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The performance of modern electronics is associated with the multi-layered interconnects, encouraging the development of a low-k dielectrics. Herein, we studied the effects of phase transition from crystalline to amorphous on dielectric, optical and electrical properties of MIL-100 (Fe) and Basolite F300 metal-organic framework (MOF) obtained using different synthesis techniques in both the radio (4-1.5 MHz) and infrared (1.2-150 THz) frequency regimes, which are important for the microelectronics, infrared optical sensors, and high-frequency telecommunications. The impact of amorphization on broadband dielectric response was established based on: (1) The comparison in the dielectric characteristics of a commercially available amorphous Basolite F300 versus a mechanochemically synthesized crystalline MIL-100 in the MHz region. (2) By tracking the frequency shifts in the vibrational modes of MIL-100 structure in the far-IR (phonons) and mid-IR regions. We showed that various parameters such as pelleting pressure, temperature, frequency, density, and degree of amorphization greatly affect the dielectric properties of the framework. We also investigated the influence of temperature (20-100 {\deg}C) on the electric and dielectric response in the MHz region, crucial for all electronic devices., Comment: 23 pages, 5 Figures, Supporting Information (34 pages)

A series of fluorescein-encapsulated zeolitic imidazolate framework-8 (fluorescein@ZIF-8) luminescent nanoparticles with a scalable guest loading has been fabricated and characterized. The successful encapsulation of the organic dye (fluorescein) is supported by both experimental evidence and theoretical simulations. The measured optical band gap is found to be comparable with the computed values of a hypothetical guest-host system. Isolated monomers and aggregates species of fluorescein confined in ZIF-8 nanocrystals have been systematically investigated through fluorescence lifetime spectroscopy. The quantum yield (QY) of the obtained solid-state materials is particularly high (QY~98%), especially when the concentration of the fluorescein guest is low. Combining a blue LED chip and a thin photoactive film of fluorescein@ZIF-8, we demonstrate a device with good optical tunability for multicolor and white light emissions. Additionally, we show that the fluorescein@ZIF-8 nanoparticles exhibit an improved photostability due to the shielding effect conferred by the nanoconfinement of host framework, making them promising candidates for practical applications such as solid-state lighting, photonics, and optical communications., Comment: 29 Pages, 7 Figures, 1 Supporting Information

Metal-organic frameworks (MOFs) are the emerging low-k dielectric materials for application in next-generation microelectronics and telecommunication devices. MOF dielectrics can function as smart sensors with high sensitivity and chemical selectivity, by leveraging the ubiquituous dielectric response of MOFs and overcoming the limitations of DC conductivity and fluorescence approaches. Herein we study the effects of materials synthesis, applied mechanical stress (37-520 MPa), varying temperature (20-100°C), and guest encapsulation on the frequency-dependent dielectric response (4 Hz to 1 MHz) and AC conductivity of the HKUST-1 MOF. Particularly, we show that the confinement of the triethylamine (NEt3) guest molecules in HKUST-1 (host) yields the NEt3@HKUST-1 system that is tuneable via mechanical, thermal and electrical perturbations. Within the frequency range of 10 kHz to 1 MHz, at 20 °C we show that the dielectric constant (𝜀‘) of the guest-encapsulated system could be tuned to attain a value of between 2.8 and 7.2; at 100 °C, an even greater range of 𝜀‘ from 3.1 to 9.5 could be achieved. Conversely, we found the dielectric tuneability of the porous (guest-free) HKUST-1 is relatively more limited (𝜀‘ = 2.8 to 4.9) whist employing the same operational parameters. Furthermore, the confinement of guest molecules in HKUST-1 enhances the mechanical resilience and yield strength of the powders subject to a compressive pelleting stress. Together, the results elucidate the new potential for exploiting host-guest interactions in MOFs, coupled with electro-thermo-mechanical stimuli to regulate the precise dielectric response of a designer low-k material.

Nanocomposites comprising metal-organic frameworks (MOFs) embedded in a polymeric matrix are promising carriers for drug delivery applications. While understanding the chemical and physical transformations of MOFs during the release of confined drug molecules is challenging, this is central to devising better ways for controlled release of therapeutic agents. Herein we demonstrate the efficacy of synchrotron microspectroscopy to track the in situ release of 5-fluorouracil (5-FU) anticancer drug molecules from a drug@MOF/polymer composite (5-FU@HKUST-1/polyurethane). Using experimental time-resolved infrared spectra jointly with newly developed density functional theory calculations, we reveal the detailed dynamics of vibrational motions underpinning the dissociation of 5-FU bound to the framework of HKUST-1 upon water exposure. We discover that HKUST-1 creates hydrophilic channels within the hydrophobic polyurethane matrix hence helping to tune drug release rate. The synergy between a hydrophilic MOF with a hydrophobic polymer can be harnessed to engineer a tunable nanocomposite that alleviates the unwanted burst effect commonly encountered in drug delivery.

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.

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.

Herein we employed high-resolution spectroscopic techniques in combination with periodic ab initio density functional theory (DFT) calculations to establish the different polarization processes for a porous copper-based MOF, termed HKUST-1. We used alternating current measurements to determine its dielectric response between 4 Hz and 1.5 MHz where orientational polarization is predominant, while synchrotron infrared (IR) reflectance was used to probe the far-IR, mid-IR, and near-IR dielectric response across the 1.2 THz to 150 THz range (ca. 40 - 5000 cm^-1) where vibrational and optical polarizations are principal contributors to its dielectric permittivity. We demonstrate the role of pressure on the evolution of broadband dielectric response, where THz vibrations reveal distinct blue and red shifts of phonon modes from structural deformation of the copper paddle-wheel and the organic linker, respectively. We also investigated the effect of temperature on dielectric constants in the MHz region pertinent to microelectronics, to study temperature-dependent dielectric losses via dissipation in an alternating electric field. The DFT calculations offer insights into the physical mechanisms responsible for dielectric transitions observed in the experiments and enable us to explain the frequency shifts phenomenon detected under pressure. Together, the experiments and theory have enabled us to glimpse into the complex dielectric response and mechanisms underpinning a prototypical MOF subject to pressure, temperature, and vast frequencies., 20 pages, 6 figures, plus Supporting Information

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 °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 reinforcements and the interaction to PC, respectively.

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 (Tg) as compared to pure PC. Effect of functionalization of MWCNTs on Tg of its of polycarbonate composites is studied and showed higher Tg 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 Tg 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.

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.

A facile mechanochemical method was employed to accomplish one-pot encapsulation of anti-cancer drug 5-fluorouracil (5-FU as guest) in a metal-organic framework (HKUST-1 as host). Vibrational spectroscopy via inelastic neutron scattering was applied to probe guest-host interactions arising from nanoscale confinement. We compare 5-FU@HKUST-1 derived from in situ and ex situ encapsulation.

There is rising interest on low-k dielectric materials based on porous metal-organic frameworks (MOFs) for improved electrical insulation in microelectronics. Herein, we demonstrate the concept of MOF dielectric sensor built from a single crystal of HKUST-1. We study guest encapsulation effects of polar and non-polar molecules, by monitoring the transient dielectric response and AC conductivity of the crystal exposed to different vapors (water, I2, methanol, ethanol). The dielectric properties were measured along the crystal direction in the frequency range of 100 Hz to 2 MHz. The dielectric data show the efficacy of MOF dielectric sensor for discriminating the guest analytes. The time-dependent transient response reveals dynamics of the molecular inclusion and exclusion processes in the nanoscale pores. Since dielectric response is ubiquitous to all MOF materials (unlike DC conductivity and fluorescence), our results demonstrate the potential of dielectric MOF sensors compared to resistive sensors and luminescence-based approaches.