 283 °C, respectively. OS‐C2‐BP offered higher thermal resistance than OS‐C6‐BP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1437–1443     

Preparation and characterization of transparent TiO2 thin films coated on fused-silica substrates

The transparent TiO₂ thin films coated on fused-SiO₂ substrates were prepared by the sol–gel method and spin-coating technique. Effects of calcination temperature on crystal structure, grain size, surface texture, and light transmittance of the films were investigated. After calcining at 600–1,200 °C, the thicknesses of the TiO₂ films were all around 80 nm and the molecular structures of the films were anatase, even at 1,200 °C. The calcined TiO₂ films had the ultraviolet light (wavelength 200–400 nm) transmittances of ≤29% and the visible light (wavelength 400–800 nm) transmittance of ≥72%. By photocatalytically decomposing the methylene blue (MB) in water, the photocatalytic activities of the TiO₂ thin films were measured and represented using the characteristic time constant (τ) for the MB degradation. While the films prepared at 1,000 and 1,200 °C photodecomposed about 54 mol% of the MB in water (the corresponding τ ≈ 14.8 h) after exposing to 365-nm UV light for 12 h, the films prepared at 600 and 800 °C had smaller τ (≈9.0 h) and photodecomposed about 74 mol% of the MB in water at the same testing conditions.     

Preparation of glutamine films on silicon substrates

Amino acids and polypeptides thin films, pure or attached to polymers, present large application as sensors and biosensors. The interactions between such films and the supports, their sensorial properties, as well as the development of techniques to produce thin regular films, are still challenges in the area. In this work, we present the preparation of L ‐glutamine thin films on silicon substrates, the factors that determine amino acid/silicon substrate interaction, and the morphology of the films. For this purpose, a 2⁴ factorial design is used, taking into account the effects of the solvent system, the glutamine concentration, the temperature, as well as the pretreatment of the substrate surface. The contact angles between a drop of glutamine solution and the silicon substrate were taken for the preliminary evaluation of the affinity between the amino acid and the substrate. The results have shown six promising experimental combinations with oxidized silicon as substrate to improve the solution/substrate interaction. Three of these promising conditions involved aqueous solution of L ‐glutamine and three alkalis solution. The obtained films were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS), and Fourier transform infrared (FTIR) spectroscopy. The selected experimental conditions permitted to prepare a variety of films with L ‐glutamine, like small crystals, lamellas, needles, and smoothed regular films. The systems prepared in presence of alkalis solution yielded regular and smooth films. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of conductive,flexible and transparent films by in situ deposition of polypyrrole nanoparticles on polyethylene terephthalate

In this study polypyrrole (PPy) nanoparticles were deposited as a thin film on the modified surface of polyethyleneterephthalate (PET) by in situ chemical polymerization in the presence of sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (DBSNa) and mixture of them as the surfactant. The surface of PET was modified by KOH before deposition and was investigated for conductivity and adhesion of PPy nanoparticles to PET. Resulting conductive flexible films were characterized by UV–Vis spectroscopy, fieldemission scanning electron microscopy, contact angle measurements and four-point-probe technique for conductivity. Direct morphological observation (FESEM) and electrical measurements indicated that the morphology, conductivity and the nature of deposited PPy films depend on surfactant, surface modification of PET and monomer concentration. In optimized process condition, uniform conductive films of PPy were obtained with good adhesion to PET.     

Growth of poly(3,4‐ethylenedioxythiophene) films prepared by base‐inhibited vapor phase polymerization

Transparent [90% transmittance at 550 nm at a sheet resistance (R_s) of 279 Ω sq^?1] poly(3,4‐ethylenedioxythiophene) (PEDOT) films with electrical conductivities up to 1354 S cm^?1 are prepared using base‐inhibited vapor phase polymerization at atmospheric pressure. The influence of reaction conditions, such as temperature and growth time, on the film formation is investigated. A simple and convenient two‐electrode method is used for the in situ measurement of resistance, enabling to investigate the growth mechanism of polymer films and the influence of different parameters (relative humidity and the amount of oxidant) on the film growth. Low humidity exerts a detrimental effect on film growth and conductivity. In situ R_s measurements suggest that a large structural change occurs upon washing the PEDOT‐oxidant film. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2014 , 52, 561–571     

Decoupling the effects of crystallinity and orientation on the shear piezoelectricity of polylactic acid

Shear piezoelectricity has been shown to be linearly proportional to the product of polymer crystallinity and orientation. However, investigations concerning the singular and cumulative effects of these parameters are incomplete since these studies relied exclusively on using orientation to alter crystallinity. In this research, polylactic acid (PLA) samples were fabricated by a dual drawing/annealing process to expand the investigation into the relationship between crystallinity, orientation, and shear piezoelectricity. The results of this study show for the first time that PLA shear piezoelectricity possesses a stronger relationship with the product of crystallinity and orientation than either of these parameters individually. However, this research also shows that processing of PLA for shear piezoelectric applications should focus only on achieving large degrees of orientation, which will inherently lead to increases in crystallinity as well. This approach will optimize PLA's shear sensing capabilities while avoiding certain detrimental effects, specifically embrittlement and a reversal of polymer chain orientation, which can occur during annealing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1555–1562, 2011     

Crystallization and flame‐retardant properties of polylactic acid composites with polyhedral octaphenyl silsesquioxane

To develop environmental‐friendly and flame‐retarded polymer composites, bio‐based polylactic acid (PLA) was loaded with thermally stable polyhedral octaphenyl silsesquioxane (OPS). Pure PLA and PLA/OPS composites with the OPS of 1, 3, 5, and 10 wt% were prepared by extrusion and injection molding, respectively. The scanning electron microscopy (SEM), polarized optical microscope (POM), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and thermal gravimetric analysis (TGA) were used to analyze the dispersion of the OPS in the PLA matrix and the effects of OPS on the crystallization and thermal stability properties of PLA/OPS composites, respectively. Limited oxygen index (LOI) and cone calorimeter (CONE) measurements were used to study flame retardancy of PLA and PLA/OPS composites. In order to study the flame‐retardant mechanism, the char residues were investigated by SEM, Fourier transform infrared spectra (FTIR), and X‐ray photoelectron spectroscopy (XPS). TGA‐FTIR was used to analyze the gaseous products of their thermal decomposition. The results show that the OPS particles were submicron in the PLA and could increase the crystallization rate of PLA and form small‐sized secondary α‐form crystalline compared with the pure PLA spherulite. The PLA and OPS decomposed individually in the PLA/OPS composites by TGA. According to the LOI tests, the PLA with the OPS loading exhibited very small reduction of LOI. However, the CONE tests indicated that the OPS could improve the flame retardancy of the PLA by means of low peak heat release rate and average heat release rate. It was obtained that the degree and type of the PLA crystalline for the pure PLA and PLA/OPS affect their flame retardancy. In the max thermal decomposition stage of PLA and PLA/OPS, their gaseous products were similar; at high temperatures, the PLA/OPS produced simple and clear gaseous products of PLA with solid SiO₂ in the gas phase.     

Characterization of polylactic acid green composites and its biodegradation in a bacterial environment

The growing interest in the preservation of our environment is pushing for solutions to develop less impacting materials. Thus, the development of biocomposites and is recyclable and compostable end-of-life resources seem an interesting alternative. In this study, the characterization of Polylactic acid (PLA) reinforced with treated and untreated Olive husk flour (OHF) were investigated. More then, their biodegradation with a Bacillus sp. has been evaluated. The main results show that the bacteria degraded both the PLA and the composite. This degradation was confirmed by the release of reducing sugars as well as increasing weight loss of PLA matrix and composites.     

Solvent‐free inkjet printing process for the fabrication of conductive,transparent, and flexible ionic liquid‐polymer gel structures

A new and solvent‐free process for the fabrication of inkjet printed ionic liquid‐polymer gel microstructures with high‐resolution (line widths of ～40 μm), good electrical conductivity (5–30 mS cm^?1), optical transparency, and mechanical flexibility is presented. Carrying out the printing and polymerization process in nitrogen atmosphere eliminates the inhibiting influence of oxygen and guarantees homogeneously gelled structures. Careful selection and combination of ionic liquids (ILs) and unsaturated monomers makes it possible to achieve low viscosities which are printable with commercially available inkjet printers and printheads without adding extra solvents. By using different types and amounts of ILs and monomers the resulting properties of the printed IL‐polymer gels can be controlled in terms of ionic conductivity, optical transmission, and mechanical flexibility. Higher conductivities are possible by using a bifunctional instead of a monofunctional monomer, which allows one to lower the amount of monomer without loss in mechanical strength. Cast samples make it possible to obtain data of transmission (～90% for 170‐μm thick films) and mechanical flexibility (E = 0.02–0.23 MPa) of bulk material. Comparing electrical conductivity of printed and cast samples, the higher values of printed samples indicate the conductivity enhancing influence of moisture absorbed from the surrounding atmosphere after the fabrication process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Molecular structure regulation of functional polylactic acid based on chain expansion reaction and its improved hydrolysis resistance

In this work, the functional polylactic acid (PLA) was synthesized using epoxy chain extender (ADR) as a chain extender agent through melt blending method. The effects of ADR content on the molecular structure, thermal properties, and tensile properties of the functional PLA were investigated. Meanwhile, the hydrolytic behavior of the PLA/ADR materials at different hydrolysis temperatures was explored. It was found that ADR effectively regulated the molecular structure of PLA in the molten state and significantly increased the relative molecular weight, storage modulus, and complex viscosity of PLA. In addition, the Cole-Cole diagram results suggested the branched structure of PLA chain expansion systems. Based on mechanical property tests, it was noted that the addition of ADR made the molecular chain form a micro-crosslinked structure. Additionally, the mass loss rate of PLA/1.6ADR (the dosage of ADR was 1.6 wt%) was 14.75% after 14 weeks of hydrolysis under hydrolysis conditions at 58°C, while that of pure PLA was 25.89%. Moreover, the functional PLA/ADR materials exhibited significantly slower decrease rates in molecular weight, melting temperature, and tensile strength, and still maintained intact morphology after 14 weeks of hydrolysis compared to pure PLA. Therefore, the molecular structure of PLA is effectively regulated by ADR, which greatly enhances the hydrolysis resistance and further promotes the range of application of PLA.     

Preparation and characterization of nanostructured thin films of Au and Ag nanoparticles synthesized by ascorbic acid on modified glass surface

Immobilization of Ag and Au nanoparticles (NPs) synthesized by ascorbic acid on chemically modified glass surface has been studied. 3‐[2‐(2‐Aminoethylamino)ethylamino]propyl‐trimethoxysilane (AMPTS), N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilan, and 3‐trimethoxysilyl‐1‐propanethiol (MSPT) were used as surface modifying agents. To improve immobilization efficiency, the ammonia solution has been used along with the silane reagents, which assisted to adsorb the metal NPs on glass surface. It was found that AMPTS and MSPT have considerable effect on deposition of Ag and AuNPs on glass substrate. The fabricated thin films were characterized by using UV‐Vis spectroscopy, atomic force microscopy, energy‐dispersive X‐ray spectroscopy and subjected to antimicrobial resistance test. The UV–Vis spectra show a distinctive plasmon resonance absorbance peak for thin films of Au and AgNPs prepared with MSPT and AMPTS, respectively. Atomic force microscopy images indicate that formation of Au and AgNPs with spherical morphology after immobilization on the glass substrate and also the dimensions of NPs on the surface appear larger than those observed in the parent colloidal solution. Energy‐dispersive X‐ray spectroscopy measurements confirmed the presence of silver and gold on the modified glass surface, and elemental composition was measured. The Au and AgNPs thin films show antibacterial activity against gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria in comparison with a blank sample. Copyright © 2015 John Wiley & Sons, Ltd.     

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In₂O₃ (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)₃, formed on the surface of the nm-sized ITO particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

High thermal conductivity polylactic acid composite for 3D printing: Synergistic effect of graphene and alumina

With the continuous development of the electronics industry, in order to meet the requirements of electronic equipment to reduce the size and increase power consumption, the development of high thermal conductivity materials is crucial. In this study, thermally conductive polylactic acid (PLA) composites were prepared by constructing graphene and alumina (Al₂O₃) hybrid filler network, and it was further successfully used in additive manufacturing. Due to the synergistic effect of Al₂O₃ and graphene, the resulting composite achieved the thermal conductivity of 2.4 Wm^?1 K^?1 with 70 wt% Al₂O₃ and 1 wt% graphene, which are superior to data reported in the literature in the same filler condition. The Al₂O₃ and graphene hybrid filler network reduced the agglomeration of graphene and the thermal contact resistance between the fillers, thereby leading a faster cooling rate. Furthermore, the obtained thermally conductive PLA composite has good thermal stability at a normal temperature. The PLA composite powder obtained by the cryogenic pulverization can be used in the laser sintering additive manufacturing process to prepare a heat conductive material with a complicated shape.     

Preparation and properties of sol-gel coating films

The present state of our knowledge on sol-gel coating films has been reviewed. A qualitative discussion is made on the limit of the film thickness which can be achieved in the sol-gel method and the factors affecting the film thickness. Considering that properties of the film are intimately related to the microstructure, types of microstructures accomplished by the sol-gel coating are introduced with examples.     

Doping of polyaniline films with organic sulfonic acids in aqueous media and the effect of water on these doped films

Polyaniline (PANI) films in the form of emeraldine salt (ES) doped with aqueous organic sulfonic acids such as camphorsulfonic acid (CSA), p-toluenesulfonic acid (p-TSA) and dodecylbenzenesulfonic acid (DBSA) were studied. The ES films were obtained by treating the PANI in the form of emeraldine base (EB) with the aqueous solution of the acids. The dopant weight fraction (w), which is related to the mass gain during the redoping of EB, was in situ determined using a quartz crystal microbalance (QCM). The behaviour of PANI doping with different acids indicates that the uptake shows a slow diffusion process. The kinetics of the doping reaction is dominated by Fickian diffusion kinetics. The diffusion coefficients (D) of the dopant ions into the PANI chains were determined and were found to vary within the range of (1.6-18) × 10⁻¹⁵ cm² s⁻¹. Moreover, the effect of water on these doped ES films was studied. The starting point is the fact that PANI-coated the electrode of QCM shows significant frequency shifts on exposure to water. The changes in the frequency as a function of treatment time in water were quantitatively measured. The response of the device suggests that the mass decrease under water exposure is due to dopant ions release. The latter films were dedoped by exposure to ammonia solution to obtain the EB film form. A further decrease in the mass of the films was observed. The percentage of the mass loss due to water exposure is found to be less than w determined during the dedoping process.     

Preparation of films from aluminum acetylacetonate by plasma sputtering

Aluminum acetylacetonate has been reported as a precursor for the deposition of alumina films using different approaches. In this work, alumina‐containing films were prepared by plasma sputtering this compound, spread directly on the powered lowermost electrode of a reactor, while grounding the substrates mounted on the topmost electrode. Radiofrequency power (13.56 MHz) was used to excite the plasma from argon atmosphere at a working pressure of 11 Pa. The effect of the plasma excitation power on the properties of the resulting films was studied. Film thickness and hardness were measured by profilometry and nanoindentation, respectively. The molecular structure and chemical composition of the layers were analyzed by Fourier transform infrared spectroscopy and energy dispersive spectroscopy. Surface micrographs, obtained by scanning electron microscopy, allowed the determination of the sample morphology. Grazing incidence X‐ray diffraction was employed to determine the structure of the films. Amorphous organic layers were deposited with thicknesses of up to 7 µm and hardness of around 1.0 GPa. The films were composed by aluminum, carbon, oxygen and hydrogen, their proportions being strongly dependent on the power used to excite the plasma. A uniform surface was obtained for low‐power depositions, but particulates and cracks appeared in the high‐power prepared materials. The presence of different proportions of aluminum oxide in the coatings is ascribed to the different activations promoted in the metalorganic molecule once in the plasma phase. Copyright © 2013 John Wiley & Sons, Ltd.