Studies on aluminum-isopropoxide doped poly(ethylene oxide), poly(vinyl alcohol), and poly(ethylene oxide)-poly(vinyl alcohol) blends

Poly( ethylene oxide), poly(vinyl alcohol): and their blend in a 40 : 60 mole ratio were doped with aluminum isopropoxide. Their structural, thermal, and electrical properties were studied. Aluminum isopropoxide acts as a Lewis acid and thus significantly influences the electrical properties of the polymers and the blend. It also acts as a scavanger for the trace quantities of water p-resent in them, thereby reducing the magnitude of proton transport. It also affects the structure of polymers that manifests in the thermal transformation and decomposition characteristics.

Chitosan Immobilized Porous Polyolefin As Sustainable and Efficient Antibacterial Membranes

Polyolefinic membranes have attracted a great deal of interest owing to their ease of processing and chemical inertness. In this study, porous polyolefin membranes were derived by selectively etching PEO from PE/PEO (polyethylene/poly(ethylene oxide)) blends. The hydrophobic polyolefin (low density polyethylene) was treated with UV-ozone followed by dip coating in chitosan acetate solution to obtain a hydrophilic-antibacterial surface. The chitosan immobilized PE membranes were further characterized by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscope (XPS). It was found that surface grafting of chitosan onto PE membranes enhanced the surface roughness and the concentration of nitrogen (or amine) scaled with increasing concentration of chitosan (0.25 to 2% wt/vol), as inferred from Kjeldahl nitrogen analysis. The pure water flux was almost similar for chitosan immobilized PE membranes as compared to membranes without chitosan. The bacterial population, substantially reduced for membranes with higher concentration of chitosan. For instance, 90 and 94% reduction in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) colony forming unit respectively was observed with 2% wt/vol of chitosan. This study opens new avenues in designing polyolefinic based antibacterial membranes for water purification.

Orthogonal biofunctionalization of magnetic nanoparticles via ``clickable'' poly(ethylene glycol) silanes: a ``universal ligand'' strategy to design stealth and target-specific nanocarriers

The present work demonstrates a novel strategy to synthesize orthogonally bio-engineered magnetonanohybrids (MNPs) through the design of versatile, biocompatible linkers whose structure includes: (i) a robust anchor to bind with metal-oxide surfaces; (ii) tailored surface groups to act as spacers and (iii) a general method to implement orthogonal functionalizations of the substrate via ``click chemistry''. Ligands that possess the synthetic generality of features (i)-(iii) are categorized as ``universal ligands''. Herein, we report the synthesis of a novel, azido-terminated poly(ethylene glycol) (PEG) silane that can easily self-assemble on MNPs through hetero-condensation between surface hydroxyl groups and the silane end of the ligand, and simultaneously provide multiple clickable sites for high density, chemoselective bio-conjugation. To establish the universal-ligand-strategy, we clicked alkyl-functionalized folate onto the surface of PEGylated MNPs. By further integrating a near-infrared fluorescent (NIRF) marker (Alexa-Fluor 647) with MNPs, we demonstrated their folate-receptor mediated internalization inside cancer cells and subsequent translocation into lysosomes and mitochondria. Ex vivo NIRF imaging established that the azido-PEG-silane developed in course of the study can effectively reduce the sequestration of MNPs by macrophage organs (viz. liver and spleen). These folate-PEG-MNPs were not only stealth and noncytotoxic but their dual optical and magnetic properties aided in tracking their whereabouts through combined magnetic resonance and optical imaging. Together, these results provided a strong motivation for the future use of the ``universal ligand'' strategy towards development of ``smart'' nanohybrids for theragnostic applications.

Engineering Nanostructures by Decorating Magnetic Nanoparticles onto Graphene Oxide Sheets to Shield Electromagnetic Radiations

In this study, a minimum, reflection loss of 70 a was achieved, for a 6 mm thick shield (at 17.1 GHz frequency) employing a unique approach. This was accomplished by engineering nanostructures through decoration of magnetic nanopartides (nickel, Ni) onto graphene oxide (GO) sheets. Enhanced electromagnetic (EM) shielding was derived by selectively, localizing the nanoscopic particles in a specific phase of polyethylene (PE)/poly(ethylene oxide) (PEO) blends. By introduction of a conducting inclusion (like multiwall carbon nanotubes, MWNTs) together with the engineered nanostructures (nickel-decorated GO, (GO-Ni), the shielding efficiency can be enhanced significantly in contrast to physically mixing the particles in the blends. For instance, the composites showed a shielding efficiency >25 dB for a combination of MWNTS (3 wt %) and Ni nanoparticles (52 wt %) in PE/PEO blends. However, similar shielding effectiveness could be achieved for a combination of MWNTs (3 wt %) and 10 vol % of GO-Ni where in the effective concentration of Ni was only 19 wt %. The GO-Ni sheets facilitated in an efficient charge transfer as manifested from high electrical conductivity in the blends besides enhancing the permeability in the blends. It is envisioned that GO is simultaneously reduced in the process of synthesizing GO-Ni, and this facilitated in efficient charge transfer between the neighboring CNTs. More interestingly, the blends With MWNTs/GO-Ni attenuated the incoming EM radiation mostly by absorption. This study opens new avenues in designing polyolefin-based lightweight shielding materials by engineering nanostructures for numerous applications.

Electron-beam irradiation effects on poly(ethylene-co-vinyl acetate) polymer

Poly(ethylene-co-vinyl acetate) (EVA) films were irradiated with a 1.2MeV electron beam at varied doses over the range 0-270kGy in order to investigate the modifications induced in its optical, electrical and thermal properties. It was observed that optical band gap and activation energy of EVA films decreased upon electron irradiation, whereas the transition dipole moment, oscillator strength and number of carbon atoms per cluster were found to increase upon irradiation. Further, the dielectric constant, the dielectric loss, and the ac conductivity of EVA films were found to increase with an increase in the dose of electron radiation. The result further showed that the thermal stability of EVA film samples increased upon electron irradiation.

Effect of Interfacial Microstructure of Adsorbed Poly(ethylene glycol) Monooleate on Steel Substrate on Sliding Friction in Oil in Water Emulsion

The concentration of a nonionic surfactant and water pH were varied in an oil-in-water emulsion to minimize the friction coefficient between a steel ball sliding on a steel flat. At a surfactant concentration near the CMC (critical micelle concentration) the oil droplet size was found to be minimum. In this paper we study the microstructure of the surfactant molecules self-assembled on the steel substrate in water to comment on the ability of the surfactant aggregate to attract and retain oil. We find that a near semicylindrical hemimiceller microstructure with hydrocarbon tails projecting into bulk water as obtained at CMC in near neutral water is best able to capture and retain oil in yielding a low coefficient of friction.

Size dependent structural relaxations and dielectric properties induced by surface functionalized MWNTs in poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Structural dynamics, dielectric permittivity and ferroelectric properties in poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) (PVDF/PMMA) blends with respect to crystalline morphology was systematically investigated in presence of amine functionalized MWNTs (NH2-MWNTs) using dielectric spectroscopy. The crystalline morphology and the crystallization driven demixing in the blends was assessed by light microscopy (LM), wide angle X-ray diffraction (WXRD) and, in situ, by shear rheology. The crystal nucleation activity of PVDF was greatly induced by NH2-MWNTs, which also showed two distinct structural relaxations in dielectric loss owing to mobility confinement of PVDF chains and smaller cooperative lengths. The presence of crystal-amorphous interphase was supported by the presence of interfacial polarization at lower frequencies in the dielectric loss spectra. On contrary, the control blends showed a single broad relaxation at higher frequency due to defective crystal nuclei. This was further supported by monitoring the dielectric relaxations during isothermal crystallization of PVDF in the blends. These observations were addressed with respect to the spherulite sizes which were observed to be larger in case of blends with NH2-MWNTs. Higher dielectric permittivity with minimal losses was also observed in blends with NH2-MWNTs as compared to neat PVDF. Polarization obtained using P-E (polarization-electric field) hysteresis loops was higher in case of blends with NH2-MWNTs in contrast to control blends and PVDF. These observations were corroborated with the charge trapped at the crystal-amorphous interphase and larger crystal sizes in the blends with NH2-MWNTs. The microstructure and localization of MWNTs were assessed using SEM.

Electromagnetic Interference Shielding Materials Derived from Gelation of Multiwall Carbon Nanotubes in Polystyrene/Poly(methyl methacrylate) Blends

Blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with different surface-functionalized multiwall carbon nanotubes (MWNTs) were prepared by solution blending to design materials with tunable EMI (electromagnetic interference) shielding. Different MWNTs like pristine, amine (similar to NH2), and carboxyl acid (similar to COOH) functionalized were incorporated in the polymer by solution blending. The specific interaction driven localization of MWNTs in the blend during annealing was monitored using contact mode AFM (atomic force microscopy) on thin films. Surface composition of the phase separated blends was further evaluated using X-ray photoelectron spectroscopy (XPS). The localization of MWNTs in a given phase in the bulk was further supported by selective dissolution experiments. Solution-casted PS/PMMA (50/50, wt/wt) blend exhibited a cocontinuous morphology on annealing for 30 min, whereas on longer annealing times it coarsened into matrix-droplet type of morphology. Interestingly, both pristine MWNTs and NH2-MWNTs resulted in interconnected structures of PMMA in PS matrix upon annealing, whereas COOH-MWNTs were localized in the PMMA droplets. Room-temperature electrical conductivity and electromagnetic shielding effectiveness (SE) were measured in a broad range of frequency. It was observed that both electrical conductivity and SE were strongly contingent on the type of surface functional groups on the MWNTs. The thermal conductivity of the blends was measured with laser flash technique at different temperatures. Interestingly, the SE for blends with pristine and NH2-MWNTs was >-24 dB at room temperature, which is commercially important, and with very marginal variation in thermal conductivity in the temperature range of 303-343 K. The gelation of MWNTs in the blends resulted in a higher SE than those obtained using the composites.

Polyester derived from recycled poly(ethylene terephthalate) waste for regenerative medicine

Despite advances in regenerative medicine, the cost of such therapies is beyond the reach of many patients globally in part due to the use of expensive biomedical polymers. Large volumes of poly(ethylene terephthalate) (PET) in municipal waste is a potential source of low cost polymers. A novel polyester was prepared by a catalyst-free, melt polycondensation reaction of bis(hydroxyethylene) terephthalate derived from PET post-consumer waste with other multi-functional monomers from renewable sources such as citric acid, sebacic acid and D-mannitol. The mechanical properties and degradation rate of the polyester can be tuned by varying the composition and the post-polymerization time. The polyester was found to be elastomeric, showed excellent cytocompatibility in vitro and elicited minimal immune response in vivo. Three-dimensional porous scaffolds facilitated osteogenic differentiation and mineralization. This class of polyester derived from low cost, recycled waste and renewable sources is a promising candidate for use in regenerative medicine.

Mechanical properties of Nylon-6/LDPE blends containing an epoxy resin compatibilizer

Binary and ternary blends of nylon-6/low density polyethylene (nylon-6/LDPE) and Nylon-6/LDPE/poly(ethylene-co-glycidyl methacrylate) were prepared by melt mixing. The blends exhibit two phase morphology with LDPE dispersed in the form of spherical domains in the nylon-6 matrix. The mechanical properties of the blends were measured by standard methods. It is shown that the use of the epoxy copolymer as a compatibilizer improves the impact strength of the blend as compared to nylon-6, which is attributed to better stress transfer across the interface due to the compatibilizer. The data for each mechanical property were also fitted into a best fit model equation and the method of steepest ascent was applied to arrive at the optimum composition of the blend for that property.

Mechanical and Thermal Properties of Eva Blended with Biodegradable Ethyl Cellulose

In this study, biodegradable blend of Poly (Ethylene-co-Vinyl Acetate) (EVA) and Ethyl Cellulose (EC) were prepared. Ethylene vinyl alcohol (EVOH) copolymer was used as an interfacial compatibilizer to enhance adhesion between EVA and EC. The melt blended compatibilized biocomposites were examined for mechanical and thermal properties as per the ASTM standards. It has been found that the EC has a reinforcing effect on EVA leading to enhanced tensile strength and also impart biodegradability. Thus, a high loading of 50% EC could be added without compromising Much on the mechanical properties. Analysis of the tensile data using predictive theories showed an enhanced interaction of the dispersed phase (EC) and the matrix (EVA). The compatibilizing effects of EVOH on these blends were confirmed by the significant improvement in the mechanical properties comparable with neat EVA as also observed by SEM microscopy. The TGA thermograms exhibits two-stage degradation and as EC content increases, the onset temperature for thermal degradation reduces. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1044-1056, 2010

Dendritic Poly(ether imine) Based Gene Delivery Vector

The nonviral vector based gene delivery approach is attractive due to advantages associated with molecular-level modifications suitable for optimization of vector properties. In a new class of nonviral gene delivery systems, we herein report the potential of poly(ether Mine) (PETIM) dendrimers to mediate an effective gene delivery function. PETIM dendrimer, constituted with tertiary amine branch points, n-propyl ether linkers and primary amines at their peripheries, exhibits significantly reduced toxicities, over a broad concentration range. The dendrimer complexes pDNA effectively, protects DNA from endosomal damages, and delivers to the cell nucleus. Gene transfection studies, utilizing a reporter plasmid pEGFP-C1 and upon complexation with dendrimer, showed a robust expression of the encoded protein. The study shows that PETIM dendrimers are hitherto unknown novel gene delivery vectors, combining features of poly(ethylene imine)-based polymers and dendrimers, yet are relatively nontoxic and structurally precise.

Ionomer based blend as water vapor barrier material for organic device encapsulation

Blends of poly (ethylene-co-methacrylic acid) (PEMA) and poly (vinyl alcohol-co-ethylene) (EVOH) were studied for encapsulating Schottky structured organic devices. A calcium degradation test was used to determine water vapor transmission rates and to determine the moisture barrier performance of neat and blend films. Moisture barrier analysis for the neat and blend compositions was discussed concerning the interactions in the blend, diffusivity of water molecules through the unit cell systems, and the occupiable free volumes available in the unit cells using molecular dynamics simulations. The experimental results of water vapor permeation were correlated with diffusion behavior predicted from molecular dynamics simulations results. The effectiveness of the blend as a suitable barrier material in increasing the lifetime of an encapsulated Schottky structured organic device was determined.

Efficient Dendrimer-DNA Complexation and Gene Delivery Vector Properties of Nitrogen-Core Poly(propyl ether imine) Dendrimer in Mammalian Cells

Dendrimers as vectors for gene delivery were established, primarily by utilizing few prominent dendrimer types so far. We report herein studies of DNA complexation efficacies and gene delivery vector properties of a nitrogen-core poly(propyl ether imine) (PETIM) dendrimer, constituted with 22 tertiary amine internal branches and 24 primary amines at the periphery. The interaction of the dendrimer with pEGFPDNA was evaluated through UV-vis, circular dichroism (CD) spectral studies, ethidium bromide fluorescence emission quenching, thermal melting, and gel retardation assays, from which most changes to DNA structure during complexation was found to occur at a weight ratio of dendrimer:DNA similar to 2:1. The zeta potential measurements further confirmed this stoichiometry at electroneutrality. The structure of a DNA oligomer upon dendrimer complexation was simulated through molecular modeling and the simulation showed that the dendrimer enfolded DNA oligomer along both major and minor grooves, without causing DNA deformation, in 1:1 and 2:1 dendrimer-to-DNA complexes. Atomic force microscopy (AFM) studies on dendrimer-pEGFP DNA complex showed an increase in the average z-height as a result of dendrimers decorating the DNA, without causing a distortion of the DNA structure. Cytotoxicity studies involving five different mammalian cell lines, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] (MTT) assay, reveal the dendrimer toxicity profile (IC50) values of similar to 400-1000 mu g mL(-1), depending on the cell line tested. Quantitative estimation, using luciferase assay, showed that the gene transfection was at least 100 times higher when compared to poly(ethylene imine) branched polymer, having similar number of cationic sites as the dendrimer. The present study establishes the physicochemical behavior of new nitrogen-core PETIM dendrimer-DNA complexes, their lower toxicities, and efficient gene delivery vector properties.

Unique nanoporous antibacterial membranes derived through crystallization induced phase separation in PVDF/PMMA blends

In this study, a unique method was adopted to design porous membranes through crystallization induced phase separation in PVDF/PMMA (poly(vinylidene fluoride)/poly(methyl methacrylate)) blends. By etching out PMMA, which segregates either in the interlamellar and/or in the interspherulitic regions of the blends, nanoporous hierarchical structures can be derived. Different nanoparticles like titanium dioxide (TiO2), silver nanoparticle (Ag) decorated carbon nanotubes (Ag-CNTs), TiO2 decorated CNTs (TiO2-CNTs), Ag decorated TiO2 (Ag-TiO2) and Ag-TiO2 decorated CNTs (Ag@TiO2-CNTs) were synthesized and melt mixed with 80/20 PVDF/PMMA blends to render antibacterial activity to the membranes. Scanning electron microscopy (SEM) was used to study the crystalline morphology of the membranes. A significant improvement in the trans-membrane flux was obtained in the blends with Ag@TiO2 decorated CNTs as compared to the membranes derived from the neat blends, which can be attributed to the interconnected pores in these membranes. Both qualitative and quantitative studies of antifouling and antibacterial activity (using E. coli as a model bacterium) were performed using the standard plate count method. SEM micrographs clearly showed that the antifouling activity of the membranes was improved with addition of Ag@TiO2-CNTs. In the quantitative standard plate count method, the bacterial colony significantly decreased with the addition of Ag@TiO2-CNTs as against neat blends. This study opens a new avenue in the fabrication of polymer blend based membranes for water filtration.