Sellamuthu N. Jaisankar

Sol-gel network silica/modified montmorillonite clay hybrid nanocomposites for hydrophobic surface coatings.

Sol-gel silica/nanoclay composites were prepared through sol-gel polymerization technique using tetraethylorthosilicate precursor and montmorillonite (MMT) clay in aqueous media. In this study, both montmorillonite-K(+) and organically modified MMT (OMMT) clays were used. The prepared composites were coated on glass substrate by making 1 wt% solution in ethyltrichlorosilane. The incorporation of nanoclay does not alter the intensity of characteristic Si-O-Si peak of silica network. Thermogravimetric studies show that increasing clay content increased the degradation temperature of the composites. Differential scanning calorimetry (DSC) results of organically modified MMT nanoclay incorporated composite show a shift in the melting behavior up to 38°C. From DSC thermograms, we observed that the ΔH value decreased with increasing clay loading. X-ray diffraction patterns prove the presence of nanoclay in the composite and increase in the concentration of organically modified nanoclay from 3 to 5 wt% increases the intensity of the peak at 2θ=8° corresponds to OMMT. Morphology of the control silica gel composite was greatly influenced by the incorporation of OMMT. The presence of nanoclay changed the surface of control silica gel composite into cleaved surface with brittle in nature. Contact angle measurements were done for the coatings to study their surface behavior. These hybrid coatings on glass substrate may have applications for hydrophobic coatings on leather substrate.

Mesoporous and biocompatible surface active silica aerogel synthesis using choline formate ionic liquid

In this paper, we report the preparation and characterization of mesoporous and biocompatible transparent silica aerogel by the sol-gel polymerization of tetraethyl orthosilicate using ionic liquid. Choline cation based ionic liquid allows the silica framework to form in a non collapsing environment and controls the pore size of the gel. FT-IR spectra reveal the interaction of ionic liquid with surface -OH of the gel. DSC thermogram giving the evidence of confinement of ionic liquid within the silica matrix, which helps to avoid the shrinkage of the gel during the aging process. Nitrogen sorption measurements of gel prepared with ionic liquid exhibit a low surface area of 100.53 m2/g and high average pore size of 3.74 nm. MTT assay proves the biocompatibility and cell viability of the prepared gels. This new nanoporous silica material can be applied to immobilize biological molecules, which may retain their stability over a longer period.

The pH-sensitive polyampholyte nanogels: inclusion of carbon nanotubes for improved drug loading.

We report a simple and facile method to prepare a novel pH sensitive polyampholyte nanogel by copolymerizing vinylimidazole (VIM) with acrylic acid (AA) using functionalized single-walled carbon nanotubes (f-SWCNTs) (as reinforcing material) and cyanuric chloride via an intermolecular quaternization reaction. The polyampholyte nanogels have been characterized by various microscopic and spectroscopic methods. These studies reveal that incorporation of nanotubes in cross-linked copolymer of poly(vinylimidazole-co-acrylic acid) (PVI-co-AA) form polyampholyte nanogel with enhanced physical properties. The thermal experiments show that the introduction of f-SWCNTs into PVI-co-AA has significant impact on the thermal stability of nanogels. The rheological study showed that the nanogel is more viscoelastic than native gel. MTT assay indicates that the prepared polyampholyte gels possess biocompatibility and cell viability. The nanogel is also useful material to load water-soluble drug such as promethazine hydrochloride. The releasing profile of the drug from the nanogel clearly shows the pH-sensitive property of the material.

Thermoplastic polyurethane/single-walled carbon nanotube composites with low electrical resistance surfaces

Thermoplastic polyurethane (TPU)/single-walled carbon nanotube (SWCNT) nanocomposite films were prepared using 1,6-hexane diisocyanate and hydroxyl-terminated polybutadiene (HTPB) in tetrahydrofuran with various concentrations of SWCNTs. The interaction between polyurethane (PU) and SWCNTs in nanocomposite was studied using different methods. The film turns yellowish to grayish-black in colour upon increasing the concentration of SWCNTs in PU matrix. This may be due to the formation of π–π interaction between polyurethane amide functional group and SWCNTs. Differential scanning calorimetric results show that the soft segment of nanocomposite interacts much stronger than hard segment, which results in lowering melting transition temperature of soft segments. The activation energy and thermal stability parameters were determined from thermogravimetric and differential scanning calorimetric analyses. The x-ray photoelectron spectroscopic results show the intermolecular interaction between HTPB-based PU and SWCNT. Mesoporous morphology of the nanocomposites was observed by scanning electron microscopy. The average diameter of the pores was calculated using Gaussian method. The TPU films exhibit about 3.5 times greater resistivity than nanocomposite films. All the analysed data prove that the SWCNTs were well distributed in PU matrix and exhibited as tough films with low electrical resistivity.

The reinforced hydrogel for drug loading: immobilization of single-walled carbon nanotubes in cross-linked polymers via multiple interactions

We report a facile method to prepare novel carbon nanotube (CNT)-based hydrogels in an aqueous environment. To maximize the bonding between nanotubes and polymers, we exploited several non-covalent interactions like ionic, π–π stacking, hydrophobic, H-bonding, etc. Importantly, the nano-hydrogels swell in both water and organic solvents. The materials showed improvements in various physicochemical properties. The new material is fairly biocompatible, as shown by MTT assay studies. It is also a useful material to load a water-soluble drug or micronutrient such as riboflavin (vitamin B2) or amitriptyline hydrochloride. The releasing study of the drug clearly showed pH responsive behaviour.

Thermoplastic Interpenetrating Polymer Networks Based on Polyvinyl Chloride and Polyurethane Ionomers for Damping Application

Thermoplastic interpenetrating polymer networks (TIPNs) based on polyvinyl chloride (PVC) and polyurethane ionomers (PUI) in different weight ratios of 15/85, 25/75, 50/50, 75/25, and 85/15 PVC/PUI were prepared by sequential polymerization technique. IPN composition of 85/15 PVC/PUI was selected for filler addition based on thermal and mechanical data. These composite films containing calcinated clay filler (CCF) in a different weight percentage from 0.5 to 15 wt % were prepared. Characterization of thermoplastic IPNs (TIPN) and filled IPNs (TIPN-F) were carried out using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), stress-strain properties, and hardness were studied. The PVC/PUI: 85/15 based TIPN and TIPN-F5 show tough films, better miscibility, and thermal stability.

Augmentation of properties on sparingly loaded nanocomposites via functionalized single-walled carbon nanotubes using a covalent approach

Polymer nanocomposites are developed, for the first time, as transparent films by the covalent addition of polyurethane (PU) prepolymers to trace amounts of functionalized carbon nanotubes, [OH]n–SWCNTs, via an efficient route using mild reagents. These PU nanocomposites, which were uniformly distributed with SWCNTs via covalent bonding between SWCNTs and the polyurethane network show enhanced mechanical, thermal and conductivity (10−4 S cm−1) properties.

A novel fuel cell membrane with high efficiency

A new class of polymer electrolyte membranes containing an azo based ionic diol (30, 40 and 50 mol%) was prepared for use in a fuel cell. Its proton conductivity, hydrolytic stability, water uptake capacity, swelling behaviour and ion-exchange capacity measurement data indicated its suitability for use as a proton exchange electrolyte membrane in fuel cells. For example, the membranes containing 30, 40 and 50 mol% of azo based ionic monomers exhibit fairly good proton conductivities of 0.073 S cm−1, 0.075 S cm−1 and 0.079 S cm−1, respectively at 30 °C. Moreover, the prepared membranes show a phase separated morphology and exhibit a high thermal stability up to 460 °C which are important parameters for successful fuel cell design. Two types of azo based sulfonated poly(arylene ether sulfone) (SPAES) such as the SPAES-30 and SPAES-50 membrane electrode assembly have been successfully fabricated and yielded a good fuel cell performance in the whole range of current density.

Properties of polyurethane nanocomposite filaments for conductive textile applications

Composite filaments of thermoplastic polyurethane (TPU) and single-walled carbon nanotubes (SWCNTs) have been fabricated via extrusion process and their properties were studied using various characterization techniques. Twin-screw extruder has been used for making the composite filaments and the processing parameters like temperature, screw speed, and pressure were optimized. Thermal, morphological, mechanical, and electrical properties were studied by varying the weight percentage of SWCNTs. Raman shift of SWCNTs is observed for the CNTs dispersed in TPU matrix. Thermal analysis shows that there is an increase in the degradation and melting temperature of the TPU/SWCNTs blends. With the addition of SWCNTs as small filler loadings of 1 wt%, the tensile strength of the blended materials increased from 13 MPa to 21.6 MPa. The electrical conductivity of the composite filaments starts with the addition of 0.01% of SWCNTs. The highest value of electrical conductivity (3.7 × 10−7 S cm−1) obtained with 2 wt% of SWCNTs. This melt extrusion process method could open up for the preparation of new high-performance nanotube composite materials.

Carbon Nanotube Reinforced Polymer-Stabilized Liquid Crystal Device: Lowered and Thermally Invariant Threshold with Accelerated Dynamics

Polymer-stabilized liquid crystal (PSLC) devices comprise a polymer matrix in an otherwise continuous phase of liquid crystal. The fibrils of the polymer provide, even in the bulk, virtual surfaces with finite anchoring energy resulting in attractive electro-optic properties. Here, we describe a novel variation of the PSLC device fabricated by reinforcing the polymer matrix with polymer-capped single-walled carbon nanotubes (CNTs). The most important outcome of this strengthening of the polymer strands is that the threshold voltage associated with the electro-optic switching becomes essentially temperature independent in marked contrast to the significant thermal variation seen in the absence of the nanotubes. The reinforcement reduces the magnitude of the threshold voltage, and notably accelerates the switching dynamics and the effective splay elasticity. Each of these attributes is quite attractive from the device operation point of view, especially the circuit design of the required drivers. The amelioration is caused by the polymer decorating CNTs being structurally identical to that of the matrix. The resulting good compatibility between CNTs and the matrix prevents the CNTs from drifting away from the matrix polymer, a lacuna in previous attempts to have CNTs in PSLC systems. The difference in the morphology, perhaps the primary cause for the effects seen, is noted in the electron microscopy images of the films.