Thermotropic glazings for overheating protection. I. Material preselection,formulation, and light‐shielding efficiency

This article presents a systematic strategy for formulation and optimization of thermotropic layers for overheating protection purposes. Specifically, thermotropic systems with fixed domains (TSFD) which consist of a thermotropic additive finely dispersed in a matrix material are considered. Based on systematic material (component) preselection regarding thermoanalytical characteristics and refractive indices, numerous thermotropic layers were formulated. TSFD with thermoplastic matrix were produced by compounding and compression molding. TSFD with resin matrix were produced by UV curing. The thermotropic layers were analyzed as to solar optical properties, threshold temperature, switching process and residual transmittance in the opaque state applying UV/Vis/NIR spectrometry equipped with a heating stage. Best performing materials exhibited solar hemispheric transmittance in the range of 72.2–84.5% and between 59.6 and 83.7% in the clear and opaque state, respectively. Threshold temperatures between 45 and 75°C were realized. Refractive index difference between matrix and additive and solar hemispheric transmittance displayed a close correlation. Hence, refractometry was shown to be an appropriate tool for material preselection. Furthermore, investigations revealed a close correlation of thermal transitions of thermotropic additives recorded by differential scanning calorimetry and threshold temperatures of thermotropic layers formulated therewith. However, thermotropic layers formulated so far have to be optimized with respect to light‐shielding performance for efficient overheating protection. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39950.     

Low noise ultraviolet photodetector with over 100% enhanced lifetime based on polyfluorene copolymer and ZnO nanoparticles

Stability and noise current of a hybrid UV photodetector with inverted planar heterojunction (PHJ) structure indium‐tin‐oxide/ZnO nanoparticles (NPs)/poly[9,9′‐dioctyl‐fluorene‐2,7‐diyl]‐copoly[diphenyl‐p‐tolyl‐amine‐4,4′‐diyl] (BFE)/Ag are investigated. ZnO NPs as the acceptor and BFE as the donor were deposited as the active layer. Under UV light illumination, light to dark current ratio of about 10² is observed at a very low bias voltage of ?1.5 V. The spectral response of the device is located near UV region with a maximum responsivity of ～57 mA/W at wavelength of 350 nm. In particular, the prepared device exhibits remarkably higher photoresponse (～350%) and stability (～115%) enhancement under ambient condition compared to the reference device. In addition, the presented results show that the noise current of our device with PHJ structure is about an order of magnitude lower than that of commonly used bulk heterojunction system. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46533.     

Thermotropic glazings for overheating protection. II. morphology and structure–property relationships

This article completes a systematic strategy for formulation and optimization of thermotropic systems with fixed domains (TSFDs) for overheating protection purposes. Focus was on characterization of morphology and on revealing optimization potential. A comprehensive characterization of scattering domain size and shape was done applying optical microscopy and scanning electron microscopy. In general, scattering domains exhibited inappropriate size and/or shape for optimum overheating protection performance. Moreover, several TSFD displayed defects (vacuoles, voids) resulting from thermomechanical or physicochemical interaction of matrix material and thermotropic additive during manufacturing. Morphological features along with solar optical and thermorefractive properties allowed for establishment of structure–property relationships. Light‐shielding efficiency of TSFD correlated well with scattering domain size and shape. The majority of TSFD showing defects exhibited an increase of solar hemispheric transmittance upon heating. Several strategies to overcome defect formation and to improve scattering morphology were suggested and proof of concept was shown partially, thus indicating a significant optimization potential of the established TSFD. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39910.     

Controllable preparation of uniform polystyrene nanospheres with premix membrane emulsification

The expansion of polymer nanosphere applications requires facile and versatile preparation techniques. In this study, combining circled premix membrane emulsification and thermally initiated miniemulsion polymerization, we developed a new strategy for preparing uniform polystyrene nanospheres within a duration as short as 1 h. The size of the nanospheres, ranging from 40 to 120 nm, was dependent on the premix membrane emulsification cycle number, the transmembrane flow rate, and the membrane pore size; this was almost consistent with characterizations of droplet size evolution. The coefficient of variation, around 15%, indicated that the size distribution of the nanospheres was still narrow, even as the monomer‐to‐water ratio was as high as 0.2. This method may be competitive for further applications because of its high production efficiency and low system requirements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dielectric and thermal studies of the segmental dynamics of poly(methyl methacrylate)/silica nanocomposites prepared by the sol–gel method

Poly(methyl methacrylate)/silica (PMMA/SiO_x) nanocomposites were synthesized via sol–gel method and studied by various techniques. The dispersion of the silica particles (10–100 nm) in the matrix was probed by transmission electron microscopy (TEM), while solid‐state NMR and Raman spectroscopy detected the formation of an inorganic network with high degree of crosslinking. To elucidate the impact of the filler on the molecular dynamics of the PMMA, different methods were used; namely differential scanning calorimetry, thermally stimulated depolarization current and broadband dielectric relaxation spectroscopy. All three methods observed a significant impact of the nanoparticles on the segmental dynamics of the matrix, which was expressed as an increase of the glass transition temperature (T_g) in terms of calorimetry and as a shift of the α (segmental) relaxation to lower frequencies in terms of dielectric spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermo‐mechanical behavior of poly(butylene terephthalate)/silica nanocomposites

In this work, experimental results about poly(butylene terephthalate) (PBT) based nanocomposites filled with various amounts of silica nanoparticles (NPs) are reported. Two different types of filler are used: silica gel NPs, produced through the Stöber method, and a commercial fumed silica, both coated by a PBT shell. Melt‐mixed samples have been thoroughly investigated by scanning and transmission electron microscopy, infrared Fourier transform spectroscopy (FTIR), thermal gravimetric analysis, differential scanning calorimetry, wide and small angle X‐ray diffraction, and dynamic mechanical analysis. A fine and very good dispersion of NPs into the polymeric matrix is revealed through the morphological analysis when Stöber NPs were used as filler with respect to systems including commercial fumed silica particles. This evidence, combined with matrix–filler interactions revealed by FTIR spectroscopy, justifies the enhancement of both storage modulus and glass transition temperature of the former samples in comparison with reference pristine PBT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46006.     

Synthesis and evaluating of carbon nanoallotrope-biomacromolecule gel composites as drug delivery systems

This work was done to assess the role of precursors (agro and graphite) on performance of carbon nanoallotropes-biomacromolecules composite as drug delivery for controlling the release of niacin. In this respect graphene oxide and bagasse-based carbon oxide were synthesized and chelated with chitosan (Cs-GO and Cs-Co). These gel composites were characterized by many techniques [morphology, differential scanning calorimetry, Fourier-transform infrared spectroscopy, swelling, encapsulation efficiency (EE) and loading (L) % of niacin. Another series of experiments was carried out for studying the role of replacing part of carbon nanoallotrope by carboxymethyl cellulose (CMC) on performance of produced drug carries, these systems were coded as Cs-GO-CMC and Cs-Co-CMC. The data showed that, the Cs-GO gel composite provided maximum release of NA, at 5 h, for pH's simulated gastric and intestinal fluids; pH. 2.1 and pH 7.4 (1120 mg/L and 757 mg/L). The incorporation of CMC is not acceptable as it provided low drug release together with burst release of NA-drug, and consequently possible caused tissue irritation or toxicity in the human body. The Cs-GO and Cs-CO systems with relatively low drug loading were recommended for their better controllability system to NA release, which prolonging benefit of human with niacin. The NA release from all investigated gels followed Fickian and non-Fickian diffusion mechanisms.     

Effect of incorporating different polyaniline-surface modified nanosilica content into polyurethane-based quasi-solid-state electrolyte for dye-sensitized solar cells

Polyaniline-surface modified nanosilica (S-PANi) was incorporated into polyurethane (PU) to form a polymer matrix able to entrap liquid electrolyte and to function as a quasi-solid state electrolyte (QSE) in dye-sensitized solar cells (DSSCs). Nanosilica was first synthesized via sol–gel technique and was post modified with aniline to form S-PANi. The effects of introducing different S-PANi content (5, 10, 15, and 20 wt%) on the nanoparticle distribution, surface morphology, surface porosity, thermal stability, and the structure of the PU matrix were analyzed using transmitted and reflected light microscopes, TGA and X-ray powder diffraction. Additionally, polymer matrix absorptivity, conductivity, and ion diffusion of the formulated QSEs were investigated by using a digital analytical balance, the AC impedance method, and cyclic voltammetry. Lastly, all of the formulated quasi-solid-state electrolytes were applied for use in DSSCs wherein their charge recombination, photovoltaic performance, and lifespan were measured. The quasi-solid-state electrolyte based on 15 wt% S-PANi (PU-15%S-PANi) exhibited the highest light-to-energy conversion efficiency, namely 3.17%, with an open circuit voltage of 708 mV, a short circuit current of 4.13 mA cm⁻², and a fill factor of 0.65.     

Amino‐functional electrospun nanofibrous membrane for detecting nitroaromatic compounds

A novel amino‐functionalized polystyrene copolymer (PS‐NH₂) was designed and synthesized with styrene and 4‐vinylbenzyl amine. Additionally, an amino modified glass (G‐NH₂) was obtained as a carrier. (PS‐NH₂/pyrene)/G‐NH₂ fluorescent nanofibrous membrane [named (PS‐NH₂/pyrene)/G‐NH₂] was designed and prepared via electrospinning technique to detect representative saturated nitroaromatic (NAC) explosive vapor. The (PS‐NH₂/pyrene)/G‐NH₂ showed highly fluorescence stability in ambient condition and further displayed a high quenching efficiency of 70.9% toward trinitrotoluene (TNT) vapor (～10 ppb) with an exposure time of 150 s at room temperature. The abundance of amino groups could effectively adsorb NACs and the binding of electron‐deficient NACs to the amino groups on the (PS‐NH₂/pyrene)/G‐NH₂ surface led to the formation of charge‐transfer complexes. The quenching constant (K_SV) to TNT was obtained to be 1.07 × 10¹¹ mL/g in gaseous phase with a limit of detection up to 2.76 × 10^?13g/mL. Importantly, the (PS‐NH₂/pyrene)/G‐NH₂ showed notable selectivity toward TNT and 2,4‐dinitrotoluene vapors. Straightforwardly, the colorimetric sensing performance can be visualized by naked eye with a color change for detecting of different vapor phase NACs explosives. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46708     

A novel polymer composite with a small optical band gap: New approaches for photonics and optoelectronics

In this article, a novel approach is presented for the preparation of small band‐gap polymer composites. The intensity of the surface plasmon resonance (SPR) peak increased from 0.64 to 3.2 for the chitosan–silver nitrate sample containing 1 wt % titanium dioxide (TiO₂). In the cases of 3 and 5 wt % added TiO₂ particles, the SPR peak disappeared. A wide shift of the absorption coefficient from 4.36 to 0.93 eV was observed. The smallest optical band gap of about 0.98 eV was achieved for the sample containing 3 wt % TiO₂ filler. The wide shift in the optical band gap was interpreted on the bases of the formation of metal‐induced gap states between the metallic silver particles and the TiO₂ structure. A novel approach was achieved that was an alternative method to Tauc's semi‐empirical model for band‐gap estimation. The optical dielectric loss parameter for the band‐gap study was easily calculated and analyzed, whereas it unfolded a deep knowledge from the physics point of view. The established quantum mechanical expression revealed a strong relationship between the energy band gap and the optical dielectric loss parameter. The scanning electron microscopy results show the leakage of white aggregated silver particles and distinguishable intense peaks of metallic silver particles between 3 and 3.3 keV appearing in the energy‐dispersive X‐ray spectrum. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44847.     

Encapsulation of magnetic nickel nanoparticles via inverse miniemulsion polymerization

In this work, the encapsulation of magnetic nickel nanoparticles in polyacrylamide particles was performed via inverse miniemulsion polymerization. The dispersion of nickel nanoparticles was characterized in polar solvents including water, ethanol, and dimethyl sulfoxide using different stabilizers. The best results were obtained when the nonionic stabilizer poly(ethylene glycol) octadecyl ether (Brij 76) was used to stabilize the nickel nanoparticles in dimethyl sulfoxide. In addition, the block copolymer poly(ethylene‐co‐butylene)‐b‐poly(ethylene oxide) was used as a surfactant to create inverse miniemulsions while minimizing the coalescence of the miniemulsion droplets. Different types of salts such as zinc, nickel, and sodium nitrates were tested as lipophobes to retard Ostwald ripening. Transmission electron microscopy images of polyacrylamide/nickel particles synthesized with zinc and nickel salts as lipophobes indicate that nickel nanoparticles are embedded in the polyacrylamide matrix. Magnetization curves show that the saturation magnetization of polyacrylamide/nickel particles is only slightly below that of the pure nickel nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of formulation and processing conditions on light shielding efficiency of thermotropic systems with fixed domains based on UV curing acrylate resins

Within this study relationships between material formulation and processing parameters and the morphology (vacuole formation) of thermotropic systems with fixed domains (TSFD) for overheating protection purposes were investigated. Main aim was on improving light shielding efficiency of TSFD based on UV curable acrylate resins by optimization of selected key parameters including photo‐initiator type and content, type of reactive diluent, radiation intensity/dose, and thermal treatment of layers during manufacturing. Variations of type of reactive diluent and thermal treatment had a minor effect on overheating protection performance. Utilization of photo‐bleaching photo‐initiator of acylphospine oxide type instead of a blend of conventional Type I (α‐hydroxy ketone type) and Type II (benzophenone) photo‐initiators enabled reduction of radiation dose to achieve properly cured layers. The results revealed that a significant reduction of radiation intensity/dose prevented formation of vacuoles. Consequently, light shielding efficiency of TSFD was enhanced significantly. Nevertheless, obtained scattering domain size was inappropriate for optimum light shielding efficiency and requires further optimization strategies. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3299–3310, 2013     

Molecularly imprinted polymer beads prepared by pickering emulsion polymerization for steroid recognition

Pickering emulsion polymerization was used to synthesize molecularly imprinted polymer beads for the selective recognition of 17‐β‐estradiol under aqueous conditions. Scanning electron microscopy analysis indicated that the imprinted polymer beads had a small diameter with a narrow size distribution (18.9 ± 2.3 μm). The reduction in particle size achieved in this study was attributed to the altered polarity of the stabilizing nanoparticles used in the Pickering emulsion. The imprinted polymer beads could be used directly in water and showed a high binding affinity for the template molecule, 17‐β‐estradiol, and its structural analogs. These water‐compatible polymer beads could be used as affinity adsorbents for the extraction and analysis of low‐abundance steroid compounds in aqueous samples. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39606.     

Thermal stability,surface wettability and mechanical behavior of highly ordered ZnO-doped thermoplastic polyurethane films with hierarchically porous structures

In this paper, the effect of ZnO nanoparticle on thermal, microstructure, mechanical behavior, superhydrophobicity of thermoplastic polyurethane (TPU), ZnO/TPU composite materials with doped-ZnO nanoparticles were obtained via a solution blending method. The results show that the melting temperature region in soft segments of ZnO/TPU composite materials was the transition temperature region. The added ZnO slightly enhances the crystalline slipped of ZnO/TPU composite materials, and effectively hinder the transfer of high temperature small gas molecules. Due to the added ZnO nanoparticles, the microphase separation and ordered structures in TPU are reduced. In TPU, and between TPU and ZnO nanoparticles, there are variations in electron density at hard phase and soft phase interfaces. The good ZnO/TPU composites exhibit high water repellence with water contact angle of ~157°. The prepared ZnO/TPU nanocomposites show mechanical properties that are superior to those of pristine TPU. Tensile strength and storage modulus increase by 47.1% and 39.8% at ZnO loading values of 10 wt%. The results indicate that thermal behavior, microstructure, superhydrophobicity and the mechanical behavior of TPU composite materials can be enhanced by the doped ZnO.     

Interfacial modification mechanism of nanocellulose as a compatibilizer for immiscible binary poly(vinyl alcohol)/poly(ethylene oxide) blends

We undertook this study to understand reinforcement mechanism of short cellulose nanocrystals (CNCs) and long cellulose nanofibrils (CNFs) as compatibility agents for improving the interfacial miscibility of poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) blends. The effects of the two cellulose nanofibers on the morphological, mechanical, and thermal properties of the polymer blends were compared systematically. The light transparency, scanning electron microscopy, and Fourier transform infrared results show that nanocellulose between PVA and PEO eliminated the negative effects generated by the immiscible interface through increased hydrogen bonding. Thermogravimetric analysis and differential scanning calorimetry results show that crystalline region reorganization around the interface facilitated the shift of the polymer blends from multiple phases to a homogeneous phase. According to the Halpin‐Kardos and Quali models, we assumed that the potential for repairing the immiscible interface would have a larger effect than the potential of reinforcement. At the same concentration, polymer blends with CNCs showed greater light transparency, strength, modulus, and crystal structure than with those with CNFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45896.     

Ultraviolet-protective thin film based on PVA–melanin/rod-coated silver nanowires and its application as a transparent capacitor

Melanin is a biopigment in many organisms with interesting intrinsic properties suitable for emerging and sustainable technologies. In this work, we report the fabrication of transparent ultraviolet (UV)-protective thin films based on synthetic melanin in poly(vinyl alcohol) (PVA) matrixes. Melanin was synthesized through the auto-oxidation of l -3,4-dihydroxyphenylalanine (l -DOPA) under oxygen pressure, resulting in excellent solubility in water. A thin film with a composition of 3 wt % melanin (synthesized at 6 atm oxygen pressure) and silver nanowires (AgNWs) deposited on the surface has good transparency in visible light and 100% UV irradiation photoprotection. Encapsulated PVA–melanin/AgNW films dipped in water for 7 days retained 98% of their UV irradiation photoprotection. Moreover, using a transparent conductive oxide substrate, this UV-protective system can be simultaneously used as a transparent capacitor. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47805.     

Influence of TiO2 nanoparticles on nonisothermal crystallization of PP in a wide range of cooling rates analyzed by fast scanning DSC

The influence of titanium dioxide (TiO₂) nanoparticles on the crystallization behavior of polypropylene was investigated by conventional differential scanning calorimetry (DSC) and fast scanning DSC measurements. The data obtained from both methods were estimated for the first time using the Lauritzen‐Hoffmann equation to analyze the behavior over a wide cooling range under nonisothermal conditions. This provides more reliable values of nucleation parameters (K_g) and surface free energy (σ_e). The variation of the effective energy (ΔE) was determined with the Kissinger method. Regardless of the cooling rate, both K_g and σ_e indicate the role of titania as a nucleating agent enhances the crystallization rate. However, the ΔE denotes that TiO₂ acts as an obstacle to the mobility of chain segments at cooling rates below 150 °C/s, while, in contrast, the presence of titania enhances the chain mobility at cooling rates above 150 °C/s. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43944.     

Synthesis of polyacrylonitrile/polystyrene latex particles that contain platinum

Studies on the incorporation of highly dispersed platinum (Pt) nanoparticles into proton‐exchange membrane fuel cells (PEMFC) as a possible catalyst have gained tremendous attention in the past decade. The major obstacle to fully commercialize PEMFCs is the high cost of Pt as the catalyst. In this study, the incorporation of highly dispersed platinum molecules into poly(acrylonitrile) (PAN) or polystyrene (PS)/PAN latex particles was carried out to form a possible a catalyst precursor for fuel‐cell applications. Pt‐containing PAN/PS particles were prepared using miniemulsion polymerization. Both transmission electron microscopy (TEM) and induction coupled plasma (ICP) measurements indicated that Pt salt was encapsulated into PAN/PS copolymer latex particles. In addition, the encapsulation percentages of Pt salt are all above 90% for different PAN/PS ratios. Additional experiments have been carried out to convert these Pt molecules into nanoparticles and will be elaborated upon subsequent studies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41933     

Effect of hydration layer on the structure of thermo‐sensitive nanocapsules

A thermo‐sensitive nanocapsule, containing the hydration layer, was synthesized through introducing N‐isopropylacrylamide into the system of styrene miniemulsion polymerization and hexadecane as liquid template. The properties and content of the water in the hydration layer were investigated by differential scanning calorimetry. With dynamic light scattering and transmission electron microscope, the effects of temperature and solvent on the particle size and morphologies were studied. The results showed that the increase of temperature and the ethanol–water mixed solvent could decrease the thickness of hydration layer and caused the polymer chain in the shell coil‐to‐globule transition, which switched on the pathway to loading and releasing substances in the nanocapsules. By using UV‐visible spectroscopy to monitor the tracer, the diffusion coefficients were determined and verified the switching process above. In addition, the ethanol–water molecule cluster can form a stable associative structure around ethanol mole fraction of 0.4, and destroyed the hydration of the hydrophilic group. The solvent interactions were proved to be the main driving force for the coil‐to‐globule transition of poly(N‐isopropylacrylamide). Moreover, an appropriate latex particle size should exclude the hydration layer but stable dispersed in the solvent was suggested. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40589.     

Polytetrafluoroethylene-intercalated MXene membranes with good photothermal performance for enhanced laser ignition

Photothermal effect has been widely used in many areas such as cancer therapy, photothermal energy harvesting, and laser ignition. However, exploring reliable and efficient free-standing energy converter for enhancing the photothermal performance is still a challenge. Herein, free-standing membrane based on two-dimensional MXene (Ti₃C₂) nanosheets and polytetrafluoroethylene (PTFE) was fabricated and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, which demonstrated a drastic temperature rise by laser irradiation and was further used as energy converter for enhancing the photothermal performance of laser ignition. Furthermore, the initiating power of the laser initiator can be largely reduced by adding a thin layer of MXene/PTFE membrane above the B/KNO₃ cylinder. This work can give great promise for MXene-based membranes as the laser energy converter for reducing the initiating energy and promote the development of laser initiators with low initiating energy.