Graphene Oxide-Grafted Hybrid Diblock Copolymer Brush (GO-graft-PEG6k-block-P(MA-POSS)) as Nanofillers for Enhanced Lithium Ion Conductivity of PEO-Based Nanocomposite Solid Polymer Electrolytes.

Nanocomposite solid polymer electrolytes (NSPEs) with PEO as the matrix and (i) GO or (ii) GO-graft-PEG6k or (iii) GO-graft-PEG6k-block-P(MA-POSS) as nanofillers have been fabricated to elucidate the impact of the filler morphology on the lithium ion conductivity. GO-graft-PEG6k was obtained by grafting PEG6k onto GO via esterification. GO-graft-PEG6k-block-P(MA-POSS) was prepared via surface-initiated atom transfer radical polymerization. Fourier-transform infrared spectroscopy revealed enhanced salt dissociation and complexation between the filler and PEO host that could be attributed to Lewis acid-base interactions. Electrochemical impedance spectroscopy revealed the improved ion conductivity of the fabricated NSPEs as compared with the pristine PEO-LiClO4. As an example, at 50 °C, the ion conductivity increased to 4.01 × 10-5 and 6.31 × 10-5 S cm-1 with 0.3% GO and 0.3% GO-graft-PEG6k, respectively, from 2.36 × 10-5 S cm-1 of PEO-LiClO4, suggesting that the filler with brush-like architecture (GO-graft-PEG6k) is more efficient in enhancing the ion conductivity. Further increase in filler content resulted in lowering of the ion conductivity that could be ascribed to aggregation of the filler. The most dramatic impact on conductivity was observed with the incorporation of brush-like GO-graft-PEG6k-block-P(MA-POSS) as a nanofiller (3.0 × 10-4 S cm-1 at 50 °C with 1.0 wt % filler content). The increase in ion conductivity in the current systems, as opposed to the conventional view, could not be correlated with the content of the amorphous phase of the matrix. The conduction mechanism is still unclear; nevertheless, it could be assumed that in addition to the ion conduction through the PEO matrix, the filler forms additional low-energy ion conducting channels at its interface with the matrix. The pendent POSS nanocages of GO-graft-PEG6k-block-P(MAPOSS) might probably increase the free volume at the interface with the matrix that is associated with higher chain and ion mobility, thus further enhancing the ion conductivity as compared with GO and GO-graft-PEG6k. The faster ion dynamics in 1.0 wt % GO-graft-PEG6k-block-P(MAPOSS) NSPEs has also been verified by the dielectric relaxation studies. Thus, integration of both the PEG and POSS nanocages into GO-grafted brush-like architecture offers a new tool for tuning the lithium ion conductivity for potential Li ion battery applications.

Selected organic dyes (carminic acid, pyrocatechol violet and dithizone) sensitized metal (silver, neodymium) doped TiO2/ZnO nanostructured materials: A photoanode for hybrid bulk heterojunction solar cells.

A photoactive nanohybrid material consisting of pyrocatechol violet, carminic acid and dithizone dyes functionalized silver and neodymium-doped TiO2/ZnO nanostructured materials is reported here, as photoactive blend, for solid-state dye sensitized solar cell. First of all we synthesized metals (silver, neodymium) doped (TiO2) Titanium oxide nanoparticles and their nanocomposites (TiO2/ZnO, M-TiO2/ZnO) using the sol-gel and reflux technique, respectively. The synthesized samples were then characterized by UV-Visible spectroscopy, X-Ray diffraction Analysis (XRD), Scanning electron microscopy (SEM), Energy dispersive X-Ray Analysis (EDX), and Fourier Transform infrared spectroscopy (FTIR). Optical studies were done through UV-Visible spectroscopy and the absorption spectra were used to calculate band gaps. The value of the energy gap for TiO2 nanoparticles is 3.10 eV which was gradually tuned to 2.47 eV after incorporating metals (Ag and Nd) and forming respective nanocomposites. X-Ray diffraction Analysis (XRD) patterns revealed the purity and crystallinity in samples. Scanning electron microscopy (SEM) confirmed the irregular morphology (nanorods and spherical shaped) of ZnO and TiO2 nanostructures respectively. The elemental composition of nanomaterials was successfully investigated using energy dispersive X-ray analysis (EDX). In the absence of any impurities, Fourier Transform infrared spectroscopy (FTIR) was used to identify the functional groups in synthesized material. For device fabrication, a solid-state electrolyte, P3HT, a hole conducting polymer was used. Characterization of fabricated solar cells was done using I-V measurements. Under simulated solar irradiation, the DSSC based on pyrocatechol violet sensitized neodymium doped TiO2/ZnO nanohybrid materials exhibited the best PCE (power conversion efficiency) of 2.38 % and significantly improved Jsc (short circuit current density) of 15.68 mA/cm2 as compared to carminic acid and dithizone in photovoltaic measurements. The improved power conversion efficiency of this device is ascribed to the particle size, increased dye adsorption, increased surface area and thus improved short circuit current density (Jsc).

Formation of Surface Wrinkles in Collapsed Langmuir Films of a Polyhedral Oligomeric Silsesquioxane Containing Diblock Copolymer.

Surface pressure versus mean molecular area isotherms of Langmuir films of a hybrid diblock copolymer of poly(ethylene glycol) (PEG) and poly(methacrylo polyhedral oligomeric silsesquioxane) P(MA-POSS) together with Brewster angle microscopy reveal details of the phase transitions. The formation of a periodic wrinkling pattern in collapsed films is observed by epifluorescence microscopy after applying several compression-expansion cycles above the surface pressure of ≈18 mN/m. The wrinkle formation is reversible upon compression and expansion of the Langmuir films. Two distinct orientations of POSS molecules are assumed in Langmuir films upon compression, vertically for chains close to the water surface and horizontally orientated upper layers with significant amounts of PEG in between them. Thus, the wrinkling forms mainly in the top stiffer MA-POSS blocks above a certain compressional stress. The wrinkles disappear during the Langmuir-Blodgett (LB) transfer. Nevertheless, atomic force microscopy and grazing incidence wide-angle X-ray scattering experiments reveal the formation of highly ordered POSS molecules in LB films.

Fabrication and characterization of amidoxime-functionalized silica decorated with copper: a catalytic assembly for rapid reduction of dyes.

In this study, amidoxime-functionalized silica decorated with copper (AFS-Cu) was fabricated and tested for its catalytic application. Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were employed to characterize its structure and morphology. The application of AFS-Cu as a catalyst for the catalytic reduction of methylene blue (MB) in aqueous media using NaBH4 as reductant was evaluated. The ability to reuse as well as the effect of catalyst dose and pH of solution on the catalytic activity was investigated. The reduction of MB followed pseudo-first-order kinetics and the rate constant (k) was 0.6224 min-1. AFS-Cu was found to be a highly effective catalyst for MB reduction reaction and can be easily recovered and reused several times with no appreciable loss of catalytic activity.

A comparative study of branched and linear mannitol-based amphiphiles on membrane protein stability.

The study of membrane proteins is extremely challenging, mainly because of the incompatibility of the hydrophobic surfaces of membrane proteins with an aqueous medium. Detergents are essential agents used to maintain membrane protein stability in non-native environments. However, conventional detergents fail to stabilize the native structures of many membrane proteins. Development of new amphipathic agents with enhanced efficacy for membrane protein stabilization is necessary to address this important problem. We have designed and synthesized linear and branched mannitol-based amphiphiles (MNAs), and comparative studies showed that most of the branched MNAs had advantages over the linear agents in terms of membrane protein stability. In addition, a couple of the new MNAs displayed favorable behaviors compared to n-dodecyl-ß-d-maltoside and the previously developed MNAs in maintaining the native protein structures, indicating potential utility of these new agents in membrane protein study.

Tandem malonate-based glucosides (TMGs) for membrane protein structural studies.

High-resolution membrane protein structures are essential for understanding the molecular basis of diverse biological events and important in drug development. Detergents are usually used to extract these bio-macromolecules from the membranes and maintain them in a soluble and stable state in aqueous solutions for downstream characterization. However, many eukaryotic membrane proteins solubilized in conventional detergents tend to undergo structural degradation, necessitating the development of new amphiphilic agents with enhanced properties. In this study, we designed and synthesized a novel class of glucoside amphiphiles, designated tandem malonate-based glucosides (TMGs). A few TMG agents proved effective at both stabilizing a range of membrane proteins and extracting proteins from the membrane environment. These favourable characteristics, along with synthetic convenience, indicate that these agents have potential in membrane protein research.

Resorcinarene-Based Facial Glycosides: Implication of Detergent Flexibility on Membrane-Protein Stability.

As a membrane-mimetic system, detergent micelles are popularly used to extract membrane proteins from lipid environments and to maintain their solubility and stability in an aqueous medium. However, many membrane proteins encapsulated in conventional detergents tend to undergo structural degradation during extraction and purification, thus necessitating the development of new agents with enhanced properties. In the current study, two classes of new amphiphiles are introduced, resorcinarene-based glucoside and maltoside amphiphiles (designated RGAs and RMAs, respectively), for which the alkyl chains are facially segregated from the carbohydrate head groups. Of these facial amphiphiles, two RGAs (RGA-C11 and RGA-C13) conferred markedly enhanced stability to four tested membrane proteins compared to a gold-standard conventional detergent. The relatively high water solubility and micellar stability of the RGAs compared to the RMAs, along with their generally favourable behaviours for membrane protein stabilisation described here, are likely to be, at least in part, a result of the high conformational flexibility of these glucosides. This study suggests that flexibility could be an important factor in determining the suitability of new detergents for membrane protein studies.

Photo-sensitization of ZnS nanoparticles with renowned ruthenium dyes N3, N719 and Z907 for application in solid state dye sensitized solar cells: A comparative study.

This article presents a comprehensive relative report on the grafting of ZnS with renowned ruthenium ((Ru) dyes i.e. N3, N719 and Z907) and gives insight into their charge transfer interaction and sensitization mechanism for boosting solar cell efficiency. Influence of dye concentration on cell performance is also reported here. ZnS nanoparticles synthesized by a simple coprecipitation method with an average particle size of 15±2nm were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Elemental dispersive X-ray analysis (EDAX), tunneling electron microscopy (TEM) and UV-Visible (UV-Vis) spectroscopy. UV-Vis, photoluminescence (PL) and Fourier transform infra-red (FT-IR) spectroscopy confirms the successful grafting of these dyes over ZnS nanoparticles surface. Low-energy metal-to-ligand charge-transfer transition (MLCT) bands of dyes are mainly affected on grafting over the nanoparticle surface. Moreover their current voltage (I-V) results confirm the efficiency enhancement in ZnS solid state dye sensitized solar cells (SSDSSCs) owing to effective sensitization of this material with Ru dyes and helps in finding the optimum dye concentration for nanoparticles sensitization. Highest rise in overall solar cell efficiency i.e. 64% of the reference device has been observed for 0.3mM N719-ZnS sample owing to increased open circuit voltage (Voc) and fill factor (FF). Experimental and proposed results were found in good agreement with each other.

Accessible Mannitol-Based Amphiphiles (MNAs) for Membrane Protein Solubilisation and Stabilisation.

Integral membrane proteins are amphipathic molecules crucial for all cellular life. The structural study of these macromolecules starts with protein extraction from the native membranes, followed by purification and crystallisation. Detergents are essential tools for these processes, but detergent-solubilised membrane proteins often denature and aggregate, resulting in loss of both structure and function. In this study, a novel class of agents, designated mannitol-based amphiphiles (MNAs), were prepared and characterised for their ability to solubilise and stabilise membrane proteins. Some of MNAs conferred enhanced stability to four membrane proteins including a G protein-coupled receptor (GPCR), the ß2 adrenergic receptor (ß2 AR), compared to both n-dodecyl-d-maltoside (DDM) and the other MNAs. These agents were also better than DDM for electron microscopy analysis of the ß2 AR. The ease of preparation together with the enhanced membrane protein stabilisation efficacy demonstrates the value of these agents for future membrane protein research.

Adsorption of porphyrin and carminic acid on TiO2 nanoparticles: A photo-active nano-hybrid material for hybrid bulk heterojunction solar cells.

A photo-active nano-hybrid material consisting of titania nanoparticles, carminic acid, and sulphonic acid functionalized porphyrin is reported here. In an attempt to extend the absorption spectrum of titania to visible region by co-adsorbing carminic acid and sulphonic acid functionalized porphyrin on its surface. Interesting changes in the UV-visible and fluorescence spectra were noticed. The adsorption of carminic acid resulted in the formation of charge transfer complex with titania nanoparticles. This was confirmed by the electronic absorption and fluorescence emission spectroscopies. Chemisorption of porphyrin on the carminic acid functionalized titania further boosted the charge transfer effect. This was noticed by the increase in intensity and width of the charge transfer absorption and emission bands. Energy level diagram showed that the interaction among the constituents of the nano-hybrid assembly permitted the flow of electron in a cascade manner from carminic acid to TiO2.This also allowed direct flow of electrons either from carminic acid or porphyrin toward titania. The material was used as an active blend in hybrid bulk heterojunction solar cells. Co-functionalized TiO2-based devices were found 3.5 times more efficient than the reference device but morphology of the device proved a major setback.

Deoxycholate-Based Glycosides (DCGs) for Membrane Protein Stabilisation.

Detergents are an absolute requirement for studying the structure of membrane proteins. However, many conventional detergents fail to stabilise denaturation-sensitive membrane proteins, such as eukaryotic proteins and membrane protein complexes. New amphipathic agents with enhanced efficacy in stabilising membrane proteins will be helpful in overcoming the barriers to studying membrane protein structures. We have prepared a number of deoxycholate-based amphiphiles with carbohydrate head groups, designated deoxycholate-based glycosides (DCGs). These DCGs are the hydrophilic variants of previously reported deoxycholate-based N-oxides (DCAOs). Membrane proteins in these agents, particularly the branched diglucoside-bearing amphiphiles DCG-1 and DCG-2, displayed favourable behaviour compared to previously reported parent compounds (DCAOs) and conventional detergents (LDAO and DDM). Given their excellent properties, these agents should have significant potential for membrane protein studies.

Molecular arrangement of symmetric and non-symmetric triblock copolymers of poly(ethylene oxide) and poly(isobutylene) at the air/water interface.

The behavior of a series of amphiphilic triblock copolymers of poly(ethylene oxide) (PEO) and poly(isobutylene) (PIB); including both symmetric (same degree of polymerization (DP) of the terminal PEO blocks) PEOm-b-PIBn-b-PEOm and non-symmetric (different DP of the terminal PEO blocks) PEOm-b-PIBn-b-PEOz, is investigated at the air/water interface by measuring surface pressure vs mean molecular area isotherms (π vs mmA), Langmuir-Blodgett (LB) technique, and infrared reflection-absorption spectroscopy (IRRAS). The block copolymer (PEO32-b-PIB160-b-PEO32) with longer PEO segments forms a stable monolayer and the isotherm reveals a pseudo-plateau starting at π∼5.7 mN/m, also observed in the IRRAS, which is assigned to the pancake-to-brush transition related to the PEO dissolution into the subphase and subsequent PEO brush dehydration. Another plateau is observed at π∼40 mN/m, which is attributed to the film collapse due to multilayer formation. The pancake-to-brush transition could not be observed for samples with smaller PEO chains. The isotherms for block copolymers, with short PEO chains, both symmetric (PEO3-b-PIBn-b-PEO3) and non-symmetric (PEO12-b-PIBn-b-PEO3), reveal another transition at π∼20-25 mN/m. This is interpreted to be due to the conformational transition from a folded state where the middle PIB block is anchored to the water surface at both ends by the terminal hydrophilic segments to an unfolded state with PIB anchored to the water surface at one end. It is assumed that this transition involves the removal of PEO3 chains from the water surface in case of non-symmetric PEO12-b-PIB85-b-PEO3 and in case of symmetric, probably one PEO3 of each PEO3-b-PIB85-b-PEO3 chain. Because of the weaker interaction of the short PEO3 chains with the water surface as compared with the relatively longer PEO12 chains, the film of PEO3-b-PIB85-b-PEO3 collapses at much lower surface pressure after the transition as compared with the PEO12-b-PIB85-b-PEO3. The AFM images reveal the formation of microdomains of almost uniform height (6-7 nm) in LB films of PEO3-b-PIB85-b-PEO3 and PEO12-b-PIB85-b-PEO3 after transferring onto silicon surfaces. These domains are assumed to be the mesomorphic domains of ordered and folded PIB chains.

Self-organization of poly(ethylene oxide) on the surface of aqueous salt solutions.

It is demonstrated that stable Langmuir films of poly(ethylene oxide) (PEO) can be formed up to surface pressures of 30 mN m(-1) when potassium carbonate K2CO3 is added to the aqueous subphase. Generally, PEO homopolymer cannot stay on the water surface at a surface pressure ≥10 mN m(-1) due to its high water solubility. To prepare stable monolayer films, PEO can be modified with hydrophobic moieties. However, by exploiting the salting out effect by adding certain salts (K2CO3 or MgSO4) into the aqueous subphase, not only very stable films but also unusual self-organization can be achieved by the PEO homopolymer on the surface of the aqueous solution. Thus, a series of OH-terminated PEOs is found to form a stable monolayer at K2CO3 concentrations of 2 M and above in the aqueous subphase, and the stability of the film increases with an increase in K2CO3 concentration. Hysteresis experiments are also carried out. During the phase transition induced by progressive compression, self-organization into well-defined domains with sizes in the micrometer range are observed, and with further compression and holding of the film for 30 min and above the microdomains transform into a crystalline morphology as visualized by Brewster angle microscopy.

New ganglio-tripod amphiphiles (TPAs) for membrane protein solubilization and stabilization: implications for detergent structure-property relationships.

Detergents are widely used for membrane protein research; however, membrane proteins encapsulated in micelles formed by conventional detergents tend to undergo structural degradation, necessitating the development of new agents with enhanced efficacy. Here we prepared several hydrophobic variants of ganglio-tripod amphiphiles (TPAs) derived from previously reported TPAs and evaluated for a multi-subunit, pigment protein superassembly. In this study, TPA-16 was found to be most efficient in protein solubilization while TPA-15 proved most favourable in long-term protein stability. The current study combined with previous TPA studies enabled us to elaborate on a few detergent structure-property relationships that could provide useful guidelines for novel amphiphile design.

Effect of angstrom-scale surface roughness on the self-assembly of polystyrene-polydimethylsiloxane block copolymer.

Self-assembly of block copolymers has been identified as a potential candidate for high density fabrication of nanostructures. However, the factors affecting its reliability and reproducibility as a patterning technique on various kinds of surfaces are not well-established. Studies pertaining to block copolymer self-assembly have been confined to ultra-flat substrates without taking into consideration the effect of surface roughness. Here, we show that a slight change in the angstrom-scale roughness arising from the surface of a material creates a profound effect on the self-assembly of polystyrene-polydimethylsiloxane block copolymer. Its self-assembly was found to be dependent on both the root mean square roughness (R(rms)) of the surface and the type of solvent annealing system used. It was observed that surface with R(rms)< 5.0 Å showed self-assembly. Above this value, the kinetic hindrance posed by the surface roughness on the block copolymer leads to its conforming to the surface without observable phase separation.

Direct patterning of TiO2 using step-and-flash imprint lithography.

Although step-and-flash imprint lithography, or S-FIL, has brought about tremendous advancement in wafer-scale fabrication of sub-100 nm features of photopolymerizable organic and organo-silicon-based resists, it has not been successful in direct patterning of inorganic materials such as oxides because of the difficulties associated with resist formulation and its dispensing. In this paper, we demonstrate the proof-of-concept S-FIL of titanium dioxide (TiO(2)) carried by an acrylate-based formulation containing an allyl-functionalized titanium complex. The prepolymer formulation contains 48 wt % metal precursor, but it exhibits low enough viscosity (∼5 mPa·s) to be dispensed by an automatic dispensing system, adheres and spreads well on the substrate, is insensitive to pattern density variations, and rapidly polymerizes when exposed to broadband UV radiation to give a yield close to 95%. Five fields, each measuring 1 cm × 1 cm, consisting of 100 nm gratings were successively imprinted. Heat-treatment of the patterned structures at 450 °C resulted in the loss of organics and their subsequent shrinkage without the loss of integrity or aspect ratio and converted them to TiO(2) anatase nanostructures as small as 30 nm wide. With this approach, wafer-scale direct patterning of functional oxides on a sub-100 nm scale using S-FIL can become a distinct possibility.

Direct imprinting of high resolution TiO(2) nanostructures.

We demonstrate a different approach to direct nanoimprint lithography of oxides, in particular TiO(2), using the metal methacrylate route which not only gives very high resolution ( approximately 20 nm) but also provides yields of approximately 100% over areas > 1 cm x 1 cm. TiO(2) was imprinted using a polymerizable liquid 'TiO(2) resin' consisting of a mixture of titanium methacrylate, ethylene glycol dimethacrylate, and azobis-(isobutyronitrile). The resin underwent free radical polymerization when imprinted using a silicon mold at 110 degrees C with pressures as low as 10 bar. Polymerization strengthens the imprinted structures, thereby giving approximately 100% yield after demolding. Heat-treatment of the imprinted structures at 400 degrees C resulted in the loss of organics and their subsequent shrinkage ( approximately 75%) without the loss of integrity or aspect ratio, and converted them to TiO(2) nanostructures as small as approximately 20 nm wide. Furthermore, our method demonstrates that large imprinted areas of sub-100-nm features can be achieved by sub-micron molds which translate into huge cost savings with the added flexibility of direct patterning of urinary as well as multi-component oxides.

Synthesis and Self-Assembly of pH-Responsive Amphiphilic Poly(dimethylaminoethyl methacrylate)-block-Poly(pentafluorostyrene) Block Copolymer in Aqueous Solution.

We report the synthesis of a novel pH-responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)-block-poly(pentafluorostyrene) (PDMAEMA-b-PPFS) using RAFT-mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, N(agg) ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, R(h) of these micelles is large, at pH 2-5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the R(h) . However, the radius of gyration, R(g) remains independent of pH as the dense PPFS cores predominate.

Self-assembly of brush-like poly[poly(ethylene glycol) methyl ether methacrylate] synthesized via aqueous atom transfer radical polymerization.

Self-assembly of brush-like well-defined poly[poly(ethylene glycol) methyl ether methacrylate] homopolymers, abbreviated as P(PEGMA-475) and P(PEGMA-1100) is investigated in aqueous solution by employing dynamic/static light scattering (DLS/SLS) and transmission electron microscopy (TEM), whereas 475 and 1100 is molar mass of the respective PEGMA macromonomer. The mentioned brush-like homopolymers are synthesized by aqueous ATRP at room temperature. The critical association concentration (CAC) of the synthesized polymers in water depends on the length of the PEG side chains but not on the overall molar mass of the polymer. Thus, approximately the same CAC of approximately 0.35 mg/mL is estimated for various P(PEGMA-1100) samples, and approximately 0.7 mg/mL is estimated for P(PEGMA-475) series. All the investigated P(PEGMA-1100) samples form multimolecular micelles in aqueous solution, where the hydrodynamic size (Rh) and the aggregation number (Nagg) of micelles decreases as the molecular weight of P(PEGMA-1100) increases. This can be attributed to the increased steric hindrances between the PEG side chains in corona of micelles formed by higher molar mass P(PEGMA-1100). The tendency of micelle formation by samples of P(PEGMA-475) series is significantly lower than that of P(PEGMA-1100) series, as demonstrated by their significantly higher CAC and micelles of lower Nagg. The Rh of micelles does not depend strongly on polymer concentration, which suggests that these micelles are formed via the closed association model. Micelles formed by P(PEGMA-1100) series slightly shrink with increase in temperature from 25 to 60 degrees C, while those of P(PEGMA-475) series are found to be insensitive to the same temperature variation. Finally, TEM is carried out to visualize the formed micelles after transferring the aqueous solution to carbon film.