Enhancement in the thermal and dynamic mechanical properties of high performance liquid crystalline epoxy composites through uniaxial orientation of mesogenic on carbon fiber

In this work, a high performance liquid crystalline epoxy composite was prepared and the effect of the alignment of LCE with long lateral substituent on the carbon fiber surface curing at low temperature on fracture toughness, dynamic mechanical, and thermal properties of liquid crystalline epoxy with lateral substituent (LCE6) was investigated by polarized optical microscopy (POM), wide angle X‐ray diffraction measurements (WAXS), dynamic mechanical analysis (DMA), thermogravimetric (TGA), and scanning electron microscopy (SEM). Curing degree of the composite was observed by FTIR. The experimental results indicate that the fracture toughness, glass transition temperature (T_g), thermal stability, degradation kinetics are associated with the alignment of LCE6 along long axis of carbon fiber. The alignment of LCE6 on carbon fiber surface can increase mesogen network density, which leads to higher fracture toughness, higher thermal stability, increase of the activation energies and higher T_g of the composite. The dynamic mechanical analysis shows that the compoaite possesses extremely higher dynamic storage moduli, which indicates that this LCE6/DDM/CF composite can be a high performance composite. Thus, the compoaite can be a potential candidate for advanced composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40363.     

High thermal conductivity of liquid crystalline monomer-poly (vinyl alcohol) dispersion films containing microscopic-ordered structure

The thermal conductivity of bulk polymers is usually very low, which is due to the amorphous domains where chains are randomly entangled, improving the degree of the chain alignment and forming a continuous thermal conduction network are expected to enhance the thermal conductivity. A series of liquid crystalline monomer-poly (vinyl alcohol) dispersion (MDLC) films with high thermal conductivity containing microscopic-ordered structure were prepared by introducing a highly ordered liquid crystalline monomer (LCM) exhibiting Smectic phase. The thermal conductivity of MDLC films was strongly related to the amount of LCM, which firstly increased and then decreased with the increase of LCM content. The thermal conductivity of MDLC film reached up to 1.20 W m⁻¹ K⁻¹ when the content of LCM was 15 wt% and rapidly decreased to 0.85 W m⁻¹ K⁻¹ as the content of LCM further increased to 25 wt%. LCM with low content (1–15 wt%) showed good fluidity, dispersity and interfacial compatibility in PVA molecular chains, which further increases the regularity of molecular chains alignment.     

Study on high thermal conductivity of mesogenic epoxy resin with spherulite structure

The microstructure of a mesogen-containing epoxy resin that exhibits high thermal conductivity (0.33 W/m K) was investigated by observations of the scanning electron microscope (SEM) and the polarized optical microscope (POM). It was found that there are many spherulite structures formed in the resin. We supposed that the reason for the high heat-conductivity obtained in the resin is ascribed to the existence of the spherulite morphology where highly ordered lamellar structures aggregated. The argument was strongly supported by preparing the resin films with size-changed spherulites which are induced by changing the initial curing temperature. The result revealed that the thermal conductivity increased with the increase in spherulite size. On the other hand, we have developed the spherulite size in the resin from 10 to 80 μm in diameter that resulted in a greatly improved thermal conductivity of up to 1.16 W/m K in the highest value. This study may provide a useful method to improve the thermal conductivities of mesogenic resins themselves by producing spherulite structures.     

Improved thermal conductivity of epoxy resins using silane coupling agent-modified expanded graphite

A silane coupling agent was used to modify the surface of expanded graphite (EG), which was subsequently used as a thermally conductive filler to fabricate diglycidylether of bisphenol-A (DGEBA)/EG composites with high thermal conductivity via hot blending and compression-curing processes. The surface characteristics of silane coupling agent-modified EG (Si@EG) were characterized by a variety of analytical techniques. The effects of the Si@EG content on the thermal conductivity, thermal stability, impact strength, and morphology of the DGEBA/Si@EG composites were investigated. The results revealed that the addition of 80 wt.% Si@EG increased the thermal conductivity of the composites from 0.17 to 10.56 W/m K, which was 61.1 times higher than that of pristine DGEBA. The initial decomposition temperature of the composite containing 80 wt.% Si@EG was 60.6°C higher than that of pristine DGEBA. The impact strength of the composites decreased from 2.0 to 0.87 kJ/m² when the Si@EG content increased from 0 to 80 wt.%. The scanning electron microscopy images of the fractured surfaces revealed that the EG sheets in the DGEBA matrix formed a continuous thermally conductive path at high Si@EG contents.     

Relationship between anisotropic orientation and curing of liquid crystalline epoxy resin

The effect of macroscopic orientation of liquid crystalline epoxy (LCE) resin, 4,4′‐di(2,3‐epoxypropenyloxy)phenyl benzoate, on the curing and liquid crystalline phase of LCE/diaminodiphenylester (DDE) mixture was investigated. Birefringence and curing rate of uniaxially aligned LCE/DDE on rubbed PI surface was compared with those of unaligned LCE/DDE. Anisotropic orientation accelerated the curing of LCE and facilitated the formation of liquid crystalline phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1712–1716, 2006     

Significant enhancement of thermoelectric properties of conducting PTB7 polymer by addition of appropriate dopants

Thermoelectric properties of poly({4,8-bis [(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl}{3-fluoro-2- [(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl}), commonly known as PTB7 conducting polymer was investigated for the first time by the first author in 2017, and it showed higher electrical conductivity or Seebeck coefficient (or even both) and hence, higher thermoelectric power factor than a variety of organic semiconductors. Therefore, it is worth working more on this semiconductor to improve its thermoelectric power factor. In this work, for the first time, 4 new dopants are introduced to PTB7 polymer to improve its thermoelectric properties. The materials are famous oxidants that are inexpensive and easily available with no need to perform any synthesis process, including antimony pentachloride (SbCl₅), iron trichloride (FeCl₃), thionyl chloride (SOCl₂), and iodine (I₂). As a result, significant enhancement of thermoelectric power factor after doping with antimony pentachloride (from 0.224 to 25.5 μWK⁻² m⁻¹,) and iron trichloride (from 0.224 to 18.2 μWK⁻² m⁻¹,) and moderate enhancement with thionyl chloride was obtained. For the case of iodine doping, simultaneous enhancement of electrical conductivity and Seebeck coefficient was observed due to increasing the mobility.     

Effect of CuBr2 salt treatment on the performance of nanocolloidal PPy:PSS multilayer thin film counter electrodes of dye‐sensitized solar cells

A thin Pt layer on fluorine‐doped tin oxide (FTO) glass is commonly used as the counter electrode (CE) for dye‐sensitized solar cells (DSCs). We have investigated thin layers on FTO glass made from spherical polypyrrole (PPy)–poly(styrene sulfonate) (PSS) nanocolloidal particles with and without treatment of CuBr₂ and used them as CEs. The colloidal polymer composite (PPy:PSS) was spin‐coated at 4000 rpm, and PPy:PSS multilayer (one, three, five) films were employed as the CEs. Aqueous solutions of CuBr₂ (0.5 M and 1 M) were coated onto the multilayer CEs, which increased the efficiency of DSCs. When compared with the untreated PPy:PSS counter electrodes, the CuBr₂‐treated PPy:PSS films showed lower charge‐transfer resistance, higher surface roughness, and improved catalytic performance for the reduction of . The enhanced catalytic performance is attributed to the interaction of the superior electrocatalytic activity of PPy:PSS and CuBr₂ salt. Under standard AM 1.5 sunlight illumination, the counter electrodes based on a single‐layer PPy:PSS composite with 0.5 M and 1 M CuBr₂ salt treatment demonstrated power conversion efficiencies (PCE) of 5.8% and 5.6%, respectively. These values are significantly higher than that of the untreated PPy:PSS CE and are comparable with that of a Pt CE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43772.     

Influence of the introduction of flexible alkyl chains on the thermal behavior and mechanical properties of mesogenic epoxy thermosets

A mesogenic epoxy resin (DGETAM) was cured with a series of curing agents having different lengths of long alkyl chain (nBAB, n = 4, 8, 12). Properties of the curings were compared with those of the DGEBA cured with the same curing agents revealing the achievement of a balance between certain levels of thermal properties and excellent mechanical properties. Moreover, some curing systems were prepared with twin mesogenic type epoxy resins (DGEnMA, n = 4, 6, 8, 10, 12) having different lengths of alkyl chain as a flexible spacer and the same curing agents (n′BABs). Combinations of the same concentrations of chemical structures in the basic units of the network structure were applied, and the thermal and mechanical properties of their curing systems were investigated. The fracture energy of each system increased considerably with the increase of the alkyl chain length that adjoins the two mesogenic groups in the epoxy resins. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44244.     

Fabrication and characterization of hybrid films based on polyaniline and graphitic carbon nitride nanosheet

Hybrid films of polyaniline/graphitic carbon nitride (PANI/g‐C₃N₄) deposited on titanium was fabricated. First, g‐C₃N₄ as a two‐dimensional graphite‐like structure was synthesized by the stepwise condensation reaction of melamine and cyanuric chloride in the presence of N,N‐dimethylmethanamide as a high boiling point nonnucleophilic base. Then composite films of PANI/g‐C₃N₄ were prepared by in situ electrochemical polymerization of an aniline solution containing g‐C₃N₄. Different concentrations of g‐C₃N₄ were utilized to improve the electrochemical performances of the hybrids. The resulting PANI/g‐C₃N₄ composite films were characterized by X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflection spectroscopy techniques. The electrochemical performance of the composites was evaluated by cyclic voltammetry (CV). Application of the prepared samples has been evaluated as supercapacitor material in 0.5 M H₂SO₄ solution using CV technique. The specific capacitances of PANI/g‐C₃N₄ composite films were higher than obtained for pure PANI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44059.     

Electrical resistivity and thermal conductivity properties of graphene-coated woven fabrics

In this study, it was aimed to develop electrically and thermal conductive textiles surfaces. Pretreated polyester fabrics were coated with nano graphene powders at different concentration rates (50, 100, and 200 g/kg) by knife over roll technique. Electrical resistivity, thermal conductivity, thickness and mass per unit area measurements, bending rigidity, and abrasion resistance tests of coated fabrics were performed. Surface resistivity measurements of coated fabrics were made according to ASTM D 257 standard with Keithley 8009 Resistivity Test Fixture. Surface electrical resistivity values of coated fabrics decreased with increasing concentration rates. Of note, 2.53 × 10⁴ Ω/sq surface resistivity value was obtained at 200 g/kg graphene concentration rate. Thermal conductivity measurements of coated fabrics were made according to JIS R 2618 standard with Quick Thermal Conductivity Meter (QTM-710). Thermal conductivity property of fabrics improved depending on graphene concentration. The highest thermal conductivity value (0.4243 W/mK) was obtained at 200 g/kg graphene concentration rate. One of the most important results of the study was that a maximum weight loss of 0.40% was observed in the abrasion resistance test even after 100 000 cycles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48024.     

Low dielectric and high thermal conductivity epoxy nanocomposites filled with NH2‐POSS/n‐BN hybrid fillers

Hybrid fillers of mono‐amine polyhedral oligomeric silsesquioxane/nanosized boron nitride (NH₂‐POSS/n‐BN) were performed to fabricate NH₂‐POSS/n‐BN/epoxy nanocomposites. Results revealed that the dielectric constant and dielectric loss values were decreased with the increasing addition of NH₂‐POSS obviously, but increased with the increasing addition of BN fillers. For a given loading of NH₂‐POSS (5 wt %), the thermal conductivities of NH₂‐POSS/n‐BN/epoxy nanocomposites were improved with the increasing addition of n‐BN fillers, and the thermal conductivity of the nanocomposites was 1.28 W/mK with 20 wt % n‐BN fillers. Meantime, the thermal stability of the NH₂‐POSS/n‐BN/epoxy nanocomposites was also increased with the increasing addition of n‐BN fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41951.     

Enhancing electrical conductivity and electrical stability of polypyrrole-coated cotton fabrics via surface microdissolution

High electrical conductivity and electrical stability play a significant role in building the component devices of wearable electronics textiles. In this study, an implementable and effective approach was established that involved successive steps of surface microdissolution and in situ polymerization of pyrrole on fabric surfaces. The cotton fabrics were pretreated using a NaOH/urea aqueous solution system at low temperature so as to add more adsorption sites to the surface and obtain a rough surface. Then more polypyrrole was firmly deposited on the surface of the cotton fabrics. The results showed that the treated fabrics had a lower surface resistance of 1.98 Ω/sq, and the value was almost unchanged after 10 washing cycles. The dry rubbing fastness degree of the treated fabrics can reach 4 grades, and good flexibility was maintained under different bending states. Higher electromagnetic shielding effectiveness of the treated cotton fabrics (15.4–62.9 dB) at a frequency range from 1 to 3000 MHz and excellent ultraviolet protection performance could be obtained, which can provide a theoretical reference for the design and research of flexible wearable electrode materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47515.     

PANI-chitosan-TiO2 ternary nanocomposite and its effectiveness on antibacterial and antistatic behavior of epoxy coating

A straightforward approach has been developed for fabricating antibacterial and antistatic epoxy coatings by using polyaniline-chitosan modified TiO₂ ternary nanocomposite. This nanocomposite was synthesized through the following steps. First, chitosan was grafted onto the TiO₂ nanoparticles and then final nanocomposite was prepared via solution polymerization of aniline. Electrical conductivity measurement revealed that nanocomposite with 7.5 wt % of the modified TiO₂ nanoparticles has noticeably higher conductivity compared to polyaniline. Evaluating the coatings' antibacterial property indicated epoxy coatings with the content of ternary nanocomposite show significant bactericidal activity against Gram-positive bacteria and have acceptable antibacterial action against Gram-negative ones. Also, obtained results showed that the ternary nanocomposite would greatly decrease coatings' surface resistivity and when nanocomposite content is about 2 wt % surface resistivity is about 3 × 10⁷ Ω sq⁻¹. On the contrary, the coating with nanocomposite loading exhibits improved thermal and mechanical performance compared to the coating made of neat epoxy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47629.     

Anhydrous proton‐conducting electrolyte based on a nematic poly(methyl acrylate) containing sulfonated side chains

A nematic poly(methyl acrylate) containing terminal sulfonic acids in side chains was prepared by etherification of a brominated mesomorphic precursor with 2‐hydroxyethanesulfonic acid sodium salt. Differential scanning calorimetry measurements and polarized light microscopy observation revealed that the sulfonated polymer exhibited the nematic mesophase at medium temperatures (189–227°C). Electrochemical impedance spectroscopy measurements showed that temperature dependence of anhydrous proton conductivity for the nematic polymer followed the Arrhenius law and that the estimated activation energy was 95 kJ mol⁻¹ in the nematic phase. The proton conductivities of the nematic polymer were two orders of magnitude higher than those of anhydrous Nafion®117 membrane at the same temperature. The enhanced anhydrous proton conductivities of the polymeric electrolyte were ascribed to the orientational order and fluidity of the nematic liquid crystal. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40382.     

Liquid crystalline epoxy resin modified cyanate ester/epoxy resin systems

Liquid crystalline epoxy resin (LCE) modify cyanate ester/epoxy resin blend systems were studied by scanning electron microscope, polarizing optical microscope, thermogravimetric analyzer, differential scanning calorimetry, thermal mechanical analysis, and rheometers. With the addition of LCE resin, the blends showed both an enhanced curing rate and increased glass transition temperature of cured samples. The phase structures of the blends changed from homogenous to liquid crystalline phase when the content of LCE was increased. At the same time, the mechanical properties were also improved and thermal expansion coefficients were lowed down. The thermal degradation temperatures showed little differences, while the residue char yields were slightly increased with the addition of LCE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ultrasonic characterization of conductive epoxy resin/polyaniline composites

This study presents the ultrasonic characterization of conductive epoxy resin (ER)/polyaniline (PANI) composites. The prepared PANI is mixed with ER matrix at weight percentages of 5%, 10%, and 15% for preparing the ER/PANI composites. The effects of PANI amount on the mechanical properties of ER/PANI composites are investigated by ultrasonic pulse‐echo‐overlap method. Also, electrical conductivity, ultrasonic wave velocity and ultrasonic micro‐hardness values of ER/PANI composites are correlated. Experimental results show that there is an excellent correlation between ultrasonic micro‐hardness and ultrasonic shear wave velocity. Also, the results of ultrasonic velocities and elastic constants values illustrate that the appropriate combination ratio is 95 : 5 for ER and PANI in ER/PANI composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42748.     

Enhancement of thermal conductivity of BN-Ni/epoxy resin composites through the orientation of BN-Ni fillers by magnetic field and hot-pressing

The construction of high thermal conductivity polymer composites by the orientation of fillers is of great significance in electronic devices. Herein, a novel strategy to prepare boron nitride-Ni nanoparticles/epoxy resin composites (hmBN-Ni/EP) through the synergistic effect of magnetic field and hot-pressing on the orientation of BN-Ni fillers has been reported. hmBN-Ni/EP composites have better BN orientation in the in-plane direction than other BN-based/EP composites obtained by hot-pressing or magnetic field orientation only. The thermal conductivity of hmBN-Ni/EP reached 2.42 W m^?1 K^?1 at 30 wt% BN-Ni loading, which was 1145% higher than pure EP. The enhancement of thermal conductivity of hmBN-Ni/EP was attributed to the high in-plane orientation of BN-Ni through the synergistic effect of magnetic field orientation and hot-pressing. Meanwhile, the as-prepared hmBN-Ni/EP composites showed good insulation and mechanical properties which were facilitated to its industrial application in electronic packaging. This work provided a new strategy for better orientation of BN-Based fillers in polymer matrix by combining the magnetic field orientation and hot-pressing.     

Significantly improving the Cu2+ removal performance of conducting polymer-based adsorbent from aqueous solution through cross-linking modification

Through cross-linking modification of poly(o-phenylenediamine) (PoPD) to increase the adsorption active sites, the Cu²⁺ adsorption capacity of PoPD was improved significantly. According to FT-IR, XRD, SEM and BET results, both PoPD and the cross-linked PoPD had porous or surface-adhesive porous morphology with a typical mesoporous character, the specific surface area of the latter was increased obviously from the former. Both of them showed excellent Cu²⁺ adsorption capabilities with the maximum adsorption q^exp_max of 76.51 and 85.49 mg·g⁻¹, and the corresponding removal ratios of 60.21% and 68.39%, respectively. The adsorption capacity was increased to its 1.54 times with pentaerythritol tris[3-(1-aziridinyl)propionate] (cross-linking agent-III) as cross-linking agent at pH = 5 and 25°C. Because temperature could affect the adsorption behavior of materials and the adsorption process is endothermic with ΔG < 0, the process should be accompanied by spontaneous chemical changes. The XRD, SEM–EDX mapping and XPS results showed that Cu²⁺ was successfully removed from the aqueous solution. Additionally, the adsorption was mainly based on the cation-π interaction and the formation of Cu-N bonds.     

Enhancement of electrical and thermal conductivity of polypropylene by graphene nanoplatelets

One of disadvantages of polymer composites is poor electrical and thermal conductivity. As a first step in this direction, graphene‐modified polypropylene polymer is being developed to improve its electrical and thermal conductivity. Two techniques were investigated: surface coating and extrusion. In the case of coating technique, the percolation threshold was found to be 0.5 wt % of graphene and electrical conductivity of polypropylene increased around 13 log cycles. Coating technique breaks the agglomerations due to magnetic stirring followed by sonication and gives homogeneous graphene‐coated polypropylene pellets. When polymer melts under compression molding, the graphene platelets network formed on the surface of polypropylene pellets as well as through‐the‐thickness of the molded disk, which provide continuous network of graphene. However, in extrusion technique, graphene segregated and did not disperse properly in polypropylene. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45833.     

Using water‐soluble nickel acetate as hole collection layer for stable polymer solar cells

We report polymer solar cells (PSCs) based on poly(3‐hexylthiophene (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) using water‐soluble nickel acetate (Ni(CH₃COO)₂, NiAc) instead of acidic poly(3,4‐ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) as hole collection layer (HCL) between the indium tin oxide (ITO) electrode and photoactive layer. The NiAc layer can effectively decrease R_s and increase R_p and shows effective hole collection property. Under the illumination of AM1.5G, 100 mW/cm², the short‐circuit current density (J_sc) of the NiAc based device (ITO/NiAc/P3HT : PCBM/Ca/Al) reach 11.36 mA/cm², which is increased by 11% in comparison with that (10.19 mA/cm²) of PEDOT : PSS based device (ITO/PEDOT : PSS/P3HT : PCBM/Ca/Al). The power conversion efficiency of the NiAc based devices reach 3.76%, which is comparable to that (3.77%) of the device with PEDOT : PSS HCL under the same experimental conditions. Moreover, NiAc based PSCs show superior long‐term stability than PEDOT : PSS based PSCs. Our work gives a new option for HCL selection in designing more stable PSCs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013