3 resultados para NEW-ORLEANS BARRIER
em AMS Tesi di Dottorato - Alm@DL - Università di Bologna
Resumo:
The object of the present study is the process of gas transport in nano-sized materials, i.e. systems having structural elements of the order of nanometers. The aim of this work is to advance the understanding of the gas transport mechanism in such materials, for which traditional models are not often suitable, by providing a correct interpretation of the relationship between diffusive phenomena and structural features. This result would allow the development new materials with permeation properties tailored on the specific application, especially in packaging systems. The methods used to achieve this goal were a detailed experimental characterization and different simulation methods. The experimental campaign regarded the determination of oxygen permeability and diffusivity in different sets of organic-inorganic hybrid coatings prepared via sol-gel technique. The polymeric samples coated with these hybrid layers experienced a remarkable enhancement of the barrier properties, which was explained by the strong interconnection at the nano-scale between the organic moiety and silica domains. An analogous characterization was performed on microfibrillated cellulose films, which presented remarkable barrier effect toward oxygen when it is dry, while in the presence of water the performance significantly drops. The very low value of water diffusivity at low activities is also an interesting characteristic which deals with its structural properties. Two different approaches of simulation were then considered: the diffusion of oxygen through polymer-layered silicates was modeled on a continuum scale with a CFD software, while the properties of n-alkanthiolate self assembled monolayers on gold were analyzed from a molecular point of view by means of a molecular dynamics algorithm. Modeling transport properties in layered nanocomposites, resulting from the ordered dispersion of impermeable flakes in a 2-D matrix, allowed the calculation of the enhancement of barrier effect in relation with platelets structural parameters leading to derive a new expression. On this basis, randomly distributed systems were simulated and the results were analyzed to evaluate the different contributions to the overall effect. The study of more realistic three-dimensional geometries revealed a prefect correspondence with the 2-D approximation. A completely different approach was applied to simulate the effect of temperature on the oxygen transport through self assembled monolayers; the structural information obtained from equilibrium MD simulations showed that raising the temperature, makes the monolayer less ordered and consequently less crystalline. This disorder produces a decrease in the barrier free energy and it lowers the overall resistance to oxygen diffusion, making the monolayer more permeable to small molecules.
Resumo:
A numerical investigation of dielectric barrier discharge aimed to simulate the electro hydro dynamic interaction is presented. A discharge drift diffusive model according to the Townsend avalanche is described and used to duplicate the plasma kinetics of a DBD actuator. The discharge characteristics dependence upon dielectric material and applied voltage are simulated and the EHD force field according to a simplified approach is presented and discussed. The coupling of DBD results with a fluid dynamic code is also shown. Finally, a new non invasive diagnostic technique for EHD interaction based on Schlieren imaging is computationally validated.
Resumo:
The environmental problems caused by human activity are one of the main themes of debate of the last Century. As regard plastics, the use of non-renewable sources together with the accumulation of waste in natural habitats are causing serious pollution problems. For this reason, a continuously growing interest is recorded around sustainable materials, potential candidate for the replacement of traditional recalcitrant plastics. Promising results have been obtained with biopolymers, in particular with the class of biopolyesters. Their potential biodegradability and biobased nature is particularly interesting mainly for food packaging, where the multilayer systems normally used and the contamination by organic matter create severe recycling limits. In this framework, the present research has been conducted with the aim of synthetizing, modifying and characterizing biopolymers for food packaging application. New bioplastics based on monomers derived from renewable resources were successfully synthetized by two-step melt polycondensation and chain extension reaction following the “Green chemistry” principles. Moreover, well-known biopolyesters have been modified by blending or copolymerization, both resulting effective techniques to ad hoc tune the polymer final characteristics. The materials obtained have been processed and characterized from the chemical, structural, thermal and mechanical point of view; more specific characterizations as compostability tests, surface hydrophilicity film evaluation and barrier property measurements were conducted.