Biopolyester fibers for sustainable and biocompatible applications

The rising of concerns around the scarcity of non-renewable resources has raised curiosity around new frontiers in the polymer science field. Biopolymers is a general term describing different kind of polymers that are linked with the biological world because of either monomer derivation, end of life degradation or both. The current work is aimed at studying one example of both biopolymers types. Polyhydroxibutyrate (P3HB) is a biodegradable microbial-produced polymer which holds massive potentiality as a substitute of polyolefins such as polypropylene. Though, its highly crystalline nature and stereoregularity of structure make it difficult to work with. The project P3HB-Mono take advantage of polarized Raman spectroscopy to see how annealing of chains with different weights influence the crystallinity and molecular structure of the polymer, eventually reflecting on its mechanical properties. The technique employed is also optimal in order to see how mesophase, a particular conformation of chains different from crystalline and amorphous phase, develops in the polymer structure and changes depending on temperature and mechanical stress applied to the fiber. Polycaprolactone (PCL) on the other hand is a biodegradable fossil-fuel polymer which has biocompatibility and bio-resorbability features. As a consequence this material is very appealing for medical industry and can be used for different applications in this field. One interesting option is to produce narrow and long liquid filled fibers for drug delivery inside human body, using a traditional technique in an innovative way. The project BioLiCoF investigates the feasability of producing liquid filled fibers using melt-spinning techniques and will examine the role that melt-spinning parameters and liquids employed as a core solution have on the final fiber. The physical analysis of the fibers is also interpreted and idea on future developments of the trials are suggested.

Ab-initio determination of x-ray absorption near edge structure (xanes) spectra in an ultrasoft and norm conserving pseudopotentials scheme

X-ray absorption spectroscopy (XAS) is a powerful means of investigation of structural and electronic properties in condensed -matter physics. Analysis of the near edge part of the XAS spectrum, the so – called X-ray Absorption Near Edge Structure (XANES), can typically provide the following information on the photoexcited atom: - Oxidation state and coordination environment. - Speciation of transition metal compounds. - Conduction band DOS projected on the excited atomic species (PDOS). Analysis of XANES spectra is greatly aided by simulations; in the most common scheme the multiple scattering framework is used with the muffin tin approximation for the scattering potential and the spectral simulation is based on a hypothetical, reference structure. This approach has the advantage of requiring relatively little computing power but in many cases the assumed structure is quite different from the actual system measured and the muffin tin approximation is not adequate for low symmetry structures or highly directional bonds. It is therefore very interesting and justified to develop alternative methods. In one approach, the spectral simulation is based on atomic coordinates obtained from a DFT (Density Functional Theory) optimized structure. In another approach, which is the object of this thesis, the XANES spectrum is calculated directly based on an ab – initio DFT calculation of the atomic and electronic structure. This method takes full advantage of the real many-electron final wavefunction that can be computed with DFT algorithms that include a core-hole in the absorbing atom to compute the final cross section. To calculate the many-electron final wavefunction the Projector Augmented Wave method (PAW) is used. In this scheme, the absorption cross section is written in function of several contributions as the many-electrons function of the finale state; it is calculated starting from pseudo-wavefunction and performing a reconstruction of the real-wavefunction by using a transform operator which contains some parameters, called partial waves and projector waves. The aim of my thesis is to apply and test the PAW methodology to the calculation of the XANES cross section. I have focused on iron and silicon structures and on some biological molecules target (myoglobin and cytochrome c). Finally other inorganic and biological systems could be taken into account for future applications of this methodology, which could become an important improvement with respect to the multiscattering approach.