Compact ultrathin conformal metamaterial dual‐band absorber for curved surfaces

A compact, ultrathin conformal metamaterial dual‐band absorber for curved surfaces has been presented in this article. The absorber unit cell composed of circular and split ring resonators which are connected with plus‐shaped structure. The proposed absorber unit cell is compact in size (0.22λ_o × 0.22λ_o) and as well as ultrathin thickness (0.006λ_o), where λ_o is the wavelength at 5.8 GHz. The designed absorber gives two absorption tips at 5.8 and 7.7 GHz with more than 90% absorptivity. The full width at half maximum bandwidths are 220 MHz (5.67‐5.89 GHz) and 250 MHz (7.58‐7.83 GHz). The proposed conformal absorber is sensitive to the polarization angle and has a stable absorptivity over a wide range of incident electromagnetic wave. The parametric analysis and equivalent transmission line model have been investigated. The surface current and electric field distribution also discussed for understanding the absorption mechanism. To analyze the performance of proposed absorber on the curved surfaces, it is wrapped on the different radius of cylindrical surface and measured the absorptivity. Simulated and measured results have good agreement between them.     

Transmission of shear waves through a self-reinforced layer sandwiched between two inhomogeneous viscoelastic half-spaces

A problem of reflection and transmission of plane SH-wave through a perfectly conducting self-reinforced elastic layer interposed between two vertically inhomogeneous viscoelastic solid half-spaces has been studied in this paper. The heterogeneity in the half-spaces is taken exponentially varying along vertical direction. Expressions of reflection and transmission coefficients are obtained in closed form and it is found that these coefficients depend on the angle of incidence, inhomogeneity parameters of the half-spaces and on the reinforcement parameters of the sandwiched layer. These coefficients are computed for a specific model against the angle of incidence for different values of inhomogeneity parameters of the half-spaces and for reinforcement parameter of the layer. The results have been presented graphically. The problem studied by Borcherdt [Reflection and refraction of type-II SH waves in elastic and anelastic media. Bulletin of the Seismological Society of America 1977;67:43–67] has been reduced as a special case.     

Effect of Plasticizers on the Moisture Migration Behavior of Low-Amylose Starch Films during Drying

We report the synergistic and competitive interactions between multiple plasticizers in plasticized low-amylose starch that result in either enhanced or reduced water migration fluxes and effective moisture diffusivities. The starch was plasticized using glycerol and xylitol either individually or in 1:1 combination. The water migration fluxes and moisture diffusivities were higher in xylitol plasticized films compared to the glycerol plasticized ones. For low plasticizer concentrations, the presence of both the plasticizers competitively reduced the effective moisture diffusivities and moisture migration fluxes due to antiplasticization. However, at higher plasticizer contents (at and above 15 wt%), the presence of multiple plasticizers enhanced the moisture migration fluxes and effective moisture diffusivities due to synergistic plasticization. The moisture migration fluxes and effective moisture diffusivities exhibited both moisture and plasticizer concentration dependence and the former was found to be stronger than the latter. These findings can be used for designing and controlling the vapor barrier properties of starch-based bioplastics during drying and formulation phase.     

Silane grafting and moisture crosslinking of polypropylene

Different approaches for free‐radical initiated grafting of functional monomers to polypropylene (PP) have been investigated with a view to enabling crosslinking of the polymer upon subsequent exposure to moisture, resulting in gel contents as high as 50–60 wt%. The first approach involved grafting a co‐agent such as triallyl trimellitate (TATM) to the polymer using peroxide initiator to add carbon–carbon double bond functionality to the polymer, followed by peroxide‐initiated grafting of mercaptopropyltrimethoxysilane (MPTMS) to the PP‐TATM adduct. The second approach was the more traditional peroxide‐mediated grafting of vinyltrimethoxysilane (VTMS) to polypropylene, and was most effective at increasing melt state dynamic storage modulus. In the third approach, peroxide‐mediated grafting of VTMS was followed by peroxide‐initiated grafting of MPTMS. This process took advantage of the unsaturation created via chain scission in the first step to provide graft sites for the MPTMS in the second step. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Freeze-dried macroporous foam prepared from chitosan/xanthan gum/montmorillonite nanocomposites

Freeze-dried macroporous foams were prepared from an aqueous colloidal suspension of chitosan/xanthan gum/Na⁺-montmorillonite nanoclay (MMT). The suspension formed gel structure as a consequence of freezing, named cryogel. Cryogel is defined as a gel formed due to the concentration increase of the substrates caused by the ice formation during freezing. This obtained cryogel was subsequently dried under vacuum condition to produce porous foam materials. Two freezing methods were employed in the present work in order to investigate the influence of the processing on sample characteristics, namely; contact freezing with a heat exchanger and immersion freezing in a cryo-bath. Based on the SEM observation, in the case of contact freezing; rapid freezing (−2 °C/min) resulted in randomly aligned pores as compared to the pore alignment obtained in the case of slow freezing (−0.25 °C/min); the mean pore size for rapid freezing and slowing freezing were 40 μm and 68 μm, respectively. However, in immersion freezing samples, aligned and bamboo-like straight structures with pore layer spacing of 22 μm were observed. The different microstructures significantly influenced the mechanical hardness of the prepared foams nanocomposites. The MMT dispersion within the bionanocomposites was found to be characteristically exfoliated from X-ray diffraction and electron microscopy analysis. Small angle X-ray diffraction data indicated that the polymeric networks were modified by the exfoliated MMT and the MMT also improved the hardness of the prepared foams.     

Synthetic, biochemical, antifertility and antiinflammatory aspects of manganese and iron complexes

Manganese(II) and iron(II) macrocyclic complexes of polyamide groups have been synthesized by the template codensation of diamines (2,6 diaminopyridine, 1,2 phenylenediamine and 1,3 phenylenediame) and triamine (diethylenetriamine) with phthalic acid in 1:2:2 molar ratios. On the basis of elemental analysis, IR, electronic, magnetic moment, M?ssbauer, mass and X-ray spectral studies, octahedral structure has been assigned to [M(N4macn)Cl2] (M = Mn(II) and Fe(II), n = 1 to 4) complexes. The complexes have been screened in vitro against a number of fungi and bacteria to assess their growth inhibiting potential. An attempt has been made to correlate the structural aspects of the compounds with their antiinflammatory and antifertility activities.     

Mathematical modeling of granular activated carbon (GAC) biofiltration system

In this study, a mathematical model of a fixed bed Granular Activated Carbon (GAC) biofiltration system was developed to predict the organic removal efficiency of the filter. The model consists of bulk transportation, adsorption, utilization, and biodegradation of organics. The variation of the specific surface area due to biofilm growth and the effect of filter backwash were also included in the model. The intrapellet diffusion and the diffusion of substrate in the biofilm were described by linear driving force approximation (LDFA) method. Biodegradation of organics was described by Monod kinetics. Sips adsorption isotherm was used to analyze the initial adsorption equilibrium of the system. The model showed that the organic removal efficiency of the biofilter greatly depends on the parameters related to the biological activities such as the maximum rate of substrate utilization (k_max) and biomass yield (Y) coefficients. Parameters such as suspended cell concentration (X_s) and decay constant (K_d) had little effects on the model simulation results. The filter backwash also had no significant impact on the performance of the biofilter.     

Dialkyl furan‐2,5‐dicarboxylates,epoxidized fatty acid esters and their mixtures as bio‐based plasticizers for poly(VInylchloride)

Dialkyl furan‐2,5‐dicarboxylates and epoxidized fatty acid esters (EFAE) of varying molecular weights and volatilities, as well as their mixtures, were investigated as alternative plasticizers for poly(vinylchloride) (PVC). The EFAE utilized were epoxidized soybean oil (ESO) and epoxidized fatty acid methyl ester (e‐FAME). All plasticizers were compatible with PVC, with plasticization efficiencies usually increasing with decreasing molecular weights of the plasticizers (except in the case of ESO, which was remarkably effective at plasticizing PVC, in spite of its relatively high molecular weight). In comparison with phthalate and trimellitate plasticizers, the alternatives generally yielded improved balance of flexibility and retention of mechanical properties after heat aging, with particularly outstanding results obtained using 30?50 wt % e‐FAME in mixtures with diisotridecyl 2,5‐furandicarboxylate. Although heat aging characteristics of the plasticized polymer were often related to plasticizer volatilities, e‐FAME performed better than bis(2‐ethylhexyl) 2,5‐furandicarboxylate, and bis(2‐ethylhexyl) phthalate of comparatively higher molecular weights. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42382.     

An overview of ordered mesoporous material SBA-15: synthesis,functionalization and application in oxidation reactions

Ordered mesoporous materials are attracting wide concern because of their applications in the field of catalysis, adsorption, separations, drug delivery systems and gas sensors owing of their extremely high surface area combined with well-defined pore structures with narrow pore size distributions. Various mesoporous materials such as MCM-41, MCM-48, SBA-15 and SBA-16 have been reported in past two decades. Synthesis of mesoporous materials involves the concept of aggregation of surfactants as structure directing agents under acidic or basic conditions. The dimensions of these mesopores can be obtained by type of surfactant, auxiliary chemicals and synthesis conditions. At present, SBA-15 has attracted more attention among different mesoporous silica structures due to their desirable properties such as thick pore wall and hexagonal mesopores (4–12 nm), high surface area, ease of synthesis and functionalization and high thermal and mechanical stability. In last few years, great effort has been made on the development of various methods for the synthesis of mesoporous materials as support for oxidation reactions. The aim of this review article is to focus mainly on mesoporous SBA-15 together with its application as support for various oxidation reactions.     

Electrospun PLA/PCL fibers with tubular nanoclay: Morphological and structural analysis

Biodegradable polymers are good candidates for a wide range of applications in tissue engineering and drug delivery because of their biocompatibility, their degradation, mechanical properties, and offer a sustained release of encapsulated drugs. The electrospun polymer nanofibrous materials can be used as carriers for hydrophobic and hydrophilic drugs. This research work focused on poly(lactic acid) (PLA) and blends of PLA with poly (ε‐caprolactone) (PCL) that are reinforced with different concentrations of halloysite nanotubes (HNTs) and various cosolvents for electrospinning including chloroform : acetone, chloroform : methanol, and dichloromethane (DCM) : N,N, dimethylformamide (DFM). The fibers produced from the DCM : DMF system without HNTs were more uniform resulting in smaller fiber diameters as compared to the chloroform: methanol system due to the increased solution conductivity. The addition of HNT nanoparticles produced electrospun fibers with large diameters because the viscosity of the solution increased. Cosolvent was important in determining fiber diameters because it strongly influenced the solution viscosity and conductivity. HNTs had relatively small impact on the growth of a crystalline morphology in PCL–HNT composites. The solvent mixture of chloroform : methanol was better for PLA‐based systems since PLA was found to have slightly higher crystallinity and larger enthalpy value indicating the improved structural orderness in the PLA polymer matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012