A novel flexible nanocomposite pressure sensor with a tensile strength of about 47 MPa is fabricated in this work. Nanolayers of titanium dioxide (titania nanolayers, TNL) synthesized by hydrothermal method are used to reinforce the polyvinylidene fluoride (PVDF) by simple solution mixing. A hybrid composite is prepared by incorporating the TNL (2.5 wt %) with reduced graphene oxide (rGO) (2.5 wt %) synthesized by improved graphene oxide synthesis to form a PVDF/rGO-TNL composite. A comparison between PVDF, PVDF/rGO (5 wt %), PVDF/TNL (5 wt %) and PVDF/rGO-TNL (total additives 5 wt %) samples are analyzed for their sensing, thermal and dielectric characteristics. The new shape of additives (with sharp morphology), good interaction and well distributed hybrid additives in the matrix increased the sensitivity by 333.46% at 5 kPa, 200.7% at 10.7 kPa and 246.7% at 17.6 kPa compared to the individual PVDF composite of TNL, confirming its possible application in fabricating low cost and light weight pressure sensing devices and electronic devices with reduced quantity of metal oxides. Increase in the β crystallinity percentage and removal of α phase for PVDF was detected for the hybrid composite and linked to the improvement in the mechanical properties. Tensile strength for the hybrid composite (46.91 MPa) was 115% higher than that of the neat polymer matrix. Improvement in the wettability and less roughness in the hybrid composites were observed, which can prevent fouling, a major disadvantage in many sensor applications.

Flexible Pressure Sensor Based on PVDF Nanocomposites Containing Reduced Graphene Oxide-Titania Hybrid Nanolayers

The dispersion of ferroelectric nanomaterials in liquid crystals has recently emerged as a promising way for the design of advanced and tunable electro-optical materials. The goal of this paper is a broad overview of the current technology, basic physical properties, and applications of ferroelectric nanoparticle/liquid crystal colloids. By compiling a great variety of experimental data and discussing it in the framework of existing theoretical models, both scientific and technological challenges of this rapidly developing field of liquid crystal nanoscience are identified. They can be broadly categorized into the following groups: (i) the control of the size, shape, and the ferroelectricity of nanoparticles; (ii) the production of a stable and aggregate-free dispersion of relatively small (~10 nm) ferroelectric nanoparticles in liquid crystals; (iii) the selection of liquid crystal materials the most suitable for the dispersion of nanoparticles; (iv) the choice of appropriate experimental procedures and control measurements to characterize liquid crystals doped with ferroelectric nanoparticles; and (v) the development and/or modification of theoretical and computational models to account for the complexity of the system under study. Possible ways to overcome the identified challenges along with future research directions are also discussed.

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Ferroelectric Nanoparticles in Liquid Crystals: Recent Progress and Current Challenges.

Polymer dispersed liquid crystals (PDLCs) using nematic liquid crystal and photo-curable polymer (NOA 65) were prepared by polymerisation-induced phase separation technique, in equal ratio (1:1) of polymer and liquid crystal (LC). We demonstrate that doping of small amount (0.125%, wt./wt.) of multiwall carbon nanotubes (CNTs) and orange azo dichroic dye in PDLC generously controlled the molecular orientation, dynamics of LC in droplet and size of droplets. The effects of multiwall CNTs and dye on PDLCs were studied in terms of transition temperature, droplet morphology, transmittance characteristic, contrast ratio and response time. The results exhibited that the values of the threshold electric fields were reduced from 8 V/µm (pure PDLC) to 1.18 and 1.72 V/µm, doped with multiwall CNTs and dye, respectively. The CNTs-doped PDLC shows faster switching response as compared with pure PDLC and dye-doped PDLC. However, dye-doped PDLC shows much higher contrast among all PDLC samples. Further, the res...

Orientational control of liquid crystal molecules via carbon nanotubes and dichroic dye in polymer dispersed liquid crystal

This account gives an overview of our recent work in the area of conjugated azomethines derived from 2-aminothiophenes. It will be presented that mild reaction conditions can be used to selectively prepare symmetric and unsymmetric conjugated azomethines. It further will be demonstrated that azomethines consisting of various 5-membered aryl heterocycles lead to chemically, reductively, hydrolytically, and oxidatively robust compounds. The optical and electrochemical properties of these materials can be tuned contingent on the degree of conjugation, type of aryl heterocycle, and by including various electronic groups. The end result is materials having colors spanning 250 nm across the visible spectrum. These colors further can be tuned via electrochemical or chemical doping. The resulting doped states have high color contrasts from their corresponding neutral states. The collective opto-electronic properties and the means to readily tune them, make thiophenoazomethine derivatives interesting materials for potential use in a gamut of applications.

Survey of recent advances of in the field of π-conjugated heterocyclic azomethines as materials with tuneable properties

The physical properties of polymer dispersed liquid crystals (PDLC) can be tuned as per the application requirement by controlling their composition ratio and microstructure. The addition of nanopa...

Role of BaTiO3 nanoparticles on electro-optic performance of epoxy-resin-based PDLC devices

We report the preparation, thermal and micro/nanomechanical behavior of poly (vinylidine diflouride) (PVDF)/multiwalled carbon nanotube (MWCNT) nanocomposites. It has been found that the addition of MWCNT considerably enhances the β-phase formation, thermal and mechanical properties of PVDF. Atomic force microscope (AFM) studies have been performed on the composites under stress conditions to measure the mechanical properties. The nanoscale mechanical properties of the composites like Young's modulus and hardness of the nanocomposites were investigated by nanoindentation technique. Morphological studies of the nanocomposites were also studied, observations show a uniform distribution of MWCNT in the matrix and interfacial adhesion between PVDF and MWCNT was achieved, which was responsible for enhancement in the hardness and Young's modulus. Differential scanning calorimetry (DSC) studies indicate that the melting temperature of the composites have been slightly increased while the heat of fusion markedly decreased with increasing MWCNT content.

Nanoindentation and thermal characterization of poly (vinylidenefluoride)/MWCNT nanocomposites

Ferro nematic suspensions are the prominent
materials to enhance the electro optical performance of liquid crystal
displays. Electro optical properties of polymer dispersed liquid crystal (PDLC)
display with the introduction of
Barium Titanate nanoparticles have been investigated in this article and it is
shown that there is a considerable enhancement in electro-optical response of
the displays. The nanoparticles lower the switch-on electric field and thereby
increase the optical transmission at certain voltages of the displays. The
electro-optical characteristics of the PDLC cells were investigated with a
He-Ne laser followed by MatLab calculations.

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Effect of BaTiO 3 Nanoparticle on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Displays

Liquid crystals of azomethine derivatives were synthesised and their molecular structures were confirmed by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. Mesomorphic studies using differential scanning calorimetry, X-ray diffraction and polarising optical microscope revealed that all of these compounds exhibit thermotropic mesophases over a temperature range. The nonlinear optical properties of these liquid crystals were studied using a Z-scan technique with 7 ns pulse duration at 532 nm. The nonlinear refractive index, and the third order nonlinear susceptibility, were measured to be of the order of and respectively. Reverse saturable absorption was identified as the main mechanism responsible for optical limiting.

Mallikharjuna Rao Darla

Papers

Nanoindentation and thermal characterization of poly (vinylidenefluoride)/MWCNT nanocomposites

Effect of BaTiO 3 Nanoparticle on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Displays

Synthesis and characterisation of azomethine class thermotropic liquid crystals and their application in nonlinear optics