Asit B. Samui

Highly selective monitoring of metals by using ion-imprinted polymers

AbstractIon imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas. Graphical AbstractIIPs for the selective monitoring of metals

A supercapacitor based on longitudinal unzipping of multi-walled carbon nanotubes for high temperature application

Multi-walled carbon nanotubes (MWCNTs) were partially unzipped longitudinally by a chemical method. Unzipped multi-walled carbon nanotubes (UZ-MWCNTs) were characterized by transmission electron microscopic analysis, X-ray diffraction and Raman spectroscopic analyses. UZ-MWCNTs were utilized for electrode preparation and the electrodes were used in the fabrication of a supercapacitor. At room temperature, the UZ-MWCNTs based supercapacitor showed a specific capacitance of ∼41 F g−1, while pristine MWCNTs based supercapacitor exhibited 22 F g−1 at the scan rate of 25 mV s−1. The increase in specific capacitance was attributed to an increase in effective specific surface area of UZ-MWCNTs due to partial unzipping. UZ-MWCNTs based supercapacitor exhibited an increase in specific capacitance with increase in temperature. It showed a specific capacitance of ∼74 F g−1 at 100 °C at the scan rate of 25 mV s−1, while the pristine MWCNTs based supercapacitor did not show any appreciable change in specific capacitance as a function of temperature. UZ-MWCNTs exhibited three-fold increase in specific capacitance as compared to pristine MWCNTs at 100 °C. Impedance spectroscopic analysis of the supercapacitors revealed that the UZ-MWCNTs based supercapacitor exhibited higher internal resistance and lower leakage resistance than pristine MWCNTs based supercapacitor. Continuous ‘charge–discharge’ cycling behaviour indicated that the UZ-MWCNTs based supercapacitor exhibited less stability during initial cycles even though it depicted higher specific capacitance as compared to the pristine MWCNTs based supercapacitor.

Versatility of polyethylene glycol (PEG) in designing solid–solid phase change materials (PCMs) for thermal management and their application to innovative technologies

The research on phase change materials (PCM) has evolved significantly in the last few decades due to the need to manage the demands of energy requirements. Polyethylene glycol (PEG) is established as an organic solid–liquid PCM offering a wide range of enthalpies and phase transition temperatures as a function of its molecular weight. Herein, we have focussed on three aspects including preparation methods, microencapsulation and applications. An attempt has been made to focus on thermal conductivity enhancement methods used in the preparation of PEG based PCMs to give way for the commercial utility of these materials. The concluding remarks address the future directions for investigation, challenges and new possibilities for practical implementation of these materials.

A molecularly imprinted polymer with flash column chromatography for the selective and continuous extraction of diphenyl amine

The aim of this study was to prepare MIP for the selective recognition of DPA and its combination with flash column chromatography for the continuous extraction of DPA from ammunition waste. The DPA–MIP was prepared by free radical polymerization using methacrylic acid as a complexing monomer and EGDMA as a crosslinker. Methanol and acetic acid (9 : 1) were used as a leaching agent for DPA. MIP showed maximum adsorption capacity at pH 4. The maximum experimental adsorption capacity obtained for MIP and NIP particles were 31 mg g−1 and 10.2 mg g−1, respectively. Langmuir and Freundlich adsorption isotherm models were used to analyze the experimental data of DPA adsorption on MIP. The Freundlich adsorption isotherm model fit very well with this. Pseudo first order and pseudo second order kinetic models were used to estimate the corresponding rate parameters, equilibrium capacities and correlation coefficients. The selectivity coefficients of MIP for DPA in the presence of NDPA, TNT and tetryl were 23.14, 47.07 and 52.30, respectively. Continuous extraction of DPA was done with the help of flash chromatography combined with MIP and showed more than 98% recovery. MIP has a good regeneration performance and could maintain almost the same adsorption capacity even after three adsorption–desorption cycles.

Main chain photoresponsive liquid crystalline polymer synthesized through hydrosilylation

Liquid crystalline siloxane azo polymers were synthesized through hydrosilylation reaction between diallyl azo monomer and siloxane dihydride. The molecular weights of the polymers ranged from 3000–4000 g mol−1. The polymers were found to be soluble in chloroform, THF, DMF, DMSO, and DCM respectively. The photoresponsive behavior was studied during exposure of the polymers to UV radiation. The trans–cis photoisomerisation rate constants were also determined. The thermotropic behavior of the polymers was studied by using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The polymers exhibited liquid crystalline texture of nematic droplets in POM images existing at room temperature and extending over broad temperature range up to 155 °C. The DSC thermogram also supported the characteristic liquid crystalline transitions.

Bisbenzylidene cycloalkanone: a versatile molecule as a polymer building block

Bisbenzylidene cycloalkanone [BBCA], a versatile photo-active molecule, has already shown its potential for applications in biology, chemistry, materials science and technology. The molecule possesses the dual nature of a photo-active molecule and a mesogenic unit. It was studied as such for medical applications and by incorporating it into polymer architectures for harnessing its properties as a photo-active as well as a mesogenic unit. It was incorporated into almost all kinds of polymer architectures from polyester to polyimide. The special features of the polymer bearing this unit are high thermal stability, photo-curing ability (for adhesives, photo-resists, holography), electronic conductivity, fluorescence, etc. Even during the past decades progress was made mostly in the methods of synthesis and structural understanding of these polymers, the functional understanding and application of these polymers are still in their infancy. Quite recently, bisbenzylidene cycloalkanone polymers (linear and hyperbranched) have been reported by our group. The hyperbranched polymers address some problems regarding the solubility and quick photo-response of bisbenzylidene polymers. We discuss the state-of-the-art of this multi-disciplinary BBCA molecule and BBCA containing polymers reported to date. We believe this article will be very useful as the progress in science and technology concerning this molecule is rather slow. Our aim is to bring together details of the work reported so-far and its significance that will be useful to the scientific community.

Synthesis and Characterization of Linear Polymers for Non-Linear Optics through Click Chemistry Route

Click chemistry is used for synthesizing polymers for second order NLO study. The molecular weights found by gel-permeation chromatography (GPC), were in the range of 7000-55000 g/mol. Differential scanning calorimetry shows glass transition temperature (Tg) above 120 oC. From electronic spectra order parameter of the poled films were calculated to be 0.1-0.5. The change in surface morphology after poling was checked by atomic force microscopy. By using a pulsed Nd:YAG laser (1064nm), the second harmonic generation (SHG) intensity was measured. The SHG intensity was also studied as a function of against temperature and time respectively.

Poly(ethylene glycol) (PEG)-modified epoxy phase-change polymer with dual properties of thermal storage and vibration damping

A novel cross-linked self-sustaining film was prepared by reaction of carboxyl-capped poly(ethylene glycol) (PEG) with epoxy resin, followed by incorporation of the prepared material (named modified epoxy, ME) into an epoxy matrix. Self-sustaining films were obtained with up to 60 wt% ME in the epoxy matrix. Fourier-transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (NMR) were used for chemical characterization of the samples. Differential scanning calorimetry (DSC) study exhibited maximum enthalpy for PCM film reaching up to 41 J g−1. The X-ray diffraction (XRD) and polarized optical microscopy (POM) indicated lesser degree of crystallinity of PEG segments due to constriction by crosslinked epoxy resin. Dynamic mechanical analysis (DMA) results indicate that the blend of epoxy and ME is compatible up to 30 wt% ME and there is distinct phase separation beyond this composition.

Tailoring of energetic groups in acroyloyl polymers

Abstract Acryloyl based novel energetic monomers having nitro acrylates and nitro triazole acrylates were synthesized and further used for polymerization. Due to scavanging properties of nitro groups, syntheses of nitro aromatic polymers are not facile at normal conditions. In this regard, we report a simple protocol to synthesize these energetic group embeded acroloyl polymers. These polymers were characterized by FTIR, and NMR spectroscopic techniques. gel permeation chromatography (GPC) technique was employed in order to understand molecular mass of these polymers along with average molecular weight, number average weight and poly dispersity index. Glass transition temperature (Tg) was determined by using DSC analysis. It was observed that with increase in nitro groups in polymers there is a decrease in glass transition temperature. Two steps degradation were depicted in the TGA thermograph in nitro containing polymers. Heat release during this reaction was found up to 951 J/g. Increase in nitrogen content in polymer unit enhanced the heat release of polymers.

Photoactive Liquid Crystalline Polymer

The control by light is achieved by introducing photoisomerizable functionality to mesogenic structures and this way new functional varieties are added. In this chapter various LC and chromophores are discussed in introduction. This is followed by general discussion on LC/chromophore blend and specifically on photoactive liquid crystalline polymer blends and composites. Specific blend behavior of photoactive polymer/LC molecules is incorporated, which is followed by various photoactive LC polymer structures containing both mesogen and chromophore. Photoactive LC elastomers (LCEs) and specifically the important Light-induced artificial muscle-like actuation by LCEs are discussed. Liquid single crystal elastomer and its opto-mechanical effect is incorporated. Nanoparticle composite, dual nature of chromophore, few specific cases are followed by application, conclusion and future prospects respectively.