Ravi Mosurkal

Nanocomposites of TiO 2 and Siloxane Copolymers as Environmentally Safe Flame-Retardant Materials †

Composites of titanium dioxide (TiO2) nanoparticles and biocatalytically synthesized dimethylsiloxane copolyamides were prepared, and their thermal and flame-retardant properties were investigated. The flammability properties such as heat release capacity and total heat release were measured from microscale cumbustion calorimetry (MCC). The thermal degradation temperatures, char yields, and the heat-release capacities of these nanocomposites were significantly improved over the pure polymers. The heat-release capacities of the siloxane copolymer nanocomposites with 20wt% of TiO2 were found to be 167 and 129 J/g K, which is a 35% less than the pure polymers (260 and 194 J/g K, respectively). The SEM/EDAX surface-analysis studies on nanocomposite films and their char revealed that nanocrystalline-TiO2 plays an important role in forming carbonaceous silicate char on the surface as a protective layer.

Simple green synthesis of polyborosiloxanes as environmentally-safe, non-halogenated flame retardant polymers

A novel class of boron-containing siloxane copolymers (polyborosiloxanes) was synthesized by simple environmentally friendly methods. A boron containing monomer, specifically phenylboronic acid (PBA), and imide forming monomers, specifically aromatic dianhydrides 4,4′-oxydiphthalicanhydride (Oxy) and 1,1,4,4-tetracarboxylicphenyldianhydride (DAH), were employed to make terpolymers with propylamino-terminated polydimethylsiloxane (A12-PDMS). The terpolymer synthesis was carried out using various PBA : Oxy and PBA : DAH compositions ranging from 0 : 1 to 1 : 0 mole ratios. The thermal and flame retardant properties of the novel polymers were investigated. Intermediate ratios of both PBA : Oxy and PBA : DAH resulted in optimal thermal stability and flame retardancy. These novel terpolymers are promising candidates as environmentally-safe, non-halogenated alternatives to traditional flame retardant polymers.

Simple fabrication of zinc oxide nanostructures

A simple and low cost methodology for fabricating one and two dimensional periodic ZnO nanostructures utilizing surface relief patterns on azopolymer films as templates is demonstrated.

Synthesis and modeling of acridine dyes as potential photosensitizers for dye-sensitized photovoltaic applications

We have synthesized novel aromatic amine‐substituted acridine dyes as potential candidates for the photosensitizers in dye sensitized nanocrystalline semiconductor based solar cells (DSSC) cells. The protonation and quaternization of the acridine nitrogen led to acridine dyes with extended absorption from 400–800 nm. Computational modeling was used to evaluate a variety of structures to achieve insights for correlating these types of molecular structures with predicted absorption spectra. Pertinent dihedral angles as well as bond lengths were evaluated to assess and compare planarity and conjugation for these dyes. Other predictions include plots of the HOMO and LUMO levels to qualitatively examine electron distributions and the potential for electron injection. The results from modeling along with the experimental data consisting of synthesis, characterization and UV‐visible absorption properties of the selected dyes are presented. †Dedicated to the memory of Professor Sukant K. Tripathy.

Influence of EDA-π interactions in drug encapsulation using nanospheres

We have evaluated the influence of aromatic and hydrophobic interactions on the strength and selectivity of encapsulation using polymeric nanospheres.

Polysiloxane-based Organoclay Nanocomposites as Flame Retardants

Polydimethylsiloxane-aromatic dianhydride copolymers (PS-Oxy-PAA and PS-DAH-PAA) were blended through several techniques with organoclays Cloisite 30B, 10A and Na+ ranging from 1 to 5 wt.%. Thermal and flame-retardant analysis revealed an in-situ blending approach was optimal, which led to the generation of a nanocomposite, PS-Oxy-PAA/30B (5 wt.%), with comparable heat release capacity (170.5 J/g-K) and total heat release (12.0 kJ/g) as seen with some commercial polymers. Concomittant dispersion and FTIR analyses revealed that the enhanced thermal stability observed with PS-Oxy-PAA/30B (5 wt.%) is not dispersion related, since the organoclay was exfoliated in all composites formed. The driving force is the interaction between the carbonyl groups of the PS-Oxy-PAA and the hydroxyl groups of the organoclay, which is limited in all other cases. These results suggest judicious selection of organoclay and siloxane copolymers can faciliate the design of new environmentally safe, heat processible, nonhalogenated alternatives to traditional flame-retardant polymers.

Fabrication of Dye-sensitized Solar Cells and Fluorescence Quenching Study Using Thiophene Based Copolymers

Photovoltaic performance of dye sensitized solar cells fabricated with a commercially available thiophene based copolymer was investigated. Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)], a highly soluble polythiophene, was used as a sensitizer. An open-circuit voltage of 0.64 V and a short-circuit current density of 0.36 mA/cm2 were measured. The incident photon to current conversion efficiency for the polymer was measured. Fluorescence from the other polythiophene, poly(3,3′-didodecyl quarter thiophene) was found to be quenched when blended with phenyl C61 butyric acid methyl ester (PCBM) (1:1 wt ratio), indicating the charge transfer from the conjugated polymer to PCBM.

Self Organization and Redox Behavior of Poly(vinylferrocene)-block-Poly(isobutylene)-block-Poly(vinylferrocene) Triblock Copolymer †

Self organization and redox behavior of a ferrocene containing triblock copolymer, poly(vinylferrocene)-block-poly(isobutylene)-block-poly(vinylferrocene), with narrow molecular weight distribution in solutions and in thin films were investigated. Dynamic light scattering studies of the block copolymer in dilute solutions indicated that the polymer chains aggregated at relatively low concentrations. The aggregations of polymer chains were observed in toluene, as well as in tetrahydrofuran at concentrations as low as 0.014 mg/mL and 0.0045 mg/mL, respectively. Thin films of the copolymer showed reversible single electron redox behavior, similar to that of ferrocene. Morphology and micro-phase separation of the copolymer was analyzed by transmission electron microscopy.

Mono- and dinuclear ruthenium complexes for nanocrystalline TiO2 based dye-sensitized photovoltaics

Abstract We have carried out synthesis, characterization, and theoretical modeling of a rigid, rod‐like homometallic dinuclear ruthenium complex and an analogous mononuclear ruthenium complex using terpyridine and bipyridine ligands. The photophysical and photovoltaic properties have been investigated. We compared the results to understand the charge transfer processes in these complexes. The dinuclear complex showed overall photoelectric conversion efficiency of 1.9% in dye‐sensitized nanocrystalline TiO2 based photovoltaic cells under simulated AM1.5 solar irradiation and is found to be an efficient photosensitizer compared to the mononuclear complex. #Dedicated to the memory of Professor Sukant K. Tripathy.

Molecules for converting sunlight into electricity

The dream of generating electricity from sunlight in large scale at low cost may not be that far from reality in this century. Rapidly emerging solar energy technology using low cost dye sensitized photovoltaic cells on plastics would be a real boost for the third world countries. Though the conventional silicon solar cells are efficient in converting solar energy into electricity until now, the non conventional solar cells based on molecular photosensitization by colored materials in wide band gap semiconductors is a fast growing field of basic scientific and industrial research. Present state-of-the-art cells using molecular dyes shows energy conversion efficiencies of 10–11%. In this article, we present the concept of dye-sensitized photovoltaic (DSPV) cell and the progress in current research. The important contributions of molecular dyes that are used as photosensitizers in these photovoltaic or solar cells are also described.