Shearing and mixing effects on synthesis and properties of organoclay/polyester nanocomposites

Mixing of solid nanoparticles in viscous fluids is a key stage in synthesis of nanocomposites and can affect their final properties. A multi-step preparatory mixing is developed to synthesize the nanocomposites of layered silicate in thermosetting polymers. This study aims to investigate the influences of mixing conditions and steps taken to process the thermosetting nanocomposites on the viscoelastic properties of suspensions. We also examine subsequent influences of mixing on the microstructure and dispersion state of cured hybrids of organically modified clays in a polyester resin. The nanocomposites were prepared in a sequential mixing process developed for the model nanocomposites of organoclays and thermoset resin. Depending on the mixing conditions, the final nanocomposites showed mixed intercalated and moderately to highly delaminated structure. TEM images show that the nanoclay galleries are dispersed in the polymer phase after curing reactions. The startup viscosities and linear viscoelastic properties of the nanocomposites are significantly influenced by the extent and the time duration of mixing. These observations indicate that extensive mechanical mixing combined with a stationary step followed by moderate shear mixing can improve the polymer and nanoparticle interactions at the interface. In the last part of this work, we develop a simple but efficient mathematical formulation on the flow of oblate spheroids in viscous media and compare selected model predictions with the measured startup shear viscosities of suspensions.     

Flow‐induced particle orientation and rheological properties of suspensions of organoclays in thermoplastic resins

The influence of nano‐scale particles on the viscoelastic properties of polymer suspensions is investigated. We have developed a simulation technique for the particle orientation and polymer conformation tensors to study various features of the suspensions. The nano‐particles are modeled as thin rigid oblate spheroid particles and the polymers as FENE‐P type viscoelastic and Newtonian fluid. Both interparticle and polymer‐particle interactions have been taken into account in our numerical computations. The nonlinear viscoelastic properties of nanocomposites of layered silicate particles in non‐Newtonian fluids are examined at the start‐up of shear flow and are interpreted using the model to examine the effects of model parameters as well as flow conditions on particle orientation, viscosity, and first normal stress difference of the suspensions. We have studied the microstructure of polymer‐clay nanocomposites using X‐ray diffraction (XRD) scattering and transmission electron microscopy (TEM). The rheology of these nanocomposites in step‐shear is shown to be fairly well predicted by the model. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2003–2011, 2010     

Synthesis and Dehydration of Oxadithia and Trithiadioxime Crown Compounds

The reaction of 2,2‐oxydiethanethiol and 2‐[2‐mercaptoethyl) thio] ethanethiol with dichloroglyoxime (DCGO) in absolute EtOH led to crown compounds, oxadithia (5Z,6Z)‐1,4,7‐oxadithiadiononane‐5,6‐dionedioxime (1) and trithia (2Z,3Z)‐1,4,7‐trithionane‐2,3‐dionedioxime (2), respectively. The compounds 5,6,8,9‐tetrahydro [1,4,7]oxadithionine[5,6‐c][1,2,5]oxadiazole (3) and 5,6,8,9‐tetrahydro[1,4,7]trithionino[2,3‐c][1,2,5]oxadiazole (4) were prepared by dehydration of 1 and 2 in aqueous solution of potassium hydroxide at 170–180°C, respectively.     

Ultrasound‐Promoted Rapid Oxidative Cleavage of Oximes with NaBrO3/Ion Exchange Resin

The oxidative cleavage of oximes has been studied under solvent‐free ion exchange resin (IER) catalysis by sodium bromate using ultrasonic irradiation. Both aldoximes and keto‐oximes selectively converted to the corresponding carbonyl compounds in high yields within short times at room temperature.     

Electronic and Chemical Characterization of Aluminum–Nitrogen (AlN) Substituted Fullerenes: C58AlN to C24Al12N12

Density functional theory calculations (B3LYP/6-311G*) are applied to devise a series of AlN-substituted C₆₀ fullerenes, avoiding weak homonuclear Al–Al and N–N bonds. The substitutional structures, energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, ionization potentials, binding energies, as well as dipole moments have been systematically investigated. The band gap (HOMO–LUMO gap) is larger for all the AlN-substituted fullerenes than C₆₀. The properties of heterofullerenes, especially, the HOMO–LUMO strongly depend on the number of AlN units. Natural charge analyses indicate that doping of fullerene with AlN units exerts electronic environment diversity to the cage. High charge transfer on the surfaces of our heterofullerenes provokes more studies on their possible application for hydrogen storage.     

Bound State Solutions of the Dirac Equation for the Eckart Potential with Coulomb-Like Yukawa-Like Tensor Interactions

In this paper, we present the approximate bound state solutions of the Dirac equation within the framework of spin and pseudospin symmetries for Eckart potential for arbitrary κ—state using Nikiforov–Uvarov method. The tensor interactions of Coulomb-like and Yukawa-like form are considered and the effects of these tensors and the degeneracy removing role are discussed in detail. Numerical results and figures to show the effect of the tensor interactions are also reported.     

Fractional-order linear time invariant swarm systems: asymptotic swarm stability and time response analysis

This paper deals with fractional-order linear time invariant swarm systems. Necessary and sufficient conditions for asymptotic swarm stability of these systems are presented. Also, based on a time response analysis the speed of convergence in an asymptotically swarm stable fractional-order linear time invariant swarm system is investigated and compared with that of its integer-order counterpart. Numerical simulation results are presented to show the effectiveness of the paper results.     

The Thermal Teleportation of a Qutrit in the Two-qutrits xxz chain

International Journal of Theoretical Physics - We study the effect of temperature, magnetic field and Dzyaloshinskii-Moriya interaction on the fidelity of thermal teleportation in the xxz...     

Experimental Observations and Quantitative Predictions of Rheological Properties of Organoclay/Poly(propylene) Nanocomposites at the Startup of Shear Flows

We study the rheological characteristics of nanocomposites containing nano-sized plate like particles in a viscoelastic fluid at the startup of steady state in the simple shear flow mode. The nanocomposites of organoclay-polypropylene with different nanoclay contents were prepared by melt mixing. A rheological equation of state, originally formulated to predict the orientation state and viscoelastic behavior of suspensions of ellipsoidal particles in polymer melts, has been modified to describe the observed phenomena for the nanoclay/poly(propylene) composites. The rotational particle motion and alignment for a group of symmetric ellipsoids with the applied flow field are investigated. Additionally, model calculations of the macroscopic rheological properties for a simple flow case suggest the presence of nano-particles significantly modify the suspended fluid at volume concentrations as low as 0.5%. The model calculations for the startup viscosity are reasonably in agreement with the experimental results at the experimental range covered in this study. At the shear rate of , we observe pronounced stress overshoots at the three nanoclay loadings level tested which are found to be related to the fast alignment of the silicate layers with the shear direction in the polymer melt.