Dharmalingam Sangeetha

Evaluation of Sulfonated Poly(Ether Ether Ketone) Silicotungstic Acid Composite Membranes for Fuel Cell Applications

Fuel cells have received much attention for clean power generation for transportation, portable power systems, etc. Composite membranes are better than the homopolymeric membranes, as their properties can be altered by varying the composition. In our present study, five samples of sulfonated poly(ether ether ketone) (SPEEK)/silicotungstic acid (SWA) composite membranes were prepared. The molecular interactions of the composite membranes were characterized by FTIR and XRD techniques. The ion exchange capacity (IEC) was studied. The thermal suitability was found to be excellent as confirmed by TGA. SEM analysis revealed uniform distribution of the hetero poly acid (HPA) in the composite membranes. The protonic conductivity determined by impedance spectroscopy was found to be in the order of 10−3 S/cm. The change in the mechanical properties of the composite membranes was observed by Universal Testing Machine (UTM). Overall, the composite membranes proved to be an excellent candidate for fuel cell applications.

Design of novel SPEEK-based proton exchange membranes by self-assembly method for fuel cells

Fuel cell represents a new energy conversion device, which promises to provide clean source of power. Fuel cell [particularly proton exchange membrane fuel cell and direct methanol fuel cell (DMFC)] is a promising candidate for transportation and portable power source applications. In DMFC, there is a problem of methanol crossover. In order to reduce such a problem, there has been an intensive research activity in the modification of Nafion. In the present investigation, self-assembled membranes were fabricated with sulfonated polyether ether ketone as the core part of the membrane. Aminated polysulfone and sulfonated polysulfone were used as the layers in order to prevent the crossover of methanol. The assembled membranes were characterized by ion exchange capacity, water and methanol absorption, and durability. The methanol permeability and selectivity ratio proved a strong influence on DMFC application. Scanning electron microscopy proved smooth surface, which established strong cohesive force for the polymer chains. Among the synthesized self-assembled membranes, the membrane with two bilayers was the best in terms of power density in DMFC. The membrane electrode assembly with two bilayers showed higher performance (~61.05 mW/cm2) than sulfonated poly(ether ether ketone) and Nafion in DMFC.

Investigation on sulphonated PEEK beads for drug delivery, bioactivity and tissue engineering applications

Poly ether ether ketone (PEEK) has wide applications in the field of medicine as a prosthetic material and can be sulphonated using sulphuric acid. This study focuses on the fabrication of water soluble SPEEK beads using infusion pump and the obtained beads were characterised using Fourier Transform Infra Red (FTIR) spectroscopy to confirm the sulphonation, while their surface morphology was studied using scanning electron microscope (SEM). In order to study the bioactivity of the prepared beads, hydroxyapatite was dispersed within them followed by their immersion in SBF. In order to study the drug release kinetics of the beads, they were loaded with amoxicillin in different concentrations. Cytotoxicity studies were performed by MTT method and ALP activity was measured using mouse osteoblast cells (MC3T3-E1). The SEM and FTIR of the prepared beads confirmed the morphology and the sulphonation of the prepared beads. Also, the apatite formation on the SPEEK beads, subsequent to their immersion in SBF, proved that the beads possessed excellent bioactivity. Moreover, the beads developed exhibited low cytotoxicity, implying good biocompatibility and safety. Thus, the results of the study indicated that the novel SPEEK beads could potentially be used as a drug carrying vehicle with low toxicity.

Sulphonated Poly(ether ether ketone) Proton Exchange Membranes for Fuel Cell Applications

Polymer electrolyte membrane fuel cells (PEMFCs) are promising new power sources for automotive and portable devices. Nafion® is the currently used membrane in PEMFCs. Although these membranes show high proton conductivity and excellent chemical stability, their high cost makes them unpractical for commercial purposes. Sulphonated poly(ether ether ketone) (SPEEK) ionomers were synthesized using chlorosulphonic acid as the sulphonating agent in dichloromethane medium. Homogeneous proton-conducting membranes were developed from the obtained SPEEK by solvent casting method. Membranes were assessed for their suitability in fuel cell applications. The extent of sulphonation was controlled by varying the reaction time, concentration of polymer, and concentration of sulphonating agent. The SPEEK membranes exhibit degree of sulphonation from 10 to 66%, ion exchange capacity from 0.29 to 1.92 meq/g and maximum water and methanol uptake up to 54 and 22%, respectively, at 25°C. The membranes were characterized by FTIR to confirm sulphonation, and DSC and TGA to investigate the thermal stability. The proton conductivities of such membranes were found to be excellent in the order of 10−2 S/cm in the fully hydrated condition at room temperature as measured by impedance spectroscopy. The durability of the membranes was also tested. The study revealed the possibility of a cheaper alternative membrane for use in PEMFC.

Fabrication and evaluation of electrospun collagen/poly(N-isopropyl acrylamide)/chitosan mat as blood-contacting biomaterials for drug delivery

The recent advances in electrospinning have resulted in technologies facilitating easy drug entrapment, obtaining high surface area and thereby higher drug loading and release efficacy, burst control as well as the specific morphology which could be controlled according to the desired requirement. The present study focused on the fabrication of collagen/poly(N-isopropyl acrylamide)/chitosan complex with incorporated 5-fluorouracil, an anticancer drug by the method of electrospinning. The effect of chitosan on the fiber morphology and release kinetics was analyzed by varying its concentration. The release kinetics showed that the increase in chitosan concentration delayed the release of the drug from the fiber network. Nano hydroxyapatite was added to the fiber matrix in order to impart bioactivity, which was confirmed by studies in simulated body fluid. The addition of poly(N-isopropyl acrylamide) increased the blood compatibility of the prepared model. Thus, the model prepared to can find potential application in the field of cancer therapy as a drug-delivery agent in post-surgical treatment of cancer and as blood contacting biomaterial.

A quaternized mesoporous silica/polysulfone composite membrane for an efficient alkaline fuel cell application

Mesoporous silica (SBA-15) was synthesized and quaternized via chloromethylation followed by amination. Quaternized SBA-15 (QSBA) was characterized by FTIR, solid state 13C NMR, BET, XRD and TEM. The QSBA was then incorporated into quaternary polysulfone (QPSu) in different weight percentages (1–4%) to form high ion exchange capacity composite membranes. The composite membranes were analysed by SEM and XRD. The water uptake, ion exchange capacity and hydroxyl conductivity of the composite membrane were studied for the suitability of the membrane in alkaline fuel cells. A membrane electrode assembly was constructed using a carbon supported platinum (Vulcan XC-72) anode, cathode catalysts and a QPSU/3% QSBA-15 composite membrane and tested in an AFC. A maximum power density of 298 mW cm−2 was achieved at 60 °C. The experimental results showed that the QPSU/QSBA-15 composite membrane exhibited a promising electrochemical performance in an AFC.

A Novel Composite Membrane from QPSU and SiO2 for Solid Alkaline Fuel Cell Applications

The goal of this work is to develop a novel composite membrane from quaternized polysulfone (QPSU) and silica (SiO2), to fabricate alkaline membrane electrode assemblies (MEAs) and to subsequently test the MEAs in 5 cm × 5 cm single cell configuration using Pt/C and Ag/C as anode and cathode catalysts, respectively. The composite membranes were characterized in terms of water absorption, ion exchange capacity and ionic conductivity. The physicochemical studies Fourier transform infra red (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) studies, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and universal testing machine (UTM) were used to investigate the relation between the structure and performance of the composite membranes. The results show that the SiO2 was compatible with the QPSU membrane. The thermal stability and ionic conductivity of the QPSU/SiO2 composite membranes were higher than that of quaternized polysulfone (QPSU) membrane. The maximum performance was achieved for 10 wt.% SiO2 with power density of 149.6 mW/cm2 at current density of 440 mA/cm2.

Surface Modification of Sulfonated Polystyrene Ethylene Butylene Polystyrene Membranes by Layer-by-layer Assembly of Polysulfone for Application in Direct Methanol Fuel Cell

Methanol permeability is a major drawback for application of sulfonated polystyrene ethylene butylenes polystyrene block copolymers (SPSEBS) in direct methanol fuel cells (DMFC). Modification of SPSEBS by layer-by-layer (LBL) assembly of aminated (APSU) and sulfonated polysulfone (SPSU) was attempted to reduce its methanol permeability. The LBL deposition of APSU and SPSU on SBSEBS was carried out by dipping in their solutions alternatively for 10 min. The LBL assembly was confirmed by SEM analysis. The methanol permeability was lower than SPSEBS and Nafion 117. The proton conductivity, ion exchange capacity, and water absorption were lower than SBSEBS but higher than Nafion 117. Its selectivity ratio (0.70 × 105) was higher than both SBSEBS (0.54 × 105) and Nafion 117 (0.06 × 105). The maximum power density of LBL (62 mW/cm2) was about five times higher than SBSEBS. These features of LBL confirm the LBL assembly method as a very simple procedure to modify SBSEBS for application in DMFC.

Evaluation of polyphenylene ether ether sulfone/nanohydroxyapatite nanofiber composite as a biomaterial for hard tissue replacement

The present work is aimed at investigating the mechanical and in vitro biological properties of polyphenylene ether ether sulfone (PPEES)/nanohydroxyapatite (nHA) composite fibers. Electrospinning was used to prepare nanofiber composite mats of PPEES/nHA with different weight percentages of the inorganic filler, nHA. The fabricated composites were characterized using Fourier transform infrared spectroscopy (FTIR)-attenuated total reflectance spectroscopy (ATR) and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) techniques. The mechanical properties of the composite were studied with a tensile tester. The FTIR-ATR spectrum depicted the functional group as well as the interaction between the PPEES and nHA composite materials; in addition, the elemental groups were identified with EDX analysis. The morphology of the nanofiber composite was studied by SEM. Tensile strength analysis of the PPEES/nHA composite revealed the elastic nature of the nanofiber composite reinforced with nHA and suggested significant mechanical strength of the composite. The biomineralization studies performed using simulated body fluid with increased incubation time showed enhanced mineralization, which showed that the composites possessed high bioactivity property. Cell viability of the nanofiber composite, studied with osteoblast (MG-63) cells, was observed to be higher in the composites containing higher concentrations of nHA.

Polymethyl methacrylate nanofiber-reinforced epoxy composite for shape-memory applications

Polymethyl methacrylate (PMMA) nanofiber-reinforced diglycidyl ether of bisphenol A shape memory epoxy composites were fabricated and their shape-memory properties were investigated. The PMMA nanofibers were found to be randomly distributed, while the tensile strength and Young’s modulus increased with increase in the percentage of PMMA. The glass transition temperature of the composites was found to decrease marginally with the addition of PMMA nanofibers. The shape recovery experiments showed that at low strain percentages, the composites exhibited excellent strain recovery. However, at higher strain percentages, the percentage of recovery was found to decrease gradually with increase in filler concentration.