EMI shielding and microwave absorption behavior of Au‐MWCNT/polyaniline nanocomposites

Electrically conducting Au‐multiwalled carbon nanotube/polyaniline (Au‐MWCNT/PANi) nanocomposites were synthesized by two different ways: (1) by direct mixing of MWCNT/PANi and Au nanoparticles (Au‐MWCNT/PANi‐1) and (2) by in situ polymerization of aniline in the presence of both MWCNTs and Au nanoparticles (Au‐MWCNT/PANi‐2). The higher electrical conductivity of Au‐MWCNT/PANi‐2 compared with the other samples (PANi, MWCNT/PANi, Au‐MWCNT/PANi‐1) is supported by the red shifts of the UV‐vis bands (polaron/bipolaron), the high value of the –NH+= stretch peak (Fourier transform infrared spectroscopy studies), the high % crystallinity (X‐ray diffraction analysis) and more uniform dispersion of the Au NPs in the material. The performance of the samples in electromagnetic interference (EMI) shielding and microwave absorption was studied in the X‐band (8–12 GHz). For all the samples, absorption was the dominant factor contributing toward the EMI shielding. Au‐MWCNT/PANi‐2 showed the best performance with a total shielding effectiveness of ?16 dB [averaged over the X‐band (GHz)] and a minimum reflection loss of ?56.5 dB. The higher dielectric properties resulting from the heterogeneities because of the presence of nanofillers and the high electrical conductivity lead to the increased EMI shielding and microwave absorption. The results show the significance of both Au nanoparticles and method of synthesis on the EMI shielding performance of MWCNT/PANi composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Regioselective synthesis of pyrimido[1,2-a][1,3,5]triazin-6-ones via reaction of 1-(6-oxo-1,6-dihydropyrimidin-2-yl)guanidines with triethylorthoacetate: observation of an unexpected rearrangement

A novel thermal rearrangement, involving pyrimidine ring opening and subsequent ring closure leading to recyclization of the system, was identified in the reaction of (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 (where NR(1)R(2) = NH(2), NH alkyl, NH aralkyl, NHCH(2)Ph(R)) with triethyl orthoacetate, affording 4-substituted-2-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 6 and their ring opened products. However, no such rearrangement was observed with (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 bearing a tertiary amino or anilino substituent (i.e. where NR(1)R(2) = N(CH(3))(2), indoline, morpholino, NHAr). As expected, 2-substituted-4-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 4 were obtained as the final products. Experimental structural determination and theoretical studies were carried out to get an understanding of the observed thermal rearrangement. In addition, an attempt to obtain similar pyrimido[1,2-a][1,3,5]triazin-6-ones using N,N-dimethylacetamide dimethyl acetal (DMA-DMA) as one carbon inserting synthon had furnished triazine ring annulated product 14 bearing N,N-dimethyl enamino substituent at position 4 as a result of further reaction with a second molecule of DMA-DMA.     

3-Helix micelles stabilized by polymer springs

Despite increasing demands to employ amphiphilic micelles as nanocarriers and nanoreactors, it remains a significant challenge to simultaneously reduce the particle size and enhance the particle stability. Complementary to covalent chemical bonding and attractive intermolecular interactions, entropic repulsion can be incorporated by rational design in the headgroup of an amphiphile to generate small micelles with enhanced stability. A new family of amphiphilic peptide-polymer conjugates is presented where the hydrophilic headgroup is composed of a 3-helix coiled coil with poly(ethylene glycol) attached to the exterior of the helix bundle. When micelles form, the PEG chains are confined in close proximity and are compressed to act as a spring to generate lateral pressure. The formation of 3-helix bundles determines the location and the directionalities of the force vector of each PEG elastic spring so as to slow down amphiphile desorption. Since each component of the amphiphile can be readily tailored, these micelles provide numerous opportunities to meet current demands for organic nanocarriers with tunable stability in life science and energy science. Furthermore, present studies open new avenues to use energy arising from entropic polymer chain deformation to self-assemble energetically stable, single nanoscopic objects, much like repulsion that stabilizes bulk assemblies of colloidal particles.     

Evolution of fuzzy classifiers using genetic programming

In this paper, we propose a genetic programming (GP) based approach to evolve fuzzy rule based classifiers. For a c-class problem, a classifier consists of c trees. Each tree, T _i , of the multi-tree classifier represents a set of rules for class i. During the evolutionary process, the inaccurate/inactive rules of the initial set of rules are removed by a cleaning scheme. This allows good rules to sustain and that eventually determines the number of rules. In the beginning, our GP scheme uses a randomly selected subset of features and then evolves the features to be used in each rule. The initial rules are constructed using prototypes, which are generated randomly as well as by the fuzzy k-means (FKM) algorithm. Besides, experiments are conducted in three different ways: Using only randomly generated rules, using a mixture of randomly generated rules and FKM prototype based rules, and with exclusively FKM prototype based rules. The performance of the classifiers is comparable irrespective of the type of initial rules. This emphasizes the novelty of the proposed evolutionary scheme. In this context, we propose a new mutation operation to alter the rule parameters. The GP scheme optimizes the structure of rules as well as the parameters involved. The method is validated on six benchmark data sets and the performance of the proposed scheme is found to be satisfactory.     

Tunable Catalytic Performance and Selectivity of a Nanoparticle–Graphene Composite through Finely Controlled Nanoparticle Loading

Graphene‐based composites offer enhanced catalytic performance of metal and semiconductor nanoparticles, but their development is challenging because catalytic performance strongly depends on the structure and composition of the composite. Herein we show that the catalytic performance of a nanoparticle–graphene composite is very dependent on catalyst loading, which can be optimized for simultaneous enhancement of activity and selectivity. A glassy carbon working electrode has been modified with a gold nanoparticle–graphene (Au–G) composite with a varied number of gold nanoparticles per graphene, so that the conducting property of graphene and the electrocatalytic property of the metal were effectively coupled to give the best catalytic activity and selectivity. The modified electrode was used for simultaneous electrochemical detection of a mixture of electroactive species with high sensitivity. This result shows that the catalytic performance of a graphene‐based composite is sensitive to the catalyst loading and should be optimized for the best performance.     

Modulation of Intramolecular Charge Transfer Emission Inside Micelles: A Fluorescence Probe for Studying Microenvironment of Micellar Assemblies

Modulation of intramolecular charge transfer reaction of ethyl ester of N,N-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) in anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and non-ionic p-tert-octylphenoxy polyoxyethanol (Triton-X 100, TX-100) micelles has been addressed using steady state and time resolved spectroscopy. The interaction of the CT probe EDMANA with micelles and its location inside the micelles have been investigated by the study of fluorescence spectral band position of EDMANA in micelle, the effective polarity of micelle-water interface and cetyl pyridinium chloride induced fluorescence quenching measurement. The effects of urea on the properties of the micelles such as Critical Micelle Concentration and the interaction between EDMANA and micelles have been explored using EDMANA as emission probe.     

Strain-Rate-Dependent In-Plane Compressive Properties of 3D Fine Weave Pierced C/C Composite:Failure Mechanism and Constitutive Model

In-plane compression experiments are performed on 3D fine weave pierced C/C composite at a wide strain rate range of 0.0001/s-1000/s.The in-plane compressive fa...     

Buffer allocation for a class of nonlinear stochastic knapsack problems

In this paper, we examine a class of nonlinear, stochastic knapsack problems which occur in manufacturing, facility or other network design applications.Series, merge-and-split topologies of series-parallelM/M/1/K andM/M/C/K queueing networks with an overall buffer constraint bound are examined. Bounds on the objective function are proposed and a sensitivity analysis is utilized to quantify the effects of buffer variations on network performance measures.     

Synthetic Applications of the Baylis–Hillman Reaction: Simple and Convenient Synthesis of Five Important Insect Pheromones

A simple and convenient synthesis of five important insect pheromones by means of Baylis–Hillman adducts is described, i.e., of (2E,4S)‐2,4‐dimethylhex‐2‐enoic acid ( 1 ), a mandibular‐gland secretion of the male carpenter ant in the genus Camponotus, of (+)‐(S)‐manicone ( 2 ) and (+)‐(S)‐normanicone ( 3 ), two mandibular‐gland constituents of Manica ants, and of (+)‐dominicalure‐I ( 6 ) and (+)‐dominicalure‐II ( 7 ), two aggregation pheromones of the lesser grain borer Rhyzopertha dominica (F). For the first time, the potential of the Baylis–Hillman chemistry for the stereoselective synthesis of trisubstituted olefins was successfully applied to the synthesis of these pheromone compounds.     

Synthesis of polypyrrole films for the development of ammonia sensor

In the present investigation, we have synthesized a polypyrrole films by chemical polymerization technique for the development of ammonia sensor. The polypyrrole films were synthesized in an aqueous acidic medium on glass substrate with mild oxidation of ferric chloride at temperature 29°C. The concentrations (molar) of monomer (pyrrole), oxidant (ferric chloride), and dopant (polyvinyl sulfonate) have been optimized for the uniform and porous surface morphology of the synthesized polypyrrole film. The synthesized films were characterized by scanning electron microscopy, ultraviolet‐visible, and Fourier transforms infrared spectroscopy. Ammonia gas sensing behavior of polypyrrole films was studied by using indigenously developed gas sensing chamber. The synthesized polypyrrole film with optimized process parameters shows excellent and reproducible response to low concentration (100 ppm) of ammonia gas. Copyright © 2007 John Wiley & Sons, Ltd.