Positive temperature coefficient and structural relaxations in selectively localized MWNTs in PE/PEO blends

The dispersion state of multiwall carbon nanotubes (MWNTs) in melt mixed polyethylene/polyethylene oxide (PE/PEO) blends has been assessed by both surface and volume electrical conductivity measurements and the structural relaxations have been assessed by broadband dielectric spectroscopy. The selective localization of MWNTs in the blends was controlled by the flow characteristics of the components, which led to their localization in the energetically less favored phase (PE). The electrical conductivity and positive temperature co-efficient (PTC) measurements were carried out on hot pressed samples. The neat blends exhibited only a negative temperature coefficient (NTC) effect while the blends with MWNTs exhibited both a PTC and a NTC at the melting temperatures of PE and PEO respectively. These phenomenal changes were corroborated with the different crystalline morphology in the blends. It was deduced that during compression molding, the more viscous PEO phase spreads less in contrast to the less viscous PE phase. This has further resulted in a gradient in morphology as well as the distribution state of the MWNTs in the samples and was supported by scanning electron and scanning acoustic microscopy (SAM) studies and contact angle measurements. SAM from different depths of the samples revealed a gradient in the microstructure in the PE/PEO blends which is contingent upon the flow characteristics of the components. Interestingly, the surface and volume electrical conductivity was different due to the different dispersion state of the MWNTs at the surface and bulk. The observed surface and volume electrical conductivity measurements were corroborated with the evolved morphology during processing. The structural relaxations in both PE and PEO were discerned from broadband dielectric spectroscopy. The segmental dynamics below and above the melting temperature of PEO were significantly different in the presence of MWNTs

Chitosan Immobilized Porous Polyolefin As Sustainable and Efficient Antibacterial Membranes

Polyolefinic membranes have attracted a great deal of interest owing to their ease of processing and chemical inertness. In this study, porous polyolefin membranes were derived by selectively etching PEO from PE/PEO (polyethylene/poly(ethylene oxide)) blends. The hydrophobic polyolefin (low density polyethylene) was treated with UV-ozone followed by dip coating in chitosan acetate solution to obtain a hydrophilic-antibacterial surface. The chitosan immobilized PE membranes were further characterized by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscope (XPS). It was found that surface grafting of chitosan onto PE membranes enhanced the surface roughness and the concentration of nitrogen (or amine) scaled with increasing concentration of chitosan (0.25 to 2% wt/vol), as inferred from Kjeldahl nitrogen analysis. The pure water flux was almost similar for chitosan immobilized PE membranes as compared to membranes without chitosan. The bacterial population, substantially reduced for membranes with higher concentration of chitosan. For instance, 90 and 94% reduction in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) colony forming unit respectively was observed with 2% wt/vol of chitosan. This study opens new avenues in designing polyolefinic based antibacterial membranes for water purification

Improving antifouling ability by site-specific silver decoration on polyethylene ionomer membranes for water remediation: assessed using 3D micro computed tomography, water flux and antibacterial studies

Blending immiscible polymer blends often results in coarse microstructures due to interfacial driven coarsening. However, by introducing specific interactions between the constituents, the evolving microstructure can be tailor-made. Herein, water insoluble poly(ethylene-co-methacrylic acid) zinc salt (Surlyn) was blended with water soluble polyethylene oxide (PEO) in 50/50 (wt/wt) ratio to construct co-continuous structures that were not possible by blending PE and PEO at the same fraction. By selectively etching the water soluble phase (PEO), porous membranes can be designed with well-defined microstructure as assessed using X-ray micro-computed tomography and the pure water flux across the membranes was studied systematically. In order to impart an antibacterial surface, silver was directly reduced on the membrane surface utilizing the un-neutralized carboxylic acid moieties present in Surlyn as the reducing sites. This led to uniform decoration of silver on the surface which enhanced the antibacterial and antifouling properties. The presence of silver on the membrane was confirmed by X-ray photoelectron spectroscopy (XPS). The distribution of silver and the morphology of the porous Surlyn membrane was evaluated by field emission scanning electron microscopy (FESEM) coupled with EDAX analysis. The antibacterial activity was assessed using a standard plate count method wherein the bacterial cells were in direct contact with the silver decorated membranes. The content of silver present on the surface and the sustained release from the membrane surface was monitored using inductively coupled plasma optical emission spectrometry. The present study opens new avenues in designing efficient and scalable antibacterial membranes

Unimpeded permeation of water through biocidal graphene oxide sheets anchored on to 3D porous polyolefinic membranes

3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and hot-pressed samples revealed a clear picture as to how the morphology develops and coarsens over a function of time during post-processing operations like compression molding. The coarsening of PE/PEO blends was traced using X-ray micro-computed tomography and scanning electron microscopy (SEM) of annealed blends at different times. It is now understood from X-ray micro-computed tomography that by the addition of a compatibilizer (here lightly maleated PE), a stable morphology can be visualized in 3D. In order to anchor biocidal graphene oxide sheets onto these 3D porous membranes, the PE membranes were chemically modified with acid/ethylene diamine treatment to anchor the GO sheets which were further confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and surface Raman mapping. The transport properties through the membrane clearly reveal unimpeded permeation of water which suggests that anchoring GO on to the membranes does not clog the pores. Antibacterial studies through the direct contact of bacteria with GO anchored PE membranes resulted in 99% of bacterial inactivation. The possible bacterial inactivation through physical disruption of the bacterial cell wall and/or reactive oxygen species (ROS) is discussed herein. Thus this study opens new avenues in designing polyolefin based antibacterial 3D porous membranes for water purification

A critical review on in situ reduction of graphene oxide during preparation of conducting polymeric nanocomposites

Graphene oxide (GO), prepared by chemical oxidation of graphite, serves as a building block for developing polymeric nanocomposites. However, their application in electrical conductivity is limited by the fact that the oxygen sites on GO trap electrons and impede charge transport. Conducting nanocomposites can be developed by reducing GO. Various strategies have been adopted to either reduce GO ex situ, before the composite preparation, or in situ during the development of the nanocomposites. The current state of research on in situ reduction of GO during the preparation of conducting polymeric nanocomposites is discussed in this review. The mechanism and the efficiency of reduction is discussed with respect to various strategies employed during the preparation of the nanocomposite, the type of polymer used, and the processing conditions employed, etc. Its overall effect on the electrical conductivity of the nanocomposites is also discussed and the future outlook in this area is presented

PE/PEO blends compatibilized by PE brush immobilized on MWNTs: improved interfacial and structural properties

Polyolefin based blends have tremendous commercial importance in view of their exceptional properties. In this study the interface of a biphasic polymer blend of PE (polyethylene) and PEO (polyethylene oxide) has been tailored to reduce the interfacial tension between the phases and to render finer morphology. This was accomplished by employing various strategies like addition of maleated PE (PE grafted maleic anhydride), immobilizing PE chains, ex situ, onto MWNTs by covalent grafting, and in situ grafting of PE chains onto MWNTs during melt processing. Multiwalled nanotubes (MWNTs) with different surface functional groups have been synthesized either a priori or were facilitated during melt mixing at higher temperature. NH2 terminated MWNTs were synthesized by grafting ethylene diamine (EDA) onto carboxyl functionalized carbon nanotubes (COOH(MWNTs) and further, was used to reactively couple with maleated PE to immobilize PE chains on the surface of MWNTs. The covalent coupling of maleated PE with NH2 terminated MWNTs was also realized in situ in the melt extruder at high temperature. Both NH2 terminated MWNTs and the in situ formed PE brush on MWNTs during melt mixing, revealed a significant improvement in the mechanical properties of the blend besides remarkably improving the dispersion of the minor phase (PEO) in the blends. Structural properties of the composites were evaluated and the tensile fractured morphology was assessed using scanning electron microscopy

Chitosan Nanocomposite-Based Triboelectric Nanogenerators with Enhanced Electrical Performance: An Opportunity for Bioelectronics

Triboelectric nanogenerators (TENG) based on natural biomaterials are essential for energy-harvesting applications. In this work, an efficient approach was proposed to enhance the electrical performance of chitosan (CS), which is a naturally occurring biopolymer with the incorporation of polyethylenimine-grafted graphene oxide (PEI-GO) nanoparticles. Triboelectric properties of the different weight combinations of PEI-GO in CS were tested against polytetrafluoroethylene (PTFE). An improvement in the mechanical and electrical properties of the nanocomposites was observed in comparison to pure chitosan. Thus, the composite with 10 wt % PEI-GO was used as the positive layer in the TENG device, and an open-circuit voltage (Voc) of ∼222 V, short circuit current (Isc) of ∼6.6 μA, and transfer charge (Qsc) of ∼149.6 nC were observed. Almost a 5.5 fold increase of the output power (∼1465.2 μW) and its power density (∼407 mW/m2) were seen for the nanocomposite in comparison to that of pure CS. The TENG was able to power calculators and wristwatches and light up 126 blue light-emitting diodes (LEDs). Further, a TENG was fabricated with the same polymer (CS and CS nanocomposite) as tribo-layers, where the pure CS polymer acts as the tribo-negative layer and PEI-GO-incorporated CS acts as the tribo-positive layer in the CS polymer-based TENG. The device was found to light up 14 white LEDs with the human hand tapping. This study thus presents opportunities for utilizing biomechanical energy found in everyday life to power bioelectronics with bioderived materials

Chitosan Nanocomposite-Based Triboelectric Nanogenerators with Enhanced Electrical Performance: An Opportunity for Bioelectronics

Triboelectric nanogenerators (TENG) based on natural biomaterials are essential for energy-harvesting applications. In this work, an efficient approach was proposed to enhance the electrical performance of chitosan (CS), which is a naturally occurring biopolymer with the incorporation of polyethylenimine-grafted graphene oxide (PEI-GO) nanoparticles. Triboelectric properties of the different weight combinations of PEI-GO in CS were tested against polytetrafluoroethylene (PTFE). An improvement in the mechanical and electrical properties of the nanocomposites was observed in comparison to pure chitosan. Thus, the composite with 10 wt % PEI-GO was used as the positive layer in the TENG device, and an open-circuit voltage (Voc) of ∼222 V, short circuit current (Isc) of ∼6.6 μA, and transfer charge (Qsc) of ∼149.6 nC were observed. Almost a 5.5 fold increase of the output power (∼1465.2 μW) and its power density (∼407 mW/m2) were seen for the nanocomposite in comparison to that of pure CS. The TENG was able to power calculators and wristwatches and light up 126 blue light-emitting diodes (LEDs). Further, a TENG was fabricated with the same polymer (CS and CS nanocomposite) as tribo-layers, where the pure CS polymer acts as the tribo-negative layer and PEI-GO-incorporated CS acts as the tribo-positive layer in the CS polymer-based TENG. The device was found to light up 14 white LEDs with the human hand tapping. This study thus presents opportunities for utilizing biomechanical energy found in everyday life to power bioelectronics with bioderived materials

Chitosan Nanocomposite-Based Triboelectric Nanogenerators with Enhanced Electrical Performance: An Opportunity for Bioelectronics

Triboelectric nanogenerators (TENG) based on natural biomaterials are essential for energy-harvesting applications. In this work, an efficient approach was proposed to enhance the electrical performance of chitosan (CS), which is a naturally occurring biopolymer with the incorporation of polyethylenimine-grafted graphene oxide (PEI-GO) nanoparticles. Triboelectric properties of the different weight combinations of PEI-GO in CS were tested against polytetrafluoroethylene (PTFE). An improvement in the mechanical and electrical properties of the nanocomposites was observed in comparison to pure chitosan. Thus, the composite with 10 wt % PEI-GO was used as the positive layer in the TENG device, and an open-circuit voltage (Voc) of ∼222 V, short circuit current (Isc) of ∼6.6 μA, and transfer charge (Qsc) of ∼149.6 nC were observed. Almost a 5.5 fold increase of the output power (∼1465.2 μW) and its power density (∼407 mW/m2) were seen for the nanocomposite in comparison to that of pure CS. The TENG was able to power calculators and wristwatches and light up 126 blue light-emitting diodes (LEDs). Further, a TENG was fabricated with the same polymer (CS and CS nanocomposite) as tribo-layers, where the pure CS polymer acts as the tribo-negative layer and PEI-GO-incorporated CS acts as the tribo-positive layer in the CS polymer-based TENG. The device was found to light up 14 white LEDs with the human hand tapping. This study thus presents opportunities for utilizing biomechanical energy found in everyday life to power bioelectronics with bioderived materials