Synergistic effect on static and dynamic mechanical properties of carbon fiber-multiwalled carbon nanotube hybrid polycarbonate composites

Carbon fiber (CF) and multiwalled carbon nanotube (MWCNT)-reinforced hybrid micro-nanocomposites are prepared through melt mixing followed by injection moulding. The synergistic effect on both the static and dynamic mechanical properties with MWCNT/aMWCNT and CF reinforcement in a polycarbonate matrix is investigated by utilizing dynamic mechanical analysis, and flexural and tensile measurements. The enhancement in the flexural modulus and strength of the composite specimens as compared to pure PC for maximum loading of CF is 128.40% and 39.90%, respectively, which further improved to 142.94% and 42.60%, respectively, for CF-functionalized MWCNTs. Similarly, the storage modulus of the composite specimens reinforced with a maximum loading of CF and CF-functionalized MWCNTs show an increment of 176.57% and 203.33%, respectively over pure PC at 40 degrees C. Various types of parameter such as the coefficient C factor, degree of entanglement and adhesion factor have been calculated to analyze the interaction between fillers and the polymer matrix. Composite specimens containing 2 wt% of functionalized MWCNTs show a lower C value than the as-synthesized MWCNTs, which is indicative of a higher effectiveness of functionalized MWCNT-containing composite specimens. These results are well supported by optical microscopy and Raman spectroscopy by confirming the distribution of reinforcement

Metal-organic framework materials for low-k dielectrics and selective sensing applications

Metal-organic frameworks (MOF) are fascinating hybrid materials, gained widespread attention from the scientific community since their emergence about three decades ago. The high porosity and tailorability of MOF structures make them an ideal candidate material for both low-k dielectrics and electrical sensing applications. In this work, an in-depth study on different MOFs was carried out to explore the influence of host-guest interaction and external stimuli including pelleting stress, operating temperature, and frequency, on MOF dielectrics. Additionally, a mechanism was proposed to identify the exceptional MOF materials for target guided electrical sensing and optimise the sensor preparation parameters to enhance its selectivity and sensitivity to revolutionise the conventional electrical sensors. Both polycrystalline (in the form of pellets) and single-crystal MOF samples were studied to gain a deeper insight into both areas. First, the influence of different external stimuli (temperature, pressure and amorphization) on broadband dielectrics (Hz-MHz and THz) was investigated for both HKUST-1 and MIL-100 MOF systems, to gain a greater understanding of structure-property relation. Secondly, by leveraging the different synthesis approaches, the role of guest molecules was also analyzed for both the polycrystalline powder pellets and single-crystal HKUST-1 MOF systems in the Hz-MHz frequency range. The single-crystal study, which is independent of pelleting pressure and free of grain boundary influence, provided a greater insight into the MOFs intrinsic properties. Thirdly, the impact of host-guest interaction dependent electrical response was materialised in the form of proof-of-concept electrical sensor applications. Overall, this work consolidates the candidacy of MOFs as an efficient low-k material and also expands its future portfolio to the realm of ultra-trace highly sensitive electrical sensing

Depression in glass transition temperature of multiwalled carbon nanotubes reinforced polycarbonate composites: effect of functionalization

Functionalized multiwalled carbon nanotubes (a-MWCNTs) and non-functionalized MWCNTs were melt mixed with polycarbonate polymer by utilizing twin screw micro compounder having a back flow channel to obtain nanocomposites with varying composition from 0.5 to 10 wt% MWCNT and 2 wt% a-MWCNT. Mechanical properties of composite samples were studied using dynamic mechanical analyzer, flexural and tensile tests. Both DMA and flexural and tensile tests suggest formation of continuous network of CNT-polymer that is supported by measured storage modulus for different loading of MWCNT and a-MWCNT. The composite sample showed lower glass transition temperature (T-g) as compared to pure PC. Effect of functionalization of MWCNTs on T-g of its of polycarbonate composites is studied and showed higher T-g depression in functionalized MWCNTs compared to non functionalized MWCNTs based composites over pure polycarbonate. In DMA, lowering of height of tan delta peak indicates that polymer in composite material participating in T-g was reduced along with loading of MWCNT, consistent with immobilization of polymer material present at the CNT interface. Effect of functionalization on morphology was investigated using scanning electron microscope and confirms the better interaction in case of a-MWCNTs compare to MWCNTs based composites. Further, Raman spectroscopic analysis indicates higher interaction between a-MWCNT and PC matrix as compared to as synthesized MWCNT

Mechanical and electrical properties of high performance MWCNT/polycarbonate composites prepared by an industrial viable twin screw extruder with back flow channel

High performance multiwall carbon nanotube (MWCNT) reinforced polycarbonate (PC) composites were prepared using an industrially viable fast dispersion process by a micro twin screw extruder with back flow channel and their mechanical and electrical properties were investigated for EMI shielding applications. A uniformly dispersed MWCNT/PC composite system was observed through SEM and TEM investigations. Incorporation of a small amount of MWCNT (2 wt%) led to enhancements in the tensile strength (up to 79.6 MPa) and flexural strength (up to 110 MPa), which were equivalent to 19.6% and 14.6% increases over the neat PC. The effect of MWCNTs on the failure mechanism of the PC under tensile loading showed a ductile to brittle transition with increasing concentration of MWCNTs. The results of enhanced mechanical properties were well supported by micro Raman spectroscopic studies. In addition to the mechanical properties, significant improvement in the electrical conductivity (0.01 S cm(-1) at 10 wt% MWCNT) of these composites was observed which yielded the EMI shielding of -27.2 dB in the Ku band suggesting their possible use as a high strength EMI shielding material

Significant improvement in static and dynamic mechanical properties of graphene oxide-carbon nanotube acrylonitrile butadiene styrene hybrid composites

Herein, hybridization of graphene nanosheets and carbon nanotubes (CNTs) has been made to solve the problem of restacking of graphene nanosheets and agglomeration of CNTs. The multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO) and graphene oxide-carbon nanotubes (GCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites have been prepared using micro-twin-screw extruder. The effect of these reinforcements on static and dynamic mechanical properties of composites is studied. The ultimate tensile strength and elastic modulus for 7 wt.% GCNT-ABS composites show enhancement of 26.1 and 71.3% over pure ABS matrix, respectively. Various parameters such as coefficient "C" factor (the ratio of storage modulus of the composite to polymer in glassy and rubbery regions), degree of entanglement, crosslink density and adhesion factor have been calculated to analyze the interaction between fillers and polymer matrix. The 3-D hybrid structure of GCNTs overcomes the associated problem of CNTs agglomeration and graphene restacking. GCNT hybrid composites show higher dispersion as well as effectiveness for increased filler amount as compared to RGO and MWCNTs based composites. GCNTs prove its superiority over MWCNTs and RGO by showing a synergistic effect in the glass transition temperature and storage modulus. Raman spectroscopy and scanning electron microscopy are used to confirm the interaction and distribution of the filler and matrix, respectively

Structural and mechanical properties of free-standing multiwalled carbon nanotube paper prepared by an aqueous mediated process

Free-standing carbon nanotube film (bucky paper) is a very important material for various applications, but its commercial production is still limited due to size, cost and properties. In the present work, different methods are used to prepare five different types of bucky papers, namely normal, pure refluxed, oxidized, oxidized refluxed and functionalized by using as-produced multiwalled carbon nanotubes (MWCNTs), refluxed MWCNTs, air-oxidized MWCNTs, oxidized refluxed MWCNTs and HNO3 functionalized MWCNTs, respectively. Morphological, physical and structural changes appeared due to different methods are analysed by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction spectroscopy and Raman spectroscopy. Changes in the relative characteristic peak ratio (i.e. I (G) /I (D), I (G') /I (D) and I (G') /I (G)) as a function of MWCNTs quality are determined. It is observed that oxidized refluxed MWCNTs have an average value of I (G) /I (D), I (G') /I (D) and I (G') /I (G) ratio as 4.12, 7.15 and 1.71, respectively, which is higher as compared to other samples. The mechanical properties of different bucky papers are studied by performing tensile tests. The result showed that tensile strength, Young's modulus and toughness of oxidized refluxed MWCNTs bucky paper are 3.9 MPa, 440 MPa and 780 Jm(-3), respectively, which are higher as compared to as-produced MWCNTs bucky paper. The air oxidation and back-to-back refluxing generates nanoscale irregularities within the hexagonal C-structure of a nanotube wall. This helps in improving intermolecular bonding and packing which resulted into significant improvement in the mechanical properties. These bucky papers prepared by economical ways of air oxidation and refluxing in an alkali-soluble emulsifier assisted aqueous medium are potential candidates for field emission devices, energy storage devices and structural materials

Structural and mechanical properties of free-standing multiwalled carbon nanotube paper prepared by an aqueous mediated process

Free-standing carbon nanotube film (bucky paper) is a very important material for various applications, but its commercial production is still limited due to size, cost and properties. In the present work, different methods are used to prepare five different types of bucky papers, namely normal, pure refluxed, oxidized, oxidized refluxed and functionalized by using as-produced multiwalled carbon nanotubes (MWCNTs), refluxed MWCNTs, air-oxidized MWCNTs, oxidized refluxed MWCNTs and HNO3 functionalized MWCNTs, respectively. Morphological, physical and structural changes appeared due to different methods are analysed by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction spectroscopy and Raman spectroscopy. Changes in the relative characteristic peak ratio (i.e. I (G) /I (D), I (G') /I (D) and I (G') /I (G)) as a function of MWCNTs quality are determined. It is observed that oxidized refluxed MWCNTs have an average value of I (G) /I (D), I (G') /I (D) and I (G') /I (G) ratio as 4.12, 7.15 and 1.71, respectively, which is higher as compared to other samples. The mechanical properties of different bucky papers are studied by performing tensile tests. The result showed that tensile strength, Young's modulus and toughness of oxidized refluxed MWCNTs bucky paper are 3.9 MPa, 440 MPa and 780 Jm(-3), respectively, which are higher as compared to as-produced MWCNTs bucky paper. The air oxidation and back-to-back refluxing generates nanoscale irregularities within the hexagonal C-structure of a nanotube wall. This helps in improving intermolecular bonding and packing which resulted into significant improvement in the mechanical properties. These bucky papers prepared by economical ways of air oxidation and refluxing in an alkali-soluble emulsifier assisted aqueous medium are potential candidates for field emission devices, energy storage devices and structural materials

Nanoconfinement of tetraphenylethylene in zeolitic metal-organic framework for turn-on mechanofluorochromic stress sensing

Mechanofluorochromic materials are of great significance for the fabrication of innovative sensors and optoelectronics. However, efficient mechanofluorochromic materials are rarely explored due to the deficiency of existing design strategies. Here, we demonstrate the incarceration of aggregation-induced emission (AIE) materials within metal-organic framework (MOF) single crystals to construct a composite system with turn-on mechanofluorochromism. A new type of AIE@MOF material was designed: integrating a zeolitic MOF (ZIF-71) and tetraphenylethylene (TPE, a topical AIE material) to generate a TPE@ZIF-71 system with exceptional turn-on type mechanofluorochromism. Using terahertz vibrational spectroscopy, we show the unique fluorochromism mainly emanates from the enhanced nanoconfinement effect exerted by ZIF-71 host on TPE guest under pressure. Compared with pure TPE, we demonstrate the nanoconfinement in AIE@MOF not only changes the TPE's turn-off type sensing behavior to a turn-on type, but boosts the original sensitivity markedly by tenfold. Significantly, because ZIF-71 prevents the spontaneous recrystallization of TPE upon unloading, this allows TPE@ZIF-71 to record the stress history. This is the first demonstration of the Guest@MOF system combining the concepts of AIE and MOF; its promising properties and potential engineering applications will stimulate new directions pertaining to luminescent stress sensors and smart optics