Localization Of Multi-walled Carbon Nanotubes Research Articles

Double percolation of multiwalled carbon nanotubes in polystyrene/polylactic acid blends

Abstract Selective localization of multi-walled carbon nanotubes (MWCNT) in polylactic acid/polystyrene (PLA/PS) bicontinuous blends is presented in this work. A masterbatch of PS with a 2 wt% content of MWCNT is prepared and then melt mixed with different amounts of PLA. This two-step process results in a double percolated morphology where PS percolates the PLA phase, and MWCNTs percolate the PS phase. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) evidence, respectively, the bicontinuous morphology and the high selectivity of MWCNT localization in the system. Double percolation leads to a very low electrical percolation threshold of about 0.45 vol% MWCNT on total volume and an electrical conductivity of 10 −9 S/cm.

Selective localization of multi-walled carbon nanotubes in bi-component biodegradable polyester blend for rapid electroactive shape memory performance

In this study, we reported a rapid electroactive ternary shape memory polymer (SMP) composites containing multiwalled carbon nanotubes (MWCNTs) and two biodegradable polyesters, namely poly(propylene carbonate) (PPC) and poly(lactic acid) (PLA). To do this, binary polymer blends were firstly prepared, and a good shape memory behavior was observed for blends with co-continuous phase morphology, where by PPC acted as the switching domain due to its good elasticity and PLA acted as the fixing domain due to its high modulus. Then MWCNTs were incorporated into PPC/PLA co-continuous phase (PPC70/PLA30, PPC50/PLA50) by simple melting blending to realize the electroactive shape memory properties. It was found that MWCNTs tended to locate more in the PPC phase than in the PLA phase. The selective localization of MWCNTs not only led to an improvement in the recovery force, but also imparted composites with high electrical conductivity in a low percolation threshold. The composites showed rapid electroactive shape memory behavior, which reached a shape recovery ratio of 97% within 30 s at 30 V. Our work provides a simple approach to utilize the selective localization of MWCNTs in the continuous phase to fabricate rapid electrical actuated SMPs with low MWCNTs loadings, which can be scaled up industrially.

Effect of the MWCNTs selective localization on the dielectric properties for PVDF/PS/HDPE ternary blends with in situ formed core–shell structure

This work demonstrated the selective localization of multiwall carbon nanotubes (MWCNTs) in poly(vinylidene fluoride) (PVDF)/poly(styrene) (PS)/high-density poly(ethylene) (HDPE) blends to be an effective method to reduce the dielectric loss.

Role of Multiwalled Carbon Nanotubes Localization on Morphology Development of PMMA/PS/PP Ternary Blends

ABSTRACTIn this work, we studied the parameters affecting the localization of multiwalled carbon nanotubes (MWCNTs) and its impact on morphology development of poly(methyl methacrylate)/polystyrene/polypropylene (PMMA/PS/PP) ternary blends, which originally have a thermodynamically preferred core–shell type morphology. We compared the results with the morphological prediction based on the thermodynamic approach. The MWCNTs localization and morphological features of nanocomposite samples were studied by means of melt linear viscoelastic experiments together with electron microscopy results. It was found that at 0.5 wt% of MWCNTs the original core–shell type morphology of the ternary blend samples almost remained intact. and this observation was independent of the sequence of feeding. At 1 wt% of MWCNTs, the core–shell morphology was retained only for those nanocomposite samples prepared using the sequential feeding mode. In addition, it was demonstrated that the thermodynamic predictions could be utilized for the nanocomposites containing low MWCNTs contents. However, this was not true for the nanocomposites with higher MWCNTs contents due to the predominating role of viscoelastic properties of the PS shell.

Studies on the selective localization of multi-walled carbon nanotubes in blends of poly(vinylidene fluoride) and polycaprolactone

A ternary system based on blends of poly(vinylidene fluoride)(PVDF) and polycaprolactone (PCL) and made the multi-walled carbon nanotubes (MWNT) selective distribution in PCL phases via melt blending has been studied. The stud- ies on conductivity of MWNT/PCL/PVDF composites with different proportions of PVDF and PCL showed that the con- ductivity was good in the mass ratio range of PVDF/PCL from 70/30 to 40/60 and that of other matching was poor. The scanning electron microscope (SEM) observation of the composites revealed co-continuous morphologies of PVDF and PCL were formed in composites under suitable proportion of PVDF to PCL. The interfacial tensions of PVDF and PCL melts was tested at mixing temperature of 200°C, the calculated wetting coefficient indicated that MWNT would selectively distribute in PCL phase owing to interfacial effects. Transmission electron microscope (TEM) observation further confirmed that co-continuous morphologies of PVDF and PCL could appear with the increase of PCL content, as indicated by MWNT selective localization in PCL.As the result, the desired structure of double percolation was built in MWNT/PCL/PVDF composites, which have much higher conductivity than that of PVDF or PCL composites with the same MWNT content. Through a strategy of selective localization of MWNT, PVDF based material with low percolation threshold (<0.5 wt%) was acquired which held promise for potential use in large-scale industrial applications.

Enhancing electrical properties of MWCNTs in immiscible blends of poly(methyl methacrylate) and styrene‐acrylonitrile copolymer by selective localization

Multiwalled carbon nanotubes (MWCNTs) were introduced into poly(methyl methacrylate) (PMMA) and styrene‐acrylonitrile copolymer (SAN) blends by melt mixing in an asymmetric miniature mixer (APAM). A composition of 70 wt% of PMMA and 30 wt% of SAN was mixed to create a co‐continuous morphology. Transmission electron microscopy images of ultra‐microtomed samples (70 nm in thickness) showed selective localization of MWCNTs inside the percolated SAN phase. The occurrence of the double percolation phenomenon resulted in lower electrical percolation thresholds of PMMA/SAN/MWCNT blends molded at high temperatures. Dielectric spectroscopy indicated a higher electrical permittivity for samples that were compression molded at 260°C. Due to the higher affinity of MWCNTs to SAN, there was a migration of MWCNTs into the SAN phase during the melt processing. Conductivity measurements revealed a significant decrease in electrical percolation threshold (0.4 wt%) for PMMA70/SAN30 blends compared with MWCNT‐filled SAN and MWCNT‐filled PMMA (ca. 0.8 wt%). POLYM. COMPOS., 37:1523–1530, 2016. © 2014 Society of Plastics Engineers

Enhanced electrical conductivity, mechanical modulus, and thermal stability of immiscible polylactide/polypropylene blends by the selective localization of multi-walled carbon nanotubes

Abstract Immiscible polylactide (PLA)/maleic anhydride-grafted polypropylene (PP) blend (50/50 by wt.%) composite films filled with different pristine multi-walled carbon nanotube (MWCNT) contents of 0.0–10.0 wt.% were manufactured by an efficient and facile melt-mixing/compression technique. The electrical, mechanical and thermal properties of the PLA/PP/MWCNT composite films were investigated by considering the morphological feature as well as the MWCNT content. SEM images of the composite films confirmed that the PLA domains were well dispersed in the PP matrix of the immiscible PLA/PP blends and that the MWCNTs were localized selectively and uniformly in the PP matrix of the composite films. Accordingly, the electrical resistivity of the composite films decreased considerably from ∼10 10 Ω cm to ∼10 1 Ω cm with the increment of the MWCNT content. The DSC cooling thermograms supported the fact that the MWCNTs served as effective accelerating agents for the melt-crystallization of the composite films as well as the development of the α-form crystals in the PP matrix. The dynamic storage modulus and the thermal degradation stability of the composite films were also increased significantly with the increment of the MWCNT content. Overall, high performance in the electrical conductivity, melt-crystallization rate, mechanical modulus, and thermal degradation stability of the PLA/PP/MWCNT composite films was found to stem from the selective and uniform localization of the MWCNTs in the continuous PP matrix.

Preparation of core-shell nanofibers with selectively localized CNTs from Shish Kebab-like hierarchical composite micelles.

A novel and facile bottom-up strategy for preparing core-shell nanofibers with selectively localized carbon nanotubes is developed using hierarchical composite micelles of crystalline-coil copolymer and carbon nanotubes as the building blocks. An amphiphilic di-block copolymer of poly (p-dioxanone) (PPDO) and PEG (polyethylene glycol) functionalized with pyrene moieties at the chain ends of PPDO blocks (Py-PPDO-b-PEG) is designed for constructing composite micelles with multiwalled carbon nanotubes (MWCNTs). The self-assembly of Py-PPDO-b-PEG and MWCNTs is co-induced by the crystallization of PPDO blocks and the π-π stacking interactions between pyrene moieties and MWCNTs, resulting in composite micelles with "shish kebab"-like nanostructure. A mixture of composite micelles and polyvinyl alcohol (PVA) water solution is then used as the spinning solution for preparing electrospun nanofibers. The morphologies of the nanofibers with different composition are investigated by SEM and TEM. The results suggest that the MWCNTs selectively localized in the core of the nanofibers of MWCNTs/Py-PPDO-b-PEG/PVA. The alignment and interfusion of composite micelles during the formation of nanofibers may confine the carbon nanotubes in the hydrophobic core region. In contrast, the copolymer without pyrene moieties cannot form composite micelles, thus these nanofibers show selective localization of MWCNTs in the PVA shell region.

Localization of carbon nanotubes in polyamide 6 blends with non-reactive and reactive rubber

Blending of two immiscible polymer matrices can be an effective way to combine favourable properties of both blend partners. The additional incorporation of multiwalled carbon nanotubes (MWCNTs) in such thermoplastic blends may further enhance the blend properties and especially generate electrical conductivity.In the present study, 20 wt.% of non-reactive rubber and maleic anhydride functionalized rubber were melt blended with polyamide 6 and 3 wt.% MWCNTs by using different incorporation strategies. For the blends containing non-reactive rubber, the MWCNTs were always localized selectively in the thermodynamically preferred polyamide phase as shown by TEM images and electrical measurements. Interestingly, the different strategies resulted in different localization behaviours of the MWCNTs in case of the reactive rubber. These findings demonstrate the significant influence of maleic anhydride groups of the rubber component on localization of MWCNTs in the different blend phases which results in different values of electrical volume resistivity of the blends.

Advanced dielectric polymer nanocomposites by constructing a ternary continuous structure in polymer blends containing poly(methyl methacrylate) (PMMA) modified carbon nanotubes

A nanocomposite with ultra-low percolation threshold and high dielectric performance is prepared by controlling the localization of multiwalled carbon nanotubes (MWNTs) in one phase of a ternary continuous polymer blend system through melt processing. Polystyrene (PS), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) can form a ternary continuous structure when the volume fractions of PS, PVDF and PMMA are 70 vol%, 20 vol%, and 10 vol%, respectively. The PS is a continuous matrix (sea-phase) whereas the other two phases are interconnected threads (the PVDF is situated as the core while the PMMA is the shell, and the thickness of the PMMA shell is about 1 μm). Adding PMMA could improve the compatibility between the PS and PVDF components. Selective distribution of MWNTs in the PMMA shell is achieved through a combination of PMMA modified MWNTs and appropriate processing procedures. The composite shows an ultra-low percolation threshold of ca. 0.3 wt%. When the weight fraction of PMMA modified MWNTs is 0.4 wt%, the dielectric constant of the composite is as high as 182 (at 100 Hz), which is about 60 times higher than that of a pure PS matrix. The composite’s dielectric properties have excellent temperature stability. This approach can provide a new and low-cost route to design high-performance dielectric materials with ultra-low percolation thresholds.

Effect of the selective localization of carbon nanotubes in polystyrene/poly(vinylidene fluoride) blends on their dielectric, thermal, and mechanical properties

The selective localization of multiwalled carbon nanotubes (MWNTs) in immiscible polystyrene (PS)/poly(vinylidene fluoride) (PVDF) blends (volume ratio of both components is 1/1) and its effect on composites’ dielectric, thermal, and mechanical properties are systematically studied. Employing two-step mixing process can make MWNTs localize in PS or PVDF phase successfully. When three components are simply mixed together by one-step processing, the MWNTs are selectively distributed in PVDF phase, which is supported by the dielectric measurements and the SEM observations and is consistent with the wetting coefficient evaluation. For the two-step mixing, when the fillers are first mixed with PS in the first step, some of them will migrate into PVDF phase in the second step although the migration is very slow. When the overall volume fraction of MWNTs is 3.9vol%, the selective localization of MWNTs in PVDF phase produces higher dielectric constant (ε′, ca. 485) than the case when the fillers are only in PS phase (ε′ of ca. 16) at 100Hz and room temperature of 25°C. Differential scanning calorimetry (DSC) measurements and mechanical tests show that the selective localization of all the fillers in PVDF phase produces little change of the melting point and crystallinity of PVDF component but slightly higher tensile strength. In contrast to the one-step mixing process, the two-step mixing to selectively localize the fillers in their favorite phase could be used to control the dielectric and mechanical properties of the materials.

Selective localization of multi-walled carbon nanotubes in thermoplastic elastomer blends: An effective method for tunable resistivity–strain sensing behavior

Abstract Conductive network morphology and interfacial interaction play important roles in determining resistivity–strain ( ρ – e ) sensing behavior of conductive polymer composites (CPCs). In this work, thermoplastic elastomer blends consisting of poly(styrene–butadiene–styrene) block polymer (SBS) and thermoplastic polyurethane (TPU) were fabricated via different melt processing procedures, which could tune the above two issues simultaneously by selectively localizing multi-walled carbon nanotubes (MWCNTs) in SBS, TPU and both in SBS and TPU, respectively. It is observed that the composite fibers with selectively localized MWCNTs show distinct different ρ – e sensing behavior. Work of adhesion calculation suggests stronger interfacial interaction between MWCNTs and SBS, however, wetting coefficient calculation indicates slightly better wetting of MWCNTs with TPU. Because of such stronger interaction and poorer dispersion, the composite fiber with MWCNTs distributed in SBS exhibits higher ρ – e sensitivity than its counterpart with MWCNTs distributed in TPU, and with MWCNTs distributed in both phases, the ρ – e sensitivity lies in between. Moreover, the ρ – e sensing behavior was fitted with a model based on tunneling theory by Simmons. It is suggested that the change in tunneling distance and the number of conductive pathways could be accelerated significantly under strong interfacial interaction. This study could offer a new pathway and provide a guideline for the preparation of high-performance CPC resistivity–strain sensors with tunable sensitivity.

Concentration Fluctuations and Segmental Dynamics in Weakly Dynamic Asymmetric Blends in the Presence of Surface‐Functionalized Multiwall Carbon Nanotubes

Surface‐functionalized multiwall carbon nanotubes (MWCNTs) are incorporated in poly(methyl methacrylate)/styrene acrylonitrile (PMMA/SAN) blends and the pretransitional regime is monitored in situ by melt rheology and dielectric spectroscopy. As the blends exhibit weak dynamic asymmetry, the obvious transitions in the melt rheology due to thermal concentration fluctuations are weak. This is further supported by the weak temperature dependence of the correlation length (ξ ≈ 10–12 Å) in the vicinity of demixing. Hence, various rheological techniques in both the temperature and frequency domains are adopted to evaluate the demixing temperature. The spinodal decomposition temperature is manifested in an increase in the miscibility gap in the presence of MWCNTs. Furthermore, MWCNTs lead to a significant slowdown of the segmental dynamics in the blends. Thermally induced phase separation in the PMMA/SAN blends lead to selective localization of MWCNTs in the PMMA phase. This further manifests itself in a significant increase in the melt conductivity. image

Functionalization of MWCNT with P(MMA-co-S) copolymers via ATRP: Influence on localization of MWCNT in SAN/PPE 40/60 blends and on rheological and dielectric properties of the composites

In this work, the localization of functionalized multi-walled carbon nanotubes (MWCNT) with random copolymers of methyl methacrylate and styrene (P(MMA-co-S)) in poly(styrene-co-acrylonitrile)/poly(2, 6-dimethyl-1,4-phenylene ether) blends (SAN/PPE) and its influence on morphological, rheological and dielectric properties of the composites were investigated. P(MMA-co-S) copolymers were grafted onto MWCNT via atom transfer radical polymerization (ATRP). The molecular weight of the copolymers was adjusted by controlling the time of reaction. In SAN/PPE blends, MWCNT grafted with low molecular weight copolymers were predominantly located at the interface of the blend and a few individual tubes were dispersed in the PPE phase. Aggregation of MWCNT was observed nearby the interfacial region because of micellization of grafted copolymers. Aggregation was more pronounced with increasing molecular weight of the grafted P(MMA-co-S) copolymer. In the melt, the composite containing MWCNT with low molecular weight copolymers had higher dynamic moduli than the one with pristine MWCNT. An increasing molecular weight of grafted copolymer led to a softening effect which resulted in a reduction of the moduli of the composite. Although a pronounced enhancement was observed for the composites with pristine MWCNT, only a small increase in electrical conductivity was achieved by adding functionalized MWCNT owing to the poor network formed by functionalized MWCNT in the blends.

Selective localization of multi-wall carbon nanotubes in homopolymer blends and a diblock copolymer. Rheological orientation studies of the final nanocomposites

In this study, pristine as well as polystyrene (PS) and poly(2-vinylpyridine) (P2VP) functionalized multi-wall carbon nanotubes (MWCNTs) were selectively incorporated in homopolymer binary blends of PS/P2VP and diblock copolymer (BCP) of the PS-b-P4VP type [P4VP: poly(4-vinylpyridine)]. Studies on the blends verified the chemical affinity of PS and P2VP grafted MWCNTs to the corresponding phase. Based on the results obtained from the blend systems, MWCNTs were incorporated in a PS-b-P4VP copolymer matrix with lamellar morphology and large amplitude oscillatory shear (LAOS) experiments were performed to achieve orientation of the BCP lamellae. The PS grafted MWCNTs (MWCNT-g-PS) were selectively sequestered in the PS phase and the P2VP grafted MWCNTs (MWCNT-g-P2VP) in the P4VP phase of the diblock copolymer. Unfunctionalized pristine MWCNTs were localized on the PS phase of the blend system and no special preference was observed towards the diblock copolymer PS domains. Small angle X-ray scattering (SAXS) analysis revealed the orientation of the alternating lamellae formed by the diblock copolymer when studied by LAOS. The localization of PS and P2VP grafted MWCNTs on the corresponding blend and BCP phase was also verified by transmission electron microscopy (TEM) studies.

One-step process to make electrically conductive thermoplastic vulcanizates filled with MWCNTs

Electrically conductive thermoplastic vulcanizates (TPVs) filled by multi-walled carbon nanotubes (MWCNTs) are prepared by a simple one-step melt mixing process, based on linear low density polyethylene (LLDPE) and ultrafine full-vulcanized rubber particles (UFRP). An ideal morphology with controlled localization of MWCNTs in continuous LLDPE matrix and appropriate size of finely-dispersed UFRP can be achieved at the same time. The controlled localization of MWCNTs in the continuous phase facilitates the formation of conductive pathway, and thus the volume resistivity of the as-prepared LLDPE/UFRP/MWCNTs thermoplastic vulcanizates is significantly decreased. The results show that both the blend ratio of LLDPE/UFRP and the loading of MWCNTs have remarkable effect on the volume resistivity. Significantly, the electrically conductive TPVs exhibit good mechanical properties duo to the fine dispersion of UFRP in LLDPE. The added MWCNTs are capable of imparting reinforcement effects to thermoplastic vulcanizates with just a slight loss of stretchability and elasticity.

The role of specific interaction and selective localization of multiwall carbon nanotubes on the electrical conductivity and phase morphology of multicomponent polymer blends

AbstractMulticomponent polymer blends involving polyamide6 (PA6), polypropylene (PP), acrylonitrile‐butadiene‐styrene (ABS) and high density polyethylene (HDPE) with multiwall carbon nanotubes (MWNT) were prepared by melt mixing technique to achieve conducting composites. MWNT were either compounded directly or by employing a masterbatch dilution approach in binary (PA6/ABS), ternary (PA6/PP/ABS) and quaternary (PA6/PP/ABS/HDPE) blends. To facilitate “network‐like'' structure MWNT were pretreated with either sodium salt of 6‐aminohexanoic acid or octadecyl tri‐phenyl phosponium bromide. Multicomponent blends with pretreated MWNT utilizing masterbatch dilution approach showed significant improvements in the bulk electrical conductivity as compared to blends prepared by direct addition approach at 2 wt % MWNT content. Phase morphology of these blends revealed co‐continuous type of morphology wherein MWNT were found to be selectively localized in the PA6 phase. The heteronucleating action of MWNT was manifested in increased crystallization temperature of mainly PA6 phase of the blends indicating preferential localization of MWNT in the PA6 phase. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Effect of styrene-acrylonitrile on the electrical resistivity of polycarbonate/multiwalled carbon nanotube composites

Multiwalled carbon nanotube (MWCNT)-filled polycarbonate (PC)/styrene–acrylonitrile (SAN) blends with a wide range of blend compositions were prepared by melt mixing in a rotational rheometer, and the effect of SAN on the electrical properties of the PC/MWCNT composites was studied. The structure/electrical property relationship was investigated and explained by a combination of MWCNT localization and blend morphology. Transmission electron micrographs showed selective localization of MWCNTs in the PC phase, regardless of the blend morphology. When the SAN concentration was 10–40 wt %, which corresponded to sea-island (10–30 wt %) and cocontinuous (40 wt %) blend morphologies (PC was continuous in both structures), the electrical resistivity decreased with increases in the SAN content. The concept of an effective volume concentration of MWCNTs was used to explain this effect. When the SAN concentration was 70 wt % or higher, the electrical resistivity was very high because MWCNTs were confined in the isolated PC particles. In addition, SAN was replaced by other polymers [polystyrene, methyl methacrylate/styrene, and poly(methyl methacrylate)]; these yielded similar blend morphologies and MWCNT localization and showed the generality of the concept of effective concentration in explaining a decrease in the electrical resistivity upon the addition of a second polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Trafficking and Subcellular Localization of Multiwalled Carbon Nanotubes in Plant Cells

Major barriers to delivery of biomolecules are crossing the cellular membranes and achieving a high cytoplasmic concentration by circumventing entrapment into endosomes and other lytic organelles. Motivated by such aim, we have investigated the capability of multiwalled carbon nanotubes (MWCNTs) to penetrate the cell membrane of plant protoplasts (plant cells made devoid of their cell walls via enzymatic treatment) and studied their internalization mechanism via confocal imaging and TEM techniques. Our results indentified an endosome-escaping uptake mode of MWCNTs by plant protoplasts. Moreover, short MWCNTs (<100 nm) were observed to target specific cellular substructures including the nucleus, plastids, and vacuoles. These findings are expected to have a significant impact on plant cell biology and transformation technologies.