Nur Amin Hoque

The role of cerium(III)/yttrium(III) nitrate hexahydrate salts on electroactive β phase nucleation and dielectric properties of poly(vinylidene fluoride) thin films

Electroactive poly(vinylidene fluoride) (PVDF) thin films modified with Ce(NO3)3·6H2O and Y(NO3)3·6H2O (1–30 mass%) have been prepared via a simple solution casting method. The thermal stability and microstructures of the films were investigated using thermal gravimetric analysis techniques and field emission electron microscopy respectively. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry confirmed the nucleation of the electroactive β phase in the composite films. Strong interfacial interaction i.e. ion dipole interaction via formation of hydrogen bonds between the water molecules of the salts and the polar –CF2 dipoles of the polymer chains resulted in improved electroactive β phase nucleation and a large dielectric constant in PVDF films.

Improvement of electroactive β phase nucleation and dielectric properties of WO3·H2O nanoparticle loaded poly(vinylidene fluoride) thin films

Tungsten oxide hydrate (WO3·H2O) nanoparticles (NPs) have been prepared by simple hydrazine hydrate reduction. X-ray diffraction, UV-Visible spectroscopy and field emission electron scanning microscopy confirm the formation of phase pure orthorhombic WO3·H2O NPs. Thereafter, poly(vinylidene fluoride) (PVDF) thin films doped with different amounts of WO3·H2O NPs (1–15 mass%) have been prepared via a simple solution-casting method to verify the role of the NPs on the enhancement of electroactive β phase crystallization and dielectric properties of WO3·H2O NP–PVDF thin films. The interface between the NPs and the polymer matrix takes a vital role in improving β phase nucleation and dielectric properties of the WO3·H2O NP modified PVDF thin films. Strong electrostatic or ion–dipole interaction between the negatively charged NP surfaces and –CH2 dipoles of the polymer matrix at the interface effectively improves the electroactive β phase nucleation and dielectric properties of the nanocomposite thin films.

Sol–gel synthesis of transition-metal ion conjugated alumina-rich mullite nanocomposites with potential mechanical, dielectric and photoluminescence properties

Nanocrystalline mullite have been synthesized from non-stoichiometric alkoxide precursors via sol–gel route with Co2+, Ni2+ and Cu2+ as dopant metal ions. Transition-metal aluminate spinel phases, formed from the reaction between dopant metal ions and dissolved alumina species, introduced prominent colors to the composites after sintering. Interesting colors combined with suitable densification lead these composites to have potential use as ceramic pigments. A comparative Vickers and Knoop hardness have been evaluated in terms of dislocation movement along grain boundaries with highest hardness and Young’s modulus values of ∼8.7 GPa and ∼207 GPa for copper and cobalt incorporated mullite, respectively. Greater porosity of pure mullite results in an unconventionally high dielectric constant of ∼91 whereas larger interfacial polarization is responsible for the varying dielectric response of transition-metal incorporated mullite composites. Formation of oxygen like defects in the composites cause prominent PL bands with highest PL intensity for dopant cobalt ions in mullite matrix.

Enhanced electroactive β-phase nucleation and dielectric properties of PVdF-HFP thin films influenced by montmorillonite and Ni(OH)2 nanoparticle modified montmorillonite

The present work lays emphasis on the synthesis of electroactive and high dielectric poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) composite films incorporated with montmorillonite (MMT) and Ni(OH)2 nanoparticle (NP) modified MMT using a facile and low cost solution casting technique. Formation of Ni(OH)2 NPs, different polymorphs and morphology of the composite samples have been investigated using UV-visible spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and field emission scanning electron microscopy. A remarkable improvement in β-phase nucleation (∼85.22% for 1 mass% MMT doped at and 82.10% for 7.5 mass% NiMMT doped polymer composites films) and promising dielectric values are the standpoints of the work. Strong ion–dipole interaction between the negatively charged surfaces of MMT and –CH2 dipoles of the polymer chains in the MMT loaded PVdF-HFP samples and formation of hydrogen bonds between the –OH group of Ni(OH)2 NPs and F atom of the polymer chains in the Ni(OH)2 NP-MMT/PVdF-HFP system play a dynamic role in enhancing the electroactive β-phase nucleation and the dielectric properties of the samples. A large accumulation of charges at the interfaces of the dopant and polymer matrix via Maxwell–Wagner–Sillars interfacial polarization effect occurred due to the disparity in the conductivity of the dopants and the polymer matrix is liable for the significant enrichment of dielectric properties of the composite films. Excellent thermal stability in dielectric properties has also been observed in these composite samples over a wide temperature spectrum. These electroactive and high dielectric polymer composite thin films may be potential candidates for application in piezoelectric nanogenerators, energy storage devices, thin film transistors and capacitive sensors etc.

Er3+/Fe3+ Stimulated Electroactive, Visible Light Emitting, and High Dielectric Flexible PVDF Film Based Piezoelectric Nanogenerators: A Simple and Superior Self-Powered Energy Harvester with Remarkable Power Density

The design of an energy-harvesting unit with superior output characteristics, i.e., high power density, is a great technological challenge in the present time. Here, simple, lightweight, flexible, and cost-effective piezoelectric nanogenerators (PENGs) have been fabricated by integrating the aluminum electrodes onto Er3+/Fe3+ stimulated electroactive, visible-light-emitting, and large dielectric PVDF films in which ErCl3·6H2O and Fe(NO3)3·9H2O act as the catalytic agents for electroactive β polymorph nucleation and the enhancement of dielectric properties. The developed PENGs exhibit excellent energy-harvesting performance with very high power density and very fast charging ability compared with the previously reported PVDF-assisted prototype nanogenerators. The PENGs lead to very large power density (∼160 and ∼55.34 mW cm-3) under periodic finger imparting for Er3+- and Fe3+-stimulated PVDF-film-based energy-harvester units, respectively. The fabricated self-powered PENG is also able to light up 54 commercially available light-emitting diodes.

Improving the thermal stability, electroactive β phase crystallization and dielectric constant of NiO nanoparticle/C–NiO nanocomposite embedded flexible poly(vinylidene fluoride) thin films

Using a simple chemical precipitation process followed by sintering at 400 °C, NiO nanoparticles (NPs) and C–NiO nanocomposites (NCs) have been synthesized and characterized by X-ray diffraction, UV-visible spectroscopy, zeta potential measurement, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Then, NiO NP or C–NiO NC loaded PVDF thin films were fabricated via a simple solvent casting or solution casting method. Thermogravimetric analysis confirmed good thermal stability of the nanocomposite films. Strong ion–dipole interaction between the negative surfaces of NiO NPs or C–NiO NCs and –CH2 dipoles of polymer chains leads to the formation of a long stabilized TTTT conformation, i.e. formation of large number of electroactive β polymorphs in the modified PVDF thin films. Detailed study of the dependency of the dielectric properties on filler content (NiO NPs/C–NiO NCs) and frequency illustrates significant increase in the dielectric constant in the three phase C–NiO NCs–PVDF system than in the two phase NiO NPs–PVDF system. The dielectric constant is found to be as large as 317.4 at 20 Hz with a relatively low tangent loss value, and good flexibility when 20 mass% C–NiO NCs is incorporated in the PVDF matrix. These results have been explained in terms of Maxwell–Wagner–Sillars interfacial polarization at the NiO NPs/C–NiO NCs and insulating polymer matrix interface, evolution of a conductive network and formation of a microcapacitive structure in the NiO NPs or C–NiO NCs modified PVDF thin films.

Tunable photoluminescence emissions and large dielectric constant of the electroactive poly(vinylidene fluoride–hexafluoropropylene) thin films modified with SnO2 nanoparticles

In the present study, SnO2 nanoparticles (NPs) have been synthesized hydrothermally at 100 °C and 150 °C. The NPs have been characterized by X-ray diffraction (XRD), UV-visible spectroscopy and field emission scanning electron microscopy (FESEM). Thereafter, poly(vinylidene fluoride–hexafluoropropylene) (PVDF–HFP) with different contents (1–15 wt%) of SnO2 NPs has been synthesized by a simple solution-casting method. An electroactive β-phase formation mechanism in the NP-incorporated PVDF–HFP thin films is confirmed by XRD, Fourier transform infrared spectroscopy and differential scanning calorimetry. FESEM images show interfacial interaction in the thin films between the polymer matrix and the NPs. Maximum β-phase nucleation of ∼74% has been reached by 10 wt% addition of SnO2 NPs synthesized hydrothermally at 100 °C. The photoluminescence emission spectra show two UV and visible emissions at two excitation wavelengths. Uniform distribution of the NPs in the polymer matrix leads to large dielectric constant ∼2578.44 at 20 Hz due to addition of 10 wt% SnO2 NPs (100SO) in PVDF–HFP matrix. The large increase in dielectric constant has been successfully explained in terms of MWS polarization effect and percolation theory.

Electroactive and High Dielectric Folic Acid/PVDF Composite Film Rooted Simplistic Organic Photovoltaic Self-Charging Energy Storage Cell with Superior Energy Density and Storage Capability

Herein we report a simplistic prototype approach to develop an organic photovoltaic self-charging energy storage cell (OPSESC) rooted with biopolymer folic acid (FA) modified high dielectric and electroactive β crystal enriched poly(vinylidene fluoride) (PVDF) composite (PFA) thin film. Comprehensive and exhaustive characterizations of the synthesized PFA composite films validate the proper formation of β-polymorphs in PVDF. Significant improvements of both β-phase crystallization (F(β) ≈ 71.4%) and dielectric constant (ε ≈ 218 at 20 Hz for PFA of 7.5 mass %) are the twosome realizations of our current study. Enhancement of β-phase nucleation in the composites can be thought as a contribution of the strong interaction of the FA particles with the PVDF chains. Maxwell-Wagner-Sillars (MWS) interfacial polarization approves the establishment of thermally stable high dielectric values measured over a wide temperature spectrum. The optimized high dielectric and electroactive films are further employed as an active energy storage material in designing our device named as OPSESC. Self-charging under visible light irradiation without an external biasing electrical field and simultaneous remarkable self-storage of photogenerated electrical energy are the two foremost aptitudes and the spotlight of our present investigation. Our as fabricated device delivers an impressively high energy density of 7.84 mWh/g and an excellent specific capacitance of 61 F/g which is superior relative to the other photon induced two electrode organic self-charging energy storage devices reported so far. Our device also proves the realistic utility with good recycling capability by facilitating commercially available light emitting diode.

Biowaste crab shell-extracted chitin nanofiber-based superior piezoelectric nanogenerator

Expeditious development of PENGs has been restricted several problems such as toxicity, high cost, and long-life. Herein, we report a biowaste crab shell-extracted chitin nanofiber (CNF) and CNF/poly(vinylidene fluoride) (PVDF)-based biocompatible, biodegradable, low cost, light weight, flexible, highly durable and efficient piezoelectric nanogenerators (PENGs) that enable harvesting of electrical energy from the mechanical energy of a living system. The pure CNF thin film-based piezoelectric nanogenerator (CPENG) shows excellent output performances (open circuit output voltage (Voc) = 22 V, short circuit current (Isc) = 0.12 μA) with a high piezoelectric coefficient, d33 = 9.49 pC N−1. The PENG based on CNF/PVDF (PCPEG) also shows very good output characteristics (Voc = 49 V and Isc = 1.9 μA). The incorporation of CNF in a PVDF matrix noticeably enhanced the electroactive β-phase nucleation, (F(β)) ∼ 81%, with a superior d33 ∼ 35.56 pC N−1. The PCPENG is able to charge a 2.2 μF capacitor to 3.6 V within a short time span (20 seconds) and illuminate 22 blue LEDs connected in series. Our as-fabricated PENGs could be suitable for long-life in vivo biomedical energy harvesting devices that can harvest energy from blood flow and heart beats and charge energy storage devices from mechanical energy such as body movements, moving cars, sea waves, air flow, and rain drops.

Antimicrobial and biocompatible fluorescent hydroxyapatite-chitosan nanocomposite films for biomedical applications

Development of fluorescent erbium doped hydroxyapatite (eHAp)-chitosan nanocomposite film is reported. Nanocrystalline eHAp has been synthesized by hydrothermal assisted precipitation method using erbium (III) ions as dopant. Physico-chemical characterization by UV/Visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), photoluminiscence spectroscopy (PL) and Field emission scanning electron microscopy(FESEM) confirmed incorporation and uniform distribution of eHAp in the chitosan films. Strong antimicrobial activity was observed using eHAp incorporated chitosan films against E. coli and S. aureus by contact inhibition on agar plates. On the other hand, excellent biocompatibility was observed with human lung fibroblast cells (WI-38) which showed strong attachment and proliferation on the chitosan films with minimal cytotoxicity. Moreover, the doped films showed good biodegradation and mineralization behavior after 2 weeks in simulated body fluid. Thus the doped fluorescent chitosan films with multifunctional attributes can be a strong candidate for diverse applications like in antimicrobial treatments, wound healing, tissue scaffolds and bioimaging.