Dirichlet boundary conditions in a noncommutative theory

We study the problem of imposing Dirichlet-like boundary conditions along a static spatial curve, in a planar Noncommutative Quantum Field Theory model. After constructing interaction terms that impose the boundary conditions, we discuss their implementation at the level of an interacting theory, with a focus on their physical consequences, and the symmetries they preserve. We also derive the effect they have on certain observables, like the Casimir energies.Comment: 19 pages, 1 figure, pdflate

Blends of Ps With Sbr Devulcanized by Ultrasound: Rheology and Morphology

The rheological properties and the morphology of blends of styrene-butadiene rubber (SBR), devulcanizated by ultrasound (dSBR), with polystyrene (PS) were studied. A compatibilizer, a styrene-butadiene block copolymer (SBS) was also added to dSBR/PS blends. The shear viscosity at low and high shear rates, the complex dynamic viscosity and the creep behavior were measured. It was observed that the addition of the dSBR to the PS caused little change in the shear viscosity at high shear rates, decreased the die swell and increased the elastic recovery. The analysis of the dSBR particles in blends after capillary rheometry showed that their shapes were extremely irregular with their sizes decreased and distribution narrowed with increase in the amount of dSBR and the shear rate. The addition of SBS to the blends was found to be more efficient on decreasing the dSBR particle size at the lowest concentration of dSBR. Depending on the dSBR concentration, the dSBR particle sizes in the blends varied between 18 and 6 pm. Thus in order to achieve a toughening of PS by an addition of dSBR, their particle size should be further reduced by changing the devulcanization process conditions

2D and 3D imaging of the deformation behavior of partially devulcanized rubber/polypropylene blends

The full understanding of the mechanisms involved in the development of polymer blend microstructure during its processing has not yet been achieved; the understanding of blends composed by a highly elastic dispersed phase is even more indefinite. The proposal of this work is to analyze the deformation behavior of a new system composed by a partially devulcanized rubber dispersed in polypropylene using 2D and 3D images, both as complementary tools. For this purpose, ground tire rubber (GTR) was partially devulcanized by microwave irradiation for different exposure periods. After this step, each treated rubber was incorporated into recycled PP. The molded blends were analyzed using effective tools as 2D and 3D images and rheological data. In general, the polymer blends exhibited refined microstructure, especially the blend composed of the most devulcanized rubber, even though they had high values of viscosity ratio (≥4). Based on the 3D images, it is clear that breakup mechanisms of the dispersed phase, like parallel breakup, have played an important role in the evolution of the blend’s microstructure, mainly in the region of higher shear rate during processing. However, in areas where the rubber is still vulcanized, the breakup may have been caused by erosion of its surface

Devulcanization of ground tire rubber: Physical and chemical changes after different microwave exposure times

Microwave devulcanization is known to be a promising and an efficient rubber recycling method which makes possible for the rubber to regain its fluidity, and makes it capable of being remolded and revulcanized. The focus of this work is to understand the physical and chemical changes that occur in the ground tire rubber after different microwave exposure periods. For this purpose chemical, thermal, rheological and morphological analyses were performed on the tire rubber, which contains natural rubber (NR) and styrene-butadiene rubber (SBR) as polymeric material. The results showed that the microwave treatment promoted the breaking of sulfur cross-links and consequently increased the rubber fluidity. However, long periods of exposure led to degradation and modification of some properties. At nanoscale, the deformation of the devulcanized NR domain under stress was observed, and the morphology obtained appears to be a droplet dispersion morphology. The most exposed samples presented only one glass transition temperature, and from this it was concluded that the treatment may have played an important role in the compatibilization of the elastomeric blend. Based on the results, it is required to control the microwave exposure time and polymeric degradation in order to achieve a regenerated rubber with satisfactory properties

Improving electrochemical stability and electromechanical efficiency of ipmcs: tuning ionic liquid concentration

In the field of soft actuators, Ionomeric Polymer Metal Composites (IPMC)-like devices are a trend, exhibiting large displacement with low applied voltage. Its working mechanism is related to solvated electrolytes migration, thus the number of counterions exchanged with the polymeric membrane plays a key role in the device’s performance. Although many kinds of inorganic and organic ions were used, there were few efforts to address a specific concentration value of electrolyte solutions. Ionic liquids (ILs) are used in IPMC to provide electrochemical stability; however, their mechanical performance is usually poor. In this study we aimed to determine a specific value of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ionic liquid concentration between 0.1, 0.3, and 0.5 mol L-1 that grants electrochemical stability at different relative humidities with best electromechanical efficiency. We synthesized [BMIM]Cl and characterized it through Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), and Cyclic Voltammetry (CV). The electrochemical behavior of Nafion®/Pt-based IPMC exchanged with IL was studied through Electrochemical Impedance Spectroscopy (EIS), CV, and Chronoamperometry (CA). Electromechanical properties were measured through blocking force and displacement. All the IPMC tests were carried out at three distinct controlled humidities (30%, 60%, and 90%). Herein, we tuned the IL concentration in 0.3 mol L-1, delivering electrochemical stability with the best electromechanical yield regardless of the relative humidity. This result will be important when bringing electrolyte mixtures to further enhance the performance and efficiency of these devices