Linear viscoelasticity of thermoassociative chitosan-g-poly(N-isopropylacrylamide) copolymer

Chitosan-g-poly(N-isopropylacrylamide) (chitosan-g-PNIPAM) was synthesized and characterized rheologically in aqueous solutions. The copolymer solution exhibits a thermoassociative behavior in which its elastic response dramatically increases when temperature is above the critical temperature or the association temperature, T _assoc. The copolymer at low concentration shows typical solution property. When the temperature is increased up to the critical temperature, the copolymer exhibits a gel-like characteristic due to the formation of physical cross-links between chitosan backbones through the self-aggregation of PNIPAM side chains. At high concentration, the system exhibits a weak elastic response due to the entanglement of the copolymer at 25°C. As temperature is raised above T _assoc, the system shows a strong elastic behavior due to the formation of additional physical cross-links via the aggregation of PNIPAM side chains. Chitosan-g-PNIPAM offers an attractive associating behavior in aqueous solution at temperature close to the body temperature, thus providing potential applications in pharmaceutical and medical industries.     

A Mathematical Model of Water Pollution Control Using the Finite Element Method

Water pollution assessment problems arise frequently in environmental science. In this research, the finite element method for solving the one-dimensional steady convection-diffusion equation with constant coefficients is presented; it is then used to optimize water treatment costs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and Sensing Properties of Single‐Walled Carbon Nanotubes Network: Effect of Alignment and Selective Breakdown

The electrical transport and NH₃ sensing properties of randomly oriented and aligned SWNT networks were presented and discussed. The results indicate that aligned SWNT‐FETs have better FET characteristics due to the reduced number of interconnected nodes. This was particularly true as the resistance of the devices increased. Gated electrical breakdown was implemented to selectively remove metallic (m‐) SWNTs, thereby reducing scattering centers. This technique provided significant improvements in FET characteristics resulting in greater on/off ratio (e.g. 10⁴). AC dielectrophoretic alignment followed by selective electrical breakdown of m‐SWNTs can significantly enhance the semiconducting properties of SWNT networks which resulted in highly sensitive sensors.     

Stable polydiacetylene/ZnO nanocomposites with two-steps reversible and irreversible thermochromism: the influence of strong surface anchoring

The influence of pH value on gold nanoparticle production in the presence of Pluronic stabilizers is systematically investigated. The reactions are studied as a function of pH and at fixed concentrations of the two reactants, HAuCl(4) and P123 block copolymer. Results indicate that the reaction pathway during the nanoparticle formation can be controlled by varying pH. The nanoparticles synthesized at pH=11.12 have an average diameter of 9.6 nm with a narrow size distribution, and the Pluronics are adsorbed on individual gold particle surfaces to form core-shell structures via hydrophobic interactions. The present work provides an economic way to improve the dispersion and stabilization of gold nanoparticles and throws further light on the understanding of gold nanoparticle production using block copolymers.     

A numerical computation of the non-dimensional form of a non-linear hydrodynamic model in a uniform reservoir

A mathematical model is used to simulate the water current and the elevation in a uniform reservoir. A non-linear hydrodynamic model that provides the velocity field and elevation of the water flow is considered. In the simulating process, the Lax–Wendroff technique is used to approximate the solutions. The numerical solution can be the input data for a water-quality model that is applicable for the optimal control of water treatment in the system to achieve minimum cost.     

A numerical computation of a non-dimensional form of stream water quality model with hydrodynamic advection–dispersion–reaction equations

Mathematical models of water quality assessment problems often arise in environmental science. The modelling often involves numerical methods to solve the equations. In this research, two mathematical models are used to simulate pollution due to sewage effluent in the nonuniform flow of water in a stream with varied current velocity. The first is a hydrodynamic model that provides the velocity field and elevation of the water flow. The second is a dispersion model, where the commonly used governing factor is the one-dimensional advection–dispersion–reaction equation that gives the pollutant concentration fields. In the simulation processes, we used the Crank–Nicolson method system of a hydrodynamic model and the backward time central space scheme for the dispersion model. Finally, we present a numerical simulation that confirms the results of the techniques.     

Conversion enhancement of tubular fixed-bed reactor for Fischer-Tropsch synthesis using static mixer

Recently,Fischer-Tropsch synthesis(FTS) has become an interesting technology because of its potential role in producing biofuels via Biomassto-Liquids(BTL) processes.In Fischer-Tropsch(FT) section,biomass-derived syngas,mainly composed of a mixture of carbon monoxide(CO) and hydrogen(H2),is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure.Fixed-bed reactors are typically used for these processes as conventional FT reactors.The fixed-bed or packed-bed type reactor has its drawbacks,which are heat transfer limitation,i.e.a hot spot problem involved highly exothermic characteristics of FT reaction,and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface.This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved,and led to higher throughput and conversion.The main goal of the research is the enhancement of a fixed-bed reactor,focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor.Two FTS experiments were carried out using two reactors i.e.,with and without static mixer insertion within catalytic beds.The modeled syngas used was a mixed gas composed of H2/CO in 2:1 molar ratio that was fed at the rate of 30mL(STP)min1(GHSV≈136mL g1 cat h1) into the fixed Ru supported aluminum catalyst bed of weight 13.3g.The reaction was carried out at 180℃ and atmospheric pressure continuously for 36h for both experiments.Both transient and steady-state conversions(in terms of time on stream) were reported.The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer.In both cases,the values of chain growth probability of hydrocarbon products(α) for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer,respectively.     

Effects of prescribed heat flux and transpiration on MHD axisymmetric flow impinging on stretching cylinder

A numerical treatment for axisymmetric flow and heat transfer due to a stretching cylinder under the influence of a uniform magnetic field and prescribed surface heat flux is presented. Numerical results are obtained for dimensionless velocity, temperature, skin friction coefficient and Nusselt number for several values of the suction/injection, magnetic and curvature parameters as well as the Prandtl number. The present study reveals that the controlling parameters have strong effects on the physical quantities of interest. It is seen that the magnetic field enhances the dimensionless temperature inside the thermal boundary layer, whereas it reduces the dimensionless velocity inside the hydrodynamic boundary layer. Heat transfer rate reduces, while the skin friction coefficient increases with magnetic field.     

Synthesis of highly pure poly(aryleneethnylene)s using palladium supported on calcium carbonate as an eco‐friendly heterogeneous catalyst

Metal catalyst contamination is a major concern in the preparation of polymeric materials. For conjugate polymers, trace amount of metal catalyst is detrimental to the optoelectronic properties. In this work, a method for synthesizing highly pure fluorescent polymers, poly(aryleneethynylene)s (PAEs), was developed using heterogeneous Pd/CaCO₃ catalytic system. Polymerization between a variety of aryl diethynes and aryl diiodides or dibromides were achieved using a catalytic amount of Pd/CaCO₃, CuI, and PPh₃ at 80 °C in good to excellent yields (79–100%). Resulting polymers possess degree of polymerization ranging from 8 to 50 with polydispersity index of 1.5–3.6. Importantly, PAEs from Pd/CaCO₃ catalytic system contain considerably lower level of Pd and Cu contamination (1.9 and 3.4 ppm, respectively) than those obtained from classical homogeneous catalyst, Pd(PPh₃)₄ and PdCl₂(PPh₃)₂ or heterogeneous catalyst Pd/C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1556–1563