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  • Open access
  • 29 Reads
Photo-responsive Properties on Locally Confined Ultrathin Silicon Nanowires
We present a concept of hybrid photo-responsive device based on the combination of ultrathin SiNW with quantum dots (QDs). High quality SiNW arrays have been fabricated using a novel top-down process. The SiNW arrays were able to detect light from the UV up to the visible range with good sensitivity, fast response and ultrahigh photo responsivity (R~ 104 A/W) at room temperature. The SiNW arrays have good stabilities over long term measurement as well as a range of experimental conditions (e.g. temperature 273 – 343 K) and even after strong UV radiation exposure (up to 585 J.cm-2).  The SiNW arrays were coated with cadmium telluride (CdTe) QDs, and the hybrid QD sensitized devices displayed a significant improvement of the photocurrent measured under UV light while preserving their performance under visible light illumination. The sensitivity over a broad illumination range, the stability and high photoresponse of the new hydrid nanostructures is very promising towards the development of novel optoelectronic and photovoltaic devices.
  • Open access
  • 30 Reads
Effects of Composites due to External Fields
The Properties of polymer differs when subjected to various external fields such as pH, temperature and light. As the external fields react with the polymer it results in deformation. In the present world construction industry plays a major role in using of composite materials. The composites such as FRP and polymer concrete deforms due to various external fields of nature. The focus on the present paper is the effects happen in composite materials due to external fields. Here in this paper the composite materials FRP and polymer concrete is subjected to external field and its effect is found with a case study.
  • Open access
  • 25 Reads
Synthesis of Degradable PolyMMA via Copolymerization with Cyclic Ketene Acetals
Polyesters play a very important part in the development of (bio)degradable materials, due to the hydrolizable ester-groups. However, it usually requires stringent conditions and removal of condensates in order to reach high molecular weights in classical polyester step-growth polymerizations. This is in contrast with free radical polymerization, where high molecular weights are reached within seconds without the need for stringent conditions, drastically lowering the cost. Combining the simple procedures for free radical polymerization with the hydrolizability of polyesters has long been a focus in research. With the introduction of radical ring-opening polymerization by Bailey et al. In 1979[1] it became feasible to incorporate ester-groups into polymer backbone by copolymerizing cyclic ketene acetals (CKAs). This method, however, did not immediately generate broad interest probably owing to the relatively complicated reaction mechanism and tedious synthesis procedures for CKAs. However, since the early 2000’s more research has been performed, mainly on the synthesis of copolymers of CKAs and vinyl monomers.[2] The development of controlled radical polymerizations also proved to be an accelerator for RROP research. In this contribution, the synthesis of degradable linear and four-arm star copolymers of 5,6-benzo-2-methylene-1,3-dioxepane and methyl methacrylate via RAFT polymerization is presented.[3] To determine exact copolymer composition, the reactivity ratios of both monomers have been determined and are thoroughly discussed.  [1] W. J. Bailey, P. Y. Chen, W. B. Chiao, T. Endo, L. Sidney, N. Yamamoto, N. Yamazaki and K. Yonezawa, Contemporary Topics Polym. Sci., 1979, 3, 29. [2] S. Agarwal, Polym. Chem., 2010, 1, 953 [3] S. Kobben, A. Ethirajan, T. Junkers, J. Polym. Sci.. A: Polym. Chem., 2014
  • Open access
  • 36 Reads
Versatility of Silsesquioxane-Based Materials for Antimicrobial Coatings
This paper is dealing with the state of the art of antibacterial nanostructured coatings with silsesquioxane content along the last decade. As follows, the requirements for achieving efficient coatings, chemical functionalization methods, working mechanisms and a classification of different silsesquioxane-based materials will be provided in order to have a complete overview of their most recent breakthrough for antibacterial/antifungal applications.
  • Open access
  • 26 Reads
Preparation of a Novel Biopolymer Cellulose-Based Nanocomposite by Coating of Gamma-Fe2O3/Cu Nanoparticles and Catalytic Application in Chemical Reactions
Cellulose, as a naturally abundant biopolymer, can be easily functionalized with various organic groups for desired purposes like applications as a biodegradable support for heterogeneous catalysis, composites matrixes and immobilization processes. Metal nanocomposites are one of the best catalysts for organic reaction beacause of their simple recoverable features. They simply can be recovered from reaction pot. A possible method simple separation and recycling of the catalysts is immobilizing catalytically active species in the surface of magnetic metal nanoparticles which can be separated from the reaction system by applying an appropriate magnetic field. In this study, we have prepared a biopolymer-based bimetallic nanocomposite via in situ synthesis of maghemite (gamma-Fe2O3) and Cu on cellulose biopolymer. It has been proven that this catalyst shows very good activities in organic synthesis. In general this nanocomposite catalyst is recoverable, green, easy separable, environmentally friendly and in the chemical reaction as a very good strategy for the synthesis of medicinal and pharmaceutical compounds compared to the traditional method.
  • Open access
  • 19 Reads
Macro-RAFT Synthesis by Single Unit Monomer Insertion (SUMI) into Dithiobenzoate RAFT Agents – Towards Biological Precision
Achieving well defined control over the monomer sequence in polymers, as e.g. biopolymers do in nature, remains a long standing challenge in polymer chemistry. Sequence control by single unit monomer insertion (SUMI), ‘one at a time’, into dithiobenzoate RAFT agents has been explored. Critical factors for success are a high chain transfer constant for the RAFT agent and addition of the radical (R.) to monomer should be fast relative to further propagation. Macro-RAFT [(CH3)3C(CN)-(M)-SC(=S)-phenyl] synthesis by SUMI of styrene and N-isopropylacrylamide (NIPAm) into 2-cyano-2-propyl dithiobenzoate was successful. However, attempted SUMI of maleic anhydride (MAH) gave low yield consistent with the low reactivity of MAH towards 2-cyano-2-propyl radicals. Insertion of methyl methacrylate (MMA) provided an oligomeric insertion product due to the low transfer constant of the dithiobenzoate in MMA polymerization. Kinetic aspects for the synthesis of macro-RAFT agents by SUMI were investigated with real time 1H-NMR experiments and byproducts were identified. Next, A step towards the controlled synthesis of macro-RAFT [(CH3)3C(CN)-(M1)-(M2)-SC(=S)-phenyl] was taken. The insertion of MAH, styrene and NIPAm into the styrene SUMI product has been investigated. Insertion of MAH into the macro-RAFT was fast, however, reactions with styrene and NIPAm were slow attributed both to the low concentration of monomer used to favor SUMI and the poor leaving group ability of the propagating species compared to the 2-cyano-2-propyl radical. This study demonstrates the potential of RAFT for the synthesis of a new generation of synthetic polymers.
  • Open access
  • 16 Reads
Electroanalysis of Dopamine Using Polydopamine Functionalized Reduced Graphene Oxide-Gold Nanocomposite
A novel polydopamine functionalized reduced graphene oxide/gold (PDA-RGO/Au) nanocomposite modified electrode was fabricated, and applied for electrochemically determine dopamine. UV-vis spectroscopy and FTIR characterizations confirm the successful reduction of graphene oxide (GO) to RGO during the dopamine self-polymerization process. Then, Au nanoparticles with average size of 120 nm were electrodeposited onto the PDA-RGO film modified glassy carbon electrode (GCE) was performed. The electrocatalytic activity of the PDA-RGO/Au modified GCE was evaluated by oxidation of dopamine using cyclic voltammetry and linear sweep voltammograms. The results showed that the obtained anodic peak currents were linearly proportional to concentration in the range of 0.01 mM to 1 mM with a detection limit of 6.237 μM (S/N = 3.0). In addition, the effect of co-existing species such as ascorbic acid, uric acid and glucose on the determination of dopamine was investigated. Therefore, the PDA-RGO/Au modified dopamine sensor with excellent sensitivity and selectivity could provide an idea matrix for clinic applications.
  • Open access
  • 29 Reads
Preparation and Characterization of Novel Poly(Vinyl Alcohol) (PVA) and Poly(Acrylic Acid) (PAA) Hydrogels for Sensitive Hydrogels
Stimuli Sensitive hydrogels have enormous potential in various applications. Various environmental variables are found in the body, such as low pH and elevated temperatures. For this reason, either pH-sensitive and/or temperature-sensitive hydrogels can be used for site-specific controlled drug delivery. Furthermore, hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used as biosensors as well as drug delivery systems. For many applications hydrogels require a very rapid time-response in terms of their sensitivity to either pH and/or temperature. Rapid time-responsive sensitivity is a research field which is still in development. In this research pH-sensitive hydrogels have been made varying the composition and molecular weight of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). After total dissolution of the PVA/PAA the hydrogel was freeze/thawed. The swelling responses were investigated as well as the drug release profile with varying pH. The drug release was studied with a model drug theophylline. The characteristic properties were examined with ac impedance, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), SEM morphology analysis and Energy-dispersive X-ray spectroscopy (EDS). The results showed that the optimum formulation to be used as a stimulus sensitive hydrogel is found with lower concentration of PVA and a higher concentration of PAA. These PVA/PAA polymer exhibited excellent thermal properties and mechanical properties and have potential in biomedical applications.
  • Open access
  • 19 Reads
Hypercrosslinked Sulfonated (poly ether ether ketone) Polyelectrolyte Membranes for Fuel Cells Applications
Sulfonated poly(ether ether ketone) (SPEEK), with excellent mechanical properties and chemical stability, is one of the promising polyelectrolyte membranes (PEMs) for fuel cells applications. However, the dimensional stability of SPEEK is reduced at certain degree of sulfonation (DS > 70%); and at operation temperatures above 60 °C. One of the practical approaches for improving membrane integrity and dimensional stability is through formation of covalent crosslinks between SPEEK polymer chains. In this article, a simple and novel approach is introduced for enhancing the dimensional stability of SPEEK membranes through hypercrosslinking methodology. SPEEK membranes were hypercrosslinked with formaldehyde and the resulted membranes exhibited reduced water swelling and methanol permeability with negligible effect on the original proton conductivity.
  • Open access
  • 18 Reads
The Theoretical Influence of the Difference Between the LUMO Energy Levels of Donor and Acceptor in Organic Photovoltaic Triplejunction Solar Cells
In organic photovoltaic solar cells, light absorption does not immediately lead to free charge carriers. Instead, an exciton is created. The highest efficiency is reached when the lowest unoccupied molecular orbital (LUMO) of the donor is as close as possible to the LUMO of the acceptor. However, a necessary condition for efficient dissociation of the created excitons is that the difference between the LUMOs of donor and acceptor is higher than the exciton binding energy. The value of the exciton binding energy in different materials is a subject of discussion. The excess of this necessary minimum of the LUMO-difference corresponds with an energy loss. Moreover, it is often not possible to optimize suitable material combinations for organic photovoltaic cells to an ideal (low) LUMO difference. Another energy loss in organic solar cells is caused by their narrow absorption windows, compared to the absorption band of inorganic solar cells. A way to capture a wider band of the solar radiation is using more solar cells with different bandgaps in a row. In this article, we study three organic cells in a row, i.e. a triple-junction. More specifically, we study the theoretical influence of the difference between the LUMO energy levels of donor and acceptor for an organic triple-junction solar cell. We study as well the monolithic as the stacked configuration.
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